Overcoming zinc whisker
Is any form of passivation able to eradicate zinc whisker.Bill Cowdrey
electronics engineer - Liverpool, Merseyside, England
Not to my knowledge, since whisker formation is believed to be be a stress relaxation phenomena rather than a corrosion reaction. If you can use an alloyed zinc, like zinc-iron, zinc-cobalt, or zinc nickel it should relieve the problem because it is more difficult for an alloy to grow a whisker, but I don't know of any published investigations of this. Theoretically there should be some baking procedure to prevent whiskering, but neither have I ever read any details on such a process.
Ted Mooney, P.E. RET
Pine Beach, New Jersey
Zinc Whiskers are relatively un-known. phenomenon.. However.. Everything is possible in plating we have come to believe, so welcome to the club.
Is it possible the zinc is blistering due to internal stress. How old is the deposit when it whiskers ? Does the whisker grow in the bath ? Or is this a age related phenomenon ? Where are the parts stored and what is the air like ? (Most zinc deposits don't grow a beard till they're over 18. Joke ! Sorry.)
But relieving the deposit at 190 to 220 Centigrade for 120 minutes may either accentuate the problem immediately which will prevent a latent occurrence, thereby saving a field occurrence. Or relieve the deposit if its a metallurgical issue . (This 190-220 centigrade treatment is used to De embrittle steel which picks up occluded Hydrogen in pickling and Plating ops. )
Passivation is carried out after cooling to Room temp with natural air circulation. And activation precedes passivation. It will be advisable to check the bath chemistry as well to ensure the organics are in balance.
Are you possibly using outdated Alkaline Zinc Chemistry. Some old processes induce stress due to unreacted compounds in the plate and this leads to blisters. These whiskers may be related to stress caused by bad organics co depositing with the zinc plate. Ensure you have the best and latest 6th generation Alkaline system installed.
No harm in running an activated carbon treat on the plating solution at 1 -2 grams per liter , 50 centigrade, to see the difference. This is best done off line in the lab on a liter sample first. Alloys do help improve corrosion resistance. However regular zinc Plate does not/ should not ordinarily whisker. Check the bath solution first.
- New Delhi, India
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