Bondwire fusing current controversy

We are indebted to an interested visitor to our website who commented on the bondwire fusing equation provided ( as well as the calculator) about the enormous levels of fusing currents predicted by that tool.The reader also referred to a paper by IDT referring to bondwire fusing currents. In that paper the bondwire fusing current presented for gold wire and based on the classical Preece equation was as follows: A 2 mil diameter gold wire was shown to have a fusing current of 0.92 Amps. These specifications for the gold wire were input into the SPG fusing current calculator and it was found that there was close agreement with the Preece equation. However, there was one interesting difference. In the SPG calculator ( based on the May equation) a time factor was required. The time required in the SPG calculator was 100 milliseconds for the wire to melt. There appears to be no time factor in the Preece equation that is based on a rms or dc current. To explain this seeming discrepancy we have to argue that if the amount of heat required to melt the wire is calculated using standard Thermodynamics then we find the heat in Joules that does the damage. Now 1 Joule is  1 Watt . second. Thus time gets involved immediately. We could have a huge wattage in the wire but if the time is very small then the melting energy would be very small. Therefore time should be considered in the equation somewhere. Debatable point?

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