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March 2014 • SMT Magazine 47 best way to specify signal on the tip of the iron. A common multimeter often used for this pur- pose provides measurements of either RMS val- ue or close to average—good for 50/60Hz, but unusable for transient high-frequency signals. IPC-TM-650 section 2.5.33.2 allows for 2V peak voltage on the tip of the soldering iron, which is extremely high; section 2.5.33.3 of the same document allows maximum of 1µA of cur- rent measurable with a multimeter, not a scope thus providing RMS or average value. In dissent with the above IPC standards, IPC-A-610-E 4 , the most fundamental document controlling quality of PCB assembly, provides the following instructions: 3.1.1 EOS/ESD Prevention— Electrical Overstress (EOS) ...Before handling or processing sensitive com- ponents, tools and equipment need to be carefully tested to ensure that they do not generate damaging energy, including spike voltages. Current research indicates that voltages and spikes less than 0.5 volt are acceptable. However, an increasing number of extremely sensitive components require that solder- ing irons, solder extractors, test instruments and other equipment must never generate spikes greater than 0.3 volt. IPC-77115, which provides directions for rework of the electronic circuits, mimics IPC-A- 610-E. Which measurements are Important Let's examine the properties of the EOS signal caused by conducted EMI. As a rule, conducted emission signals are high-energy signals(i.e., having low output impedance and capable of delivering high currents). The rea- son for this is that creation of disturbances on low-impedance power line requires power and only truly low-impedance sources of noise can feaTure EOS EXPOSUrE OF cOmPONENTS IN SOLDErING PrOcESS continues Figure 3: Test setup for measuring eoS exposure.