Author Topic: Whatever happened to...?  (Read 874 times)

0 Members and 1 Guest are viewing this topic.

Offline Fred BassetTopic starter

  • Regular Contributor
  • *
  • Posts: 52
  • Country: us
Whatever happened to...?
« on: July 10, 2020, 01:33:50 pm »
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?
 

Offline TimFox

  • Super Contributor
  • ***
  • Posts: 8995
  • Country: us
  • Retired, now restoring antique test equipment
Re: Whatever happened to...?
« Reply #1 on: July 10, 2020, 03:23:24 pm »
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.
 

Online coppice

  • Super Contributor
  • ***
  • Posts: 10031
  • Country: gb
Re: Whatever happened to...?
« Reply #2 on: July 10, 2020, 03:26:55 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.
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.
 

Offline TimFox

  • Super Contributor
  • ***
  • Posts: 8995
  • Country: us
  • Retired, now restoring antique test equipment
Re: Whatever happened to...?
« Reply #3 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.
« Last Edit: July 10, 2020, 03:30:53 pm by TimFox »
 

Online coppice

  • Super Contributor
  • ***
  • Posts: 10031
  • Country: gb
Re: Whatever happened to...?
« Reply #4 on: July 10, 2020, 03:37:18 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.
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.
 

Offline TimFox

  • Super Contributor
  • ***
  • Posts: 8995
  • Country: us
  • Retired, now restoring antique test equipment
Re: Whatever happened to...?
« Reply #5 on: July 10, 2020, 04:07:06 pm »
If I remember correctly, the polystyrene caps were about 1.5 inches away from the edge of a roughly 5 by 14 inch 4-layer board.
I have beautiful General Radio decade capacitor boxes and lab-standard single units.  They made both polystyrene and silver-mica versions (as well as air-dielectric singles), and the catalog listed the pros and cons of each.  Basically, they recommended polystyrene for low-frequency applications, since the "apparent capacitance" of the mica caps increased at low frequencies.   Hermetically-sealed polystyrene caps hold their accuracy:  I found no errors measuring them with more modern equipment.
 

Online Benta

  • Super Contributor
  • ***
  • Posts: 6420
  • Country: de
Re: Whatever happened to...?
« Reply #6 on: July 10, 2020, 05:23:16 pm »
Polystyrene caps disappeared, because the only company making suitable polystyrene foil discontinued the production; IIRC DuPont.

 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf