January 11, 2007

This is an e-mail for all you CAF experts out there.

We have an OEM that manufactures a 10-layer VME backplane assembly that has press-fit power studs installed in the backplane.  The manufacturer has experienced system level test failures.  Some of these failures did not occur during the initial testing but the assemblies failed at some subsequent time during testing.  The failure mode was shorting of the +12V layer 1 to the +5V layer 3 via the pressed-in power studs.  The OEM had the backplane sent to an outside lab to determine the root cause of the problem.  After looking at the pictures taken from the evaluation, it appears to me that the problem could be due to CAF because of the damage done to the glass fibers in the FR4 board material.  CAF is also suspected since the test failures do not occur on initial testing of the equipment.  We verified that the PWB conductor spacing meets IPC-2221 requirements.  Another factor is, we believe the OEM may have used some Type H flux per J-STD-004.  Not sure this is an issue unless some of the flux residue entered the PWB internally via the press-fit power studs.

Steve Gregory was kind enough to post 13 pictures on his web site.  They are files GLB CAF # 1 through GLB CAF#13.

Can folks identify whether CAF could be the root cause of the problem?  Any help would be appreciated.  

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