As is well known, designers are squeezing ever more performance out of printed circuit boards. Power densities are on the rise, and with them, high temperatures that can wreak havoc on conductors and dielectrics. Elevated temperatures - whether from I2R losses or environmental factors - affect thermal and electrical impedances, causing erratic system performance, if not outright failure. Differences in thermal expansion rates – a measure of the tendency of a material to expand when heated and shrink when cooled – between conductors and dielectrics generate mechanical stresses that cause cracking and connection failures, especially if the boards are subject to cyclic heating and cooling. If the temperature is high enough, the dielectric can lose its structural integrity altogether, knocking over the first domino in a cascade of trouble.
Of course, heat-generation has always been a factor in PCB performance, and designers are accustomed to including heat sinks into their PCBs, but the demands of today’s high power-density designs frequently overwhelm traditional PCB heat-management practices.
Mitigating the effects of high temperatures have far-reaching implications, not just for the performance and reliability of PCBs, but also for such factors as:
Component (or system) weight