Roger,

Depending on the CTE and Youngs' modulus of the type of urathane you are using any thickness
over 3 mils can crack solder joints and conponents with large temperature changes. Wait tell
conplete cure (up to 1000 hrs at roonm temperature) and run some samples through temp
cycling.

D. A. Douthit

"Roger M. Stoops" wrote:

> Y'all,
> Question engineer asked me today,  how thick can polyurethane coating be
> applied?  We apply three coatings with the following procedure:
> 1) dip  2) dry for 2-3 hours to eliminate most solvent vapors  3) bake for
> 4 hours @ 60 deg C  4) repeat until 3 coats.  Third coat is also baked.
> Question to my able colleagues:  Anybody know of any long-term problems
> with this method?  Any test results?
> We need to do this to cover all sharp edges for electrical isolation during
> operation in potentially high moisture environment.  Specifically, a
> housing that can fill with condensation before draining away, and we can't
> seal enclosure.  Considered paralene, but it costs more to coat the board
> than to build it...
> TIA
> Roger M. Stoops, C.I.D., PCB Designer
>
> Trimble
> Engineering and Construction Division
> 5475 Kellenburger Rd.
> Dayton, OH 45424-1099 USA
> Ph: +01 937.233.8921 or +01 937.233.4574 ext 288
> Fax: +01 937.233.7511
>
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