This is not uncommon. Individual crystals, and crystal oscillators
are indeed quite fragile, and won't withstand too much mechanical abuse.
The typical failure mode is that the crystal is cracked, sometimes even a
piece will fall out of the wafer and rattle around in the can. You can hear
it if you shake it next to your ear. You need to look at the overall process
where they're used, and make everyone aware that these parts cannot be
dropped on the floor, poured into bins, dumped onto benchtops, or whacked by
other cards, carts, ATE fixtures, etc. If you're careful, they can easily
be opened up by grinding around the lids or around the bottoms, depending
upon the part. It'll save you valuable FA time and let you see firsthand
what's going on with the part. Once in a while you will find oscillators,
in which the conductive epoxy used to cement the crystal to the shock
absorbing spring mounts, has been slopped down into the center of the
springs. This is a vendor workmanship defect that turns the springs into
rigid columns, and makes the part much more susceptible to shock damage.
Bruce Tostevin
Benchmark Electronics
Hudson, NH
> ---------
> From: Rick Vernon[SMTP:[log in to unmask]]
> Reply To: TechNet E-Mail Forum.;Rick Vernon
> Sent: Wednesday, May 05, 1999 6:33 AM
> To: [log in to unmask]
> Subject: [TN] SM Crystal damage
>
> Does anyone have experience with damage to surface mount crystals due to
> mounting or handling issues in processing PWAs?
>
> We see a failure mode where the crystal fails to oscillate due to
> mechanical shock or damage (according to FA from crystal mfg). Failures
> are detected at ICT. Some have made it to ESS and failed there.
>
> Thoughts and experiences appreciated.
>
> Rick Vernon, QA Engineer
> Phoenix International Corp.
> Fargo, ND
>
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