TR04-0600, PLASTIC ENCAPSULATED MICROCIRCUIT (PEM) - DERATING, STORAGE AND QUALIFICATION REPORT (NO DATE)

TR04-0600, PLASTIC ENCAPSULATED MICROCIRCUIT (PEM) - DERATING, STORAGE AND QUALIFICATION REPORT (NO DATE)., Plastic Encapsulated Microcircuits (PEMs) have been a consideration for military/space use for about thirty years. Early in the development of PEMs, silicon and the epoxy molding compounds (EMCs) had several shortcomings and left a lot to be desired from reliability point of view. Moisture, which is present in most military/space applications, had a devastating impact on the early PEMs due to the impurities in the EMCs. These failures did not originate from an electrical standpoint (die level) but were chemical or mechanical in nature. The typical failure mechanism seemed to revolve around Kirkendall voiding (see Fig. 1). Kirkendall voiding, or purple plague, is the formation of voids in wire bonds caused by the intermetallic formation between the gold bond wires and the aluminum bond pads. This intermetallic formation between gold and aluminum is significantly accelerated in the presence of an encapsulant contaminant, such as certain halides (chlorine, bromine, fluorine), moisture and elevated temperatures. This voiding is normally considered an end of life failure mechanism. Other random failure mechanisms occur and are usually lot or manufacturer dependent. These failures are detailed later in this report. In PEMs process improvements, EMCs have evolved over time. This evolution has made PEMs more reliable; however, reliability is still a concern, when considering usage of PEMs in military/space systems. This report will review general derating storage and qualification guidelines for PEM devices. Also included in this report is some test data (from 1996-1999) that Naval Surface Weapons Center (NSWC) Crane, Indiana, has completed on some PEM lots.