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conformal coating - masking problem with ammonia

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#58780

conformal coating - masking problem with ammonia | 12 May, 2009

We do a conformal coating for a customer with copper-nickel-gold pads on his board. The pads are masked prior to coating with a standard gel, containing ammonia. After thousands of boards, being processed like this, now the gold pads seem to be less solderable and the pads have dark/brownish areas. Can anyone help me? What has happened here? Any known chemical reaction with copper seems possible but what is so critical in NiAu-processes?

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#58793

conformal coating - masking problem with ammonia | 12 May, 2009

Did the board fabricator forget to apply the nickel undercoat?

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#58823

conformal coating - masking problem with ammonia | 15 May, 2009

Ammonia based masks can create solderability issues after they are removed. You can get non-ammonia based latex mask material but down side is slower cure and cost a little more as they have higher levels of latex etc

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#58832

conformal coating - masking problem with ammonia | 18 May, 2009

Unfortunately I have no information about the metal layers and the processes. I only see the effect. Is it possible or common that the nickel undercoat could have been forgotten?

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#58833

conformal coating - masking problem with ammonia | 18 May, 2009

It's happened perviously. If that happens, there is a widespread solderabily issue, not just on selected pads.

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