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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


PCB Warpage in Reflow

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#51019

PCB Warpage in Reflow | 12 July, 2007

I�m having problem with PCB with 16mil thickness due to warpage. the board convex up in the middle after 1st reflow. It seams the warpage is caused by CTE mismatch between PCB and multiple TSOP's, which are covering ~80% of the bottom side board area. This makes difficult to print the secondary side especially for fine pitch devices. The boards are on the carrier for top and bottom process but there is no place to hold the middle. It would have been easier to add a clamp. I�m looking for suggestions or guideline to minimize the warpage on the board like this by adjusting reflow parameters. Thanks, Sean

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#51021

PCB Warpage in Reflow | 13 July, 2007

Good afternoon,

Heating/Cooling rates contribute to warpage most of all. Try to tweak you profile so that heating/cooling rate would be minimized. Try to switch cooling blowers off maintaining required peak/TAL. Check copper balance for this PWB, by the way.

BR, Pavel

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#51022

PCB Warpage in Reflow | 13 July, 2007

Has your board house reviewed the PCB layer stack? Make sure that the layers are balanced in copper weight, etc?

Have you tried pre-baking the boards? We just had an issue with some boards warping that have never warped before for us. It happened during an incredibly humid time up here in the Northeast of the US. Pre-baking the boards to remove any trapped moisture helped with the warpage issue.

Checking the profile to ensure that you're not over-heating the board...or not ramping the temperature too quickly is also important. The layout of your secondary side may invite warpage due to the copper pours for heat sinking those components. If they're unevenly heating up during the ramp cycle, the uneven heating could pull the board out of true.

Cheers ..rob

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#51037

PCB Warpage in Reflow | 13 July, 2007

Thanks for your inputs. The board construction seams to be balanced and boards comes back to flat after top side process. we'll be performing experiement variing the profile parameters. if that does not do it, any printing suggestings? Would more squeeze pressure help?

Thanks, Sean.

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