Book Excerpt: 'The Printed Circuit Designer’s Guide to… High Performance Materials', Chapter 1

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Evolution of the Resin System
Most basic resin systems have been around for a long time. Here is a little timeline of developments through more recent introductions.

• In 1907, the first laminate was made with pure phenolic resin by Westinghouse in Pittsburgh, Pennsylvania. Formica became the first true sheet laminate.The first application—a radio by Paul Eisler in 1936—led to practical manufacturing for military radios in the U.S., and use of single-sided copper-clad phenolic laminate started in about 1943 using paper and cotton as the structural component. Epoxy resin was introduced shortly after in 1947.
• Still reigning as the lowest loss resin system, a PTFE, RT/Duroid^® was introduced in 1949.
• The first polyimide was discovered in 1908 by Bogart and Renshaw. However, the high heat-resistant polyimide laminate material was brought to the market in 1951.
• Isola began production of copper-clad laminate in 1956.
• Epoxy-based laminate systems followed around 1960 and used woven E-glass fabric.
• Shortly after, G-10 epoxy laminate (non-flame retardant epoxy resin plus E-glass) and a flame-retardant epoxy version called FR-4 (flame-retardant epoxy resin plus E-glass) were introduced in 1968.

From that time forward, there have been various blends, such as PPO (polyphenylene oxide)/epoxy, CE (cyanate ester)/epoxy, and polyimide/epoxy, that were created to balance properties of pure resin systems to achieve specific enhanced properties. Each new resin system was built on learning from previous products. Resin system developments for high heat applications such as LED lighting, ultra-thin non-reinforced films for capacitance and halogen-free systems to meet RoHS and REACH environmental requirements, continue to be developed to address the performance and reliability needs. With each new need, laminate material manufacturers go into the lab and see what new raw material can be used to improve resin system performance.

The process of developing a new resin system requires deep knowledge of how the PCB will be manufactured. PCB designers are most concerned with assembly process capability, long term reliability, thermal cycling performance, CAF resistance, and electrical performance, therefore, all these attributes must be balanced within the design of a resin system. The market requirements mean that laminate manufacturers must continue to research available options that will provide incremental improvements to the resin system performance.

Follow this link to download your copy of The Printed Circuit Designer’s Guide to… High Performance Materials.

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