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44 SMT Magazine • March 2014 SummarY: this article examines the nature, consequences and mitigation of electrical over- stress (eoS) caused by electromagnetic interfer- ence (emi), or electrical noise, on power lines and ground in a manufacturing environment. Introduction Soldering irons, solder extractors and other equipment that comes in direct electrical con- tact with sensitive components can inject sig- nificant energy into these devices. Specifically, metal-to-metal contact between the tip of the soldering iron and pins of the components can be a gateway for high current that can cause sig- nificant device damage. Where would a soldering iron tip get volt- age? After all, it is supposed to be grounded, just like the PCB to which the components are being soldered, so theoretically there should be no difference in voltage and thus no harmful currents between the tip of the iron and the de- vices. This, however, may only be true for DC or for very low frequencies such as power mains (50/60Hz). For high-frequency signals it may be very different. Transient Signals: a Source of Electrical Overstress Assuming the tip of the iron is properly grounded, the voltage on it can arrive mainly via ground connection and to some degree via capacitive coupling between the heating ele- ment and the tip. Ground by itself is not a generator of any signal. However, grounding wires connect the entire factory and once some stray electrical sig- nal enters grounding network, this signal can reach quite far. by vladimir kraz onfIlTer Inc. EOS Exposure of Components in Soldering Process feaTure

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