Board Warpage

Your warpage problem could be caused by change in: * Multilayer board construction (not homogeneous or unbalanced - too resin rich or poor) * Supplier process capabilities (lamination cycles) * Material selections (usually cheap and dirty), etc.

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My guess is that either the board house did not cool the boards down properly coming out of the lamination oven.

Typically after they come out of the heat chambers they go into a cool down chamber for x amount of time, if they cool to fast or are pulled out and taken out of the plates to early with out proper cool time the material will warp, severity will be based on board thickness and laminate selection.

They may have changed material if the print does not call out for a specific material to be used. This should not be done without Approval. But if this is an offshore shop I would not be surprised. (discloser) I Sell for an offshore fabricator and we have had to put this in writing with our Facilities, That this type of practice is not acceptable without Customer approval. If this is not done they feel that if the print just calls out for FR4 that they can substitute any fr4 materials.

I would talk to the board shop and see what they disclose about the stack-up to see if they have altered, if they did not I would lean to a process error.

Regards, Boardhouse

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Another area to look is on any breakaway. If they did not add copper to breakaway, it can warp your board if long enough. Seen it happen many times.

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