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January 13, 2010

How To Prevent PCB's Warpage When Baking

When baking PCB assemblies we are seeing some slight warpage? Should we position the PCB's vertically or horizontally in the oven to reduce the potential of warpage?

Can you suggest some type of universal fixture that we should use?



S. M.

Experts Comments

Boards are to be baked for a couple of hours above the tg temperature of the material during the fabrication process using heavy steel platens to protect the top and bottom of the stack.

If the boards are secured properly during the baking process there should not be warping. Are the boards quick turn prototypes that are being processed too quickly for adequate curing?

Another possibility is an unbalanced board design. An uneven inner layer ground plane design could be to blame. Not to mention the variability of laminate types and the affects that non uniform heating and cooling may have on the board.

This is an issue you may want to communicate with your board supplier. Bottom line, boards should be cured properly at the board manufacturer prior to you receiving them.

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Michael Ray
President
Integrated Ideas & Technologies, Inc.
Mike Ray is founder and president of Integrated Ideas & Technologies, Inc., a manufacturer of SMT stencils. Mike Ray developed the first successful universal frame and holds patents on the AXIS laser system.

If your PEC's are warping during bake then they are likely to warp during reflow so constraining them is probably not the best plan.

You must consider the cause of the warp in the first place which has many potential contributory factors very few of which are in the assembly area.

A balanced PEC construction is highly unlikely to warp under most circumstances so perhaps you should have a look at the PEC construction design.

When baking my preference is to lay PEC's flat on a shelf one up.

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Bryan Kerr
Principal Engineer - CMA Lab
BAE Systems
Bryan Kerr has 35 years experience in providing technical support to PEC assembly manufacturing. His experience ranges from analysis of materials and components to troubleshooting and optimizing, selecting reflow, cleaning, coating and other associated processes.
Reader Comment
At major electronics company in Japan, I had studied more than ten years about PCB's Warpage using CAE. Surely, an unbalanced board design would cause a warpage. Although there remains a problem in terms of cost, I will recommend to set up a dummy layer for cancel the unbalance.
Ichiro Hirata, Japan
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