Conductive foam causing corrosion.

[Argus25]

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=131807

It appears that some types of foam rubber attack metal as they break down.

Here is a discussion on a vintage computer forum, because the black conductive foam rubber corrodes the IC pins, of IC's in storage:

http://www.vcfed.org/forum/showthrea...8-Chip-storage

It would be good to have a definite chemical explanation of how this corrosion comes about and why some types of foam rubber become corrosive, but only as it ages. Polyurethane suffers from a process called reversion.

[cmjones01]

I've also seen this foam rubber corrosion problem. In this case it's on the plug-in modules for the HP 16500 series test equipment. Some of them have plastic guides attached to the underside of the PCB using double-sided adhesive foam rubber, which seems to decay and cause corrosion to nearby PCB tracks. I have three of the super-whizzy (2Gsample/s, not bad for 1992) 16534A digital scope modules,and they've all suffered terribly from this corrosion. Removing the foam strips and then laboriously finding and repairing all the broken PCB tracks does get them working again, though.

If similar foam is or was used inside capacitors I can well see it causing havoc.

Chris

[Refugee]

Black conductive foam can get quite toxic if not kept in check.

http://www.forum.radios-tv.co.uk/vie...hp?f=15&t=2558

[dseymo1]

That's very worrying; one tends to carefully store particularly valuable semiconductors in conductive foam, trusting that it will protect them.
Is it just the common black stuff which causes this problem?

[Refugee]

It is the black non springy type that poisons the stored components. It is pretty common so it is most likely the type you are thinking of.
I have no idea if those plastic bags that modern parts are shipped in are any better.

[Diabolical Artificer]

Thanks for that Argus25. I've noticed other caps that use foam inside to pad out small cap "windings" in big can's, IE on the Revox A77, though that one was ok, no corrosion.

I noticed something similar on a bit of HP gear, and have noticed marking on scope CRT's where foam was used to pad the CRT where it meets the chassis, I put it down to the glue at the time.

That's a good point about NOS components where foam is used as storage. I had some styluses that were ruined and corroded by the foam they were stored in. Might be worth looking at your stock if you have a lot of stuff stashed away in foam.

Old foam, a potential can of worms. I wonder if the new stuff is any better? Considering that there are lot's of different types it would take some looking into.

Andy.

[MrBungle]

Foam is the devil. I bought a massive bag of ICs and other components from eBay a few years back and all the leads on the ICs had corroded away. Most of it went in the bin.

[Argus25]

Well Andy, its interesting what this chat on electrolytic capacitors had led to. At the weekend I went though my extensive stocks of TTL IC's and cmos. Nearly all the ones in black foam, if put under a microscope, had some traces of a reaction. I think we only notice it otherwise when it is macroscopic corrosion, so I got rid of all of it (took most of the day) and saved my IC's. I also rubbed WD40 on the pins of many.

Has anyone ever seen this type of corrosion associated with white polystyrene ?

[HamishBoxer]

I have had black foam go sticky too, I had a box of fuses that used it. In the days when you bought a fuse kit for servicing.

[MrBungle]

Originally Posted by Argus25

Has anyone ever seen this type of corrosion associated with white polystyrene ?

If you leave it somewhere too warm it turns into yellow goop which is difficult to get off as well.

However the big problem with polystyrene is that it's a static nightmare. There's nothing worse than taking some tinfoil, sticking it on some polystyrene then whacking some nice CMOS 4000 series ICs into it. Some of them don't come back again. I have no idea why people do this.

Best solution I've seen are how RS ship ICs these days which is in individual plastic production carriers all in a conductive bag. I keep all mine (all 17 of them) in an RS anti-static box but I tend to just buy what I need and not keep a large stock around these days. The foam gets ruined and replaced before there are any problems.

[Herald1360]

Originally Posted by Argus25

Has anyone ever seen this type of corrosion associated with white polystyrene ?

I don't know about IC legs and polystyrene foam but it certainly disagrees with PVC insulation on cables!

I've seen polystyrene foam wrapped in ally foil used for storing CMOS parts and it's a useful way to protect the legs on TO3/TO66 devices from getting bent.

[Refugee]

They usually ship mains cables in a polythene bag to stop them from sticking to the white foam packaging parts.

[Lloyd 1985]

This is interesting, and worrying! I have a load of IC's and some LED displays packed in little blocks of this black foam. I also have some little anti-static boxes with a block of this foam in for storing IC's, I think a session of digging it all out and binning it is in order. I did get some parts arrive in plastic tubes, maybe these are better for storage than foam?

Not a fan of foam in general here, especially on speaker surrounds!

Regards,
Lloyd.

[paulsherwin]

I've just checked my (small) IC stock and the legs on some LM386s were starting to degrade. They're all out of the foam now and in an old Elastoplast tin. This thread has been a timely warning.

[G4_Pete]

HI,
I have used RS 557-102 (now 820-810) boxes for all IC,s and transistors! I had noticed tin whiskers on leads and cases particularily TO5 case types, I just put that down to aging but maybe the foam/box environment is accelerating that process. I have not seen corrousion as such but that could be down to the dry environment.

Perhaps time for a re-think on storage, any ideas? Of course there is allways the question on what is actually needed but that will allways be the thing that was thrown out.!

Pete

[MrBungle]

Just chuck them in ziplock bags if they're not CMOS. If they are, grab some conductive bags. Ziplock bags go slightly hard after about 30 years but you just rebag them then.

[threeseven]

Rubber and plastic materials very tremendously in long term stability, it is dependent on the constituent ingredients in any given formulation.
I have items with rubber and plastic parts that are in excess of 50 years old which are still virtually as new, but on other, much more recent items, as little as a few years old, rubber and plastic parts are degrading rapidly.
One of the most common materials that display this problem is that tactile, rubber grippy compound used on power tools. I have a cordless drill which is about a year old and the rubbery stuff has turned into a sticky mess! The same applies to a number of other similar items I have.
When some rubber and plastic does degrade, the constituent ingredients begin to return to their original state. That state may be corrosive or reactive to other materials, especially when combined with water. It all depends on how suitable, or well produced, the original rubber or plastic material was.
I remember observing many years ago, when the adoption of plastic components was replacing metal wholesale, that it would be a time bomb for the future of equipment so afflicted! So now we are seeing plastic mechanical parts becoming dimensionally unstable, cracking, breaking up etc, rubber parts disintegrating, all of which can destroy an otherwise good piece of equipment. I even had a Snap-On dead blow hammer shatter on me recently. The Urethane material had turned brittle, not good for a hammer! I will be pursuing Snap-On for an FOC replacement.
Rubber and plastic materials can be perfectly good but it's totally dependent on how well the materials are produced.

[Boater Sam]

I sold a new Royal Scot engine ( we are talking a model train here ) in its original polystyrene cradle and see-through lid ( for a lot of money ).
The buyer found that the poly had removed the paint from one side!

It was scrap.

Beware of any man-made oil derived plastics. Even the acid in newspaper ruins things.

[threeseven]

The strange thing is, Bakelite, one of the very first plastics, seems to be very stable!

[Lloyd 1985]

More to add to the list, extra flexible silicone earphone cables! I had 2 pairs of Philips (quite expensive...) earphones and the cable started oozing some sort of smelly liquid, first noticed when it ruined one of the earpieces, as the liquid went into it and clogged up the piece of material over the bass port, effectively stopping any bass in one earpiece! Shame as they were the best sounding earphones I've ever had, and they were really comfortable. The same thing is happening to our Sony TV remote, smelly liquid oozing out of the buttons all over the PCB, and insulating the conductive carbon bits, stopping the buttons working unless you press them really hard. Sony Playstation 3 controller joysticks have rubbery bits that also turn to snot if left alone for any length of time too.

It would seem that any attempt to clean up these affected items with soapy water, or IPA makes it degrade faster!

I wonder what state our collections will be in many years from now? All the plastic cased things crumbling or turning to blobs of goo as if left near a fire too long.

Regards,
Lloyd