Thanks, Glenn ... But I'm having a difficult time visualizing what you are
doing ... the solder joint is made, then the epoxy is applied then the part
is injection molded?  My situation is a resistor with the leads soldered in
PTH on an FR4 double sided PWB.  The bottom half of the resistor, including
the leads, is then potted or bonded to the board with an epoxy adhesive.
The epoxy was probably 3/8" inch thick.  The entire assembly is then potted
with a thermally conductive silicone.  During temp cycling, the solder
joints are failing.  The reported failure (although I haven't seen it to
verify) is that the solder joint is failing and the lead is pulling out of
the board.  I believe the leads have a stress relief loop in them, but I'm
not sure it does any good when the whole thing is encased in epoxy.  Anyhow,
the electrical guy thinks that if we change to an epoxy with a glass
transition that is above the upper limit of the temp cycle, the CTE won't be
as bad and the parts will survive.  I'm not sure I buy that cause I don't
think we've identified the root cause of the solder joint failure properly.
I was trying to see what experiences other have "endured" in this area.

Sheila Smith


At 09:00 AM 9/23/97 PDT, you wrote:
>Hi Sheila,
>
>        Hope this helps.  We have an SMT process where some connectors are
>given a bead of epoxy along the solder joint to give it additional mechanical
>strength.  The part then goes through an injection molding process.  Tests
>have shown the epoxy adds considerable strength to the joint.
>
>        Let me know if you need more info, and I'll supply what I can.
>
>Glenn Pelkey
>Quality/Reliability Engineer
>Maxtek Components Corp.
>
>Sheila Smith <[log in to unmask]> Wrote:
>|
>| Hi!  Does anyone have any experience with using epoxy to
>| encapsulate
>| components, including the leads, soldered in PTHs?  The
>| entire assembly is
>| subsequently potted with a thermally conductive silicone.
>| The goal is to
>| keep the solder joint from moving during temperature
>| cycling.  Any
>| suggestions would be appreciated!  Thanks, Sheila Smith @
>| Tracor AES
>|
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