Hello All,
I encounter a touch problem with ENIG (Electroless Nickel / Immersion Gold)
PCB in assembly process. This problem maybe so-called "Black Pad".
This problem happen on a ten layers RCC build-up PCB's uBGA pads. The BGA
pad on PCB is 0.4mm in diameter with 0.8mm pitch. On some BGA pads, there
are 6 mil laser via connecting layer 1 and layer 2 (via in pad).
In ICT station, detect this problem as open. When I remove the BGA wit hot
air, find some pads didn't wetted with solder at all and have a dark/black
appearance. I think the surface of black pad is passivated nickel.
I don't know what kind of source caused this defect and how to prevent it.
PCB vendor or our assembly process cause this problem?
Is there anybody who ever encounter this kind of problem? Please kindly
offer me a hand.
Thank you in advance for your kindly help!


Best regards,
Zhu Xiang

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