Advanced Reinforcement Technology Presents New Design Opportunities for Printed Circuit Boards

An innovative approach to glass fiber reinforcement in laminates offers a flatter, thinner weave that result in a smoother, more uniform surface for mechanical and laser drilling as well as improved dimensional stability. The manufacturing process has been completely redesigned to be more efficient and flexible. Glass fabric produced with this new process offers superior properties for high performance circuitry, including lower Dk and Df values, enhanced PTFE compatibility and the opportunity for improved CAF resistance. Background Traditional fiber glass fabric technology has remained essentially unchanged for over 30 years. The glass composition, applied chemistries, yarn configurations and woven fabric constructions are basically the same as those used in the 1970s. Glass yarn and fabric production technology is a direct outgrowth of the traditional textile industry. The established infrastructure simply took on the task of servicing a rapidly growing glass fabric industry and equipment designed for weaving cotton and synthetics was adapted to glass yarns with minimal changes. Prior to the development of large scale integration in electronics, woven glass fabric was used for many years as electrical insulation, as well as in curtains and drapes. Meanwhile, the composites industry was bringing science to bear on reinforced polymer technology, and glass fiber became firmly established as the dominant reinforcement medium. Based on strength to weight ratio, glass reinforced composites are stronger than steel and have displaced metal in many weight-sensitive applications. But electrical laminate applications are less demanding in terms of strength and weight with more importance given to chemical and electrical properties. For example, a structural composite application would never use glass fibers that were originally coated with food starch and vegetable oil (the standard sizing ingredients used for fiberglass weaving). These ingredients are not chemically compatible with polymer resins and the subsequent removal of these chemicals causes a significant reduction in structural properties. PCB laminate, on the other hand, must withstand multiple immersions in chemically demanding aqueous processes, followed by the extreme temperature fluctuations of soldering. The end product must still possess excellent electrical properties. In the face of the diverging requirements seen in the composites and electronics industries, it is not difficult to understand why the electronics industry has been slow to take advantage of technical advances in polymer reinforcement. However, by applying the idea of compatible coatings from the composites industry and combining it with new weaving technology, an improved glass fabric has been developed with specific application to the electronics industry. An excellent description and overview of the traditional glass fiber production and fabric weaving process is given by Eng. Process A three-pronged approach has been developed to address a number of issues associated with glass fabric manufacture. The fiberglass forming and weaving processes have been integrated into a single facility. The application of a dual-purpose finish has been coupled with twist free weaving to create unique fabrics with superior properties for today’s demanding electronics applications. Twist free weaving One of the most time-consuming, costly and damaging steps in the process of producing glass fiber yarn and fabric is yarn twisting. Yarn is twisted prior to weaving in order to consolidate the glass strand, so that it can be woven into fabric without excessive fiber damage and weave defects. However, the actual twisting can damage the glass filaments and impart a helical spring structure to the fiber bundle. Yarn twisting converts the flat fiber strand into a “rope-like” round strand. Once woven into fabric the twisted yarns form a bump or “knuckle” at every crossover point. These knuckles impart a noticeable 3-dimensional element to the fabric, which is especially visible in certain laminate types. Through innovative weaving technology, a new process has been developed that completely eliminates yarn twisting in both the X and Y directions. The result is a very flat, ribbon-like glass strand. The twisted yarns have been replaced with Presented in the ECWC 10 Conference at IPC Printed Circuits Expo®, SMEMA Council APEX® and