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Copper migration

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Copper migration | 4 December, 2006


I did EDX on BGA just to find out copper wt% at the package- ball interface. Is wt% ranging from 20 to 32 considered as normal?? As far as I know lead free BGA and solder paste just have little copper..Where is this excess copper come from?? What is the impact on BGA if too much copper migration took place? Can we control this phenomenon?

Thanks in advance

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Copper migration | 6 December, 2006

It's surprising that you have that much copper. Copper contamination of leadfree is usually tolerable up to 1%.

So, the copper is moving from the pad to the solder ball. Right? If that's correct, the pad requires a buffer material between it and the solder ball.

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Copper migration | 7 December, 2006

Hi Davef,

The BGA pad is with ENIG finish, the PCB pad is with immersion silver and the solder paste is with SAC type. I already checked, the solder paste Cu is just 0.5%..Hence, I am guessing that copper migration is from PCB pad. No way it is from BGA pad as already protected by Nickel layer.. BTW, what do you mean by "the pad requires a buffer material between it and the solder ball." Is that mean to change the PCB pad finishing to ENIG type as well?? Besides this method, is there any other method we can use by controlling our reflow profile??

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