Re: Power MOSFETs
Is it possible the resin encapsulation is standing ever so slightly proud of the metal plate, causing it not to make proper contact with the surface against which it is mounted? As the trapped air gets hotter, its pressure will increase, so worsening the contact.
Might be worth a few minutes going around the edges with a sharp blade. (Or a few seconds with a bench grinder, if you are feeling brave!)
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