Tin whisker problems????

The relay is most likely in a vacuum if it's in a satellite. Thus, when the whisker blows, there will be a nice conductive path in "air" which can conduct many amps. I got to see a nice flash-over in a vacuum chamber once. When they were pumping it down, someone left the heater on in the chamber which promptly flashed over when it hit the right pressure. Coated everything with copper! What a mess.

If I remember right, the tin whiskers in those space stories came from a tin coating on the relay frame and from tin coated boxes.

Mark

I remember reading that one :-)

Much of this stuff is purely politically motivated. Somebody wanted to feel important and can now pound their chest. "I made a law! Oh yeah, I am important now!" Just like changing DST cutoff by one week which was rather ridiculous and senseless. And caused mess-ups. For example, our VCR missed half of the old 1941 Jack London movie because of it. Arrgh!

--
Regards, Joerg

http://www.analogconsultants.com/

Jeff Liebermann hath wroth:

Foundit, compliments of the USGS. See:

For the 2007 report (for 2006) at:

The summary states: "Estimated world use of lead again increased by 3% to 4% in 2006. Much of the growth was attributed to increased production of SLI and industrial batteries in China. Growth also was attributed to increased manufacture of SLI batteries for automobiles and industrial batteries for the telecommunications and information technology industries." It doesn't break down production or consumption by industry, but a 4% overall increase doesn't sound like we're taking much lead out of the system. Perhaps there's some assumption that most leaded solder ends up in the landfills, as compared to auto batteries, which are 93% (by lead weight) recycled.

These are only good to 2004 but do show a big drop in lead consumption for solder starting in 2001. That's 2 years before the RoHS document was adopted (in Feb 2003). Also a big drop in lead use for paint in

1998. (lead production) (lead consumption) The spreadsheet version has a graph of sorts:

RoHS became manditory in Europe on July 1, 2006, and China on Mar 1,

2007. It may take a while for the statistics to be collected and cooked.

My main complaint is over the brilliantly conceived test for leaching lead out of products, which specifies grinding the product (i.e. CRT glass) to a powder prior to performing the test. We encapsulate dangerous materials (i.e. nuclear waste) in glass to keep them out of the environment, but that's not good enough for burying lead.

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Jeff Liebermann     jeffl@cruzio.com
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Skype: JeffLiebermann     AE6KS    831-336-2558

That's the crux of it.

Well, landfill and incineration, both of which are quite effective at dispersing lead (and cadmium, mercury, etc) throughout the environment, either by water or by air.

I don't think anyone's assuming that a landfilled CRT will leak lead at the same rate as the powdered version. It's more likely to be an issue of estimating the behaviour over decades or longer without the actual test taking decades.

Even when vitrified, nuclear waste doesn't get dumped into ordinary landfill sites.

By far the biggest source of heavy metal pollution is coal fired power stations.

for example.

The quantity of fly ash generated is enormous, some of it escapes into the air past the scrubbers. Some stations don't even have scrubbers. The Ash is either dumped in landfill, or sold as a a constituent of concrete the concrete gets used in buildings which eventually get demolished, and end up in land fill. The quantity of lead, nickel, vanadium, arsenic, beryllium, cadmium, barium, chromium, copper, molybdenum, zinc, lead, selenium, not to mention traces of uranium and thorium far outway any electronic scrap. The idea that removing a little bit of lead from electronic garbage is going to clean up landfill in any appreciable way is absolutely fanciful.

Andrew

Sarason sarason_not snipped-for-privacy@alphalink.com.au posted to sci.electronics.design:

Thank you for a good link. I was aware of some of the heavy metals from coal including the Actinide (radioactive) elements. The coal plant output of radioactive elements into the environment per Megawatt-year of coal plants is over ten times the amount allowed for nuclear fission based power plants total wastes.

Jeff Liebermann snipped-for-privacy@cruzio.com posted to sci.electronics.design:

Maybe, it has been 20+ years, but metal whisker growth (a bane in NiCad {and other} batteries, MLC ceramic capacitors, and several other applications). The growth conditions may exist for a longish time before the relay switches and full power is applied. Then the tin whisker may indeed be more robust than a marginally rated fuse.

That's not necessarily the same mechanism of formation. NiCds for example are electrochemical. Oxidizing and reducing and removing and plating back the cadmium and nickel can do weird things; it's already amazing that it works for a cycle, the electrodes retaining their form.

I will admit that cadmium, like zinc, probably forms whiskers by the same mechanism this thread is about.

AFAIK, whiskers don't "grow ... robust", they grow axially. What diameter they are depends on the conditions beneath each whisker. I'm not aware that whiskers change diameter in any way as they grow.

Tim

-- Deep Fryer: A very philosophical monk. Website @

Right, it is good to distinguish the difference between whiskers, which are extruded from the surface of metals with high atom mobility like pure tin and zinc due to internal compressive stress, and dendrites, which grow due to electroplating on the surface of the dendrite, requiring current flow through an electrolyte (often surface contamination) rather than compressive stress and atom mobility for growth. Whiskers cannot increase in diameter with growth, dendrites can.

I think that a whisker could initiate an arc which will be self sustaining even after the whisker has evaporated under the right conditions, which could easily blow a fuse.