Electronic Packaging Science and Technology

9Irreversible Processes in Electronic Packaging Technology

9.1 Introduction

Electronic packaging technology is wafer‐based and flux‐driven. Its applications occur in the operation of microelectronic devices built on semiconductor chips or wafers. The basic steps in processing of these devices consist of adding or subtracting a monolayer of atoms on or off a wafer surface, respectively, or in joining two materials together as in solid–liquid interdiffusion (SLID) reaction to form a solder joint. In these processes, we are not dealing with equilibrium states, rather we deal with kinetic states in going from one state to another or we deal with the steady state of a flux of atoms, or electrons, or heat.

Furthermore, if we consider a p‐n junction in a transistor, it is not at an equilibrium state. If we anneal the junction at a high temperature for a long time, it will disappear by interdiffusion of the p‐type and n‐type dopants. At device operation near 100 °C, the dopants are super‐saturated but frozen in place in the semiconductor in order to produce the electrical potentials needed to guide the transport of charges. In doping a semiconductor, we need to diffuse or to implant a flux of atoms into the semiconductor to obtain the desired concentration profile of dopant.

During the operation of electronic devices, we can have a flow of matter, a flow of energy (heat), a flow of charge particles, or all of them in a device system, which is an open system. Most importantly, from ...