Failure at the ENIG finish on the BGA substrate

On May 7, B.G. asked a question about BGA joint failures on ENIG finished boards. We have a similar problem, but the failure is at the ENIG finish on the BGA substrate. The part is an Alterra Stratix package, and we see the issue in at least 3 different applications. The failure happens in downstream assembly operations, sometime after the board-level boundary scan testing. Is this a common problem?

J.K.

Expert Panel Responses

We are dealing with a similar issue at this time. Most BGAs are electrolytic nickel/immersion gold, but sometimes you have an ENIG finish, which can be susceptible to black pad. Where are the failure points? Do you see mud-cracking? You could also be simply overloading the package, as SnNi intermetallics are weaker than SnCu. Have you measured the board level strain during manufacturing in that general vicinity?

Dr. Craig D. Hillman
CEO & Managing Partner
DfR Solutions

Dr. Hillman's specialties include best practices in Design for Reliability, strategies for transitioning to Pb-free, supplier qualification, passive component technology and printed board failure mechanisms.

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