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In the 1980s, Electrochemicals, Inc. (now Electrochemical Products) made a significant shift from furniture and industrial goods to electronics and manufacturing. During this journey, a tin-nickel plating alloy was developed. In 1984, Mike Carano, a young engineer, published a paper on tin-nickel plating alloy, but after some initial attention, the plating solution fell into obscurity.
Today, PCB fabrication looks largely the same, yet changes are afoot, chiefly due to the demands for very fine feature capability on printed circuit boards, as well as environmental sustainability. So, in this fascinating conversation with Mike Carano and Happy Holden, we take another look at tin-nickel and its advantages in both performance and sustainability.
Marcy LaRont: Mike, please explain the unique metal properties of the tin-nickel alloy and why fabricators should consider this as a surface finish solution today.
Mike Carano: Tin-nickel is a metastable alloy. It is monatomic, meaning that no matter what you do with the chemistry or how you manipulate the grams per liter of one metal or the other (or the amps per square foot), it always comes out as 65% of one metal and 35% of the other. I’m not aware this is true with any other combination of metals.
Typically, if your chemistry is out of balance—if you have more tin in the solution than you have lead—you will plate more tin. It’s precisely why there are so many alloys out there. In that respect, tin-nickel is pretty amazing.
Happy Holden: When I was at Hewlett-Packard, Dr. Morton Adler from Bell Labs called me and said he wanted us to fab his boards using tin-nickel, because he knew we were using it. I plated the boards with tin-nickel and added a gold strike. This thin gold was cobalt-hardened and the final thickness was still only 3–5 microinches when we finished. About a month after I sent them back to Adler, I got another call. He said, “What the hell did you send me? We’ve completed our reliability testing and your 3–5 microinches on tin-nickel outperforms our 120 microinches of sulfamate nickel on our contacts and other relays.”
Continue reading this conversation in the November 2024 issue of PCB007 Magazine.
