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Lightning Laminates: Efficient Simulation Using High-Frequency Printed Circuit Materials

The general type of simulation software most often used for high-frequency laminates is impedance modeling or electromagnetic modeling tools. These software tools all require that circuit geometry be input, such as the conductor thickness, width, substrate thickness, and other details. The substrate properties which are generally most important are the dielectric constant (Dk or εr) and dissipation factor.

The Dk value is provided on material datasheets; however, anyone who is less savvy with material issues may be unaware that the Dk value can be very different depending on the test method. If the test method is not the same configuration as the circuit the designer is concerned with, the Dk value may be less accurate. A simple example: A common test method used for high-frequency circuit materials is the clamped stripline resonator at 10 GHz. If the designer is using this material and concerned with a microstrip transmission line circuit operating at 2 GHz, the Dk data from the stripline resonator may not be as accurate as needed.

The different test methods are designed for specific reasons. The clamped stripline test method is a very good test method for evaluating raw substrate properties at a specific frequency and in a relatively high-volume testing environment. The stripline structure has a layering configuration of ground-signal-ground and this test method uses a clamping fixture that can test raw substrate quickly. The test uses a thin circuit (signal layer) which features the copper resonator pattern. On both sides of this circuit, the raw substrate will be placed and then the outer metal plates (ground planes) will be clamped together. The Dk can be tested within a few minutes, and when a materials manufacturer requires testing several hundred substrate samples per day, this is a good test method to use.Read the full column here.Editor's Note: This column originally appeared in the February 2013 issue of The PCB Design Magazine.