We had a few tough periods... at one
point we were having field failures from a variety of components and
could not figure it out. They didn't fail if they were mounted in
ceramic packages (expensive) but seemed to stop working after about
two years in the plastic packages we wanted to use (cheap). We mounted a
campaign called 'ISO in plastic' and studied everything we could think
of: conformal die coatings, new package materials, new packaging techniques, sources of contamination in our fabrication line (even to the extent of firing off the halon fire extinguishers to see if they were leaking contamination).
It was an incredible time in the industry, we were all just geeks working on cool problems and we instantly shared information if it would help someone else. The head of Process R&D, Jack Morris, asked a friend about this problem and he found out that we had
been increasing the amount of phosporous in our passivation glass
(PSG) to make it more resistant to cracking. At about 7% phosphorous we
had reached the point where moisture coming through the package could
leach it out and make corrosive phosphoric acid which was attacking the aluminum interconnect on the chips. The answer was to
replace half the phosphorous with boron and make borophosphosilicate
glass (BPSG). It had cost us millions to sort this out...
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