Whats inside this transistor?

[Beamin]

Hello!

I recently "tore down" this transistor with HCl and heat. Two legs were lost in the process. Sadly it can't be repaired.

My question is this:
There are three parts: The back plate, the middle square that seems to have a boundary from the back plate, and the small off center square in the front.

Which part is the actual transistor? Just that little square on top? Or is the base the back plate, collector the middle plate, and the emitter the small square on top? (Guessing the smallest part is the emitter since it can handle the least amount of current and therefore heat.)

[mikerj]

That little square is the entire transistor!  If you hadn't dissolved them, you'd also have seen two sets of bond wires attaching the base and emitter pins to the top of the die.

[Beamin]

That little square is the entire transistor!  If you hadn't dissolved them, you'd also have seen two sets of bond wires attaching the base and emitter pins to the top of the die.

So is the NPN junction under that little square?

[rstofer]

Probably not...  The little square is the entire transistor.  The back plate is the heatsink and will be electrically connected to either the collector or emitter but not for semiconductor purposes just to help get the heat away from the device.

[free_electron]

the junctions are a thin layer on top of that little square.

[Beamin]

Its strange that it seems like they just stuck the transistor to the plate at an off center angle. Is that on purpose or do some just come out crooked??

[mikerj]

It's probably to align the base and emitter bonding pads on the die with the pins on the package, to minimise bond wire length.

[tronde]

Almost the same, but a different package.

TO3 (as in the image below), TO5 and TO18 metal transistors are easy to open without damaging the chip or wires.




https://commons.wikimedia.org/wiki/File:Darlington_transistor_MJ1000.jpg#/media/File:Darlington_transistor_MJ1000.jpg