Whisker short is not easy to pin point. Many of them are loose and can be fall off during disassemble of the parts for the FA. Therefore, it should be aim for no whiskers (or not have potential of whisker growth at all) and eliminate all the potential sources, such as high stress in couple with pure tin plating, etc. To do FA of whisker is life shortening experiences (not like good wine that aged properly... it enhances white whiskers growth on your head great deal).
Jk (I had my share 20 years ago... enough)
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Bob Landman
Sent: Thursday, February 10, 2011 5:05 PM
To: [log in to unmask]
Subject: Re: [TN] NTC: Excuse me, but...
Thanks for commenting Mike.
Engineers ARE at fault if they ignore the serious problems with lead-free manufacturing. Readers should download the full report and then use Adobe's search tool to search for the term "whisker". Engineers should go to their management and tell them the truth; the RoHS lead ban is a gross mistake that must be overturned. This is what happens when politicans legislate science.
NASA had only a few vehicles to inspect out of the many millions that are on the public highways. A very poor sample size, don't you agree? Yet, they did find tin whiskers! This is an ominous sign. SAC solder and tin plated leads were the cause. There was no attempt to mitigate the growth of whiskers.
Page 118 of the 177 page report: "If the (tin whisker) resistive short occurs while the vehicle is off, starting the vehicle with the accelerator pedal partially depressed will not trigger a diagnostic trouble code (DTC). When the accelerator is pushed slowly, the vehicle has a jumpy response, and is capable of full throttle without brake override."
NASA's findings do not solve the question of what caused Kevin Haggerty's well documented sudden acceleration event. Haggerty owned a 2007 Toyota Avalon that experienced at least 5 different sudden acceleration events. Haggerty did not have accessory floor mats and his OEM mats were secured in place. Sticky pedals couldn't have caused the problem because he didn't have his foot on the pedal. On Haggerty's final incident, he was actually able to drive the vehicle while the engine was racing out of control into his local Toyota dealership.
He got to the parking lot, shifted to neutral and stopped the car with its brake smoking and engine racing out of control. He got out of the car and the engine was still racing (no pedal misapplication) Service technicians were able to look at he car and confirm the unintended acceleration was not caused by floor mats, sticking pedals or driver error. They also confirmed no computer error codes (meaning the computer was not detecting whatever was causing the problem).
Bob Landman
www.ldfcoatings.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Mike Buetow
Sent: Thursday, February 10, 2011 4:16 PM
To: [log in to unmask]
Subject: Re: [TN] NTC: Excuse me, but...
I don't think it's that simple. In fact, I think this report raises as many questions as it answers.
Note that there are two reports on the NHTSA website. One is the NHTSA report (77 pages); the other is the NASA report (177 pages).
http://www.nhtsa.gov/UA
http://www.nhtsa.gov/staticfiles/nvs/pdf/NASA-UA_report.pdf
The NASA report is very clear about the presence of tin whiskers (page 120-123). It also noted a failed pedal assembly contained multiple whiskers, while several other pedals reviewed also contained tin whiskers, although no failures were (yet) seen. Keep in mind only a handful of vehicles were used for the analysis, which means the results might not be representative of the entire fleet of Toyotas in use. In some cases an all-tin solder was used. The CTS-built pedals lacked conformal coating on the boards (page 125). The Denso-built pedals were built with SAC solder and embedded in a "potting substance" (page 127).
I find it very interesting that the number of complaints of unintended acceleration have tapered off to zero. How is it that there was such a cluster of bad drivers, and then none at all? Is Toyota designing something different (other than the shimmed pedal)? Using a different solder and/or finish? Something doesn't add up. There are a lot of unanswered questions, IMO.
Not to put anyone on the spot, but I would also be curious whether the Joint Group on Pollution Prevention is planning to take any of the NASA findings into account?
Best,
Mike
Mike Buetow
Circuits Assembly
w/m 617-327-4702
VIRTUAL PCB: the electronics industry's only online trade show!
www.virtual-pcb.com
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Stephen Pierce
Sent: Thursday, February 10, 2011 3:36 PM
To: [log in to unmask]
Subject: [TN] NTC: Excuse me, but...
where can engineers go to get their reputation back?
http://tinyurl.com/ToyotaEETimes
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