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28 PCB007 MAGAZINE I DECEMBER 2021 Printed electronics (PE) continues to be a growing technology. But one of its advantages, as well as a drawback, is that low-cost sub- strates, like paper, cannot take the temperature of solder paste reflow. Also, the inks need to be cured. One current way to cure the printed inks is with ultraviolet radiation curing, such as that used with solder mask or legend inks. One innovation is the curing or annealing of printed inks with flash tubes, which pro- duce a high-intensity, broad-spectrum white light as seen in Figure 1. 1 You might be famil- iar with the technology from photography, as electronic flash or strobes. But these, on the other hand, are much larger and much higher in power. You have probably noticed from photography that these electronic flashes pro- duce heat. But this heat is limited to the surface only, so that the inks can be cured or annealed but the substrate remains cool. Inks cured to the temperature at which they become conductive using IR ovens requires substrates that can withstand these temper- atures, like polyimides, ceramics, and epoxy Photonic Soldering Happy's Tech Talk by Happy Holden, I-CONNECT007 Figure 1: From photonic curing and annealing to photonic soldering/sintering, the flash tube can transfer a significant amount of energy quickly. (Source: NovaCentrix)

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