Electronic Packaging Science and Technology

13Failure Analysis

13.1 Introduction

When a device is manufactured to provide a specific function in application, it is hoped that the microstructure in the device will not change in its lifetime of use. Unfortunately, this is not true! Failure occurs when an unwanted microstructure change has taken place such as void formation at the cathode in an interconnect in the device, for instance. This is because Si device is a current–voltage device, so we have to apply electric current to operate the device. It is an open system. Under a high current density, electromigration induces microstructure change in the interconnect and can lead to circuit failure due to opening by void formation at the cathode or shorting by whisker extrusion at the anode. Furthermore, the high current density can cause Joule heating and the temperature rise will produce thermal stress between materials having different thermal expansion coefficients in the device. Heat conduction will produce a temperature gradient, which can be large enough to cause thermomigration. The thermal stress and temperature gradient will induce atomic diffusion, phase instability, and microstructure change.

What is unique in these microstructure changes is that they occur in the domain of nonequilibrium thermodynamics, or they are irreversible processes. This is because of the coexistence of electron flow, atomic flow, and heat flow in the open system. Thus, the reliability science on the basis of entropy production is needed, ...