OVERVIEW

Adhesives used in the assembly of electronic circuits serve four main functions:

• Mechanically attach parts such as semiconductor die, components, substrates, packages, and heat sinks.

• Electrically interconnect components on a substrate or in a package.

• Dissipate heat from components and circuits.

• Dissipate stresses.

The prime function of adhesives is to mechanically attach or bond devices, components, heat sinks, wire, connectors, and other parts onto a circuit board or an interconnect substrate. Adhesives are also used as pastes or films to attach lids in sealing cavity packages and as dielectric films in fabricating multilayer interconnect substrates. The most important consideration in obtaining a reliable adhesive bond is the ability of the adhesive to flow and wet the surfaces. For a reliable bond, strong adhesion to both surfaces and strong cohesion within the adhesive are necessary.

Besides this prime role of attachment, electrically conductive adhesives are widely used to form electrical contacts between components and the printed-wiring board or other interconnect substrate, such as thin-film or thick-film ceramic substrates or flexible cable. For this function, adhesives serve as low-cost alternates to wire, solder, and other metallurgical connections.

The third function, one that is becoming increasingly important, is to draw heat away from components. With increasing circuit densities and power generation, it is essential to avoid excessive operating temperatures to prolong device lives and avoid premature failures. High heat-generating devices are generally cooled by conduction of heat through metal heat sinks, metal tabs, metal or ceramic substrates or packages, and through liquid...