Silver plating started as a common way to provide cheaper versions of household items, which were originally made of silver.
At its beginning in the 18th century, this included cutlery, platters, plates and candlesticks among other items. In the 19th century, electroplating arose as a rapid method of finishing mass-produced items. Although the 20th and 21st centuries have seen declines in the use of silver for household wares, this reduction was followed by a rise in the use of silver plating for the electronics industry.
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As communications protocols and technologies have begun requiring faster and faster signal rates, silver is replacing copper as the metal of choice in printed circuit and connector designs. However, the extra cost of bulk silver makes it more reasonable to plate underlying copper, instead of replacing it outright. The beneficial electrical skin effect of silver gives it a lower resistance and it can achieve higher communication frequencies than the underlying copper can provide on its own.
Silver plating, with all of its benefits, still has several drawbacks. From a functional standpoint, silver is a porous material and in highly corrosive environments, the underlying copper will undergo rapid galvanic corrosion and break up the overlying silver, rendering it useless.
The chemistry of silver plating also has adverse environmental impacts. Silver plating solutions contain large quantities of silver cyanide (AgCN - solid) dissolved in potassium cyanide (KCN - Liquid), both highly toxic chemicals. Using these chemicals requires strict procedures for its transport, storage and disposal in quantities.
TRI-M3™, the Solution
Modern communications require faster RF technologies. The use of silver plating on copper substrates has been the most common solution to this need. However, the costs of silver plating, in material, safety risks, and environmental impact leave additional room for innovation.
The engineering team at Electro-Spec, Inc. has confronted this obstacle and developed a plating process that enhances the performance of RF connectors without the use of silver. This plating innovation is TRI-M3™ (also, sometimes known as a Tri-Alloy, Tri-Metal or White Bronze finish).
The composition of the alloy is on average of 55% Cu (Copper), 30% Sn (Tin), and 15% Zn (Zinc). It has a shelf life that far exceeds that of traditional silver plating. Cyanide is used in the make-up of the bath.
The Tri-M3™ finish equals or exceeds silver plating in the following ways:
Hardness:
The Tri-M3™ deposit resembles a nickel finish, possessing a hardness of approximately 600 HV on the Vicker's Pyramid Hardness Test.
Wear:
Tri-M3™ has a coefficient of friction 70% less than that of Silver. Due to this favorable coefficient of friction, its lubricity and hardness, less than 50mg of material is removed per 1,000 revolutions of Tri-M3™.
Corrosion:
The corrosion resistance is virtually identical to Nickel and returns extremely favorable results from tests such as Quick T-change, Mixed Gas, Salt Spray, Kesternich, and Heat Damp.
Solderability:
The Solderability of connectors is significantly enhanced with Tri-M3™ finishes. Soldering on Tri-M3™ can be done with or without a flux, depending upon the deposit's age. In most cases, an R or RMA flux is usable with a Sn/Pb solder on parts that have aged significantly.
Reinforcing and Reduction of other plated materials:
It can also be deposited as an underplate with Gold, replacing the previously required copper or nickel. This mitigates the drawbacks of either material. When copper and gold are deposited on top of each other, the copper atoms will eventually migrate and diffuse into the gold. Nickel, on the other hand, is a magnetic finish, presenting an intermodulation issue in RF connectors at medium and high frequencies.
Tri-M3™, as an underplate with Gold, presents both an excellent immersion barrier for molecular migration and diamagnetic finishes. As an underlying layer, it also reduces the thicknesses required for additional precious metal processing - saving additional material costs.
Environmental Considerations:
There are many environmental concerns in America, Asia, and Europe over the use of both nickel and lead in components and products. Tri-M3™ provides an alternative finish that either surpasses or conforms to all applicable regulatory standards.
Conclusion:
Electro-Spec's Tri-M3™ finish is fast becoming the benchmark for tri-alloy plating. It is a dramatic improvement in plating for both RF and Microwave components that both require high corrosive resistance and tarnishing behavior. Tri-M3™ is quickly becoming the finish of choice as a replacement for nickel, silver, tin and tin/lead.
Want to learn more about the benefits and uses of Tri-M3? Check out our Tri-M3 Plating Guide.
