Hello 'netters,

I debated posting this, as it seems to me to be an obscure problem, but then, I'm always amazed at your knowledge base. I have a JFET 2N6550 component to be used for space application. Unfortunately, it is not manufactured at JANS space quality, so we buy the commercial grade, plus an option 2 screening, which upscreens the part to "like" JANTXV. I think this is called re-branding. Then, we send it to a lab for further upscreening to JANS. The problem is that the parts are failing the moisture test of the residual gas analysis (RGA). I found out that epoxy is used for the die attach, and likely the epoxy is outgasing during subsequent baking as part of the testing. My first question is who knows of a standard for die attach of this component type stating that epoxy is forbidden for military and space use?  The epoxy  used by the manufacturer is Ablestik p/n 84-1LMI; Material # 1119570.  I just found out today that they do have the capability of eutectic die attach, and I'm pursing this option, expecting a huge expense and lead time.

Secondly, I had two independent labs perform the RGA. The first lab had results averaging ~28,000 PPM.  The second lab results averaged ~5600 PPM.   The standard is no more than 5000 PPM.  They both performed the testing to the same MIL-STD-750.  I can't understand the wide range of results, but my second question is who knows of any studies related to the negative effects of excessive (>5000 PPM) moisture inside hermetically sealed devices used in space?  By the way, they all passed the seal tests. Perhaps some of you are knowledgeable in this area.  Thanks in advance for your help.

Howard Watson

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