Investigation of a connector electrical failure

Abstract

AbstractA PC product built by Celestica experienced a high rate of functional failure. Failure was associated with the CPU and CPU connector (known as a zero insertion force, ZIF type) since mechanically flexing the CPU stack induced failure. This problem became particularly serious when the customer adopted an uncontrolled (manual) “press” test, resulting in a large amount of rejected product which may have been functional under normal operating conditions.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 localized contamination, the presence of a probable insulating 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. Copyright © 2010 John Wiley & Sons, Ltd.