Yield loss during final evaluation was occasionally associated with low level leakage current between neighboring pins on a Motorola IC product. A series of simple experiments on reject samples indicated that the source of the leakage was on or near the package surface and likely to be due to a conductive film on the backside of the package between the leads. A technique was developed to detect and analyze the film using high tiltangle and low accelerating voltage on the SEM and EDS. The shallow penetration depth of the electron beam permitted observation of a thin and continuous film on the backside of the failed package. Likewise, the EDS sampling volume was constrained to the outermost layers of the specimen surface, such that a significant signal was generated from the identified film, even at low accelerating voltage. An EDS line scan across a surface region containing the film resulted in an excellent correlation between increased levels of metallic elements gold and copper and the presence of the film.

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