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RF Electronics Chapter 11: Circuit Manufacture Page 367 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. FR4 is a much better circuit board in that it has a better heat tolerance, is stronger and the dielectric constant is specified to 10 GHz. FR4 PCB's can be made with many layers. Simpler PCBs have 4 layers, with one layer being earth, one layer being the supply voltage and the outer layers containing the tracks that are connected to the IC's and passive components. FR4 is normally light green and semi-translucent, often this can be seen at the left edge of the board as in figure 11.3. The dark green colour is due to the solder resist and not due to the laminate. The large component at the left edge of the board is a ceramic diplexer. Normally many printed circuits are etched together, on one sheet, or panel, as shown in figure 11.4. Cut-outs are provided to enable the individual circuits to be removed easily. Figure 11.4. FR4 PCB showing cut-outs. (Layout by JCU). FR3 and FR4 are ANSI terms, manufacturers such as Isola have fibreglass and epoxy products under names like FR408, IS400, IS410, and IS 420. Different resins used have different dielectric constants, typically ranging from 4.7 shown in table 11.1 to 3.67 for FR408. Microwave and RF Printed Circuit Board Materials FR3 and FR4 can be used for PCBs to 1 GHz, however above these frequencies the losses may become significant. The laminate thickness for FR3 or FR4 is not tightly controlled, causing variations in impedance of Microstrip lines across the laminate and from batch to batch. That is not suitable for many RF designs. The major laminate manufacturers make many different PCB laminates, especially for the RF and microwave frequency range. As an example several different laminates from Rogers Corporation, are described here, to illustrate that different applications require RF laminates with different properties. RT/duroid RT/duroid are high frequency PTFE (Teflon) filled laminates for use in high reliability, aerospace and defence applications [4], with dielectric constants between 2.0 and 10.2. Some laminates are reinforced with glass fibres for strength. RT/duroid laminates were developed in the 1960's and are the oldest Rogers products. Others have a low weight or are dimensionally stable. RT/duroid 6010 has a high dielectric constant, which reduces the size of the circuit. For frequencies above 20 GHz, circuits with a high dielectric RF Electronics: Design and Simulation 367 www.cadence.com/go/awr

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