Temperature effects on a printed-circuit board (PCB) can make it difficult to achieve target performance goals, even with the best PCB substrate materials. Modeling these effects takes imagination—to visualize different sources of heat, for example, and thermal paths where the heat might travel. It also requires an understanding of both thermal-mechanical and electromagnetic (EM) relationships to account for the assortment of variables that can influence PCB performance with changing temperatures. As a result, modeling thermal effects on PCB performance combines predictions provided by the heat diffusion equation as much as from Maxwell’s equations for EM fields.
In a high-frequency circuit, heat can come from the environment (the ambient temperature) or from DC and RF sources: from the flow of supply current, for example, or from RF input power to the circuit or power generated by an active device, such as a power transistor. Ideally, heat will flow away from the circuit, without creating an
