Hi Scott:
“In general, the users and testing houses are referring to the rating of UL
yellow card rather than the actual test on individual final designed pcb.
Should we use it to object their normal practice. How often is it successful?”
Testing in place is a once-per-product-model (and board design) test. Passing
the test will depend on how much copper clads the epoxy versus exposed epoxy.
Only boards with lots of copper are likely to pass. So, it is an “iffy” test
and the outcome cannot be predicted with certainty.
As a general rule, use a board with ratings prescribed by the standard. Where
you must use a rating not prescribed by the standard, or you are using a
non-rated board, and if the board design uses lots of copper, then testing the
completed board in its end-product orientation may pass the flammability test.
Rich
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