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Transistors - die pictures

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With the AT-32011, Hewlett Packard had a fast bipolar transistor in its portfolio. The AT-32011 is optimized for applications with low supply voltages in the frequency ranges 900MHz, 1,8GHz or 2,4GHz. According to the datasheet, the transistor is based on a self-aligned transistor process with a cut-off frequency of 10GHz. The maximum reverse voltage is 11V. The collector current must not exceed 32mA. In order to achieve a high cut-off frequency, a very high doping was selected, which is reflected in the low base-emitter breakdown voltage of -1,5V.

The edge length of the die is only 230µm. The labeling shows that Hewlett Packard developed the design in 1994. 320 appears to be the designation of the basic project, from which at least two bins emerge. In addition to the AT-32011, the datasheet also lists an AT-32033. The AT-32011 offers a slightly higher amplification factor than the AT-32033. The emitter connection is marked with an E, which is covered here by remnants of the bondwire.

The transistor structures themselves are too small to be resolved. They are located under the dark strip in the center, which is approximately 70µm x 15µm in size. The datasheet reveals that there are 20 emitters with a pitch of 3,2µm. The base connections are located between the emitter connections and both must maintain a certain distance from each other. This means that a resolution of less than 1µm is required in order to be able to image the structures to some extent. The comb-shaped contacts can just be guessed.




The Philips BLX15 is a RF power transistor in a SOT-55/3 package. In North America, it was distributed by Amperex, which belonged to Philips. The advertisement above is from Electronic Design 18 magazine from September 1973 and shows which transistors are optimised for which power and frequency classes. The BLX15 is the most powerful transistor in the 30 MHz frequency range.

The blocking voltage of the BLX15 is specified as 53V. The large gap to the maximum collector-base voltage is striking, it is specified as 110V. The datasheet allows a continuous collector current of 6,5A and a peak current of 20A. The cut-off frequency is 275MHz. The housing can continuously dissipate up to 195W power loss.

The BLX15 has four large contacts. The collector contact has a rectangular opening and is labelled with a C on the package. The emitter potential is led out to the right and left. The base potential is applied to the lower contact.

The transistor can be screwed into a heatsink with a thread. The thread merges into a thick metal plate. The upper part of the housing consists of two plastic elements, between which the connections are led out.

The upper plastic element can be broken off. Underneath is a metal cover that is glued to the package. This bond protects the semiconductor from the environment. The plastic housing itself is obviously not sufficiently sealed.

The cover can be removed from the housing with a knife. The transistor was declared defective. The damage is already obvious here. The left side of the cover and the corresponding area in the housing are heavily blackened. But there is also clear damage on the right-hand side.

With a little more magnification, the structure of the BLX15 becomes clearly recognisable.

From below, the collector potential is fed to the transistors and led through the substrate into their active area. A metal bracket connects the emitter potentials supplied from the left and right. Four bondwires are available per transistor for the emitter current. The base current, which arrives from above, is even transmitted with five bondwires each.

The transistors are located on a ceramic carrier. This means that the BLX15 can be screwed into a heat sink without additional insulation. However, the ceramic slightly impairs heat conduction. It is remarkable that the datasheet nevertheless specifies a continuous power dissipation of 195W.

The bondwires on the emitter side of the left die have completely melted. An arc must have been burning for some time, as the edge of the metal rail also was melted considerably.

The insulation area of the ceramic is blackened over a large area. Metal has accumulated in front of the die. As the bondwires do not have that much volume, it must be material from the emitter bud bar.

The energy input into the die was so high that the silicon broke in several areas. Nevertheless, the structure of the transistor can still be recognised. There are eight columns, each of which is grouped into pairs. The base current is supplied from one side of each column and the emitter current is dissipated on the other side.

Obviously, there were high equalising currents between the gaps. The metal layer is completely destroyed in the upper area where it connected the gaps.

Each of the eight columns contains 52 rows, each with four emitter contacts. It appears to be an overlay transistor, as described in more detail in the 2N3553 (https://www.richis-lab.de/Bipolar22.htm). On the right, all rows are connected to a common resistor strip, which then leads to the emitter potential. The resistor strip ensures symmetrical current distribution across the rows.

The right-hand side of the BLX15 is less badly damaged. All four bondwires are melted but still recognisable. The die is partially melted and discoloured in the area where the bondwires were attached, but the area around the transistor is still intact.

Here, too, all the connecting elements on the upper edge have been destroyed.

Where the bondwires made contact with the emitter potential, the metal layer melted over a large area.

Here you can see a second defective BLX15. The package and labelling corresponded to the BLX15 above. The metal cover of this transistor was thermally opened.

Here, too, both transistors are destroyed. The degree of destruction is slightly less severe. The emitter bondwires of both transistors are completely melted.

The transistors are constructed in exactly the same way as in the first BLX15. Here, the connections between the emitter areas are still intact.

There is an artefact on the right-hand transistor slightly away from the bondwires that could be the starting point of the destruction. The emitter resistor between two emitter lines appears to have been destroyed locally, regardless of the surroundings. The collector line for the emitter current and some of the emitter lines have also melted in this area. Of course with such massive destruction, it is not possible to say for sure whether this was really the starting point of the failure.




Just a small transistor...
The BC178 is a PNP transistor that is the complementary type to the BC108. A manufacturer cannot be determined. 7244 could be a date code. The year of production would therefore be 1972, which seems plausible. The maximum collector emitter voltage is 25V. The current carrying capacity is 100mA continuous, 200mA maximum. The variant with the index A is specified with a current amplification of typically 180 (125-260). The cut-off frequency is 150MHz.

The structure of the transistor shows no special features. The edge length of the die is 0,34 mm. The silicon is broken at the lower edge.



I talked to a guy who is very familiar with markings. He said this is probably a Valvo transistor.  :-+

Do you remember I once showed you some IRF3708? I now have some more and I have a different opinion if they are a genuine part or fake.

I won´t post all the pictures here because I´m to lazy.  ;D

Here we have a list of all the IRF3708: https://www.richis-lab.de/Transistoren_FET_IRF3708.htm

#1 to #3 are the old MOSFETs. Back then I thought that all of them are fake parts but since I found some IRF3708 with the same die as the #1 I assume this one is genuine.

#4a and #4b are interesting fake parts from AliExpress with two different transistors relabeled.

#5 and #6 look somehow strange as #1 but they all have the same die and came from different suppliers: Reichelt 2022, Reichelt 2013, Völkner 2022.

#7 finally looks like the datasheet describes the package. It was bought 2022 from ELV. The die is the same as in #1, #5 and #6 so approving that these are originals.



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