New Findings on Toyota's Unintended Acceleration
Wednesday, August 24, 2011 | Safety Research & Strategies, Inc.

"In our analysis, a significant number of tin whiskers were found. Using the CALCE Whisker Risk Calculator (CALCE) Tin Whisker Risk Calculator, 2005) to assess the failure risk posed by observed tin whisker formation on the conductor pairs, it was determined that the potential for a tin whisker shorting failure was 140/1 million. Considering the number of vehicles on the road, it is expected that this would present a significant safety hazard."

In addition to tin whisker formation in the APPS, the CALCE researchers found the potential for tin whisker formation in the ECM (engine control module):

 "The ECM contains surface mount electronic devices connected with tin-lead solder to a multilayer PCB. . Interconnect terminals of the perimeter leaded devices were found to be plated with tin. In addition, tin plating was found on terminal pins of the edge connections. As previously discussed, tin-finished leads can grow tin whiskers which can lead to unintended electrical shorts."

"We know whiskers can form on tin finished terminals," Osterman said. "In this case, Toyota has tin plating in a rather sensitive area, where the system relies on changes in resistance to provide a signal for acceleration."

In their discussion about the printed circuit board manufacturing processes of Toyota Camrys, CALCE scientists questioned the lack of a safety standard regarding automotive electronics, given broad range of whisker-induced failures. They were openly critical of NHTSA's lack of action.

"It is highly likely that tin whiskers could induce a failure that is later undetected. For this reason, best practices for electronics design stipulate that tin not be used as a plating material. It is very questionable why the National Highway Traffic Safety Administration, with a stated mission to 'save lives, prevent injuries and reduce economic costs due to road traffic crashes, through education, research, safety standards, and enforcement activity,' has not come out with a requirement that no electronics use pure tin as a material component, since the potential for tin whiskers presents an unreasonable and unnecessary risk."

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