How Can I Model Real-World Effects of Printed-Circuit Boards?
A printed-circuit board adds some capacitance, resistance, and inductance to the circuit. These parasitic circuit elements can change with temperature, mechanical stress, and even age. If you are a fan of SPICE models, you can always add these parasitic elements to the circuit to check for sensitivity. But it’s impossible to develop a rigorous model without verifying physical performance. You need to build a prototype. Consider a typical four-layer FR4 dielectric PC board with 1-ounce copper plating and a net thickness of 0.0625 inches. The thickness of 1-ounce copper plating is 0.00139 inches. The distance between layers is 0.019 inches. You can estimate the resistance of a PC-board trace based on its shape. Tile the trace with squares, and then multiply the foil sheet resistance by the number of squares. Standard 1-ounce copper foil has a thickness of 0.00139 inches, which corresponds to a sheet resistance of 0.49 milliohms per square. (This resistance varies ±25% over -40°C to +85°C
