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Transistors - die pictures

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This Siemens 2N3055 has two character sequences that could be a date code: 5E and S8. According to DIN EN 60062, the E would stand for the year 1974, S would refer to the year 1984. The Siemens 2N3055H from 1983 (https://www.richis-lab.de/2N3055_14.htm) is already printed with the modern four digit date code. This indicates that the 2N3055 shown here was manufactured in May 1974.

As in the Siemens 2N3055 from 1975 (https://www.richis-lab.de/2N3055_01.htm), there is a white powder in the package, which presumably is a drying agent.

The die is located on a base, which can also be seen on the back of the housing. The connection between the pins and the die is made with ordinary wires, not with bondwires. The wires are soldered on both sides.

The die shows the typical irregular surface of a hometaxial transistor. The wires were soldered directly to the metal layer.

The die is coated with a kind of protective varnish that peels off in some places.

A piece of the metal layer is missing at one point. There you can see what the openings in the passivation layer look like, through which the semiconductor is contacted.

The base-emitter junction only breaks down at -50V. High values are typical for hometaxial transistors. However, such high values have so far only occurred with 2N3055 transistors from Siemens.

A large part of the current flows in the upper range of the die (50mA, 100mA, 200mA).




--- Quote from: Noopy on January 26, 2024, 04:20:39 am ---As in the Siemens 2N3055 from 1975 (https://www.richis-lab.de/2N3055_01.htm), there is a white powder in the package, which presumably is a drying agent.

--- End quote ---

When we were kids, we were never discarding broken power transistors.  We were keeping them for their thermal paste inside.  They were easy to open by squeezing the cap a little, in a vice.  Smaller transistors were also having some thermal paste inside (e.g. the Ge type AC180/AC181), but way little than a TO-3 capsule.  The thermal paste was matte white, and slightly less thick than toothpaste, about the same as the white thermal paste available now for CPU radiators.  Though, I'm not sure is any of those power transistors I've opened were 2N3055.  Maybe they were Ge power transistors.  :-//

Could that white powder be, in fact, thermal paste solidified with time?

I know that there is often thermal paste in smaller packages. Up to now I just have seen it in Ge transistors:

It makes sense to enhance the power dissipation from the die to the housing.

In TO3 packages I have never seen thermal paste. Just this one had a strange potting:

I´m not sure if thermal paste makes sense in a TO3 package. The thermal resistance through the base plate is quite low. I don´t think thermal paste would enchance that very much. On the other hand the upper part of the TO3 has a very high thermal resistance compared to the base plate and the heatsink. I don´t think you can dissipate a lot more thermal power if you enhance this path.
Are you sure you found the thermal paste in TO3 transistors?

On the other hand corrosion was quite a problem, so a drying agent absolutely makes sense. Often we saw something like a pill.


--- 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 is not a thermal paste.. It is an expressionistic vision of the late twentieth's century technology progress ("Controlled Currents in a Pot")..

GE transistors in TO3 and TO66 packages had the thermal paste, simply because the junction is lifted off the actual die attach, and the low temperature limit for Ge means any improved contact is desperately needed. Thus the compound, while a silicon planar transistor could get away with just having a soldered connection, and a drying agent to keep it dry and oxygen free, with the large silicon area providing enough thermal transfer, plus the max junction temperature of 150C as opposed to 70C helps a lot.

Got some genuine Newmarket transistors, courtesy of Sir Clive, in an unused and old amplifier kit, the infamous ones that were rather notorious because they were made from all reject transistors from the scrap test pile at Newmarket, bought by the ton by Sinclair, and binned into dead, sort of dead, sort of working and works good enough, at least at 15V. Might dig them up, though there are some Ge transistors in older packaging I also have around, OC36, unmarked as to manufacturer or date. Might have to open one and see what is inside.


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