Materials for Advanced Encapsulation

Abstract

Early transistor and diode encapsulation was accomplished by dispensing a small amount of silicone or flexible epoxy over the die and bond wires in a process known as ‘glob-top’. However, the drive for low-cost, high-volume packaged semiconductor production soon initiated the introduction of transfer and injection moulding methods (see Chapter 5 for more details of transfer moulding materials and techniques). This move allowed polymeric encapsulants to replace the traditional but more expensive ceramic and metal packages in most areas except those requiring the highest reliability. The standard packaging format through the 1970s was the ubiquitous dual in-line plastic package and this really was the father of low-cost electronics packaging. The 1980s brought revolutionary changes in electronics technology in general, and in plastic packaging in particular. The main change from a packaging and assembly perspective was the move away from the use of through hole leaded components to the use of surface mount technology and the use of so-called surface mount devices (SMDs). These newer surface mount devices were both cheaper and easier to assemble than their predecessors and with leads on all four sides of the IC packages, surface mount technology initially offered opportunities for increased packaging density. This change to SMD, although not requiring any radically different package moulding techniques, did initiate a lot of work in the modification and optimization of moulding compounds for these generally much smaller packages. Unfortunately, it soon became apparent that conventional plastic quad leaded flat pack packages could not continue to accommodate the increasing numbers of leads required of future devices without either unacceptable increases in package area or moves to much finer pitches that would be difficult to handle and assemble. There has thus been major development of packaging techniques over the last few years, which in turn have necessitated the development of many new materials.