PCBA flatness

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Hi Experts, We have requirement from our customer to cont... - Mar 13, 2006 by

Wow. I'm always just happy to get 100 mils/10 inches from a ... - Mar 13, 2006 by Steve Thomas

Warp depends on: * How close the board gets to its Tg durin... - Mar 13, 2006 by davef

Daniel

#40368

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.

Thanks.

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Steve Thomas

#40390

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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davef

#40395

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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