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Sometimes when I order semi-conductors, there pins are put in this black foam (im guessing static sensitive stuff). If I put a high voltage through it, it conducts and burns. What is this stuff called and what is it made out of?

skyler
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  • I can't answer your questions, but it's indeed to prevent static stuff. MOSFETs for example are very sensitive for static charges (that's why you have to discharge yourself before soldering them), so they have to be packed in that black foam. –  Apr 22 '13 at 15:41
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    +1 for running a high voltage through something you have no idea about! –  Apr 22 '13 at 15:44
  • wait so its bad to remove it from the foam when I store it? I never have had a problem with leaving it in a plastic bag. – skyler Apr 22 '13 at 15:47
  • For most semiconductors it doesn't really matter. There are static-sensitive parts, like MOSFETs, that do care. They may explode when you remove them without first discharging yourself. –  Apr 22 '13 at 15:56
  • irfp250 and irfp450 don't explode :) – skyler Apr 22 '13 at 15:57
  • Whether ambient ESD is a problem seems to depend mostly on ambient humidity. I've _rarely_ had a problem with it myself, but that's not to say it's not real. – pjc50 Apr 22 '13 at 16:02
  • is there like a youtube video of a mosfet exploding when you take it out of its package? – skyler Apr 22 '13 at 16:12
  • It's probably foam! ;) – Polynomial Apr 22 '13 at 16:24
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    ESD damage while handling the parts is very real and must be taken seriously. The problem with ESD is that you might not see the damage for months or years later. Typically, an ESD discharge has to be more than 500+ volts to be felt/heard/seen, but damage can occur at much lower voltages. If you haven't had issues with ESD then you either haven't been doing EE long enough, or you did have damage but just didn't recognize it as such. And it is not at all limited to MOSFETs. Any semiconductor can be damaged, and even some caps and resistors! –  Apr 22 '13 at 16:44

2 Answers2

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The black stuff is a rubber and/or plastic foam that is heavily loaded with elemental carbon (graphite) in order to make it conductive. It keeps the pins effectively "shorted" together (through a resistive path), and if it's sitting on a grounded surface, it also provides a current-limited path for ESD currents, helping to prevent damage to the parts.

It's cheap and effective for short-term storage, but I've found that over long periods of time, it can break down and/or absorb moisture and corrode the leads of parts that are stuck into it.

Dave Tweed
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2

Essentially, it prevents a difference in electrical potential that could be discharged through the circuit which could damage or destroy the chip.

THIS series produced by Apple in the '80s, while it seems to have a hint of propaganda, is very well done, and explains the risk well.

Butters
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