Overview

Many factors have contributed to the evolution and widespread application of printed circuit technology as we know it today. Undoubtedly, the most significant of these are

• Development of a repeatable and relatively economical process for manufacturing circuit boards

• Invention of the solid-state transistor and then incorporation of many of these semiconductor devices into a single, integrated circuit

• Use of the eutectic soldering process to produce highly reliable electrical connections between the circuit board and its associated electronic components

Serious use of printed circuit assemblies (PCAs) began shortly before the end of World War II. The boards were made initially by attaching a layer of copper foil to a paper-based laminate, applying a silk-screened ink pattern to the foil, and etching it to form an interconnecting circuit. One of the first applications for these crude assemblies was in a radio set. Another type of circuit board, designed for use in proximity fuses, was made by directly printing a metallic conductive pattern on an insulator. By the end of the war, these were being produced successfully in very large quantities.

The processes, materials, and equipment that evolved from the latter approach eventually became the foundation for today s hybrid circuit technology. The former circuit board fabrication concept, augmented by development of processes for electroless metallization, electroplating, photo-imageable resist, precision drilling, multilayer lamination, along with the availability of a large variety of copper-clad dielectric materials, matured into what is now the most widely used technique in the electronics industry for...