KT315 - the workhorse of domestic electronics

Although I was late for the day of Radio - but I will write about KT315 though. This transistor has been seen and soldered by many, but today we will see the difference between the KT315s released in different years, what is its design, and compare its design with modern foreign analogues.

About production

KT315 - the first transistor, produced according to the latest fashion squeak of the late 60s - is a planar-epitaxial transistor, i.e. the collector, the emitter and the base are made successively on the same silicon plate: a silicon plate doped into type n (this will be the collector) is taken, then doping is performed at a certain depth into type p (this will be the base), and then - from above depth to type n (this will be an emitter). Next, the plate must be cut into pieces, and pack in a plastic case.

Such a manufacturing process was much cheaper than the alloy technology, and made it possible to obtain previously inconceivable transistor parameters (in particular, the operating frequency of 250-300 MHz).
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The next novelty, which led to cheaper production, was the installation of a crystal not in a metal case, but on a metal tape with leads: a crystal, on the lower side of which the collector was soldered to the central terminal, and the base and emitter were connected by a welded wire. Then all this was filled with plastic, the extra parts of the tape were cut off - and the KT315 was obtained the way we used to see it.

Explanations to the figure on the right: a - scribing and separation of the plate into crystals with ready-made structures; b - soldering of crystals to the tape; in - the connection of the output; g - trimming tape; d - sealing; e - extraction from the form; W - cutting the tape and separation of the diodes / transistors; 1 - tape; 2 - crystal; 3 - crystal output

Mass production began in 1967-1968, for mere mortals, the price at the beginning was 4 rubles per transistor. But in the mid-70s, it dropped to 15-20 kopecks, which made it a truly affordable transistor. With an engineer’s salary of 120 rubles, one could buy 600 transistors per month. By the way, now for a conditional salary of an engineer of 45 thousand rubles, you can buy 121'000 transistors BC856B, so the transistor living standard of an engineer has increased 201 times

It is noteworthy that the first devices assembled on KT315 are transistor (chips only gained momentum) “calculators” Electronics DD and Electronics 68 .

Here is a meeting I found:

Those where there is no sign of the manufacturer is KT361, pnp option. The rest, with the logo - KT315 (even if the "letter in the center"). It is noteworthy that in times of planned economy, fixed prices, and a formal lack of speculation, the price was sometimes written directly on transistors.

What is inside?

The oldest transistor I have found is KT315A, released in March 1978.
We see that the crystal is broken off from the plate is far from ideal, around the transistor - a lot of unused space.

Here the crystal itself is the collector, in the center, if I am not mistaken, the base mugs, and around it is a wider “belt” of the emitter. The base somehow dives under the emitter, and comes out from the back of the ring.



Next, look at KT315G, produced in February 92nd, after 14 years of evolution.

Here it is immediately obvious that the place is being consumed much more economically, the crystal is cut almost perfectly, small non-critical defects in photolithography are noticeable, apparently contact photolithography is still used here. However, for transistors, this is quite enough.



And finally, KT361G, July 1984.

Comparison

If we compare the scale with the modern NXP BC847B transistor, we can see that the size was reduced by 2 times due to "squareing", but the transistor itself has not changed fundamentally - the same collector at the bottom of the crystal, and the emitter and base outputs welded to it.

It is noteworthy that in BC847 the width / height of the crystal is almost equal to the thickness of the plate, this is practically a silicon cube, not a plate. It is difficult to reduce the area further, at least without further thinning of the plate ( plate thinning is written correctly).

Future

Has KT315 died? Definitely not. Until now, it is, for example, in Integral price lists for 248 Belarusian rubles (~ 1 Russian ruble), i.e. probably still in production. Of course, with the development of automatic installation of printed circuit boards, he had to give way to SMD variants, for example, KT3129 and KT3130, and many others, including foreign analogues of BC846-BC848, BC856-BC858.

But in our memory it will remain forever :-)