Controlled Electromigration for Field Failure Acceleration

The advent of SMT has caused a new concern for the electromigration failure mechanism. The new smaller electronic assemblies with higher density interconnections now are prime candidates for catastrophic field failures. Since the failure mechanism is so well-known and documented, it is possible to take advantage of these known responses to environmental, chemical, and physical properties and develop a procedure for testing components, boards, and entire assemblies. In order for electromigration to occur three things are necessary: ions, moisture, and an electric potential. Since removal of any one of these three necessary items will inhibit the process and prevent electromigration, a carefully controlled experiment Can be established to determine threshold values for each parameter. Once these threshold values are quantified, they can be used to predict the outcome of a device under test. A simple test for stressing specific areas of an assembly has been developed. This test can then be applied to a functional system or component and a life expectancy can be predicted. In this manner, incompatible components can be eliminated from the system or their surfaces prepared in such a manner as to prevent its premature demise. Some of the areas to which this type of testing is well-suited are printed circuit board platings, component platings, and final assembly cleaning. With this information the best possible process can be determined for coating the exposed metal surfaces so that maximum reliability is achieved.