TABLE OF CONTENTS Over the years, successful circuit board layout activities have been guided by the so-called three-legged stool philosophy, with each leg representing full optimization of a printed circuit assembly s (PCA s): cost, schedule, and performance requirements. These three factors should be given equal consideration to ensure overall design integrity. Unfortunately, many companies place the greatest weight on time to market constraints and, by doing so, sacrifice one or two of the three legs. The consequence is that during the layout effort, primary emphasis may be placed on meeting a restrictive schedule, resulting in possible degradation of the cost-effectiveness or performance of the design. Schedule pressures will always be imposed on layout activities, but establishment of structured, efficient design processes and procedures can reduce their effect on the quality of the end product.
In today s global market, achieving an efficient circuit board layout cycle requires that accurate, well-defined, and well-controlled information be available to the designer when needed. A complete understanding of the content and structure of the information and how it affects the layout activity will aid in the creation and establishment of balanced processes and procedures. Figure 4.1 shows the normal flow of critical data to the layout process and where and when throughout the layout cycle these data should be defined. In addition to design-related data, the following programmatic information should be provided and evaluated prior to and throughout the design cycle:
Program requirements
Budget/schedule
