Printed Circuit Board Assembly & PCB Design SMT Electronics Assembly Manufacturing Forum

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

PCB pad contamination

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PCB pad contamination | 21 August, 2007

Hi All, I would like to get some inputs regarding this.... I have bare PCB which were stored with kapton tape attached on the Au plated pads. These were stored for close to a year. Upon removal of kapton tape, we noticed discolorations on the edges of the Au plated bond pads. There are 2 kinds of "surface contamination/discoloration" that we are seeing. One is brownish (transparent)and the other one is blackish. They are basically occurring around the edges of the plated area. Our plating is wire bondable ENEPIG (3umNi/0.3umPd/0.03umAu). We have done EDX@10kv on 2 points of the affected pad (1 on "clean" area and another one on the blackish area). The only difference is the presence of Copper on the blackish area. I would like to have inputs: 1) How these "surface contaminants" came out? 2) What is their impact on the PCB quality (longterm)? Are they going to propagate? 3) Can they be removed? 4) Can the PCB be still use? Thanks a lot.

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PCB pad contamination | 22 August, 2007

Questions are: * Do these pads take solder? How well? * Have you stripped the gold and evaluated the condition of the nickel?

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PCB pad contamination | 23 August, 2007

Hi, in past we had an issue with ENIG surface, black was Ni that get pass the Au - but it was discovered after reflow (SnPb) and the IC was losing contact with Cu customers application :| Reason was as I remember too thin Au sufrace... we called it BLN - black line nickel ;)

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PCB pad contamination | 26 August, 2007

Hi Davef, Thanks for the reply. There seem to be no issues on SMT reflow based on some samples done. We have not stripped the gold yet. We did a X-section+EDX and we are seeing traces of copper on the nickel layer. Any idea what is the implication of this? Thanks.

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PCB pad contamination | 27 August, 2007

Actually, you will be soldering and wire bonding to the palladium layer, so we should have asked if you checked that layer, rather than the nickel.

We not sure of the source of the copper that your see on EDX. It's possible copper from the pad migrated over the nickel.

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PCB pad contamination | 30 August, 2007

EDS @ 10kV maybe going too deep. I've talked to a surface science physicist that recommends Auger spectroscopy because it's more of a true "surface" examination tool.

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