EFFECT OF ENCAPSULANT ON HIGH-TEMPERATURE RELIABILITY OF THE GOLD WIREBOND ALUMINUM BONDPAD INTERFACE

Abstract

Conventional plastic encapsulated microcircuits (PEMs) are increasingly being used in harsh environments such as automotive, well-logging, aerospace and military applications. There is a need, therefore, to examine their performance and reliability at high temperatures. A commonly used first level interconnect in PEMs is the gold wirebond aluminum bondpad interface. This interface has been found to have a very limited life at temperatures above 180 °C, due to intermetallic formation and subsequent corrosion. The corrosion is caused by brominated flame retardants and antimony trioxide in the molding compound. Given a set of environmental requirements, it is necessary to choose the right PEM for that set and to predict the life of the PEM based on the effect the flame retardants will have on the wirebond-bondpad interface. It is also necessary to look for better molding compound alternatives, such as environmentally-friendly halogen-free compounds, to mitigate high temperature corrosion. Thus, the focus of this study is to characterize the Br-related wirebond weakening process and to establish the high temperature reliability of halogen-free molding compounds. Several conventional PEMs have been tested at high temperature, and the wirebond strength profile has been found. A set of next-generation molding compound PEMs have also been tested at high temperature and high humidity, and their life at those conditions has been determined.