IPC-3406 : 1996

1.0 SCOPE

This document covers guidelines for selecting electrically conductive adhesives for use in assembly of components to printed circuit boards (PCB) or similar wiring interconnect systems. The focus is on the use of adhesives as solder alternatives. The process discussion attempts to stay within the bounds of the existing solder assembly infrastructure as much as possible. Both major types of adhesives, isotropic (conducting equally in all directions) and anisotropic (unidirectional conductivity), are covered. The two major divisions of polymer adhesives, thermosets and thermoplastics, are described.

1.1 Introduction

Polymers are long-chain molecules, such as epoxies acrylics and urethanes, that are widely used to produce structural products such as films, coatings and adhesives. Although polymers occur naturally, most are now synthesized. Their properties can be tailored to meet thousands of different applications. Polymer-based adhesives are used in virtually every industry because of this capability to customize performance. Polymers have excellent dielectric properties and, for this reason, are used extensively as electrical insulators. Most wire insulation is made from polymers. Although a narrow class of conductive polymers, called Intrinsically Conductive Polymers (ICPs), does exist, their other properties do not lend themselves for use as conductive adhesives. Therefore, virtually all conductive adhesives are made by adding conductive fillers to nonconductive polymer binders.