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February 2017 • The PCB Design Magazine 15 it is around the outside of the corner. The out- side of the corner is cooler because there is more board area for the trace to "cool into," not be- cause the current density is lower there. TRM has the capability to look at the cur- rent density at every point along a trace. Fig- ures 5 illustrates the current densities for the right-angle corner, above, while Figure 6 shows the current densities around a trace with 4 vias. When we analyzed the current densities in the vicinity of the vias, especially the "near vias," there were some surprising discoveries. Again, I know of no other way to look at the current density at a point along a trace other than with a tool like TRM. TRM has some capability of looking at tem- peratures related to current pulse streams of ar- bitrary frequency and duty cycle. In this sense it is analyzing the temperatures related to AC currents, although the capability does not ex- tend all the way to analog waveforms. But a lot of insight can be gained from looking at traces carrying a pulse width modulated (PWM) AC Figure 5: Current density around the right-angle corner shown in Figure 4. Figure 4: Thermal profiles of a right-angle corner; (a) is for a narrow temperature range, and (b) is for the full temperature range. EXCITING NEW TECHNOLOGY: THERMAL RISK MANAGEMENT