Materials for High Temperature Electronic Packaging

Abstract

Normally, the operating temperature of consumer electronic devices is from 0oC to 70oC. However, some industries are interested in electronics that can operate in extreme environments. The working environment temperature of power devices in hybrid electric vehicles is between 150oC and 200oC, while instruments for well drilling and exploration in the gas and oil industry demand more than 150oC operating temperature. As engineers seek to extend the benefits of electronics to more applications, the demand for high-temperature electronics is increasing. Electronic coatings like conformal coating, potting and encapsulation are used widely to protect electronic modules. Acrylic resin, epoxy, silicones, and polyurethane are used as the coating materials. However, few of these materials can withstand high temperatures above 300oC. Parylene HT is a potential candidate for high temperature (short term up to 450oC) encapsulation. It can provide uniform, pin-hole free conformal coatings, which protect the circuit from moisture and other contamination. In this work, a test pattern was designed to evaluate Parylene HT as an insulation coating material for electronic devices during a 300oC storage test. In addition, some other coating materials that were advertised for use at 300oC were investigated. Nickel/gold finishing is quite commonly used as a solderable and protective surface finishing for direct bonded copper (DBC) substrates used in high-temperature power applications. Many forms of Ni are available based on the plating process (electroless or electrolytic) and the plating chemistry ( phosphorus, boron, or cobalt). During soldering and high temperature aging, the formation of Ni intermetallics and voids occur that may impact reliability. Reactions between different Ni plating and BiAgX® (Indium Corp.) and AuGe were investigated. The decrease in shear strength after formation of Ni-Ge and NiBi3 intermetallics were specifically studied. The growth kinetics and activation energy of Ni-Ge intermetallic formation were calculated.