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

Printed Circuit Board Assembly & PCB Design Forum

SMT electronics assembly manufacturing forum.


Second Pass In Wavesolder

Hany A. Salam

#18521

Second Pass In Wavesolder | 31 December, 2001

Dear all:

We had a severe curvature in our boards after wave soldering.Could a second pass in the wavesolder m/c reduce this curvature. If not then what do you recommend to solve this problem. Also how it can be avoided.

Best Regards Hany

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#18526

Second Pass In Wavesolder | 31 December, 2001

Warp depends on: * How close the board gets to its Tg during the solder 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.

Best suggestion - get the copper balanced and if possible go to higher Tg materials. * MLB constructions (not homogeneous or unbalanced - too resin rich or poor) * Poor supplier process capabilities (lamination cycles) * Poor material selections (usually cheap and dirty), etc.

You may be able to dewarp there boards by * Securing them in a rack * Baking them at Tg for an hour * Letting the board cool * Removing the rack

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Hany A. Salam

#18544

Second Pass In Wavesolder | 3 January, 2002

Thanks Dave , but what is meant by Tg & MLB ? Hany

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Scott Davies

#18545

Second Pass In Wavesolder | 3 January, 2002

Hany,

Tg is "Glass Transition Temperature". For an informative explanation of what this is, take a look at;

http://www.psrc.usm.edu/macrog/tg.htm

MLB = Multi Layered Board

Does the board which you have the problem with only pass through the wave solder process, or is it first reflowed for SMT? Is it a single circuit PCB, or a step and repeat panel with scoring and/or routing?

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#18547

Second Pass In Wavesolder | 3 January, 2002

Scott is correct. Expanding a bit, the SMTnet Library has a "Terms & Definitions" listing in the "Standards & Terms" section.

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Hany A. Salam

#18548

Second Pass In Wavesolder | 3 January, 2002

Thanks Scott: The Assembley is Mixid ( reflow then wavesoldered). It is One curcuit.

Is the Tg averagely known for FR4 PCB assemblies?

Hany

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#18552

Second Pass In Wavesolder | 3 January, 2002

The Tg of the resin commonly used in FR-4 is 140�C. Consider checking with your supplier to better understand the specific materials used in constructing your board.

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#18553

Second Pass In Wavesolder | 3 January, 2002

Just thought of something. Sorry to be late with this.

If you decide to dewarp these boards, consider: * Marking the boards perminantly with a code to help key your failure analysis people that a customer return was processed differently than other boards. * Recording the serial numbers of the dewarped boards and the identification of end-use products where the boards are incorporated.

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