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Whatever happened to...?

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Fred Basset:
Thought it might be fun (under general chat) to have question where other might know what happened to components / companies or whatever?

In my case it was because I suddenly realised that as a kid, so many of the electronics kits I had (and even bargain packs of assorted components) would contain lots of polystyrene capacitors, while now they are a great deal less common than they were.

I checked on eBay and they cost a fortune on there - a great deal of them being old stock from the 70s.  Does anyone know why they fell out of favor so quickly?  Certainly no one in China seems to be making them, which might be why they are relatively expensive?

TimFox:
Polystyrene capacitors have great electrical properties, but a low service temperature (85 C).  This does not allow modern automated PCB soldering techniques, which can melt the dielectric.  Around 1982, in the days of DIP and through-hole components, we used polystyrene capacitors in the sample-hold of a digitizing board, and they had to be hand-soldered, while the rest of the board was wave-soldered.
See  https://www.electrocube.com/pages/white-paper-what-happened-to-polystyrene-capacitors-data-sheet  for a discussion from a capacitor manufacturer.

coppice:

--- Quote from: TimFox on July 10, 2020, 03:23:24 pm ---Around 1982, in the days of DIP and through-hole components, we used polystyrene capacitors in the sample-hold of a digitizing board, and they had to be hand-soldered, while the rest of the board was wave-soldered.

--- End quote ---
That's strange. A well controlled wave soldering line doesn't usually get the component side of the board that hot. You can usually get away with using all sorts of low temperature plastics for connectors and other hardware items.

TimFox:
That was the recommendation of our board assembly house.  Of course, maybe only a small fraction of the caps would be destroyed but that was not acceptable.
Interesting note:  a recent search for polystyrene on Mouser turned up a couple of Xicon units (conventional construction), but more of the items returned were actually polypropylene, which is far more popular now.

coppice:

--- Quote from: TimFox on July 10, 2020, 03:29:09 pm ---That was the recommendation of our board assembly house.  Of course, maybe only a small fraction of the caps would be destroyed but that was not acceptable.
Interesting note:  a recent search for polystyrene on Mouser turned up a couple of Xicon units (conventional construction), but more of the items returned were actually polypropylene, which is far more popular now.

--- End quote ---
Polystyrene caps have become niche. Pretty much anything that isn't easily made as an SMD part has become niche. Polystyrene won't got away, though. Its properties are too interesting.

Did you have capacitors near the edge of the board? Heat spilling up around the edges makes those areas hotter and the central area of the board.

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