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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

Board Warpage

Views: 10201


Board Warpage | 25 April, 2008

We just started having board warpage problems with one of our suppliers. The product has been in production for some time with no design changes, no material changes from the board supplier.

Someone told me once that if the PCB cure was not correct, it could result in warpage after reflow. Anybody familiar with PCB processing problems that could manifest as warpage after the customer's reflow?

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Board Warpage | 26 April, 2008

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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Board Warpage | 28 April, 2008

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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Board Warpage | 29 April, 2008


I am also facing the same probelm. I assembly a substrate with a thickness of 0.30mm and the board warp after reflow. If I bake the substrate at 125 Deg C for 2 hours will it help to solve this problem?


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Board Warpage | 29 April, 2008

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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Board Warpage | 29 April, 2008

Warpage typically (not always) kinda, sorta points to a fabrication bake induced issue that is the racking technique & may be relieved by "flat baking" under weight. Your baking at 125* won't do dip. You need to get the laminate temperature above it's Tg. You should be above Tg for about a half hour.

If you're dewarping assembled boards, you need to remove thermal sensitive parts and clamp the board edges rather than flat baking under weight. Find more on this in IPC Rework and Repair Guide

Twist is often more of a "memory" type condition caused by design, build symmetry, "cross ply construction", excessive cool down rates during lamination or reflow at assembly. You will have more of a struggle in your attempts to flatten these boards.

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Board Warpage | 29 April, 2008

Dedrites cause this to happen.

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Board Warpage | 29 April, 2008

basically your problems come from the copper balance top and bottom side

we are using substrate down to 0.18mm (semiconductor industry/ Bga package / SIp business)

you have to respect 5% difference maximum between Top and bottom side otherwise you will face a severe warpage after the first Reflow

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Board Warpage | 30 April, 2008

Please, do explain.

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Board Warpage | 2 May, 2008

It could be as simple as a new operator in lamination lay-up who is laying up 90 degrees against warp and fill.

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