[tinwhiskers] FW: Whiskers info posted on IPC LeadFree forum.
- From: "Fritz, Dennis D." <DENNIS.D.FRITZ@xxxxxxxx>
- To: <tinwhiskers@xxxxxxxxxxxxx>
- Date: Fri, 2 May 2008 13:24:59 -0400
The following e-mail messages about tin whiskers were posted to the "LeadFree"
e-mail forum of the IPC. There is some good data and literature refererences
here, so I compiled the sequence and post them here to the Whiskers Forum.
This started from an inquiry about the current cost of RoHS around the world -
a figure of $32 Billion and climbing $4-5 each year.
Denny
________________________________
Subject: Whiskers info posted on IPC LeadFree forum.
> From: Steve Gregory [mailto:SGregory@xxxxxxxxxxxxxxxxxx]
> Sent: Monday, April 21, 2008 5:22 PM
> To: (Leadfree Electronics Assembly Forum); SCHMIDT, WOLF-DIETER - PFHO
> Subject: RE: [LF] The Cost of EU RoHS: $32.7B
>
>
> Hi Wolf!
>
> Here's a link you might want to look at:
>
> http://nepp.nasa.gov/whisker/failures/index.htm
>
> Steve
***********************************************************
Hello Steve,
in between I've read most of the available reports related to the your link.
Nearly all reports point out that the tin cover on mechanical parts have
been the base for tin whisker growth:
<< DirecTV 3 ...... Boeing 601-model satellite ......
being caused by the growth of metal filaments in a relay ..... <<
>> Galaxy VII Lost ..... failures in Boeing 601 satellites........
tin whiskers grow in the vacuum of space on internal
tin-plated relay latching switches..... <<
(a lot of reports on the 601 - bad luck for Boeing products)
>> report by Gordon Davy1, Northrop Grumman Electronic Systems,
Baltimore, MD: "Relay Failure Caused by Tin Whiskers" <<
... and a lot more reports decribing the same.
Interesting are the two Westinghouse reports:
# diode lead as base of a whisker
# mechanical part of a potentiometer
The link
>> Patriot Missile: Anoplate WWW Site:
Suspected tin whisker related problems (Fall 2000) <<
gives explanations under which conditions tin whiskers will grow and this is
due to my knowledge as well. Tin covered mechanical parts will be able to
produce tin whiskers if mechanical stress ist introduced to them. In all
those cases the tin cover was made by galvanic processes but not by melting
tin on a copper or brass metal sheet. It is also well known, that the risk
of tin whiskers out of tin on copper (or alloys containing a high percentage
of copper) is much higher than whiskers out of tin on a nickel barrier.
It is reported that even out of Sn60Pb40 you may have some tin whiskers if
the conditions are given.
The only report which not basicly refferes to a mechanical part is one of
the two mentioned Westinghouse reports. There the anode lead of a diode was
diagnosed to be the root of failure. In this very case it would be
interesting to know whether the whiskers have been grown out of the lead at
it's bend or not.
So in my oppinion the risk of tin whiskers on an printed board assembly with
electronic components (not regarding electromechanical parts !) is quite
low, especially when produced using reflow soldering. Then most of the
stress on components leads and the tin coverage - if there has been some
stress - will be removed. And the copper lines on the board themselves
normally cannot be mechanically stressed. An additional method to be more
aware of tin whiskers is to use gold over Nickel as metal plating on the
board - we have experience with this for about 15 years and thousands of
boards with very good results.
I would like to know what's your thinking on the points mentioned before.
Regards
Wolf-Dieter Schmidt
Industrial Engineering
-----------------------------------------------------------
THALES Defence Deutschland GmbH
Land & Joint Systems
Ostendstrasse 3
D-75175 Pforzheim - Germany
-----------------------------------------------------------
Phone: +49 7231 15 3386
Fax: +49 7231 15 3390
mailto: wolf-dieter.schmidt@xxxxxxxxxxxxxxxxxx
http://www.thalesgroup.com
*******************************************************
From: Richard.Stadem@xxxxxxxxxx
Wolf,
I would caution you not to downplay the tin whisker issue.
I am a consulting engineer, and a very busy one. Right now a lot of my
time away from GD is working tin-whisker issues. Although most of those
I see are on lead-free product, they are showing up on leaded products
as well, typically at the portion of the termination where the leaded
solder stops and the tin-plated area begins.
It is nearly impossible to completely coat 100% of the tin-finished
RoHS-compliant leads with tin-lead solder. Often it is simply not
feasible without automating the process, and as a result there are many
instances where the tin-finished portion of the lead is exposed near the
component body, and that is where I am continually seeing the tin
whisker growth on RoHS-compliant parts.
Behind the few articles published are many more cases of tin whiskers
that never go public.
The issue is such that many military, automotive, avionics, and
high-reliability companies are investing in fully automatic robotic
tinning cells such as those manufactured by V-Tek or Corfin to
automatically dip all of their component leads in Sn63Pb37 solder prior
to assembly and soldering. Other mitigation methods have not proven to
work very well, including conformal coating.
Many of the assemblies with whiskers are on ENIG-finished PWBs. I don't
see how the plating finish works as a mitigation scheme, except possibly
with HASL finishes where the HASL is tin/lead. The few microinches of
gold in the solder volume are not enough to present any effective
mitigation up around the top of the fillet.
The last thing I would recommend to anyone is to switch to ENIG. That is
simply switching from one set of problems to another.
******************************************
From: SGregory@xxxxxxxxxxxxxxxxxx
Hi Wolf!
I don't have any direct experience with tin whisker failures, but as a
production engineer for an EMS company, I wouldn't really know of any
failure unless one of our customers told us about it. We just build
things and ship them. We don't follow the product through their lives
like our customers do.
We also don't build that much lead-free here, but we have the capability
(dual wave solder pots etc.), and it's just because of our customer
base. Most of our customers are either high-rel or military, and forbid
tin plated components.
Another link that talks about more than just relay whiskers is from
CALCE:
http://www.calce.umd.edu/lead-free/tin-whiskers/TINWHISKERFAILURES.pdf
Steve
****************************************************
From: Richard.Stadem@xxxxxxxxxx
Steve, I am sending you a couple of pictures via a separate email of
recent (last week) tin whiskers seen on a RoHS I.C. on lead-free
product, if you could be so kind as to post them on your website. This
is just one example, I have lots more. The point I am trying to make is
that the whisker issues are becoming widespread, and will eventually
carry over into more COTS parts used in high-rel applications.
***********************************************
From: CNJ@xxxxxxxxxxx
Richard - You might like to submit the/a picture(s) to the NPL defect
data base http://defectsdatabase.npl.co.uk/ as they currently only have
one picture it would appear.
************************************************
From: jrbarnes@xxxxxxxxx
Wolf-Dieter,
I have been studying lead-free electronics, the RoHS and WEEE
Directives, and the like since December 2004, and have already collected
over 12,000 published documents on these subjects, including:
* 235 books.
* Over 100 Ph. D. and Master's Theses.
* Over 11,650 reports, papers, magazine articles, etc.
* Over 240 web pages.
My bibliography of these materials is at
http://www.dbicorporation.com/rohsbib.htm
and is some 800 pages long....
To date, I have found *two* documented cases of tin whiskers growing on
tin-lead solders or platings:
* http://nepp.nasa.gov/whisker/photos/pom/2003dec.htm
* Liang, J., Dariavach, N., and Shangguan, D., "Tin Whisker Nucleation
and Growth on Sn-Pb Eutectic Coating Layer Inside Plated Through
Holes With Press-Fit Pins," IEEE Transactions on Components and
Packaging Technologies, vol. 31 no. 1, pp. 152-158, Mar. 2008.
I have collected well over 1,000 documents that discuss the growth of
tin-whiskers on lead-free solders and platings. These include many
cases where unused components are fine, but the same components soldered
to printed circuit boards will grow tin whiskers.
I personally do not trust the quality, reliability, or longevity of
lead-free electronics, because of:
* Tin whiskers.
* Tin pest (tin plague, tin leprosy. tin disease, tin blight).
* Broken solder joints from physical shock.
* Kirkendall voids.
* Conductive anodic filaments (CAF).
* Copper dissolution.
Before 2006, I would buy electrical and electronic equipment/products
expecting to use them for 3 to 20+ years. But now I buy new
electronics-- manufactured since early 2006-- only if I figure that I
will recover their total purchase price within 3 months. I also take
these precautions:
* Plug lead-free (or suspected lead-free) electronics into AC power
only when someone will be in the area.
* Put batteries into battery-powered lead-free (or suspected lead-free)
electronics just before using the item, and remove the batteries as
soon as I finish.
I may be in trouble when my wristwatch quits...
John Barnes KS4GL, PE, NCE, NCT, ESDC Eng, ESDC Tech, PSE, SM IEEE
author of Robust Electronic Design Reference Book, Volumes I & II
dBi Corporation
http://www.dbicorporation.com/
*********************************************
From: Chris.Hunt@xxxxxxxxx
Thanks for this, and please use the data base, any problems, let me know
Chris Hunt
NPL
***********************************************
From: SGregory@xxxxxxxxxxxxxxxxxx
Hi Richard!
Have your pictures posted now. Go to:
http://stevezeva.homestead.com/Whiskers.jpg
http://stevezeva.homestead.com/Whiskers_2.jpg
SCAREY STUFF!
Steve
*********************************************
From: gherzog@xxxxxxxxxxxxx
Richard,
I've just seen your two "whiskers" pictures. The brilliance and smoothness of
the leads tends to convince me that this is a bright tin plated lead - not
matte tin. Supposedly, bright tin has more organic material in it that
promotes
whiskers.
Glen
***********************************************
From: Richard.Stadem@xxxxxxxxxx
Done. Thanks. They want all pictures/information on tin whiskers and
other issues as well, but be sure to specify what type of process was
used, etc.
************************************************
From: Richard.Stadem@xxxxxxxxxx
You could be right. I cannot vouch for the finish, only that it is
described on the print as matte tin. Nowadays, who knows where the part
came from, and what finish was really used?
**********************************************
From: Chuck.Patten@xxxxxxxxxxxxx
You might also be interested in this link
http://nepp.nasa.gov/whisker/failures/
cheers,
chuck...
**********************************************
From: john@xxxxxxxxxxx
The finish after reflow may be academic Tin melts at 231.93 Centigrade
John Burke
(408) 515 4992
***********************************************
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