Im trying to fix a car amp. i got a couple of mosfets that need to be replaced. there are 4 to a channel and each set of four is glued to a mica circuit board which is then screwed to the amp casing. my question is how do i get these fets off of the board?? then what do i use to glue them back?
Depends on what the "glue" is. If it's a simple thermal compound, then you might need to heat the MOSFETs up until the TIM goes to its liquid phase, then you can pull them off. If that doesn't work, then odds are its a thermal paste, which means those suckers are not coming off without some serious hacking. Might not be the best solution though, becuase you definitely need that mica board. The MOSFETs are using the amp's case as a heatsink, and the mica board is there to transfer heat while not shorting the tabs of the MOSFET to each other. That probably means they're not the same type of MOSFET or are wired in a way such that the tabs on all 4 are not at the same voltage.
You can try acetone, which you can likely get at a hardware store, just don't get it on anything other than what you want to disolve. Commercially you would use a "stripping agent" designed for organic glues and epoxies. Not too likely you would be able to buy that tho.. I have had some luck with acetone, but for the epoxies that are designed to have mechanical strength, like the self shimming 2 part adhesives, a full-on stripping solvent was always needed. These epoxies often have a high metal oxide or glass component, with an epoxy binder, so its not just the glue you are fighting, its also a nearly solid metal/glass layer
ok well i beat a razor blade underneath the fet case with a hammer.. that got it. then i ran a fine film of plastic epoxie around the parameter of new fet plus i put alittle bit of thermal grease in the center of it.. should do the job. hopefully the amp wont be dead when i try to turn it on
