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Adhesion techniques are among the most important elements of packaging technology for electronic products. Recently, advanced adhesives for electronic packaging have diversified, along with remarkable advances in microsystems. Adhesives must exhibit functions such as electrical and thermal conductivities in some cases, but achieving a reliable bond is an immutable requirement.

This chapter identifies and explains in detail the main factors which determine the bond strength of adhesive joints, with the aim of establishing adequate guidelines for the development of advanced adhesives from the point of view of reliable adhesion. Although the chemical composition of adhesive compounds appears complex, their design is derived from the basic theory of adhesion and bonding, which is briefly presented in this chapter.

Adhesives are often named for their type of polymer. The main types of polymers used in electronic packaging are epoxies, silicones, acrylics, polyurethanes, polyimides and cyanate esters. Some generic properties apply to each type but be careful when generalizing as there are hundreds of formulations of each type on the market, each with minor or major property differences.

Even for a specific formulation, the processing conditions of an adhesive, such as its curing schedule, can affect final properties. Chapter 3 presents a discussion of the main types of polymers and their properties.

Polymeric adhesives can be further classified as thermoplastic or thermosetting, depending on whether their molecular *, after curing, are linear or crosslinked. Linear polymers can be straight chains or branched chains (Fig. 1.1). Thermoplastic adhesives melt and flow at a specific temperature or within a narrow temperature range, then resolidify rapidly upon cooling.