Plating with a tin-lead alloy is often used when a softer and more ductile surface is desired. Depending on the application, the alloy can consist of anywhere from 50 to 95 percent tin. A tin-lead alloy offers a wide range of appearances, as matte, semi-bright or bright finishes can be achieved. Tin-lead plating also offers excellent corrosion resistance, and additional corrosion protection and increased shelf life can be attained through a reflowing process. Tin-lead is also known for its solderability.
Tin-Lead Applications
By far, the most common use of tin-lead plating occurs in the electronics industry. Tin-lead alloys are an excellent conductor of electricity and feature a relatively low melting point. The alloy’s ductile quality also protects the material from harm during subsequent manufacturing operations such as stamping. The lead component of the alloy is extremely useful in preventing the development of “whiskers,” which are thin strands of tin that protrude from the surface. Whiskers can be a serious issue in electronics components, as they can create arcing and electrical shorts if they break away from the material.
The Need for Tin-Lead Plating Alternatives
While tin-lead plating can serve many useful purposes, environmental and health concerns associated with lead has created a demand for lead-free plating alternatives. Several acceptable tin-lead substitutes are now available.Tin
Tin
While other tin-free alloys — including tin-copper, tin-silver, tin-bismuth and tin-zinc — can be used as an alternative to tin-lead, pure tin is viewed as a better choice over each of these options. Plating with pure tin is simpler and more cost-effective than when using any of the tin alloys. Another advantage is that plating with tin offers superior stress control. And while the formation of whiskers is still a risk when plating with tin, the risk can be mitigated more easily than when plating with tin alloys.
Another advantage of pure tin plating over tin alloys is you can plate with tin using existing conventional plating equipment, which eliminates the need for expensive equipment upgrades. You also won’t have to redesign connectors or terminals. Another key benefit is pure tin coating offers greater protection against corrosion than most tin alloys, particularly tin-silver.
Gold Flash Plating
Gold flash plating is viewed as a better alternative to pure tin plating when coating electrical connectors. The two available gold flash plating methods include a gold flash over nickel and gold flash over a palladium-nickel alloy. Both processes are extremely easy to implement and offer good solder ability, joint reliability and heat resistance (due to gold’s much higher melting point). There is also minimal risk of whisker formation. The biggest downside is the high cost of gold, which can make gold flash plating more expensive than tin and tin alloy plating.
Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG)
Another type of finish that has been developed over the past decade or so is Electroless Nickel/Electroless Palladium/Immersion Gold (ENEPIG). As with any electroless plating process, ENEPIG provides the coating via autocatalytic chemical reaction as opposed to the use of electric current. This enables a more uniform, even coating and a greater ability to control coating thickness.
ENEPIG is particularly suitable for lead-free soldering and wire bonding applications. A key advantage is that the issue of brittle fracturing of BGAs is virtually eliminated. Another ENEPIG application that is showing promising results is as a replacement for the secondary image technique commonly used in the manufacturing of cell phones.
Contact Sharretts Plating to Learn More About Tin-Lead Plating Alternatives
As part of our continuing effort to implement the most environmentally friendly plating solutions, SPC has replaced our tin-lead plating process with a variety of “green” metal finishing alternatives that deliver superior results. Contact us to learn more about our lead-free plating options and receive a no-obligation plating quote today.
