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tarnishing gold surfaces

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#63099

tarnishing gold surfaces | 10 November, 2010

subject board fabrication calls for .05 -.125um of gold over 2 - 5 um of nickel. When doing double sided reflow using same profile, parts of the gold are tarnishing and causing test pad failures. any ideas as to the cause?

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#63100

tarnishing gold surfaces | 10 November, 2010

Were the gold surfaces acceptable: * At incoming inspection * After first reflow ...

How do know this issue was caused by the second reflow?

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#63102

tarnishing gold surfaces | 10 November, 2010

I don't. However we perform inline ICT and functional testing on both sides and the first side has never had issues. It is only when we flip the board and start reflowing on the bottom side.

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#63108

tarnishing gold surfaces | 11 November, 2010

When you say 'tarnished,' is that based on: * Appearance of the gold over-plate * That you can't get good contact during ATE processing ... OR ... * Something else?

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#63110

tarnishing gold surfaces | 11 November, 2010

Getting adaquate contact with the test fixture. I have given a board to our vendor to perform analysis. Maybe we will see something there.

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#63112

tarnishing gold surfaces | 11 November, 2010

We guess the nickle has a rougher that normal finish AND the gold is at or below your specification. The nickle bumps are poking through the gold and are oxidized, preventing contact with you ATE probes.

If this is correct, it would be interesting to do sections on some of your second side solder connections.

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#63189

tarnishing gold surfaces | 26 November, 2010

Hello Esoderberg.

Did you get the analyis report from your vendor? If so, could you pls share it wiht us? Based on my experiance, this issue may be caused by the Au plating. You need to ask your vendor to check the Au thickness or Au plating process.

Thanks.

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#63190

tarnishing gold surfaces | 26 November, 2010

An independant analysis might also be warrented.

And what I've seen is that you can't save money on PCB's. If you go with cheap providers you end up with boards that cost big time in other ways.

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