components and interconnects eventually leading to mechanical failures: via barrel wall cracking in PCBs and solder metal fatigue and failure in the attached components. Remember, FR4 is an entire class of materials. And there are other classes of materials that don’t have fiberglass inside them. If high temperature use or multiple temperature fluctuations are expected in your use case, choose a material with an isotropic CTE closer to that of copper. Component Failure Chemists predict reaction rates using the Arrhenius equation.
Electronics engineers adopted that equation to predict the lifespan of components. When used correctly, the equation allows the prediction of mean-time- to-failure with some degree of accuracy. When used incorrectly by an unsupervised junior engineer, the predicted lifespans are often expressed in geological timescales. But if you’ve ever wondered how engineers determine that LEDs will last for 40 years without waiting 40 years for a failure, they accelerate failure in heated chambers and use the
Summary Heat at Temperature are different things, and a decent understanding of how both topics relate to resistance will help you improve your next high-reliability PCB Design. To learn more about designing “Heavy- Copper” PCBs, read another article in this issue titled “You Want to Put How Much Current in Your PCB?”
modified Arrhenius equation to work backwards to room- temperature failures.
we get technical
23
Powered by FlippingBook