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Wed, 9 Aug 2006 19:43:37 EDT |
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Hi Jim,
I do not know what kind of housing you are putting your PCB in, but from your
outline description I am guessing some cast housing. You are also not giving
us a clue about your application. You are also talking about punching instead
of routing, so i am guessing CEM-3 instead of FR-4 as the PCB material.
In that case, your routing tolerances are your least problem; much more
worrisome are likely the different thermal expansions of the PCB and the housing as
well as swelling of the CEM-3 with moisture absorption.
GM ran into this with their windshield wiper controls: single-sided CEM-3
PCBs in some combination of routing and housing tolerances requiring
press-fitting the PCBs. The result: windshield wiper failures for some of the more
high-end [read: high-powered=running hotter] SUVs within as little as 1 year after
sale due to solder joint failures caused by PCB warping—over 4 million vehicles
were ordered by NHSTA to be recalled.
Werner
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