Inside one of my retro treats, the Soviet calculator Электроника МК-52, about which I have already prepared an article“Электроника МК-52 – Soviet calculator in orbit”, as well as in some respects its twin design Электроника МК-61, one can find rather mysterious-looking integrated circuits.
In fact, it is difficult to clearly define what they are and where they came from these rather puzzling integrated circuits. As you can see, the design is quite unusual, the silicon core is placed on a piece of metallized foil and protected from the top by something like white silicone. What is also worth mentioning, by their design these chips were surface mounted.
Searching the Internet for this type of “on foil” circuits, as I have laboriously called them, one will not find much information. It is known that they were produced in the late 1980s/early 1990s, including at the Minsk Интеграл plant, and were used in both commercial and military devices. However, the fact that this type of construction appears in photos or on online forums quite rarely may suggest that it was a rather niche manufacture.
For quite a long time I wondered if the chips could somehow be “opened” or, in other words, see what their silicon cores look like. As both calculators in my collection are “fully” functional, as for old Soviet equipment I did not want to deliberately spoil it. However, fate smiled on me and some time ago I managed to acquire a damaged copy of Электроника МК-52, which could be a parts donor for my experiments. In addition, recently, while continuing to search for any information about “systems on foil”, fate smiled for the second time and something absolutely unique reached me, which I will tell you about later.
First attempts
Whatever the case, the first attempts at reverse engineering did not go very well. By the fact that the chips were placed surface-mounted, it was fairly easy to desolder them. However, after carefully removing the white “silicone”, it turned out that it protected the underside of the core, and the surface I was interested in was on the other side.
The other side of the circuit was also covered with a thin layer of silicone, after removing which I was able to expose part of the metal-foil frame, under which I suspected the core is located.
The most difficult and destructive, at least for the first layouts, proved to be the removal of the aforementioned rack and silicone. On my first attempt, I decided to remove successive layers of white glue with a scalpel and a cover of isopropanol added later. This turned out to be quite difficult, because there was much more of the core-protecting substance than I expected, besides, any harder squeezing of the scalpel in a situation where the layer of silicone was already small resulted in running the blade over the top layer of silicon. This one was probably covered with a kind of varnish, or was simply silicon oxide, which was unfortunately very easy to damage. When breaking it off, the actual silicon was exposed, but more than once this also resulted in damage.
As you can see from the photo, the first attempt did not go very well. Although, with later microscopic photos, it turned out that it was not so bad. Unfortunately, I damaged the surface of the circuit in many places.
Subsequent approaches
Subsequent approaches have turned out to be slightly better. Here I experimented with a slightly different type of isopropanol and preheating the silicone, but the procedure itself looked roughly the same. Perhaps it was already the result of more skill, but now the cores looked a bit better, and their surface was already less hounded, although it was still far from perfect. In the end, I am reasonably satisfied with the result that was achieved.
Extracted from the calculator, there are seven circuits, with five types (pictured before identifying core No.3, which is the same circuit as No.5). In what follows, I will try to describe each of them individually, based on the documentation of Электроника МК-52, information found on the Internet and my own thoughts.
К745ИК1801-2 - bus controller
К745ИК1801-2 was the first chip I decided to get inside, so it is in the worst condition. Besides, physically it was also one of the larger chips. It is a microcontroller that handles data exchange between the system bus and the internal memory or external expansion module, which I mention more in the article describing the calculator.
Stosowany był tylko w trzech typach urządzeń Электроника МК-52, МК-54 i МК-61, natomiast jego produkcja odbywała się na Ukrainie w zakładach „Квазар” i „Квадр”.
К745ИК1303-2 - arithmetic processor
К745ИК1303-2 is an arithmetic processor that handles all the operations performed by the calculator. Interestingly, this chip is doubled, which I suspect allows it to handle numbers in a larger than standard range.
К745ИР2-2 - shift register
Another circuit is К745ИР2-2 which is a shift register where the device stores the currently used information. This chip also doubles as an arithmetic processor. I won’t hide, this chip is a bit of a surprise to me, because I assumed that the calculator would use SRAM or DRAM. Here, however, the Soviet engineers decided to use a rather peculiar design, namely a 1024-bit shift register.
К745ГФ3-2 - clocking circuit
Electronic devices, as a rule, require a timing signal. In the Электроника МК-52 calculator, it is implemented by the К745ГФ3-2 circuit, which is a four-phase pulse generator. Interestingly, this circuit does not need any external components for operation, but the frequencies of the generated signal remain a mystery.
К745ИК1302-2 - display controller
The last circuit is the VFD controlling the display К745ИК1302-2. Like many similar relics of the old era, it works with a slightly higher voltage than the classic 5V, so there is no need for additional transistors. Besides, the circuit looks quite complicated.
Soviet integrated circuits on film
While searching the Internet for the history of Soviet film chips, I accidentally came across a foreign ad in which someone, offered what I thought was this type of construction in the original case. Thinking little, I decided to order them and this is how I managed to get two copies, brand new Б1533ИР33-2 chips.
This is a rather simple design, an ordinary 8-bit register, coming from the Minsk plant “Интеграл”. As the marking on the plastic cover indicates, the chip was manufactured in March 1992. Besides, right next to the markings you can notice a rhombus sign indicating that the design was to be installed in military equipment. However, as you can see, it never made it to its original destination. Here we can also mention the very method of marking this type of construction. It is Б1533ИР33-2, but you might have already noticed some inconsistency in the designations in the case of the calculator chips. Although a specific description was printed, the target chip would most likely be described as Б7533ИР33-2. From what I was able to read, it was the number seven that was substituted for the one in the designation, thus informing that it was just a core placed on a metallized film.
As I mentioned before, the subject of this type of construction is quite mysterious. There is not much information about them and one can only rely on residual descriptions that appear when Soviet calculators are mentioned. Even so, the most puzzling thing is why someone came up with the idea of using such a fancy enclosure, if you can call it that, but that will probably remain a mystery.
