Technologies and Trends to Improve Power Electronic Packaging

Abstract

In the realm of power modules a strong trend toward high temperature and high reliability applications can be observed, which entails new technological challenges, especially for the assembly and packaging of power semiconductors. Because of the well known failure mechanisms of established lead-free standard soldering and heavy aluminum wire bonding technologies, such as fatigue and creep of die attach material and wire bonds at thermal cycling, academic and industrial research focuses on more reliable interconnection technologies. A priority is the research of alternative top and bottom side chip interconnection materials or technologies to improve the temperature cycling capability of power chips that are typically assembled on ceramic substrates. The scientific focus is on Ag sintering as die attach and/or heavy ribbon bonding, for example with Al or bi-metal (Al-Cu). Another focus is the material behavior of ribbon bonds in combination with bonding machine improvements (higher bonding parameters, cutting tool). But there are other very promising technologies like transient liquid phase bonding, for example with Cu-Sn or Ag-Sn systems or Cu heavy wire bonding (up to 400 μm wire diameter) or Cu/Al-Bi metal ribbon bonding. Challenges posed by these technologies have to be discussed focusing on materials and process selection and reliability issues. Process temperatures and temperature profiles must be optimized, wire bonding machines and the chip surface structures as well as finish metallizations need to be adapted. This paper will give an overview of alternative power chip interconnection technologies and discuss the challenges related to processing and reliability.