Bga failure

could be black pad, or it is just bad reflow profile that did not get all balls soldered down. OR it could be a planarity issue between BGA and fab during assembly.

Can we assume that this is proven design? Somewtimes in new design touching a BGA adds capatitance or timing to circuit making it work.

Russ

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Profile, profile, and profile.

If you can sacrifice a board, the best is to drill a small hole into the a ball from the other side of the board and insert a thermocouple there.

I'm 99.99% certain you won't be able to sacrifice a board. (who can these days?)

But the most likely cause is your reflow profile. Although not enough paste might cause it as well. And even if you are reflowing the joints properly maybe you are warping the boards during reflow and they are not forming a good joint.

I've seen black pad only once.

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We had a issue on the SBGA and found stress built up at the corner of the SBGA after cool down to room temperature. It is confirmed by the warpage analysis. I expected that the stress caused by the heat spreader and the epoxy to the copper frame. Our finding was intermittant contact at the corner and cracked at the nickel layer, we press the BGA and passed. When we change to the ImAg and the problem resolved.

What type of your BGA?

Rgds.

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The different coefficient of expansion of materials used in some BGA can cause warping issues. We've talked about this previously on SMTnet. Search the fine SMTnet Archives. For instance: http://www.smtnet.com/forums/Index.cfm?CFApp=1&Message_ID=28669

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