Issue link: https://iconnect007.uberflip.com/i/1190860
38 DESIGN007 MAGAZINE I DECEMBER 2019 There are many different types of PCB de- signs and constructions that can be used as test vehicles to evaluate electrical properties. If the test vehicle will be used for an evaluation that is specific to an application, it should be as similar as possible to the application. That may sound like common sense, but I have seen many companies use the same test vehicle for every evaluation they perform. However, if an evaluation is being done that is not specific to an application, but for general comparisons— such as evaluating the electrical performance of different circuit materials—there are multi- ple things to consider for the test vehicle. A proper test vehicle to compare different circuit materials would be a design and construction that takes into consideration the different ma- terial properties and have the least amount of PCB fabrication variables that can impact the results. It is obviously desirable for a company to show it has well-defined and very consistent testing procedures for its electrical evaluation program used to evaluate different circuit ma- terials. To do this will probably cause the eval- uation procedures to be more complicated, but, in the end, the results will be more meaning- ful for the materials being evaluated. For exam- ple, it probably makes sense to have a differ- ent set of evaluation procedures for materials which are significantly different, for example, FR-4 materials would have a different evalua- tion procedure than high-frequency materials. For evaluating high-frequency materials, there are many different test vehicles used. Some of the more common test vehicles are ring resonators, transmission lines, and delay lines. The circuit construction should also be a consideration; often, the ring resonators are used as a microstrip. The transmission lines and delay lines are also commonly microstrip, but sometimes, they are a stripline construc- tion. If the evaluation is purely electrical per- formance related to the material only, the sim- plest construction and PCB fabrication process should be used. If the evaluation is a combi- Test Vehicles for Material Evaluation Lightning Speed Laminates by John Coonrod, ROGERS CORPORATION