Investigation of a Connector Electrical FailureAuthors: Peter Arrowsmith, Al Hawley, Prakash Kapadia, Mustafa Al-Salman, and Rana Sodhi
Company: Ops A La Carte, Celestica Inc., Colt WorleyParsons, and University of Toronto
Date Published: 5/17/2010 Conference: ICSR (Soldering and Reliability)
A failure analysis method involving static loading the CPU and epoxy potting the connector stack was developed to mechanically "trap" the fail condition. Sectioning and electrical probing was used to determine which of the 240 active connector pins have high resistance.
Analysis of suspect connector pins and contact surfaces pointed to several possible causes of failure. SEM-EDX revealed localized damage to the Au plating with exposed Ni and NiO. XPS and TOF-SIMS with depth profiling confirmed the presence of a ~100 nm layer of a fluorocarbon on the Au surface. Although it was not possible to clearly locate the individual electrical contact spots (1-10 µm diameter) to identify specific contamination, the presence of a probable insulating organic coating was sufficient evidence to follow-up with the connector supplier. The connector spring contacts were found to be coated with an "anti-flux" agent to prevent wicking of liquid solder onto contact surfaces during the wave solder assembly process. The corrective action was to change the ZIF connector to a type without anti-flux coating and the failure rate was significantly reduced.
Keywords: electrical connector, failure analysis, surface analysis, fluorocarbon, contact resistance
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