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Transistors - die pictures

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--- Quote from: Noopy on January 26, 2024, 02:53:15 pm ---Are you sure you found the thermal paste in TO3 transistors?

--- End quote ---

It was very long time ago, maybe not TO-3, but certainly the same kind of capsule with a thick diamond shaped metal plate, like TO-3 use to have.  Could have been Ge power transistors, can't say for sure.  We were kids in the 5th grade or so, maybe it was some other goo inside, and we believed it to be thermal paste just like in the AC180/181K.  :-//

Well, took one and not so gently asked it to open up. Inside a clear sticky gel fill, not white, but still both a heat transfer compound and a protective blob. Rather interesting smell on opening, a faint smell that is similar to old oil, and showing the nice clean copper of the mounting and the copper top. Interesting is the wires in the package are made of a ferrous alloy, tinned outside.

It seems I have to open some more transistors!  ;D

I vaguely recall seeing white silicone heat compound in ASZ15(Tunsgram); but that was around '79...


The darlington transistor shown here was marked by Motorola with an application-specific label. The transistor came from a power supply of a CDC magnetic disk station. It was obviously manufactured in 1978.

The schematic of the power supply shows that it is a Darlington transistor.

The die is located on a round heatspreader and is protected by a transparent potting. The design is similar to the Motorola MJ3001 from 1979 (https://www.richis-lab.de/Bipolar60.htm), but the die is significantly smaller.

There is a dark line on the side of the heatspreader. The color appears unusual. Perhaps it is the remains of a flux which was applied before the die was soldered onto the heatspreader.

The potting is transparent, but distorts the view of the structures.

The potting can be removed very easily with the help of a silicone remover. In the bottom left corner, however, the potting adheres surprisingly strongly. Perhaps the material in this area has changed. The transistor had failed, so high temperatures may well have occurred locally.

The structures are typical of a medium-power Darlington transistor. The driver transistor is isolated to some extent in the top right-hand corner. In contrast to a normal transistor, the emitter contact is arranged in a U-shape around the base contact. From this emitter, the metal layer leads to the base area of the power transistor, which takes up the rest of the die. There, the base contact runs around the emitter as usual.

The size and design differ significantly from the Motorola MJ3001. This could be due to a different blocking voltage. The MJ3001 is specified with a blocking voltage of 80V. The transistor shown here only has to generate a 5V power supply from a 9V power supply.

The outer edges are etched down to create the familiar MESA structure, which ensures a clean base-collector interface. An edge can be seen on the surface of the MESA structure. This could be the passivation layer that protects the active areas of the transistor.

The driver transistor is surrounded by insulation trenches created with the MESA structure. The geometry extends the line between the driver and power transistor. As described in MJ3001, the base-emitter resistor of the driver transistor is located underneath this metal line.

The metallization of the power transistor is damaged in one corner. According to the visual impression, this is a manufacturing error and not a damage caused by an overload.




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