Industrial Gold Plating Overview

Hard Gold Plating on interconnect pins to provide durable, conductive parts

Industrial gold plating is utilized across a range of industries for both the conductive and noble properties that gold provides. Gold is the third most conductive metal behind silver and copper but unlike these metals, gold’s contact resistance is extremely consistent since gold does not oxidize or tarnish. This makes gold an excellent choice for low-voltage applications such as signal transmission when small changes in resistance can be problematic. In addition, gold provides excellent barrier corrosion resistance in many industrial applications since it does not corrode.

Functional industrial gold plating is plated as soft gold with 99.9% purity (Type III) as well as hardened 99.0-99.7% pure (Type I or II) deposits alloyed with nickel or cobalt.   Unlike decorative gold applications which often use a gold flash of less than 0.00001” inches (0.25um), industrial gold deposits are normally thicker to provide improved function and durability.  Industrial gold is commonly plated in thickness typically ranging between 0.00001 inches (0.25 micrometers) to 0.0001 inches (2.5 micrometers) and is commonly plated over underlayers of nickel and/or copper.

Table 1: Common Gold Plating Thickness for Functional Gold Use

Considerations when Specifying Industrial Gold Plating – Gold Purity and Hardness

Industrial gold plating is divided into two primary categories – hard and soft gold plating – based on the hardness of the deposit.  Soft gold is the highest purity (99.9% minimum) and is used where the noble properties of gold take priority over wear resistance.  Soft gold lives up to its namesake with a maximum hardness of 90 Knoop; whereas hard gold plating has reduced purity (99.0-99.7% Pure) but can have hardnesses of up to 200 Knoop due to the addition of alloying elements such as nickel and cobalt.  Common industrial uses for soft gold include wire bonding or soldering of electronics, lapping electrical contacts with low contact pressures (< 10 Pa), infrared reflectors and high corrosion resistance contacts or electrodes.

Soft Gold Plating for medical applications due to Gold’s biocompatibility

Soft gold is deposited without any alloying elements, allowing for the natural grain structure of gold, alongside gold’s natural low porosity, to provide a corrosion resistant barrier coating over the substrate. Soft gold is often seen in connector applications that are designed to remain connected for long periods of time.  Soft Gold is also an excellent reflector of near-infrared (NIR) and infrared (IR) radiation and making it an excellent choice for thermal shielding in extremely low temperature quantum computing applications. The properties of soft and hard gold can also be combined into a “duplex” coating, where the hard gold outer layer provides wear resistance, while the soft gold underplate increases the corrosion resistance considerably due to the offsetting of pores between the hard and soft gold plating layers.

Figure 1: Visualization of Grain Structure for Barrier Corrosion Protection

Hard Gold Plating for a conductive, rotational application

Hard gold is not truly hard in terms of other metals such as nickel or titanium; however, its hardness is relative compared to the very soft nature of pure gold.  The increase in hardness of hard gold affords greatly improved wear resistance where sliding wear or repeated contact can abrade gold from the surface.  Hard gold is commonly used in electrical terminals and contacts where higher contact pressures (> 10 Pa) and repeated engagement occurs such as male/female connectors or pogo pin contacts.  In addition, hard gold plating provides a lubricious surface that is not prone to fretting and resists galling. Hard gold can be utilized for joining applications such as soldering even with a mild rosin-only flux; however hard gold is not recommended for wire bonding due to its alloying elements.

Figure 2: Impact of Nickel Underplate on Hard Gold for Wear Protection at Different Contact Pressures and Underplate Thicknesses

Comparison of Industrial Gold Plating to Other Conductive Finishes

In industrial uses, gold plating is often compared to other plated conductive finishes, most commonly, silver, copper and tin. Silver plating, like gold, is often used in connector applications.  Like gold, industrial silver plating provides excellent conductivity and lubricity – even at high temperatures.  However, silver readily reacts with sulfur forming a blue or black tarnish of silver sulfide. Although silver sulfide is relatively conductive, it still will increase contact resistance which can be problematic in sensitive low-voltage or signal transmission applications.  While numerous anti-tarnish treatments exist, they only mitigate and do not eliminate silver tarnish from forming.  Due to gold’s nonreactive nature, it will never tarnish or corrode, which makes gold desirable for applications sensitive to slight changes in contact resistance.

Copper plating, like silver and gold plating, is a highly conductive metal.  In fact, copper is second only to silver in conductivity.  Since copper is not a precious metal, it can be plated to a much higher thickness than silver and gold without as great of a cost impact.  This is very beneficial for promoting corrosion resistance when used as an underplate since copper is a relatively noble metal that provides very good barrier corrosion protection. The downside of copper as a final finish is that copper reacts readily with sulfur, oxygen or even chlorine to form copper oxide (CuO or Cu₂O), copper sulfide (CuS), copper sulfate (CuSO₄) or various halides.  Any of these compounds have a major impact on the conductivity of copper and will increase contact resistance and create hot-spots in conductors that can lead to thermal run-away events (fires). For this reason, copper plating is typically used as a “supporting character” in conductive finish stack-ups to help promote overall conductivity and corrosion resistance with the ultimate or topcoat being an alternative finish such as gold, silver, nickel or tin.

Tin plating is often referred to as poor-man’s silver since it provides many of the similar properties as silver but just not as well.  Tin has reduced conductivity and corrosion resistance over silver or gold plating, but it performs adequately for many industrial applications.  Matte tin plating provides good solderability but unlike industrial gold plating, the solderability of tin degrades over time due to the formation of tin oxides. However, tin does maintain solderability longer than nickel plating and the solderability of tin can be extended with proper packaging techniques.

Unlike gold plating, tin has a low melting point and as such, the service environment should be considered; nickel is preferred for a conductive finish in higher temperature applications where a precious metal is not needed.  Tin or nickel plating are most commonly used for plating of larger conductors such as bus bars and connector terminals where the application has some forgiveness for contact resistance increasing over time. By comparison industrial gold plating is used for critical conductor applications where increases in contact resistance over time pose a design concern.

There are many considerations to account for when specifying a finish for a component. The technical sales and engineering staff at Advanced Plating Technologies (APT) can help with specifying the right plating or plating stack-up for your tin or nickel plating application.  APT has over 75 years of experience plating tin and nickel across a range of industries and can assist with proper test plans and packaging methods to ensure deposit properties are maintained and protected.

A member of our engineering group can be contacted at sales@advancedplatingtech.com or 414.271.8138.

Blog Authored by Zach Hatseras, Estimating Engineer; Technical Editing by Matt Lindstedt, President – Advanced Plating Technologies

References:

• Bulwith, Ronald A “Soldering to Gold- A Practical Guide” chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://advancedplatingtech.com/wp-content/uploads/2016/04/Soldering-to-Gold-A-Practical-Guide.pdf
• Dr. Bob Mroczkowski Founder at connNtext associates Dr. Bob Mroczkowski was one of the connector world’s most significant innovators and educators. “Connector Degradation Mechanisms-Corrosion Part II.” Connector and Cable Assembly Supplier, 31 Oct. 2019, connectorsupplier.com/connector-degradation-mechanisms-corrosion-part-ii/.
• Scardinio, Dominic. “How to Prevent Corrosion of Gold Plated Contacts or Terminals.” Advanced Plating Technologies, 21 July 2023, advancedplatingtech.com/blog/prevent-corrosion-of-gold-plated-contacts-terminals/.
• Zednicek, Antonin. “Nickel Underplates and Noble Metal Finish Wear.” Passive Components Blog, 7 Sept. 2021, passive-components.eu/nickel-underplates-and-noble-metal-finish-wear/.

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Similarities and Differences Between Nickel and Tin Plating

Tin and nickel plating are both conductive finishes that are typically used in electrical or power applications such as plating of copper or aluminum terminals and bus bars.  Both tin and nickel provide improved corrosion protection, conductivity and are used to facilitate common joining methods such as soldering, brazing or ultrasonic welding.  From a material property standpoint, tin is a much softer, more ductile metal than nickel.  These core elemental differences separate the two metals functionally and differentiate when each should be specified.  In addition, tin and nickel are each plated with different variants including matte or bright tin, sulfate (Watts) or sulfamate electrolytic nickel as well as an entire family of alloy processes such as tin/lead or electroless nickel deposits of nickel phosphorous or nickel boron.

The table below provides a high-level overview of a few of the fundamental properties of tin, electrolytic nickel and common electroless nickel deposits:

When Tin Plating Is Preferred Over Nickel Plating

Tin is typically plated in the pure form as either an unbrightened process (matte tin) or a chemically brightened process (bright tin) in which organic brighteners are added to refine the grain structure of the metal resulting in a bright process.  Tin is also commonly alloyed with lead for applications within the lead acid battery market, critical soldering applications or bearing applications.  The primary advantages of tin include its ductility for applications that must flex or bend as well as for solderable applications.  In addition, since tin is a soft metal, it is often preferred for lapping bus-bar connections to improve the long-term conductivity of the connection points.     Tin is also resistant to galling and can be used as a conductive, metallic lubricant on sliding contacts or threads.

The Ductility Factor – Advantage Tin

Tin is an extremely ductile metal with a percent elongation of 49.5%; as shown in Figure 1, tin is near the top of the list in relative ductility of metals, especially of non-precious metals.  This property makes tin ideal for conductive applications that must flex as well as for applications in which components are formed post-plate such as bus bars or fuse caps that have secondary forming operations after plating.

Being a soft metal, tin easily conforms to mating surfaces under compressive loads.  This properly makes tin ideal for maximizing metal-on-metal contact in lapping connections such as bus bars, especially when plated to higher thicknesses.  This property minimizes the airgap between the joined components which in-turn reduces oxidation and corrosion within the bolted joint.  This can improve conductivity over time of tin plated bus bars as compared to nickel plated bus bars.

Soldering and Solderability – Advantage Tin

Soldering is a common method of joining electrical components.  The basic process involves melting a metal solder onto the surface of two components.  The solder flows or “wets” the two components and as it cools, forms a solid joint that has very good electrical and thermal conductivity.  When soldering to tin plating the tin deposit melts and becomes part of the joint with the molten solder.  The bond is made with the base metal or underplate beneath the tin.  This contrasts with soldering to nickel plating in which the solder joins directly to the nickel without melting or flowing the deposit.

This difference makes nickel plating much more susceptible to dewetting due to oxides forming over time.  The solderability of both tin and nickel deposits is perishable and reduces over time due to the natural oxidation of the deposits.  Storage conditions greatly impact how quickly this degradation occurs.  However, since tin melts to join with the solder, tin deposits solder more consistently as they age, especially with rosin-only (R) fluxes.  Nickel deposits will typically require acid activated fluxes (RA or RMA fluxes) to remove the oxide layer as they age.  Since acid activated fluxes leave a corrosive film on the surface, they are generally not preferred in most applications.  Matte tin deposits are recommended for soldering applications since they are free of organic brighteners that can impede consistent wetting of the surface.

 When Nickel Plating is Preferred over Tin Plating

High Hardness, High Melting Point and Diffusion Barrier – Advantages of Nickel Plating

One of the greatest advantages of nickel over tin is its improved hardness and high melting point. As noted in Table 1 above, electrolytic nickel has an average hardness of 300 HV and a melting point of 1455 °C.  Electroless nickel has hardness of 600 HV with a melting point around 1000 °C.  These properties make nickel a great finish for high temperature and high wear applications. Many switches, contacts, fuse stabs and terminal pins are nickel plated when they must endure high contact loads and pressures especially for switching applications with thousands of cycles.

The face centered cubic (FCC) structure of nickel it is superior to the body centered tetragonal (BCT) structure of tin at preventing solid state diffusion or migration of base elements.  When tin is plated directly over brass, zinc readily migrates through solid state diffusion tin the tin deposit.  This forms an intermetallic boundary layer that degrades the electrical performance of the tin over time.  This reaction is accelerated with temperature making tin less preferred within higher operating temperature electrical applications.

Tin Whiskers and Tin Pest – Areas of Caution when Specifying Tin Plating

Tin also suffers from several unique degradation mechanisms including tin pest and tin whiskers.  Tin pest is an autocatalytic phase change of tin from the white beta phase into a brittle grey alpha phase that is not conductive.   This transition is slow to occur at normal temperatures but at very low temperatures of -30 °C, the transition can initiate and occur rapidly degrading the tin properties.

Tin whiskers form to relieve stress within the tin deposit.  The whiskers are thin (2.5um diameter) conductive filaments of tin that grow outward from the surface and can extend up to 25mm from the surface².  Whiskers can grow within a period of months or may take years after plating.  They are especially problematic in tightly packaged electronic applications in which whiskers can form short-circuits with a current carrying capacity of up to 10mA.  The driving mechanism for whiskers of tin is to relieve stress within the deposit.  As such, organically brightened tin deposits are more susceptible than matte tin deposits.  To avoid tin whiskers the following steps can be taken:

1. Alloy the tin with lead, bismuth or antimony. Tin/lead deposits with 10% or more lead have been proven very effective at eliminating whiskers.
2. Anneal tin deposits after plating to reduce internal stress
3. Plating matte deposits in lieu of bright deposits of tin
4. Use a nickel underplate prior to tin plating
5. Increase the thickness of the tin deposit to avoid epitaxial effects of stress

Electroless Nickel Plating – Finish that Can be Engineered for an Application

One of the advantages of nickel plating over tin plating is the diversity coating properties that can be customized if electroless nickel plating is specified.  Electroless nickel deposits are plated from a chemical reduction of nickel from a hypophosphite solution in which the deposit is an alloy of nickel and phosphorous.  The percentage of phosphorous can range from low phosphorous deposits (1-6% P), to medium phosphorous deposits (6-10% P) to high phosphorous (11-14% P).

Since the mechanism for electroless nickel plating is a chemical reduction rather than an externally applied voltage, electroless nickel deposits plate very uniformly everywhere the part is wetted by the solution provided the solution can be continuously replenished (agitated) at the surface.   The uniformity of electroless nickel is a fundamental advantage that allows for tighter manufacturing tolerances as well as heavier deposits that provide improved wear and corrosion resistance.  Figure 4 provides an illustration of how electroless nickel plates very uniformly without buildup on edges or corners as occurs with electrolytic plating.

As shown in Table 1 above, the electrical and mechanical properties of electroless nickel plating vary as a function of the percentage of phosphorous within the deposit.   Figure 5 is taken from Appendix X5.1 of ASTM B733 and further illustrates how the hardness, strength and even magnetism of nickel phosphorous coatings vary with increasing phosphorous content.

It is the ability to plate very uniform deposits and match the properties of the deposit to the application that make electroless nickel plating superior to traditional electrolytic nickel and tin in many applications.  The cost of electroless nickel is higher than electrolytic plating with high and low phosphorous nickel being a higher price point than medium phosphorous electroless nickel.

Ultrasonic Welding (USW) – Advantage Nickel Plating over Tin Plating

Ultrasonic welding is a joining process that is growing in popularity in manufacturing specifically within the Electric Vehicle (EV) market.  USW provides a mechanism to join dissimilar metals in a very reliable manner that reduces contact resistance over traditional crimped or lapped joints.  In addition, USW provides a very durable joint that will not increase in contact resistance over time even when exposed to corrosive or thermal cycles.  USW is especially popular for joining aluminum conductors to plated copper terminals to utilize the light weight of the aluminum conductors with the improved electrical performance of the plated copper terminals.

USW is performed by pressing two metals together in a mandrel and using ultrasonic generators to vibrate the metals against one another.  The energy and pressure cause the metals to diffuse into one another at temperatures below the melting point of most metals.  The low melting point of tin, however, is an issue for USW.  During the process the tin will melt cooling the interface and preventing full diffusion from occurring.  As such, any tin plated terminal must be selectively plated to avoid plating of the weld zone.  This selective plating requirement can add significant cost especially for loose plating methods such as rack and barrel plating.  This limitation of tin plating is a major disadvantage as compared to nickel plating of terminals or bus components that will be jointed using USW.

When Tin Plating over Nickel Plating is Preferred

Another idea to consider when designing for both corrosion resistance and solderability is to use both nickel and tin plating cooperatively. As noted above, a problem that occurs in tin plating involves the formation of an intermetallic of tin and copper or tin and zinc. The intermetallic layer grows and consumes tin available for soldering and also reduces the ability of the tin to uniformly flow or wet the surface when melting. A great way to prevent an intermetallic from forming is to use a nickel underplate as a barrier between the tin and the substrate.  The Face Centered Cubic (FCC) structure of nickel is tightly packed and resists intermetallic diffusion.  This prevents the formation of the intermetallic layer thereby improving and preserving solderability.

Another benefit to using both tin and nickel would be to improve corrosion resistance. Good corrosion resistance can be achieved by plating to 0.0005” or greater for a single layer of nickel or tin, however larger deposits may affect the tolerances of a part. Using a duplex or 2-layer system can help limit the porosity and improve the corrosion protection.  The tin grain structure differs from the nickel which limits overall porosity to the substrate. This helps prevent corrosion and could lessen the overall thickness of plating required.

Conclusion:  Tin Verses Nickel Plating

Nickel and Tin Plating have been used in metal finishing for nearly a century and will continue to be used as further advances are made in industries that require good corrosion protection, conductivity, and solderability. Tin plating provides excellent ductility and solderability for parts that are to be used in moderate temperature and low wear environments. The corrosion resistance and conductivity of nickel plating is best utilized in environments that experience high wear and high temperatures.   If a plated component will be ultrasonically welded, nickel is preferred as it is compatible with the USW process without the need for costly selective plating.  There are also times where having tin over nickel would improve a parts capability by preventing an intermetallic from forming and promoting overall corrosion performance with a duplex (2-layer) plating system.

There are many considerations to account for when specifying a finish for a component. The technical sales and engineering staff at Advanced Plating Technologies (APT) can help with specifying the right plating or plating stack-up for your tin or nickel plating application.  APT has 75 years of experience plating tin and nickel across a range of industries and can assist with proper test plans and packaging methods to ensure deposit properties are maintained and protected.

A member of our engineering group can be contacted at sales@advancedplatingtech.com or 414.271.8138.

Blog Authored by Ryan Kliger, Estimating and Process Engineer with Technical Editing by Matt Lindstedt, President – Advanced Plating Technologies

References:

• Failurecriteria.com – Physical Ductility of Elements https://failurecriteria.com/physicalductilit.html
• ASTM B545-97 (2009) Standard Specification for Electrodeposited Coatings of Tin, Appendix X6.3
• Tin Pest: Allotropic Transformation – Wikipedia https://en.wikipedia.org/wiki/Tin_pest
• Metal Whiskers: Failure Modes and Mitigation Strategies, Jay Brusse/Perot Systems; Dr. Henning Leidecker, NASA Goddard –  http://nepp.nasa.gov/whisker
• ASTM B733-22: Standard Specification for Autocatalytic (Electroless) Nickel-Phosphorus Coatings on Metal, Appendix X5.1
• Ultrasonic Welding Images Courtesy of Telsonic Ultrasonics, Billerica, MA – https://www.telsonic.com/

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Tin plating is a common coating applied to a large variety of copper products including busbars, electrical terminals, battery connectors or any other copper component used in the passing of current. With the electrification vehicles, power equipment and interconnectivity of the internet of things, the need for conductive coatings such as tin plating is growing due to its low cost, conductive and solderability properties.

One of the most common uses of tin is for copper plating of bus bars used in transferring electrical power.  This article focuses on the application of tin plating on copper busbars and what you need to know when specifying tin plating.  In addition, the various properties of tin plating are covered as well as how those properties are affected by bright, matte or even tin/lead alloy plating of tin.

 What are Copper Busbars used for?

Copper bus bars are used to distribute high amounts of current and used for mounting components and dissipating heat in various electrical and electronic applications. The main purpose of a busbar is to carry electricity and distribute it. Typically, C110 copper – a general purpose copper per ASTM B152 – is used in bus bar applications due to it having a very high conductivity and offering excellent formability.  These properties make this copper grade a cost-effective choice for electronics, power equipment and automotive applications.

 Why are Copper Busbars tin plated?

Copper Busbars are plated with bright or matte tin to further enhance the corrosion protection, electrical conductivity and solderability of the copper bus bar.  Tin has many favorable properties including excellent conductivity, solderability, corrosion protection and it provides an optimal surface for electrical and heat transfer. Unlike raw copper bus, the tin coating provides a soft and ductile barrier which does not easily oxidize when exposed to oxygen or other elements. A raw copper bus will oxidize and lose conductivity very rapidly as compared to a tin coating.  Although tin will eventually lose some conductivity tin forms a relatively thin oxide is still reasonably conductive.

What Industries use Tin Plated Copper Busbar?

Tin-plated copper busbars are used in a variety of industries and applications, including:

Electrical power transmission and distribution: Tin-plated copper busbars are commonly used in electrical power systems to transmit high-voltage electrical current. The tin plating helps to protect the underlying copper from corrosion, improving the reliability and lifespan of the busbars.

Manufacturing: Tin-plated copper busbars are used in manufacturing environments to provide power to machinery, tools, and other equipment. The tin plating greatly improves the soldering process to ensure a reliable joint with low voltage drop.

Construction: Tin-plated copper busbars are used in the construction industry to provide power to buildings and other structures within power panels. Tin plating helps to extend the life of the busbars and breaker components as well as improve their appearance.

Transportation: Tin-plated copper busbars are used in the transportation industry to power electric vehicles, such as electric buses, trains, and trams. The tin plating can help to improve the electrical conductivity and reliability of the busbars.

Renewable energy: Tin-plated copper busbars are used in renewable energy systems, such as solar panels and wind turbines, to transmit electrical current from the generation source to the point of use or point of storage (battery banks). The tin plating can help to improve the electrical conductivity and corrosion resistance of the busbars especially in humid environments.

Overall, tin-plated copper busbars are used in a variety of industries and applications due to a range of properties that are favorable to reliable transfer of electrical current and heat transfer over the lifespan of the product.

What type of Tin Should I use on my Copper Busbar?

Busbars can be used in a wide variety of applications. When specifying a tin coating for a busbar application, there are a few key characteristics to consider. There are several types of tin that can be used to plate copper busbars, including:

Electrolytic Bright Tin: Bright tin should be specified for copper bus bars or contacts that require improved electrical conductivity, corrosion protection and lubricity.  Bright tin is a lustrous deposit that offers improved cosmetic appeal as well as these improved functional characteristics. However, bright tin should not be used in soldering applications as the brightener systems used to create the bright deposit will co-deposited organic elements into the tin deposit.  These organic brighteners can cause de-wetting or even charring or blackening of the solder joint which can impede the durability of the solder joint especially when using mild fluxes.

Electrolytic Matte Tin (Solderable Tin): Matte or solderable tin should be specified for copper bus bars or contacts that require soldering, improved electrical conductivity, and corrosion protection with an industrial non-reflective finish. Due to the coarse grain structure, matte tin can result in higher initial insertion forces of mating contacts.  A un-brightened nickel underplate is recommended prior to the matte tin to minimize diffusion of base material elements such as copper or zinc (for brass components) into the tin deposit.  The nickel underplate provides an excellent base to solder to and ensures the longest possible shelf life of a solderable, matte tin deposit.

Matte tin is less aesthetically pleasing compared to bright tin but will provide a functional finish for soldering since it is free of any intentionally added organic compounds.  The dull finish of matte tin can be burnished by part-to-part contact and as such care should be taken in packaging of larger parts to minimize contact if a uniform, dull finish is desired.  Larger of heavier barrel plated parts will naturally have burnishing marks on the surface.

Hot-dip tin: Hot-dip tin is applied by immersing the part in a bath of molten tin. This process produces a heavy deposit of tin often 0.001” or more.  It also can be used to coat complex or irregularly shaped parts since the tin deposits wherever the part is wetted during immersion in the molten bath.  Hot-dip tin will result in buildup or pooling in corners, threads and ID features of parts and as such, should not be used on parts with tight tolerances.

Tin/Lead: Tin/lead plating is an alloy of tin and lead that can range from 5/95 (5% tin to 95% lead) to 95/5 (95% tin to 95% lead) tin/lead.  The specific alloy will affect coating properties such as corrosion & chemical resistance, melting point and solderability.  Tin/lead plating of copper bus bars or contacts is often used when tin/lead solder is specified.  The addition of a small percentage of lead within the tin prevents the formation of tin whiskers which is desirable for critical electronic applications where whiskers can cause a short circuit path.  The addition of lead greatly improves the chemical resistance of the deposit to mineral acids such as sulfuric acid making tin/lead plating of copper bus bars popular for lead/acid battery applications.

Ultimately, the best type of tin to use on a copper bus bar will depend on the specific requirements of the application, including factors such as corrosion & chemical resistance, electrical conductivity, soldering characteristics and cosmetics. It is important to carefully consider these factors and consult with a plating specialist to determine the best type of tin for a particular application.

 Benefits of Tin plated Copper Busbars

Tin plating is a versatile and functional plating for copper busbars and electronic applications due to its low cost, corrosion protection, conductivity, solderability, heat-transfer and anti-galling characteristics.  A brief summary of these benefits is provided below:

• Highly Solderable: A matte tin coating is recommended for solderable applications as it is free of brighteners that can impede soldering, especially when using mild fluxes. Matte tin readily flows and creates a reliable solder joint. When a base material such as brass is specified, an under-plate of copper or nickel is recommended to help prevent zinc migration which will cause issues with the solder joint. A nickel underplate on copper or copper alloys will ensure the longest possible shelf-life for solderability.
• Improved Corrosion Protection: Tin is a corrosion-resistant metal and tin plating on copper bus bars can help protect the underlying copper from corrosion, especially in environments with high humidity or other corrosives. Tin plating provides barrier corrosion protection and is therefore, directly proportional to the deposit thickness. Depending on the application for the busbar, a general guideline for good corrosion protection is around 0.0005 inches (12.5um) of tin and excellent corrosion protection occurs around 0.001 inches (25um).
• Enhanced Electrical Conductivity: Tin is a highly conductive metal, and its oxides are more conductive than that of copper or aluminum. In addition, tin oxides remain relatively thin and are easily wiped for sliding contacts such as male/female pins or stab finger-style contacts.   In lapping contacts such as joined copper bus bars, there is minimal oxide formation within the contact joint.
• Thermal Conductivity: Tin plating provides good thermal conductivity of 0.67 W/cm*K to allow for the transfer of heat away from joints or contact surfaces.  Since tin is a soft, malleable metal, it reduces the air-gap within lapped joints further improving the ability to transfer heat away from the joint.
• Lubricity: Tin is a naturally lubricating metal that resists galling in metal-on-metal wear applications.  It is relatively soft and offers some embeddability of debris to reduce abrasive erosion within a contact or wear surface.  Tin is commonly used as a dry-film lubricant on stainless steel fasteners to avoid galling in high load applications.
• Cost Savings: Since tin is readily available and non-precious, it is a considerable cost saver when compared to other precious coatings such as gold, silver, or palladium. In addition, tin electroplating is a very efficient process and can achieve over 0.0005” (12.5um) of thickness in under 1-hr of barrel plating and under 20-mins of rack plating at typical plating rates.  This is less than half the time that an equivalent deposit of nickel would require.  The affordability of tin metal combined with the fast plating rate, makes tin a more competitive option when compared to other non-precious, conductive metals such as nickel or electroless nickel.

Conclusion

With the on-going developments within the electronics, electric vehicle, and power distribution industries, the need for a cost-effective and conductive metal is growing in demand.  Tin plating provides many desirable attributes for these industries including improved conductivity, lubricity, solderability, heat transfer and corrosion resistance.  Tin plating of copper bus bars is commonly used to provide a cost-effective, conductive coating to ensure reliable current transfer over the life of the product.  Tin plating is offered in both matte and bright formulations and can be alloyed with elements such as lead to improve solderability and chemical resistance.  Tin plating can be preceded by an underplate of copper or nickel to optimize the function, solderability and longevity of the plated bus, contact or terminal.

Advanced Plating Technologies (APT) has a team of dedicated engineers and technical sales members who can assist with any application, specification or general questions for your tin plating needs.  APT has 75 years of experience plating tin and tin alloys for various power industries and can help assist with most company specifications.

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Protection of metal fabricated components is critical to the long-term durability of the final product. Surface finishing through powder coating or wet painting are both common solutions to protect various components. Both powder coating and wet paint systems contain similar resins, additives, and pigments; however, there are marked differences between these two painting systems. Most notably, wet paint systems require the use of solvents to suspend the mixture in the fluid form.

Powder coating is applied as a dry powder without solvents, however, the powder paint must be baked or cured on the surface of the part. This primary difference in application method results in several advantages and disadvantages between these two coating options.

Powder Coating Background

How Does Powder Coating Work?

Powder coating is performed by emitting dry powder paint via compressed air through an electrostatic gun onto the exterior of the coated part. The electrostatic gun provides the powder with a negative charge, and the negatively charged powder is attracted to the grounded metal components.

The attraction between the powder and the components as well as the dry application method allows for a heavier paint thickness ranging between 0.002-0.006 inches per side. Since powder coat systems are applied in the dry state there is no need for a solvent to carry the resins and pigments to the surface.

After the powder is applied it is cured on the part by baking. Typical cure cycles range from 300-400F and from 10-30 minutes. During the curing the solid powder particles melt to form a liquid that is held to the surface through surface tension.

The melted powder cross-links and cures to again form a solid. The paint first solidifies on the outermost surface forming a solid skin and eventually cures throughout the entire layer. After the baking cycle the paint is fully cured and parts can be immediately handled upon cooling.

Types of Resins Used in Powder Coating

Like wet spray paint, various resin systems are available including epoxy, urethane, polyester and hybrid (mixed) resins. Each resin system has pros and cons in various properties including UV stability, hardness, flexibility, corrosion protection, chemical stability. Some powders are very easy to apply with excellent flow properties that result in a smooth finish, whereas other powders with reduced flow are more prone to a visible texture or orange peel.

Both urethane and polyester powder coating are recommended for external applications due to their UV-resistant properties. Chalking is prevalent in epoxy-based powder systems when repeatedly exposed to UV light. Chalking is the deterioration of the coating from extended UV exposure. The initial signs of chalking are faded color, which will progress to complete deterioration of the coating.

Figure 1: Attributes of various resin based powder coat systems.

Figure 1 summarizes some of the other properties of the various powder coating resin systems. Most commonly epoxy and hybrid (polyester/epoxy blends) are used in applications where chemical resistance is most critical and UV stability is not needed. Urethane coatings offer excellent flexibility and UV stability but do not have the hardness and chemical resistance of epoxy or polyester systems. The best all around resin system is a polyester as they provide UV stability with good corrosion resistance and hardness.

Advantages of Powder Coating  Over Wet Spray Painting

–         Environmentally Friendly: Powder coating does not use any harmful Volatile Organic Compounds (VOCs) which react with sunlight and nitrogen in the atmosphere to form smog. In addition, any overspray powder is collected in filtration systems to either be reused or disposed of easily due to the lack of any hazardous materials within the dry formulations. The electrostatic nature of powder application results in a higher transfer efficiency reducing overall waste as compared to wet spray paint.

–         Durability: Powder coat is typically 3-6 times thicker than wet spray paint. The higher thickness improves the corrosion resistance and overall durability verses wet spray paint. In addition, the thermal bonding process of powder paint provides a stronger bond and structure of the paint making less prone to chipping.

–         Life Cycle Cost: Although the initial application costs of powder coating may be higher than wet spray paint, the improved durability and corrosion protection of powder coat paint often result in a longer life of the product as such this can help reduce the overall coating cost per year of product service.

–         Safety: The solvent carriers used in wet spray paints are a health risk as well as well as highly flammable. Build-up of wet paints within spray booths pose a significant fire risk as do the storage of wet paints. Inhalation of solvents can lead to irritation of the nose and lungs and can lead to various VOC related health issues.

Wet Spray Paint Background

Application

Liquid paint is applied in a fine spray, in which the resin of the paint is suspended within a solvent or carrier. The solvents used are Volatile Organic Compounds (VOCs) such as methyl ethyl ketone (MEK), turpentine, methylated spirits (mixture of methanol and ethanol), xylene, toluene and acetone. The paint is held on the surface of the part through surface tension making it very prone to drips and sags if applied too heavily.

The solvent then evaporates from the surface of the part resulting in a cured painted surface. This process can be accelerated through baking of the parts and multiple coatings of paint are often applied to increase overall thickness.  Commonly, wet spray paints are applied between 0.0005-0.001 inches per side.

Advantages of Wet Spray Painting Over Powder Coating:

–         Self-Drying: An oven is not required for spray-painted parts. Powder coated parts require an oven for the cure process

–         Color Matching and Touch-Up: Color alterations are easily adjusted with wet paint systems. Wet paints are readily mixed on site to achieve the desired final product. In addition, wet spray paint systems are very easily reapplied to the surface for touch-up or repairs as required.

–         Thickness (thin): Wet paint can be applied to a surface with minimal thickness and still achieve a smooth coat. Although thinner coatings provide less durability, they are preferred in some applications where part tolerances, fitment or a mirror-like smooth finish are important.

–         Expense: The cost of getting a component coated via sprayed paint for example is generally lower than powder coating. In addition, parts can be reworked or painted multiple times with wet spray systems much more easily than with powder coating.

–         Range of Substrates: Because wet spray paints do not require electrostatic attraction to be applied nor do they require baking to cure, they can be readily applied to any substrate including non-metallic parts such as fiberglass, plastics and wood. Powder coating requires the component to be electrically conductive such that the negatively charged particles are attracted to the grounded part. Although specialized processes exist for powder coating nonmetallic components, they are not readily available.

Comparing Powder Coating vs Wet Spray Painting

Both powder coating and wet spray paint systems use similar resins including epoxy, polyester and urethanes. Powder coating results in a coating 3-5 times thicker which offers superior durability and achieve a longer lifetime than wet paint systems. Powder coating provides a more effective corrosion barrier that in turn protects the base substrate from the surrounding environment.

The durability of powder coat finishes reduces the likelihood of chips, flakes, or chalking. The powder coating price will initially exceed the cost of a wet paint system; however, powder coated finishes achieve a longer life than a wet paint system which will more than cover the difference in initial expense which can make it more cost effective.

Wet spray paint offer advantages for both color matching and touch-up painting since the part does not need to be baked to cure the paint. Unlike wet paint applications, powder colors cannot be simply mixed to make a different color, if two different powder coat colors are mixed the final finish will be a speckled combination of the two.

Although the thinner coating of wet spray paint offers reduced durability, it may be preferred for parts or applications where coating buildup must be minimized or an extremely smooth finish is required. Finally, wet spray paint can be readily applied to nearly any substrate including nonmetallic parts made from plastic or wood.

Powder Coating at Advanced Plating

History

Advanced Plating Technologies was one of the pioneering companies to offer powder coating services in Milwaukee, Wisconsin when the original powder coating system was installed in 1982. Today, Advanced Plating Technologies is a premier provider of industrial powder coating services offering a diverse selection of resin systems, textures and colors.

In addition, APT can simplify your supply chain offering both powder coating and plating services and can provide powder coat over a wide range of plated finishes. Advanced Plating Technologies offers industrial powder coating services within various industries including the medical, defense, marine, power distribution, agricultural and food processing industries.

Selective Powder Coating Capabilities

Powder coating offers key advantages over competing painting processes such as e-coat or wet spray paint including improved corrosion resistance and durability. However, the thickness of the powder typically ranges between 2 to 6 mils (0.002-0.006 inches). As such, functional surfaces of coated parts must often be masked including sliding wear surfaces, interference fit and threaded features, sealing surfaces, and conductive surfaces.

APT has an extensive background in selective powder coating techniques and is up to the challenge of the most demanding or selective paint requirements. Over 80% of APT’s powder coating jobs require some sort of selective coating, with some applications having upwards of thirty masks per part. APT has a dedicated engineering department that can pull from over forty years of selective experience to develop custom masks and a selective process matched to your specific application.

Contact APT for Your Specific Powder Coating Project

Advanced Plating Technologies an ISO 9001:2015 & 13485:2016 certified powder coating company that offers a full range of powder coating services for any application such as epoxy powder coating and polyester powder coating. Reverse engineering of existing or failed applications and components is available to provide design assistance. Feel free to contact a member of APT’s technical sales team for further assistance at sales@advancedplatingtech.com or 414.271.8138.

Blog Authored by Justin Koch, Manufacturing & Process Engineer

The post Advantages of Powder Coating Over Wet Spray Painting-What You Need to Know appeared first on Advanced Plating Technologies.

One of the greatest shortcomings for the longevity of copper, brass, or even stainless steel contacts is corrosion of the base material. This issue is a greater problem in harsh or extended duty contacts which is why gold plating is preferred for these applications.

Gold plating deposits a noble gold layer that will not corrode or form oxides or compounds even at elevated temperatures or when exposed to highly corrosive environments. An added benefit is that gold is a better electrical and thermal conductor than the many of the base materials contacts are fabricated from.

Corrosion & Oxidation of Contacts or Terminals

Most gold connectors and contacts are not made from pure gold but are rather fabricated from a base metal such as C172 or C173 beryllium copper, C510 phosphor bronze, C360 leaded brass or austenitic stainless steel. This is for obvious cost reasons but also to provide a foundation material with the strength and spring temper that the design requires. Since these base materials are not precious metals, they are subject to corrosion which forms compounds on the surface such as oxides, sulfates or sulfides.

Since these compounds are not conductive metals, they interfere with the transfer of current or signals through the conductor. Corrosion and the formation of these compounds occur mainly when the base metal is exposed to the atmosphere or galvanic corrosive effects from contact with other metals.

Copper and Copper Alloys (e.g. C101 Oxygen Free Copper, C110 Copper, C172 or C173 Beryllium Copper, C510 Phosphor Bronze) corrodes when exposed to elements in the environment including oxygen and sulfur. Copper corrosion products such as cupric or cuprous oxide as well as copper carbonate, sulfide or sulfate can appear brown, blue or green (patina) depending on the compound formed and the pH of the environment.

The Statue of Liberty is a great example of the patina that is formed when copper is exposed to the acidic environment of New York’s acid rain. The compounds that form on copper becomes a protective film that slow the rate of future corrosion. The negative effect of this is that the copper compounds formed are not conductive and degrade the performance of the electrical contact or connector.

Brass (e.g C260 Brass, C360 Free Machining Brass) being an alloy of copper and zinc, oxidizes and corrodes very similarly to copper. It also corrodes because of the high amount of zinc that is alloyed with the copper. The addition of the zinc makes the brass less corrosion resistant than copper and more susceptible to both corrosion and loss of zinc or dezincification. In either scenario the brass will become less conductive and will not be a good electrical connector.

Stainless Steel (e.g. 304 or 316 Stainless Steel or 303 or 416 Free Machining Stainless Steel) is often thought of as being free from corrosion. However, stainless steels are very susceptible to attack from chlorides found in bleach or salt water and can form traditional rust readily in these environments.

In addition, in less aggressive environments, stainless steel naturally forms a thin nickel/chrome oxide on the surface that protects the steel from further oxidation. However, this film like all oxides is less conductive and will increase the contact resistance of the terminal or contact.

Underplate Role in Minimizing Corrosion of Gold Plated Contacts

Gold plating will not corrode but having a layer of gold on the parts will not stop the substrate from corroding or oxidizing. This is due to the fact that thin layers of plated metals have small pores which allow for corrosion to propagate through.

To minimize gold plating corrosion through the plating there are several design factors that must be taken into consideration. The first is the thickness of the plating, in most scenarios the thicker the gold plating the better the corrosion resistance will be. But the second and more important factor is the porosity of the plating.

Although the thickness of gold plating is key to making contacts have more corrosion protection, there are limitations to the gold thickness primarily due to cost. In addition a higher gold thickness, nickel plating is used to increase overall plating thickness and make the parts more corrosion resistant.  It is the combination of gold plating and nickel plating that can help make gold plated electrical contacts and connectors corrosion resistant.

Plating Porosity is a major factor in corrosion resistance of any gold plated parts. At thin thicknesses below 0.0005” per side, most plated metals have an intrinsic porosity that allows corrosive products to reach the substrate and likewise, corrosion products to propagate back to the surface.

Each plated layer has a unique porosity similar to a fingerprint, as more layers are added it is less likely for the pores to reach the base material.  This is due to the fact that pores are concentrated at the grain boundaries and each plated layer has a unique grains structure. Adding layers adds the complexity of the path from the substrate to the surface for a continuous pore to exist.

Figure 1: Example of Grain Structure in Copper- Pores Are Concentrated at the Grain Boundaries

A tangible example of this phenomena is pouring water through a screen.  The water will not pour thru the screen as fast as pouring water straight from a pitcher. Likewise, as more screens are added, the water will flow more slowly. The rate of the water flow through the screens can be thought of the rate at how quickly corrosion will occur in plated layers.

As the thickness of the plated layers are increased, the pore size and density in the screen becomes smaller and smaller. By plating thicker layers to reduce the pore size and adding more layers (screens) eventually, the water flow can be stopped. This condition is what is referred to as a pore-free barrier coating.

Nickel Plating is a common underplate for gold plated contacts because it is a hard metal that is load-bearing, which is useful when both the base material and the final plating layer are soft metals (such as a copper part and gold plating).

Nickel plating prevents parts from corroding by becoming a barrier between the substrate and the environment and it works by physically stopping the moisture and air from getting to the copper, brass, or steel. Nickel also can work as a diffusion barrier to prevent the copper from migrating through the gold to the surface which is undesirable since the copper could then oxidize or corrode on the surface.

ASTM B488, Standard Specification for Electrodeposited Coatings of Gold for Engineering Uses, summarizes the reasons for utilizing a nickel underplate in Appendix X6 which is provided in Figure 2 below:

Figure 2: ASTM B488 Appendix X6 Summarizes Reasons for Using Nickel as an Underplate to Gold

Copper Plating is an additional layer that can be added to gold and nickel plated contacts in order to increase the overall corrosion resistance. Figure 2 illustrates the porosity of a part that has a gold over nickel plating (top) and one with gold over nickel over a copper subplate (bottom). The reduction in pore density is significant which directly correlates to better corrosion resistance.

Figure 2: Pore Density of a Gold and Nickel Plated Contact with a Copper Underplate (lower plot) and Without a Copper Underplate (upper plot)

The reduction in porosity is due to the additional layer of plating pores that would need to line up in order for the moisture to reach the substrate. However, copper is not recommended to be the penultimate layer before the final gold since it can both oxidize through the gold as well as form a gold/copper eutectic through solid state diffusion. This will not only reduce the effective gold thickness but will also form a weak eutectic that can reduce adhesion and conductivity.

Gold Plating Specifics to Optimize Corrosion Resistance of Contacts

Gold Plating is the final deposit in connectors and contacts due to its outstanding electrical properties and noble properties. Because of gold’s inert nature it will not corrode or oxidize. However, the above noted underplate porosity and thickness characteristics need to be taken into consideration to ensure the gold plated contact is sufficiently robust for the intended application.

Duplex Gold Plating is a special type of plating gold that combines two different types of gold – soft gold (99.9% pure) and hard gold (99.0-99.7% pure). This is done to decrease the effective porosity in overall gold plated layers since the two gold layers have unique grain structures which do not align. Which gold layer should be the final or ultimate layer is a function of the part use as summarized below:

·        Static Connectors: Gold plated static connectors are connectors that, when installed, make a connection with something that is intended to stay in contact with it. A few examples of this are grounding nuts or studs, fixed contacts or solder pads. Due to the small amount of movement the hardness of the gold plating is not as important and soft gold is the preferred final or ultimate layer.

·        Dynamic Connectors: Gold plated connectors that make repeated connection with something are considered dynamic. A few examples of this are male/female pins/sockets and battery contacts. Since the wear of these connectors is of principle concern, hard gold is the preferred final or ultimate layer. As such, with most dynamic connector duplex gold applications, the hard gold should be the outermost layer.

Gold Thickness is a key characteristic in the corrosion resistance of gold plated connectors. Since the cost of gold plating is directly proportional to gold thickness, the target thickness should be carefully considered and evaluated.

Figure 4 below details four common connector thicknesses and common applications for each. This also illustrates how higher thickness correlates to improved corrosion performance. As noted in the table, a thin layer of gold is sufficient for static connections in controlled environments. However, as the wear resistance and/or corrosion requirements of the application increase, so must the gold thickness as well as the thickness of the respective underplates.

Figure 4 below: Thickness of Gold Plating Based on End Use and Environment

Conclusion

Gold plating offers many advantages for connectors and terminals including excellent electrical and thermal conductivity and reliable contact resistance for electronic applications and more. However, gold plated connectors need to be designed properly to meet the corrosion resistance of the intended application or the parts will not perform reliably.

All base materials used for making contacts or terminals will form compounds or oxides which can migrate to the surface of the gold plated layer increasing the contact resistance. By using multiple plated layers including copper, nickel, gold and even duplex gold plating the overall porosity of the deposit is decreased thereby increasing corrosion resistance.  Increasing the thickness of each of the plated layers helps reduce the pores in the plating of the parts which makes it harder for the atmosphere and moisture to get to the substrate.

The above information is provided as a general guide for engineering a finish for a specific contact or connector. There are many additional considerations specific to each plating application that are beyond the scope of this article.

Advanced Plating Technologies an ISO 9001:2015 gold plating company offers extensive surface engineering support for gold plating services or other applications. Reverse engineering of existing or failed applications and components is available to provide design assistance. Feel free to contact a member of APT’s technical sales team for further assistance at sales@advancedplatingtech.com or 414.271.8138.

Blog authored by Dominic Scardino, Estimating Engineer

References:

1. Reid, F. H., & Goldie, W. (1987). Gold Plating Technology (Reprint ed.). Amer Electroplaters Soc.
2. (2021, September 28). Protecting electrical connectors from water ingress with Nyogel 760G. Newgate Simms Tech Support. https://support.newgatesimms.com/protecting-electrical-connectors-from-water-ingress-with-nyogel-760g/
3. Ignition Switch, Repairing electrical parts, MGA. (2014). MGAGuru. http://mgaguru.com/mgtech/electric/et126.htm
4. (2018, June 11). How Much More Chromium Does D2 Need to be Stainless? Knife Steel Nerds. https://knifesteelnerds.com/2018/06/11/how-much-more-chromium-does-d2-need-to-be-stainless/
5. Grain size analysis in copper. (2019, July 26). Clemex. https://clemex.com/analysis/grain-size-analysis-2/

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Metal Finishing Environmental Stewardship Benefits More Than Just the Environment

Advanced Plating Technologies has always taken a clear stance on the environment.  Since the beginning of the clean water act in 1972, APT has been committed to not only meeting but exceeding all local, state and federal environmental laws.  This record speaks a silent assurance that many “low cost” metal finishing suppliers cannot.  In fact, metal finishing companies with substandard environmental systems is a liability not only for their continued operation but for potential litigation down the road against themselves and their customers.

APT’s Modern Waste Treatment Facility

The metal finishing industry continues to be one of the most highly regulated industries in the country with new regulations and requirements added each year.  New regulations on PFOA and PFOS compounds and additions to the Toxic Substances Control Act (TSCA) are just a few of the latest impending regulatory restrictions. For this reason, APT continues to invest in improved treatment technologies and self-imposed compliance standards below permit levels as an example within the Industry.  APT’s leadership has been recognized with numerous local, state and national environmental awards from the Milwaukee Metropolitan Sewage District (MMSC), Wisconsin State Department of Natural Resources (DNR) and the United States Environmental Protection Agency (EPA).

The history of environmental compliance within the metal finishing industry is marked by various landmark laws that have far-reaching implications counter to what many would consider sound environmental practices.  In 1980 the Resource Conservation and Recovery Act (RCRA) mandated that the F006 wastewater treatment sludge produced by electroplaters shall be listed as hazardous waste categorically. This designation was applied without testing the waste product for its actual chemically hazardous profile using the TCLP methodology.  Thus, the applied arbitrary designation limits the ability of the waste to be recycled to recover the valuable metals contained therein. Since then, this legislation has come under increased criticism from many in the industry as it results in the waste of thousands of tons of valuable metals each year.

However, there have also been moments of true partnership in between agencies and industry towards a common environmental goal.  In 1994, under the Clinton Administration the US EPA launched the Commonsense Initiative which promoted cleaner, cheaper and smarter environmental standards. This initiative engaged several industries including the Metal Finishing industry. The Finishing Industry was challenged to propose a package of improved policies which were to be based on projects and discussions between industry and committee members. This resulted in the passing of an extension of the 90 day storage rule to 270 days for materials recycled and transported over 400 miles.

APT CEO John Lindstedt has been a principal leader within the metal finish industry in environmental compliance and sound legislation based on facts.  John has served on government regulation committees with local state and federal agencies, including 30 years work with the Government Activities Committee (GAC) for the National Associate of Surface Finishers (NASF).  Recently John was interviewed by Scott Francis of Products Finishing Magazine to discuss ways that current legislation could be improved to further promote recycling of valuable resources contained within the sludge by-product of many metal finishing shops.

Checkout the recent On the Line Podcast from Products Finishing to hear John discuss how current environmental regulations could be improved to benefit industry and the environment alike.

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When it comes to selecting a coating for your firearm or firearm components there are several key features you need to consider. When going through options you need to ensure your firearm finish can meet several key characteristics such as the ability to hold tight tolerances, provide enhanced lubricity, wear resistance, corrosion protection, and, of course, provide a uniform and consistent black appearance.

Advanced Plating Technologies has worked hand-in-hand with numerous firearm OEMs throughout the years to provide a superior black finish that meets all the above requirements. Tacti-black® HP+ was developed in response to feedback received from numerous firearm OEMs that needed a finish that could meet all of the above requirements on a range of materials including steel, stainless steel, and aluminum.

A Firearm Finish for Any Base Material

Unlike common firearm coatings such as black oxide, nitriding, anodizing, and QPQ, Tacti-black® HP+ is “material blind” meaning it can be plated onto any metal material. This tactical firearm finish is perfect for a large array of firearm components like custom lower receivers, trigger sears, hammers, and stamped magazines.

APT can provide this proprietary tactical firearm finish to most any metallic substrate from CNC firearm components to 3D printed and MIM alloy components with a density of over 90%.

Superior Corrosion Resistance for Your Firearm & Its Components

Having a tactical firearm and gun component finish that provides not only enhanced lubricity, but high corrosion resistance is paramount. Tacti-black® HP+ is available in both medium phosphorus and high phosphorus versions and can be engineered to meet application-specific corrosion demands.

Medium phosphorous Tacti-black® HP+ can achieve up to 96-hrs salt-spray per ASTM B177; however, high phosphorous Tacti-black® HP+ can withstand over 500-hour salt-spray for the most aggressive environments. Unlike traditional Parkerizing (phosphates), nitriding, or black oxide, Tacti-black® HP+ can be engineered to meet an application-specific corrosion requirement.

Uniform Firearm Finish that Resists Fouling

Consistency is Key! Tacti-black® HP+ is recommended throughout the firearm industry because of its consistent black finish. Many firearms can consist of different base materials, so a consistent and uniform black color is needed irrespective of the material finished.

This tactical black firearm finish is perfect for firearms that have MIM or 3D printed components. Unlike basic black finishes, Tacti-black® HP+ can hold consistent black throughout separate substrates.

Utilizing our HP+ molecular sealer applied to the finish our proprietary finish helps repel sand, dirt, and water making it an ideal finish for tactical applications. In addition, the sealer helps resist carbon fouling, facilitates cleanup, and is compatible with all CLP products.

Coating Hardness Without Affecting Base Hardness

Increased hardness to your firearm and components means increased part life. With the increase in hardness, you will also get a more reliable firearm for years to come. As-plated the hardness of Tacti-Black® is between 50-56Rc.  Tacti-Black is plated at a ‘cool’ temperature below 200F which, unlike Nitriding or QPQ, will not alter the hardness or temper of base materials.

If you need a harder finish, Tacti-black® can be heat treated which in return can transition the deposit which will increase the deposit hardness to ~ 69Rc which is near the hardness of hard chrome. This hardness allows for a high wear coating for your tactical firearm finish.

Conclusion

With future firearms and components being pushed to the extremes due to higher pressures, more corrosive environments, and demand for higher precision performance, the need for more durable, lubricious coatings will only increase. APT’s Tacti-Black HP+ is our fastest growing finish ever.

Tacti-Black HP+ electroless nickel offers the outstanding uniformity, lubricity, corrosion resistance and hardness of electroless nickel with a tactical black color  making it ideal for tight tolerance fire control applications including magazines, triggers, sears, actuators, bolts and hammers. Check out our TACTI-BLACK® HP+ page to learn more about our capabilities, finishing process, and how we can help with your upcoming firearm finish application or project.

Reach out to a member of our Technical Sales staff for more information on how we can help with your application. 

Blog Authored by Luke Copp, Sales & Marketing Associate 

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Gold has and continues to be a principle finish for electrical components especially with the continuing miniaturization of electronics.  One of the primary benefits of gold plating services is a finish that is both conductive and receptive to soldering. When soldering gold plated components there are a variety of important considerations when specified the surface finish. The primary considerations are thickness, purity and the proper selection of an underplate.

Plating Thickness

Gold plating thickness is a critical, and often misunderstood, tenant of gold soldering. In gold soldering the physical bond is made between the underlying nickel layer and the solder itself, with the gold layer serving as barrier to help maintain the solderability of the nickel layer. Typical gold thickness for solderability is in the range of 10uin to 30uin as it provides adequate protection against oxidation to preserve wetting while keeping the cost of the finish as competitive as possible.

When soldering, gold dissolves into the solder through solid state diffusion.  With heavier gold deposits, more gold alloys within the solder joint.  In the diffusion process the gold reacts with the solder creating a gold intermetallic amalgam.  If the gold in the solder exceeds 3% by mass, the solder joint can become embrittled causing joint failure, especially in dynamically or thermally stressed joints.  The level of impurity and thickness of gold are directly related, thus thickness of the gold must be balanced between corrosion/oxidation protection, contact cycle life and solderability.  (Soldering to Gold – A practical Guide).

Purity

Purity of both the gold and underplate layers is critical to achieve the best solderability. For gold plating there is an importance to minimize organic impurities through proper tank maintenance. Organic impurities that are imparted into the plating layer can interfere with the soldering and can cause dewetting or voids in the solder.  Soft gold of 99.9% purity is typically the preferred gold for bonding or soldering applications.  However, nickel or cobalt hardened gold can solder well and provide improved wear resistance on contact surfaces.  However, the purity of the hard gold needs to be preserved through proper analytical work and tank maintenance.

Nickel purity is critical as this layer is the functional bonding layer. For nickel soldering the higher purity nickel the better the soldering. Often plating companies use an organically brightened nickel layer such as a brightened Watts or sulfate-based nickel to give a bright finish at the expense of solderability. Advanced Plating Technologies offers an engineered sulfamate nickel-plating layer recommended as an underplate for gold plating including soldering applications.  This nickel system is free of codeposited organics that can outgas or volatilize during soldering thereby causing voids in the solder joint.

Another common underplate for gold plating is electroless nickel. While there are many advantages to electroless nickel plating including hold tight tolerances, large deposit range, corrosion protection, lubricity – one issue is that phosphorus is deposited in conjunction with nickel on the surface. The phosphorous acts as an impurity in soldering and can impedes soldering. When specifying electroless nickel deposits a medium phosphorous electroless nickel can give you the balance of the positives of electroless nickel while preserving solderability.

Solder Process

When designing a solder process for gold plated parts it is important to remember that the solder joint forms between the solder and the nickel. Therefore, when performing multiple solder operations or reflow soldering, additional liquidous time must be allotted for to provide ample time for the solder to bond to the nickel.  In addition, typically a rosin-only flux is needed when soldering to gold plating.  However, for very thin gold deposits that are significantly aged, a rosin mildly activated (RMA) flux can help with removing any nickel oxides that may have propagated through the gold layer to the surface.

Conclusion

Soldering to gold plating is becoming more and more prevalent with the rise in high-end microelectronics. More than ever it is important to understand the process of soldering to gold and designing surface finishes to provide the most robust, cost effective finish. The proper gold finish must balance corrosion and wear performance with solderability to ensure the best possible design.  A member of Advanced Plating Technologies technical sales staff can assist with designing a finish the meets the specific design requirements of your application.

Blog Authored by William Troske., Process & Estimating Engineer  

Edited by Matt Lindstedt, P.E. , President

References:

1. Ronald A. Bulwith ; Soldering to Gold – A Practical Guide

The post Solderable Gold Plating of Electrical Contacts appeared first on Advanced Plating Technologies.

Nitric vs Citric Passivation Methods

Stainless steel is an inherently corrosion resistant material, however when stainless steel is machined, formed or fabricated free iron can be introduced to the surface that can corrode independent of the base material.  Proper passivation of stainless steel with an oxidizing acid such as nitric or citric acid removes this free iron and promotes the growth of a thin, dense protective oxide layer which maximizes the corrosion resistance of the stainless steel. Depending on the type of stainless steel and end application certain passivation processes may perform better at passivating than others. In this article we will compare nitric vs citric acid passivation which are the two primary chemistries specified in ASTM A967 and AMS 2700.

Nitric Acid Passivation

When comparing nitric vs citric passivation, the most common method used throughout industry is nitric acid passivation. The Nitric acid passivation processes was the original passivation processed specified in QQ-P-35, the first military specification covering passivation, revision A being released in the 1960s.  Nitric acid passivation offers a range of options to customize the oxidizing potential of the acid to suit a specific grade of stainless steel. The various methods and types of nitric acid passivation include several heated options as well as options that include a sodium dichromate.

The higher nitric acid concentration and the higher the nitric acid temperature, the more oxidizing potential the passivation chemistry has.  Sodium dichromate can also be added to the nitric acid to increase the oxidizing ability of the bath making it better for less corrosion resistant stainless steels, such as precipitation hardened, martensitic and ferritic grades of stainless steel.  These grades of stainless steel have less nickel and chromium in them making them more susceptible to etching.  The higher the oxidizing potential of the chemistry, the faster and more effective the passive oxide barrier is formed on the surface, reducing the potential for etching.

A summary of the various nitric acid passivation methods per ASTM A967 is provided below:

• Nitric 1: 20-25 v% Nitric Acid, 2.5 w% Sodium Dichromate, 120-130F, 20 Mins minimum
• Nitric 2: 20-45 v% Nitric Acid, 70-90F, 30 Mins minimum
• Nitric 3: 20-25 v% Nitric Acid, 120-140F, 20 Mins minimum
• Nitric 4: 45-55 v% Nitric Acid, 120-130F, 30 Mins minimum
• Nitric 5: Other combinations of temperature, time, and acid with or without accelerants, inhibitors or proprietary solutions capable of producing parts that pass the specified test requirements

ASTM A967 also offers a very useful reference of stainless steel grades to the recommended method of nitric acid passivation. A summary of this table is provided:

Contamination of passivation chemistry can lead to flash attack of the surface, which produce a heavily etched or darker surface. A common containment that leads to flash attack is chlorides which can come from several sources including dragging in acids or using having chloride in the water. In addition, organic buildup in passivation baths such as the drag-in of machining oils from parts that are not properly cleaned, can lead to flash attack or etching of the stainless steel.  As such, regular analytical analysis and maintenance of passivation chemistries is required. Certain passivation methods are also more resistant to flash attacks than others. For nitric acid passivation the baths with increased oxidizing potential are also more resistant to flash attacks. Nitric acid also is more resistant to flash attack compared to citric acid. ^[1]

Citric Acid Passivation

Citric Acid passivation was developed by Adolf Coors brewing company for the passivation of the inside of beer kegs. It offers an effective alternative to nitric passivation with less handling concerns and is consider environmentally friendly being on the GRAS (Generally Recognized as Safe) list for the FDA making it ideal for food and beverage applications.

When comparing nitric vs citric passivation, citric solutions can effectively passivate a wider range of stainless-steel alloys compared to any one nitric acid passivation solution, allowing for assemblies of several stainless-steel alloys to be passivated.

Passivation chemistries remove free iron from the surface but can also remove some nickel and chromium from stainless steel. Removing nickel and chrome reduces the corrosion resistant material at the surface leaving a thinner oxide layer. Citric acid passivation selectively removes iron over nickel and chromium leaving a thicker corrosion resistant oxide layer than nitric acid passivation ^[2] 

Once of the other advantages of citric acid is the bath formulation can be adjusted to reduce cycle times over nitric acid, allowing for increase throughput and reduced costs of passivation verses that of nitric acid.  Cycle times as low as 4 minutes are possible with certain citric acid passivation formulations.  A summary of the various citric acid passivation concentrations and times from ASTM A967 are provided below.

• Citric 1: 4-10 w% Citric Acid, 140-160F, 4 Mins minimum
• Citric 2: 4-10 w% Citric Acid, 120-140F, 10 Mins minimum
• Citric 3: 4-10 w% Citric Acid, 70-120F, 20 Mins minimum
• Citric 4: Other combinations of temperature time and concentration of citric acid with or without chemicals to enhance cleaning, accelerants or inhibitors capable of producing parts that pass the specified test requirements.
• Citric 5: Other combinations of temperature time and concentration of citric acid with or without chemicals to enhance cleaning, accelerants or inhibitors capable of producing parts that pass the specified test requirements.  Immersion bath to be controlled at pH of 1.8-2.2

Passivation Pretreatment

A universal requirement when comparing nitric vs citric acid passivation is the need for parts to be properly pretreated. For the martensitic grade and precipitation hardened grades of stainless steel that are heat treated, there is a potential for scale on the parts after the hardening process. For machined parts there is cutting fluids and other oils. Finally, for assemblies there is weld scale and heat marks. Any of these scales or oils left on a part lower the corrosion protection of the material and in passivation will inhibit the effectiveness and can damage parts. Scales and oils should be removed before passivation. Oils can simply be cleaned or vapor degreased off parts. While scale needs to be removed either with descaling mineral acids such as hydrochloric acid, or inorganic deoxidizers such as potassium permanganate or with abrasive methods such as media blasting or vibratory polishing.  Mechanical scale removal methods are recommended for those parts that require a very uniform surface especially for parts with heat-affected zones such as weldments.

Conclusion

Passivation of stainless steel is a critical component in the manufacturing of stainless-steel components to ensure fully optimized corrosion resistance. There are many different factors when choosing a citric vs nitric passivation method and this article covered some of the basics of choosing a passivation process. For additional information and what process may be right for your application please feel free to contact a member of Advanced Plating Technologies Sales & Engineering group at sales@advancedplatingtech.com or 414.271.8138.

Blog Authored By: Will T., Process Engineer

References:

[1] Mohr, J. H. (2007, August 1). Making Stainless Steel Stainless. Retrieved from PF Online : https://www.pfonline.com/articles/making-stainless-steel-stainless

[2] R. Kremer, Stellar Solutions, Inc. (2007). Developments In Citric Acid Passivation of Stainless Steel. McHenry : NSF.

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Silver Tarnish and Its Properties

Silver Tarnish (Left) vs No Tarnish (Right)

Silver plating is often used for cosmetic applications and is found on items such as silverware and jewelry. While silver provides value and an aesthetic appearance to these items, it is also used in multiple sub sectors of manufacturing – Power Transmission, Medical, Aerospace, Electronics, Electric Vehicle and many more. The reasons silver plating is used is vast: ductility, electrical and thermal conductivity, solderability, high temperature lubricity, as well as excellent optical reflectivity. Although there are many positive attributes to silver plating, silver tarnish is one is a common occurrence when the proper steps are not taken.

Silver tarnish occurs when the silver plating is exposed to air or water containing an oxidant and a source of sulfur. This chemical reaction is what forms the silver sulfide on the surface of the part and can turn the white luster finish to a yellow or sometimes a black or brown. Aside from an unpleasant appearance, the tarnish can continue to increase over time.  Although the cosmetic aspect of silver tarnish is not typically a desired outcome, silver sulfide is still conductive, which is different than other metal oxides that form over time.  However, industries typically desire a more pleasing cosmetic outcome and Advanced Plating Technologies can help avoid silver tarnish through post-plate processes as well as protective packaging.

Two commonly used silver plating specifications, ASTM B700 and AMS 2410, both contain call outs for supplementary anti-tarnish applications. It is crucial to include the instructions on a print or plating call out to ensure that a post-plate anti-tarnish application is provided. Advanced Plating Technologies has a wide vendor base that can locate any specific anti-tarnish application that a job may require. Additionally, packaging options can be put in place to help avoid silver tarnish. These packaging options can be as simple as including desiccant packs with the plated parts to nitrogen bagging. Nitrogen bagging fills the bag of parts with nitrogen and removes the oxygen which plays a key role in forming oxides.

While there are many ways to avoid silver tarnish, two good questions to ask before looking at anti-tarnish applications is how long the parts will be stored and what type of environment the parts will be stored in. By answering these questions APT can ensure that the proper post-plate tarnish application is selected.

Have Questions? Contact us at sales@advancedplatingtech.com for more information.

By: E. Probasco, Plant Manager

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