Metallurgical Interconnections for Extreme High and Low Temperature Environments

Abstract

The material properties and requirements for wire bond and flip chip interconnections that can be used in packaging chips for extreme high and low temperature environments [from +460°C (HTE) down to −200°C (LTE)] are described. The most commonly used Au–Al wire bonds should be avoided in the HTE range, along with any other metallurgical interfaces that form brittle intermetallics and/or Kirkendall voids. Gold–gold bonds improve with time and temperature. Thus, a clear preference is given for gold (or other noble metals) in the HTE environment for both wire and flip–chip bonds. For LTE and intermediate temperature ranges, such as on Mars and most earth satellites, conventional interconnections (Au and Al wire bonds) to Al chip metalization (bond pads) are acceptable. Also, normal flip-chip solder bumps are acceptable, but without plastic underfill. Information and techniques for using extreme temperature range materials, such as coefficient of thermal expansion (CTE) matching between chip and substrate, high temperature polymers, etc., are presented. Unusual failure mechanisms, such as possible electromigration of wire interconnections in HTE, are described. It is concluded that, with proper selection of materials, interconnections can be reliable in both extreme environments.