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Beware of old AntiStatic foam

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TerraHertz:

--- Quote from: intabits on March 22, 2021, 08:13:07 am ---They were stored in a parts draw cabinet. Admittedly, in a room exposed more to the outside air, so with higher humidity.

--- End quote ---

Ah ha. I think that's the culprit. The foam itself degrades and produces some potentially corrosive substances but it seems they are not very mobile. Moisture multiplies the effect greatly by acting as a solvent and transporter.

Thin gold plating is porous. The underlying metal of the pins is an iron alloy. Without moisture the corrosive substances don't transport into the pores and reach the iron. Moisture alone will make gold plated surfaces on old chips corrode - but it's simple rust that starts in the pores and bubbles off the gold plating.

Add water transporting corrosives into the pores, and the mess in your photos is the result. Very sad.

I'm currently sorting out a quite vast quantity of moderately mixed ICs. It's an old collection, had been in plastic parts drawers in a dry location. Most of the ICs are loose, some in black foam, some al-foil wrapped. They are old enough that some of the loose ones have a dark silver-tarnish appearance to the pins. That's OK, not corrosion. Most are still shiny. Of the ones in black foam _most_ are still fine, but now and then I come across one or two that are a little corroded where in contact with the foam. Some of the foam is very decayed and falls apart into dust.

But so far nothing like your pics. I suspect the differentiating factor was the low humidity storage conditions of this collection.

As I sort them, ALL are ending up in stacks of 20 or less wrapped in alfoil, placed in small yellow paper envelopes in rows in boxes. It's an extremely dense and versatile storage system, easy to keep in good sorted order. The boxes have lids, so it's pest and dust proof.




--- Quote from: coppercone2 on June 24, 2021, 10:41:49 pm ---check old instruments with cards for this foam shit, they like using it to stabilize the cards from the top to save money on braces

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That's urethane foam rubber, the bane of restorers of old equipment. It decays to a sticky gunk, falling apart into small pieces that get all through the equipment, and is extremely corrosive to many metals. It's a 'remove on sight' menace.

The black antistatic foam otoh, seems to be something else. Not sure of its composition, other than probably containing a lot of carbon powder additive to make it conductive.

coppercone2:
are you sure its not that mixed with carbon and freeze dried or something like softee ice cream

Zero999:

--- Quote from: tszaboo on March 21, 2021, 04:50:03 pm ---
--- Quote from: zener on March 21, 2021, 01:15:07 pm ---An ultrasonic cleaner is NOT your friend.   The ultrasonic vibrations can break the bonding wires that go between
the chip carrier and the silicon wafer.

--- End quote ---
Got any evidence to back this up?

--- End quote ---
Obviously the person who posted doesn't have any evidence and nor do I but, it's plausible ultrasound could damage come components. I belive most DIPs should be fine, as the bond wires will be secured by the encapsulation, but metal can packages might be vulnerable, as well as some crystals and oscillators.

--- Quote from: coppercone2 on June 25, 2021, 07:05:53 am ---are you sure its not that mixed with carbon and freeze dried or something like softee ice cream

--- End quote ---
It's a commmon problem. I've seen it on new, old stock, components where I work. I think the old ant-static foam is made of celulose, which produces corrosive decomposition products.

Ian.M:
The O.P. had a pair of side-braze CERDIP package MCUs.  CERDIPs and other ceramic IC packages will almost invariably have unsupported 'naked' bond wires in the cavity running from the leadframe or leadout metalization to the die.  If the ultrasonic cleaner hits a mechanical resonant frequency of any of the bond wires, failure is highly likely. 

coppercone2:
you can reduce power level by increasing bath temperature and then dampening it with extra items to make it safer

higher temp = more soap action, it should compensate for the loss due to other materials absorbing energy in the tank

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