02-01-2016, 03:50 PM
Atmospheric bourn contamination of chemical or bacterial contamination of semiconductors has always presented a problem even back to the old cat's whisker, even if they didn't know it. There were even products on the market that claimed to protect the sweet spot by sealing the whisker to your lump of whatever, preventing mechanical or chemical disturbances. Mullard in the times of the AF transistors were still finding their way as it were, and death by contamination was still an early life failure mode for transistors in general, characterized by ever greater leakage current as the germanium died. I think however that Mike's point was that it's possible that some of the strange phenomena exhibited by mainly tin plated packages was caused by bacteria or similar present during production. Some transistors with metal enclosure's were made with gold plating to the can and lead outs, I'm sure this must have been done to improve the environmental resilience and therefore reliability. I don't recall reading the data sheets on these types to know what the exact reason was for it being done. Regards. Andy.
