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edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 4 16 between acting as an excellent dielectric, perform as an ideal high-voltage capacitor. The high voltage generated duringmetal plate removal reachesmore than 10 kV, often delivering painful electric shocks to the line operators through their rubber gloves (Fig. 5) and ruining some of the cards. Figure 6 shows that punching burrs promote discharge paths through the chips when using inlays with small metal plates. These effects are described in more detail in the latest version of guideline 1013 of the ESD Forum e.V. to be published in November 2019, first in German and later in English. [1] Of course, the huge variety of RFID packages and applications presents further ESD risks. A detailed description of all of them is not possible within this article. COUNTERMEASURES As these examples illustrate, ESD protection during manufacturing requires an individual viewof the product. At the outset, it is acknowledged that even the best chip- internal ESD-protection structures will never fully cope with the electrostatic charging/discharging reached in high-speed smart card mass production. Therefore, ESD risks must be minimized during the production process. Basically, four steps are involved in the process: In the first step, foil is unwound and prepared for assembly with the RFID devices. As long as there are no electronic compo- nents inside, electrostatic charging does not matter. Next is the second stepof theprocess: At the verymomentwhen electrostatic sensitive devices (ESDS) approach the plastic tape for landing, ESD risks begin that require careful con- sideration. One widespread countermeasure is to use air ionizer fans and ionizer bars. Bars work well to neutralize foils but when leaving the bar area, the foil is immediately recharged again by any kind of friction (rolling or gliding) such as the ongoing transportation flow of the plastic foil on a fixedbaseplate. Some ionizer bars enable self-regula- tion, which involves a displaced feedback/self-regulation measurement point. But the problem remains that air ionization requires time—sometimes too much, considering the high speed of manu- facturing. Another, lesser known method is to discharge charged foils by using discharge combs. Their principle function is identical to those used in Van de Graaff generators. Discharge combs (Fig. 7) do not need to touch the foil. It is sufficient to mount them at a distance of 0.5 to 10mm fromthe plastic foil surface for reliabledischarge. Anexample in Fig. 8 shows the plastic tape leaving the second process step to enter the third step, where a cutting motion is applied—again accompanied by charging. Charging may also occur during the fourth step, where the foils are stapled before baking. In this final step, mechanical effects like electrostatic attraction and Coulomb repulsion of stapled foils are a primary concern. In general, evenwhen using a discharge comb, recharging starts at the first encounter withmechanical friction after leaving the comb area. Therefore, useful ESD protection in the RFID assembly area consists of four components: • A baseplate which should not be conductive, but electrostatically dissipative. A good target value is about 10 9 Ω/sq. • Discharge combs shortly before and after the placement zone. • An air ionizer nozzle at every pick and place nozzle, targeted to the landing point. • Electrostatically dissipative nozzles for pick and place handling of RFID devices. Even in combination, these four countermeasures cannot completely avoid electrostatic charging but are useful to suppress the charges to a level that devices can cope with. Further details on this topic can be seen in References 1 and 2. Fig. 5 Metal plate removal, generating high electrostatic charging. Fig. 6 ESD through the foil stack during removal of metal plates. Peaks from punching burrs in lead frames (left) generate preferred discharge paths through the plastics.