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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.

PCBA flatness

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PCBA flatness | 13 March, 2006

Hi Experts,

We have requirement from our customer to control the PCBA flatness at 10 mils diagonally. Weird but this is the requirement due to the need for some through hole pins (spreaded acroos the board must touch the copper sheet while they are installed in the box build. The flatness measurement is done thru' CMM machine and to the best of our process setup (improvemnet on the profiling, pallet, clamp, stiffeners etc), we only managed to get around 30~40 mils Flatness. The board size is 12 inch X 12 inch.

Any suggestion to improve the flatness would be much appreciated.


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PCBA flatness | 13 March, 2006

Wow. I'm always just happy to get 100 mils/10 inches from a bare board, let alone < 10% of that after reflow and wave.

That really sounds unreasonable to me, but maybe they're paying you REALLY nicely for them?

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PCBA flatness | 13 March, 2006

Warp depends on: * How close the board gets to its Tg during the reflow cycle (the closer you get to the Tg the worse the warp gets) * Amount of copper on each side and the balance between the two * Thickness of the board * Overall length x width * Time under temperature * Rate of cool down * Multiple thermal cycles, such as rework, are never a good thing.

Our best suggestion: Get the copper balanced and if possible go to higher Tg materials.

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