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68 DESIGN007 MAGAZINE I FEBRUARY 2021 ere are multiple libraries of information nowadays for a PCB fabricator. A circuit mate- rial library for the fabricator can be advanta- geous for multiple reasons. Sometimes these libraries are intended to be used for electrical predictions, such as impedance, insertion loss or other issues. Other times the information found in the circuit material libraries are used to assist with thermal issues, potential reliabil- ity concerns, circuit construction stackups, and some processing issues. When a PCB manufacturer is creating and building a circuit materials library, there are some property values which should be defined by the circuit fabricator while other property values should be obtained from the circuit material supplier. As general statements, the circuit material property values which can be affected by the PCB fabricator should have data that was collected by the fabricator using their specific processes. e circuit material properties which are unaffected by circuit fab- rication can be obtained from the circuit mate- rial supplier. e common circuit material properties which can be affected by the fabricator are related to some of the electrical evaluations which the circuit manufacturer performs. It is common for a PCB supplier to perform impedance testing on the final circuit, as a "go/no-go" test for shipping the product. e material properties which relate to impedance are dielectric constant (Dk), substrate thick- ness, and copper thickness. Most PCBs today are using plated through-hole (PTH) technol- ogy, which means the final and overall copper Circuit Material Library Considerations Lightning Speed Laminates Feature Column by John Coonrod, ROGERS CORPORATION