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EOS Exposure of Components in Soldering Process
April 1, 2014 |Estimated reading time: 1 minute
Introduction
Soldering irons, solder extractors and other equipment that comes in direct electrical contact with sensitive components can inject significant 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 significant device damage.
Where would a soldering iron tip get voltage? 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 devices. 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 element 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 signal enters grounding network, this signal can reach quite far.
Main source of voltage on ground is transient signals leaked from power lines. Transient signals can come from a number of sources, such as switched power supplies, thyristor control, servo motors, equipment commutation and so on. These signals can reach significant magnitude. Figure 1 shows a transient signal on a power line caused by turning on ubiquitous heat gun. As seen, the peak signal reaches 8.7V and this is not the highest magnitude found in manufacturing environment where plenty of high-current equipment is operating.Read the full article here.Editor's Note: This article originally appeared in the March 2014 issue of SMT Magazine.