At about 20 minutes the board began to smoke. At about 15 minutes, the aroma of burning dielectric began to permeate the room. The threshold points are not easy to identify in Figure 4, but it is not hard to imagine how the process is working.
There are several board material thermal parameters that are relevant here : Tg: Glass Transition Temperature Td: Thermal Decomposition Temperature and Delamination Temperature(s) and Times.Īs the temperature of the board reaches each of these thresholds, the effectiveness of the cooling process diminishes, and the rate of heating of the board increases. Figure 2 is from a video of this illustration, at about the moment of fusing. The entire process took about 30 minutes. After about 30 minutes the temperature had increased to about 514 oC, at which point the temperature began rising quickly to the point where the trace melted. But then it continued to increase slowly. trace carrying 8.5 Amps.Īs before, the temperature rose quickly to about 214 oC. Which figure do you think goes with which scenario ?įigure 4. The temperature will rise more slowly, ultimately melting the trace at its weakest point.įigures 1 and 2 illustrate these two scenarios. A current just larger than the fusing current is applied to the trace. We would expect the current to significantly overload the trace, increasing the temperature, and melting a point on the trace quickly.ī. A large sudden current (significantly larger than the fusing current) is applied to a trace.
For a discussion of what is known about these two people and for references to possible source documents, see. The time frame for validity of Onderdonk’s Equation is usually given as under 10 seconds, since this equation assumes there is no cooling effect. Onderdonk is believed to have derived his (her) equation, probably in the 1920s. He assumed he had reached the fusing temperature when the wire under study began glowing. Preece conducted his experiments in a laboratory. T = the rise in temperature from the ambient or initial state (assumed to be 40 degrees C)
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