Jason,

Your problem is not that uncommon. I assume you are using THL components
( from the diode part number). The most likely cause is the CTE mismatch
between the urethane and the component. "Potting" with urethane is not a
good idea. They
typically have a higher CTE then most other materials used in assemblies
(up to 3 to 5 times higher). This is why there is a
strick limit on their thickness.

You need to review your environmental protection options plus your
application options very carefully to improve your reliability. The
coating is cracking the glass body and moisture (all coatings are
permiable by moisture to some degree)
is degrading the diode.

If you desire I can provide some background info off line ( for your
education) but you must consult the coating manufacturers
and coating application experts to determine your best options for your
conditions. If Graham is listeneing he is a very good
choice to communicate with.

Good luck, you have landed in a very difficult situation.

D. a. Douthit

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