Issue link: https://iconnect007.uberflip.com/i/786015
16 The PCB Design Magazine • February 2017 waveform. Figure 7 illustrates the temperature profile of a trace carrying a pulsed current wave- form with a 50% duty cycle. Figure 8 illustrates the same trace carrying pulse streams with 20% or 80% duty cycles. The software can show us the thermal pattern through time, but also the ultimate stable temperature that will be reached for any pulse condition. My final illustration of TRM's power relates to what we could discover about the fusing process (i.e., what happens when a trace is sub- jected to a sudden overload). (Those who know me know that this is one of my favorite topics!) The early work on this topic was done by W. H. Preece in the 1880s, and I. M. Onderdonk, probably in the 1920s. Onderdonk is the author of a famous equation that bears his name that is frequently referenced in fusing investigations (Equation 1). Eq. 1 Where: I = the current in amps A = the cross-sectional area in circular mils S = the time in seconds the current is applied t = the rise in temperature from the ambient or initial state Ta = the reference temperature in degrees C Figure 6: Current density around vias. Figure 7: Temperature profile of a trace carrying a pulsed waveform with 50% duty cycle. Figure 8: Temperature profiles of a trace carrying a pulsed waveform with 20% and 80% duty cycles. EXCITING NEW TECHNOLOGY: THERMAL RISK MANAGEMENT