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March 2014 • SMT Magazine 51 EOS EXPOSUrE OF cOmPONENTS IN SOLDErING PrOcESS continues Soldering Iron Properties Are all soldering irons alike in generating and/or passing the noise down the tip? What about top-of-the line soldering irons? If there is a current from the tip of the soldering iron, does it mean that the iron itself is defective or unsuitable for work with sensitive components? High-frequency currents from the tip of the professional-grade properly-installed iron are caused not by the iron itself, but by the reality of complex facility topology, wiring and operation of equipment. Soldering iron is just one com- ponent in soldering process and no matter how good it is it cannot fundamentally solve the issues of facility by itself. In short, if you have a quality soldering iron, it is doing its job. It is a user's task to provide safe EOS environment for the entire bench where the iron is only one of components. mitigating Effects of Transient Signals on Power Lines and Ground If the sources of transient signals on power lines is known and can be removed without af- fecting production process, then the reduction of current from the tip of the soldering iron is relatively simple. However, too often the source is either unknown or cannot be removed. The only remaining options are grounding manage- ment and filtering out the transient signals on power lines and ground. Grounding management Re-routing of ground connection and sepa- ration of "noisy" ground from a clean one can help to reduce harmful currents. Techniques recommended and explained in this paper 4 help to alleviate some of the noise issues. Spe- cifically, low impedance to facility ground and separation between noisy and quiet grounds and connecting soldering iron and the work- bench to the quiet ground often result in lower level of transient signals. As shown in Figure 6, grounding of the workbench and of the soldering iron as close as possible to each other can significantly reduce current exposure during soldering. Grounding management alone, however, cannot satisfactory resolve noise issues since the source of EMI is not removed and the prob- lematic signal still present in the soldering iron. Filtering Out the Noise Unless noise on power lines and ground is greatly reduces, there always will be a possibil- ity of EOS exposure during soldering. Intel rec- ommends 10 power line filters as the first line of defense against EOS. These filters suppress noise on power lines and provide soldering iron with relatively clean power. Some EMI filters also suppress noise in ground line. Figure 7 shows recommended application of power line EMI filter with the soldering iron. It is important to connect ground of your work- bench or tool to the ground terminal of the fil- ter, not to the facility ground—the filter creates a quiet "EMI ecosystem" at its output. Figure 8 shows the current from the tip of the iron used feaTure figure 6a: Pcb is grounded ~1.5 m from the iron. figure 6b: Pcb is grounded ~18" from the iron. Figure 6c: pCb is grounded next to the iron.