At 02:59 PM 5/1/2006, William Bordy wrote:
>>Problems with tin whiskers have been around a lot longer than RoHS
>>(perhaps
>>as far back as WW II?). It presents a problem with reliability of
>>equipment
>>designed for low cost production, with no budget for re-engineering, sure.
>>But for the rest, it's not so clear.
Yes, as the listed WEB explains, tin whiskers have been around a lot longer
than RoHS. But, as the below excerpt from the WEB site,
http://nepp.nasa.gov/WHISKER/background/index.htm , explains, it is
believed that no-lead solders will increase the risk of tin whiskers.
"
There is a wealth of information on the tin whiskers problem at the NASA URL
I listed. I won't repeat it here, but I would suggest that those, (I suggest
anyone who buys consumer electronics should be), who are interested read the
information at the URL and resources suggested.
To simply say it has existed, does not resolve the believed increase of tin
whiskers due to the use tin plated only components and the use of no-lead
solder.
Indeed. It IS a problem, but only for pure tin (and pure zinc). The pure
tin thing was a "quick fix", that, as you note, has been thoroughly
discredited as a solution.
Obviously, the removal of lead is a good thing, but the introduction of a
new problem without a known solution is short sighted.
There are known solutions, they're just not as cheap as tin/lead, nor is
there decades of experience with them. Most manufacturers, being fairly
short term bottom line oriented would prefer to keep things the way they
are, rather than spend NRE money on redoing the process engineering and RE
money on more expensive substrates and/or solder.
There IS an exemption for the tiny amount of lead used inside the
semiconductor package.
The exemption for "mission critical" isn't forever, either. I believe it
expires in 2010. Besides, the space industry is so tiny, compared to the
commercial industry, that we in the space biz have to figure out how to use
what's commercially available, since they're not going to run two different
production lines. The same is true, in the longer run, with military
stuff. Their volumes are higher, so they have a bit more clout.
I discussed RoHS with a US distributor representative expressing my concerns
of product reliability. His response was products are obsolete in a few
years anyhow. My response is I really wouldn't like to replace a $3000 piece
of consumer electronics equipment in 2 years or less.
Your distributor was right, though. The vast volume of consumer
electronics (in a dollars, and pieces basis) is disposable/consumable
stuff: cellphones, MP3 players, computers, etc. There's actually
relatively little volume in the $3K and up range with expected life >3
years. For equipment in that range, one can expect that the cost of RoHS
is a much smaller fraction of the total unit cost, and so, a mfr can afford
to invest in the needed reengineering to make it work, or, to cover
warranty returns. There's also a huge difference between the "design use
life" for piece of consumer electronics (typically 1-2 yrs) and the actual
life (which could be much longer). This is why, for instance, consumer
computers are much cheaper than "real" server computers (at least, when the
mfr is taking the risk of failure). In the consumer market, sell price is
everything, because most consumers don't factor in the largely speculative
future costs. In the commercial/industrial/professional market, life cycle
cost (TCO) is what they buyer looks at, and gear is designed and priced
accordingly.
This comes up a lot for people building things like server farms or cluster
computers, where the cost of a failure is known, and includes things like
the time for the administrator to figure out it's broken, pull it out of
the rack, the time to rerun the job from a checkpoint, etc. The "all-in"
cost of a single failed cluster node could be several thousand dollars.
It's not too hard to figure out how much more you can afford to pay for
changing the failure rate from 5% in the first year to less than 1%.
I have discussed this with manufacturers also. They are concerned with the
shelve life of products, as tin whiskers are a result of time, not
environment. In fact, one has mentioned changing his warrantee to reflect
time from factory shipment.
This sort of thing is why I think that what you'll see is more of a
stratification between "throwaway consumer electronics" and
"commercial/professional electronics". Where it will get ugly is in that
"pro-sumer" sort of regime, where people are expecting consumer type
pricing, but also expect long-lived, durable designs.
Kind of like the difference between an inexpensive imported machine tool at
Harbor Freight and a watchmaker's lathe from Germany.
Although goods sold in the US do not currently require no-lead components,
the EU RoHS requirements are rippling into the distribution chains.
Regardless, tin whiskers appear to be a real problem that is being sweep
under the rug in the rush to no-lead solutions
I don't know that it's being swept under the rug, per se. Businesses are
having to make the hard choices of cost vs reliability, and as is often the
case, the consumers don't have a lot of visibility into the process.
James Lux, P.E.
Spacecraft Radio Frequency Subsystems Group
Flight Communications Systems Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
tel: (818)354-2075
fax: (818)393-6875
