Issue link: https://iconnect007.uberflip.com/i/1511130
NOVEMBER 2023 I DESIGN007 MAGAZINE 25 for the total conducting cross-sectional area of the vias to equal the trace's conducting cross- sectional area. In this example, that would mean 14 vias. e top image shows the results for a single via, the middle image for a pair of vias, and the bottom image for three vias. e trace itself (without any vias) heats to about 56°C. e single via results in a via temperature of approximately 80°C, 24°C above the board temperature. is might be tolerable in some consumer applications. e use of two vias lowers each via temperature to about 67°C, 11°C above the board. ree vias results in individual via temperatures of about 62°C, only ~6°C warmer than the trace tempera- ture itself. Adding 11 more vias only gains us about 6°C in temperature closure but locks up quite a few more routing channels. Bottom line: We don't need nearly as many vias as our common (mis)understanding would have us believe. Rules of Thumb Unfortunately, these illustrations are all case-specific. at is, there are no general rules of thumb that reliably flow from them. e only way to determine with any precision what gains can be made, and where, is with thermal simulations using good thermal simulators. Thermal Vias Figure 3 shows a simulation using the same board as in Figure 1, but with two one-inch square heated pads instead of traces. e pad on the right is over a plane on the bottom layer. Each pad is heated by a two-watt source. Figure 3: Heated pads, top and bottom layers.