Part 1: PCB Designers Notebook — Flexible Circuit Design for SMT Assembly

摘要

The flexible circuit has proven to be one of the most versatile substrates for a wide range of products, even those exposed to harsh environments. These circuits traditionally have come from a rather specialized group of suppliers, but a growing number of rigid board fabricators currently are offering flexible substrate capability as well. Flex circuits rely on thin, non-reinforced films for the dielectric base layer and can be furnished with copper conductors on one or two sides. The two-sided circuit can be interconnected with plated vias typical of rigid board processing. The fabrication processes, however, can vary a great deal, depending on base material and the method for applying the copper conductor layer(s). In addition, when planning the flexible circuit for SMT the design engineer must review base material properties and thickness options. Poly-imide films are preferable and widely adopted for SMT applications, but polyester films often are selected for less demanding or price-sensitive commercial products.