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8 The PCB Design Magazine • April 2017 Choosing the right material for your PCB was so simple a few decades ago. All but the most high-tech PCBs were constructed with FR-4. The lowly FR-4 has been improved and re-engineered many times in the past few de- cades, and rumors of its demise have proven unfounded. But at today's high speeds, FR-4 often doesn't measure up, and designers must select an advanced low-loss PCB material with low Df and Dk values that isn't prohibitively expen- sive or terribly difficult for fabricators to regis- ter during lamination. High-speed PCB signals now exhibit characteristics previously seen only in the RF and microwave world, requiring PCB designers to consider using lok-Dk RF materi- als such as PTFE and Teflon, which are much "softer" than FR-4 and tougher for the fabrica- tor to work with. We started out with a reader survey. We asked, "If you are a PCB fabricator or designer, what are the greatest challenges for you work- ing with high-speed materials?" and some of the answers were quite interesting. Answers included: • Dielectric constant is too high • Material movement • Getting accurate performance data • Customer knowledge • Performance for signal integrity • Getting accurate dielectric material properties from data sheets • Availability • Too many materials to stock • Mechanical stability in the z-axis • Materials adhesion • As a PCB fabricator, understanding designers' needs • Hole wall quality • Educating the customers on what they actually need • Impedance control • Lead time • Cost Many of the fabricators' biggest challenges were related to manufacturability. The more by Andy Shaughnessy I-CONNECT007 The State of High-Speed Materials THE SHAUGHNESSY REPORT

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