Method for testing encapsulation integrity

Abstract

A procedure is disclosed for detecting and documenting flaws in the glassivation layer protecting the active device region of an integrated circuit. A droplet of dilute sulfuric acid solution is placed on top of the glassivation layer and a positively biased electrode is immersed in it. The leads coupled to circuit under the glassivation layer are coupled to a more negative voltage. The release of hydrogen bubbles into the solution through flaws in the glassivation via an electrolysis reaction are readily observable. Defects in a glassivation layer over nichrome devices may be documented by reversing the polarity of the bias to cause a reversal of the electrolysis process and a release of oxygen from the defective sites. This causes oxidation and disfigurement of the nichrome which can be documented using ordinary photographic means. Defects in a glassivation layer over aluminum may be documented by replacing the droplet of dilute sulfuric acid with a droplet of dilute sodium chloride; the resulting disfigurement may be photographed.