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Why do they build them like that?

N

Norm Dresner

Jan 1, 1970
0
A week or so ago I was removing a TO-39 can transistor from a board and two
of the legs broke off at the base of the transistor so I just ripped it off
the board and threw it across the workbench in disgust.

Anyway, I came across it today and, in a fit of idle curiosity, I cut the
top off the can to see what was inside.

The die itself was less than a millimeter on a side and there were discrete
wires actually soldered to the base and emitter leads and to the die.

What surprised me was that the die was mounted almost exactly halfway
between the emitter and base leads, very much off-center on the base plate.
I had been expecting to see a mouch more centrally located die for better
heat dissipation. Why do they build them like that?

TIA
Norm
 
G

Graham W

Jan 1, 1970
0
Norm Dresner said:
A week or so ago I was removing a TO-39 can transistor from a board and two
of the legs broke off at the base of the transistor so I just ripped it off
the board and threw it across the workbench in disgust.

Anyway, I came across it today and, in a fit of idle curiosity, I cut the
top off the can to see what was inside.

The die itself was less than a millimeter on a side and there were discrete
wires actually soldered to the base and emitter leads and to the die.

What surprised me was that the die was mounted almost exactly halfway
between the emitter and base leads, very much off-center on the base plate.
I had been expecting to see a mouch more centrally located die for better
heat dissipation. Why do they build them like that?

To keep the bond-out leads short. The thickness of the material in
the can-base spreads the heat to the heatsink if used.
 
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