Hi Doug,
 
See my responses below:
>>Steve,
>>I have not used that specific material before, but have worked with 2-part 
>>systems.  A few questions and observations:

>>1.  What did you mix the material with?  Metal spatula (good) or popscicle 
>>stick (bad)?
 
Answer: I mixed it with a plastic spatula
 
>>2.  How well did you scrape the sides of the container?  Was it a clean 
>>plastic mixing cup (good) or wax-coated Dixie cup (bad)?
 
Answer: I thought I scraped the sides pretty good. It was a clean plastic mixing cup, just a regular kitchen mixing cup with graduations on the sides.
 
>>3.  Did you bake out the potted assemblies first?
 
Answer: No I did not. In retrospect I should have...
 
>>4.  Was there a primer involved? 

Answer: No primer.
 
>>5.  What kinds of "schmutz" may be on the assembly that may poison the 
>>cure reaction?  Urethanes don't like water.

Answer: I thought the boards were clean. I learned afterwards that there was some no-clean rework done to a programmed part (it was removed and replaced), although I didn't see any residues.
 
>>6.  Does the manufacturer recommend a rest time before potting?  Degassing 
>>before potting?
 
Answer: I didn't see any rest time or degassing recommendations in the datasheet.
 
>>You might want to pick up IPC-HDBK-850, The Potting and Encapsulation 
>>Handbook for lots of good information.
 
Yep, will ask that we get the Handbook. 
 
I called Epic and talked to them about what happened, and they told me that I should mix by weight to be more accurate. So as a test of the material, I did that. I mixed 300-grams of part A to 129-grams of part B (100:43 ratio per the datasheet). Mixed it the same way I did last week, then poured the material into two containers. This time I did the alternate oven cure of 65 C. for 1 to 1.5 hours. It turned out beautiful. Smooth, with no bubbles except for some very tiny ones around the edges of the container. I am at a loss as to why I had the results that I did last week. So frustrating...
 
Steve


From:   stephen gregory <[log in to unmask]>
To:     <[log in to unmask]>
Date:   07/22/2013 01:46 PM
Subject:        [TN] Epic Resins S7144A 2-part polyurethane potting 
material
Sent by:        TechNet <[log in to unmask]>



Hi All,

Have any of you used Epic Resins S7144A 2-part polyurethane potting 
material?

I tried to last week, and pretty much made a mess. Followed the datasheet 
and mixed it in the volume ratio of 3-parts part-A (300-cc) to 1-part 
part-B (100-cc). I mixed more material than I actually needed. I'm mixing 
it by hand because we don't have a MMD system. 

I thought I had mixed everything thoroughly (4-5 minutes). I determined 
ahead of time how much material would be needed for each unit (35-cc's). 
After mixing, I drew the material into a 60-cc syringe and 
dispensed 35-cc into each case. I let it room cure (24-30 hours).

I did 4-units and each one of them had a different result, from swelling 
and bubbling of the material completely out of the case, to little or no 
cure. I'm at a loss as to why that happened.

Just wondering if any of you have ever used the material and can give me 
some pointers.

Thanks guys,

Steve

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