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If solder is plated on silver

I meet a problem in one of my design projects for one leadframe design. I can't make the decision whether to allow the silver plating to be on extra metal area which is out of the compound package outline. Some engineers insist that silver can't be out of the package outline because it will cause the quality issue after the solder plating later. Solder can't be plated well on silver, so it will result in whisker, bubbles, etc. However, it was not demonstrated with some line experiments. Hence, I'd like to ask any experts on metal finishing what's the reaction it could be with solder plated on silver, are there really the problems as the concerns above though they were not found probably because of small quantity of specimen? Thanks a lot!

David King
Design engineer for Semiconductor IC Packaging - Shanghai, China
2004

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In regards to your question, we use a coverage of Nickel between Silver and Solder, The nickel protect the silver and will not create any whiskers. If solder is applied over the silver it will cover it but with any exposure to the heat the silver will be affected. Doing this you will have a very strong adhesion of solder to the silver.

Thanks,

Eduardo Anaya
- Mexico
2004

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2004

I just read your email today. Hope this info will still help.

We encountered a problem with copper leadframes whose silver plating extended outside of the package. During the activation process (acid dip before plating) the silver plating lifted/peeled from the leadframe. This resulted to plating protrusions - the lifted silver were plated and formed spikes on the leadframe.

Comparing the process flow of our two leadframe suppliers, we discovered that the problematic leadframes are those that were silver-plated first before being stamped. The leadframes that were stamped and then silver plated did not manifest the problem even if the silver extended beyond the package.

Amy Bancud
semiconductor component assembly - Philippines