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Kovar Plating Problems
Quickstart:
Kovar is a ferrous alloy rich in nickel (≈29%) & cobalt (≈17%), often used for hermetic glass-to-metal seals because it's coefficient of thermal expansion matches that of glass.
Kovar may be plated with other metals for solderability or other purposes. But getting plating to properly adhere onto Kovar is difficult because it instantly oxidizes like stainless steel does, whereas proper plating must be metal-on-metal, not metal on oxide. The typical prep for stainless, a Wood's nickel strike
⇦ huh?, should work for Kovar.
Q. We are trying to gold plate short pieces of Kovar. We use 3-5 micron nickel coat then .05 -.1 micron gold plate. The plating appears to be flaking off over relative short time. To try and solve this, the parts were stripped and then heat treated (to burn off oils) and replated. Now the gold plating does not adhere to the Kovar.
If there is someone who can clarify what is happening or is familiar with gold plating of Kovar, a prompt response will be appreciated.
Andy Millner / Silvio MarinJohanson Mfg. - New Jersey
2001
A. I plate Kovar on a weekly basis. I treat it like if I was plating stainless steel. A woods or sulfamate nickel strike is necessary to get good adhesion.
Todd Huehn- Minneapolis, Minnesota
Multiple threads merged: please forgive chronology errors and repetition 🙂
Q. My question is: A kovar flat lid is stamped from strip material between 0.003 to 0.005 thick. There is an issue of particles coming off this part after it has been plated with electroless nickel. The particles are in the micron size and can be a problem should they drop on an exposed I.C chip. To correct this issue I need to find the root cause. The particles test to be the plating material how can I be assured that the plating is not flaking off on its own. I can work on the raw material should that be the root cause.
Thanks,
Walt Sacilowski- Clearwater, Florida, USA
2001
A. Dear Mr. Walt
We regularly plate kovar with nickel for use in transmitting tubes in aqueous plating baths. Deposits are extremely adherent to base material even in harsh environments. If your problem is still there please let me know
Pilani Electron Tubes India - Sangrur, Panjab, India
2005
Multiple threads merged: please forgive chronology errors and repetition 🙂
One of our customers is requesting a change in plating to a Kovar strip which is soldered to a silicon solar cell. They have asked for Nickel strike 0.00003", then Copper plate to 0.00005 to 0.00015 thick, followed by a silver plate, type I, grade B to 0.00008 to 0.00012. Finally a solder plate 0.0002 to 0.0003 which is then fused. Does anyone have experience of this sequence of plating, with the advantages and dis-advantages?
Thanks in advance.
John Hugheselectronics - Hawthorne, California, USA
2004
A. Hi John.
The nickel plating is needed for adhesion onto Kovar because you need to plate metal on metal whereas Kovar instantly acquires an oxide surface. Wood's Nickel and similar strikes dissolve the oxide skin while simultaneously plating.
The solder plating is obviously necessary for the soldering operation.
But as for the copper plating and silver plating, I don't really understand their function, and am not sure that they are actually needed for successful soldering. I think nickel plating might be better.
I'm not a solder expert, but the step where you solder plate on top of the silver doesn't sound right to me. Most of the layers sound a bit thin to me.
Ted Mooney, P.E.
Striving to live Aloha
(Ted can offer longterm or instant help)
finishing.com - Pine Beach, New Jersey
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