Issue link: https://iconnect007.uberflip.com/i/1529411
58 PCB007 MAGAZINE I NOVEMBER 2024 disbanded, was what we used at that time.) You didn't get fumes, so you didn't need ven- tilation. By operating at a lower temperature, you had a more stable pH and fewer issues with the volatilization of other chemicals, making it safer to work with. All those things were better. Holden: Also, it doesn't cause dermatitis, a potential issue with other metals and handling. It has a very high melting point and instantly forms a protective oxide for corrosion. Because tin-nickel is unlike any other barrier metal, it should be considered when looking for pro- cess improvements that provide bet- ter quality and reliability and cost less. Every 30 to 50 years, things come around full cir- cle. It's time to talk about tin-nickel again. With such potential, why didn't tin-nickel get more traction in the 1980s as PCB fabrication was developing? Is there a place for it today? Carano: We oen get so enamored repeating the same processes. It needs a champion to see innovation and be willing to run with it and see what happens. ese are called step changes, and sometimes you need that. Many people today aren't willing to take a risk; they aren't willing to even look at things. ey want to stay safe, so they wait for others to prove something out and then they will jump onboard. Why didn't tin-nickel catch on? PCBs were being manufactured and money was being made. ere was not enough reason for peo- ple to make a change when things were going pretty well. It's time for our industry to take another look at it. ere may be things now that are pushing more favorably in that direction. We still bat- tle a prevailing attitude that "our boards are still offered the same performance as much thicker gold or palladium—all very expensive precious metals. It may be time to take a hard look at this once again. So, omitting the stripping process and using fewer precious metals—a tin-nickel process— would cost significantly less? Carano: Yes. Gold is a very dense metal—19.3 grams per cubic centimeter—compared to nickel which is about 8.9 grams per cubic cen- timeter. For every microinch of gold you put down, you're actually using twice the amount of gold than you would if it were another type of metal because gold is so much denser. You're putting twice as much gold down and you're paying for it. As Happy has said, if you could replace half the gold and still get a great deposit and performance, you'd be saving thousands of dollars per rack. Beyond that, it would also improve the distribution of the gold across the panel. If you have a more uniform six-sigma rather than a three-sigma distribution, you will use even less gold. What are the potential benefits and draw- backs to using tin-nickel as a plating surface finish? Carano: It is an electroplated process. It's per- fect because it's a 1:1 monatomic ratio, with one atom of tin to one atom of nickel, and it's always a 65:35 percent ratio of the two metals. We made it more ductile by developing some organic additive agents to deal with the issue of brittleness, which was part of the proprie- tary process. We also raised the pH, so it was more environmentally friendly to work with. We could run it at a lower operating tempera- ture than what the conventional Tin Research Institute textbook indicated. (is group, now