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100 PCB007 MAGAZINE I MARCH 2020 Laminate materials are the building blocks on which PCBs are manufactured. Circuit board designers rely on the critical electrical properties of the materials to design the inter- connect. And with the drive toward the inter- net of things (IoT), autonomous driving, vir- tual and augmented reality, material properties take on a very high level of importance. The crux of the issue is quite simple: Design- ers are looking for electrical performance, and printed board fabricators are concerned with manufacturability and yields. As the complex- ity of circuit technology increases (and it is not going to stop anytime soon), there will be a continual pressure to improve yields. However, that is the conundrum, or the "rock and a hard place" cliché. For the purpose of this discussion, let's con- sider the requirements for high-speed data transmission. System designers are looking at Material Challenges for PCB Fabricators several factors, most importantly signal speeds, loss characteristics, and laminate selections. Laminate Selection: Dk and Df The Dk is the property that determines the relative speed that an electrical signal will trav- el in that material. A low dielectric constant will result in higher signal propagation speed while a high dielectric constant results in low- er signal propagation speed (i.e., the lower the Dk, the less impedance there is to the signal propagation). The characteristic impedance of a PCB is determined by the thickness of the laminate and its Dk. Impedance control, and impedance matching of critical linked func- tional modules, becomes especially important in very high-speed designs (i.e., high-frequen- cy designs). Dk also tends to shift with tem- perature, so heat generation by such designs is another important factor. Trouble in Your Tank by Michael Carano, RBP CHEMICAL TECHNOLOGY

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