So we had a few transistors in to-220 pacs de-laminate at the metal tab/ plastic interface. (lost electrical connection to the collector.)I bent it up...it was just cracked along the edge. The circular mark around the mounting hole was made by the belleville washer. Which I think might be the problem. Washer is from Seastrom mfgr. 5809-13-16-P,
These take a lot of force and have less defection than other belleville's. I also think they were put in with too much force.
I'm wondering if there are any spec's for lock washers on TO-220 pacs? These are being used as temperature sensors over a large range, so I do want a lot of compliance (or deflection.)
Thanks George H.