13.1 INTRODUCTION

Over the past several decades, the attachment of components to printed wiring boards (PWBs) has been accomplished primarily by solder joining technologies. Electronic assembly designs have incorporated various types of technology configurations to form mechanical, electrical, and thermal interconnections. These configurations have developed from through-hole technologies that incorporate, single-sided, double-sided, and plated-through hole (PTH) architectures, to surface mount technology (SMT) designs, which includes standard, fine, and very fine pitch devices for leaded and leadless component mounting. Recently, new SMT designs based on ball and column grid arrays, located under the component, have received wide interest and application. This technology maximizes the input/output-to-component size ratio without excessive use of board acreage. Other soldered interconnection technologies focus on direct chip attachment; for example, flip-chip applications. With this type of interconnection, solder bumps located on the chip are directly mounted to the board. These various types of solder joining technologies provide for durable, long-lasting, and inexpensive methods of mass or isolated interconnect production. Due to the low temperature melting aspects of these types of solders, the soldered joints can be reworked or repaired easily and selectively.

Depending on the operational environment(s), electronic assemblies may incur use for months or years and may experience extensive power and thermal cycling, vibration and other mechanical degradation mechanisms, and exposure to hostile environments. The failure of soldered interconnections is not only directly dependent on the environmental conditions experienced, but is also inherently associated with the...