27.1 INTRODUCTION

The structure of multilayer printed wiring board (PWB) has evolved immensely. While the building block processes of the PWB industry are still prevalent, the sequences and material utilization employed continue to emerge into new technologies. The driver for this is the density revolution, which is caused by changes in electronic component technology. Since the circuit board was born as a means to an end, that is, to provide electrical connectivity between components, it has had to evolve to meet new demands as the components evolve. Nowhere is that more evident than in the materials and processes used to make multilayer PWBs. It is that need for interconnectivity that brings the challenge.

One of the components most responsible for the enabling of advanced technologies is the ball grid array (BGA). The on-board density of the area array component family creates a unique challenge to the circuit routing of the multilayer configuration. This new configuration, known as high-density interconnect (HDI), drives the new structure of PWB. Highdensity designs, driven by the need for smaller, faster, cheaper products in all fields, have common issues to deal with, e.g., high operating signal speeds (1 GHz and higher), thermal management, and mechanical fatigue, all of which affect multilayer construction. In addition, life cycle management is crtical in determining the correct multilayer board technology (MLT) to employ. Product requirements place serious demand on all aspects of the MLT process, e.g., the materials...