Conformity Magazine - March 2008 - (Page 38)

the ground plane is reduced until an arc forms between the pogo pin and the DUT pin and eventually the two pins touch. This is equivalent to closing the switch S in Figure 3. 4. Closing S in the circuit diagram produces a very rapid grounding of the DUT and a redistribution of charge between the three capacitors. Only the 1Ω resistor, arc resistance and the inductance within the pogo pin and the DUT pin limit the current pulse. The peak current can be anywhere from a fraction of an Amp to 20A depending on the size of the DUT. At this point the DUT is charged and the potential between the field plate and the ground plane has fallen as the capacitor CFG provides charge to the DUT. During this redistribution of charge, which lasts under 5ns, the high voltage power supply and the high value resistor can be ignored because of their slow response time. After the initial redistribution of charge the field plate will slowly return to the voltage on the high voltage power supply, while the DUT remains at zero potential but in a charged state. At this point the single pulse and dual pulse procedures begin to differ. We will continue with the single pulse procedure. 6. With the pogo pin still touching the DUT pin the HV power supply voltage is set to zero. The field plate will slowly return to zero volts and the charge on the DUT will slowly bleed off through the pogo pin. When the field plate is at zero volts the distance between the field plate and ground plane can be returned to the original separation. At this point the procedure can be repeated for another stress on the same pin, a stress on the same pin with opposite polarity or testing can be continued on a different DUT pin. 7. A sample FCDM waveform for a small JEDEC calibration module is shown in Figure 4. The waveform shows the typical CDM characteristic; a very high current short duration pulse. The dual pulse procedure continues after step 5 of the single polarity procedure. 6. Without changing the voltage on the HV power supply the distance between the field plate and the ground plane is increased so that the pogo pin separates from the DUT pin. The DUT is still charged and will stay at approximately zero volts while the field plate is at the HV power supply voltage. The potential on the field plate is slowly returned to zero by setting the HV supply to 0V. Changing the field plate potential to zero volts does not change the fact that there is a nearly 500V potential across the capacitor CDUT. The result is that when the field plate reaches zero volts, the DUT potential is close to -500V. At this point the separation of the field plate and ground plane is decreased until an arc forms between the pogo pin and the DUT pin, rapidly grounding the DUT. This results in a second stress pulse with approximately equal amplitude as the first, but opposite polarity. After a suitable delay, to allow the field plate to return to zero volts after the arc, the separation between the field plate and the ground plane is increased and the test sequence is complete. Further stresses can be performed on the same pin or testing can be continued on other DUT pins. 5. 7. 8. Figure 4: Field-induced CDM waveform of a small JEDEC module at 500V Organization Standard Insulator Thickness (mm) Insulator Dielectric Constant Calibration Modules Nominal Module Capacitance pF Peak Current (1GHz oscilloscope) (A) JEDEC JESD22-C101C 0.381 ± 0.038 4.7 ±5% Metal Coins 6.8 & 55 5.75 & 11.5 (±15%) ESDA JESD22-C101C No Insulator or ≤ 0.13 Not Specified Metal Film on 0.8mm Thick FR-4 4 & 30 4.5 &14 (±20%) 9. The dual pulse method can save some time during FCDM testing. FCDM Standards Three standards bodies issue CDM measurement standards using the FCDM method, JEDEC,1 the Electrostatic Discharge Association (ESDA),2 and Automotive Electronics Council (AEC).4 The AEC standard closely follows the ESDA standard and will not be discussed explicitly. Table 1: Comparison of JEDEC and ESDA FCDM standards 38 Conformity marCh 2008

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Conformity Magazine - March 2008 NewsBreaks Editor's Note Adelstein Renominated to the FCC Industry Canada Publishes FAQs On RF Fields FDA Gives Its Scientific Capabilities Poor Marks FDA Offers Guidance On its Product Review Process FDA Publishes Updates to List of Recognized Standards FDA Warns of Patient Risk From Electric Dental Handpieces Complying with the EMC Directive, Second Edition ESD Open Forum Emerging Issues in Standards - Korean "RoHS": Not Like RoHS at All The iNARTE Informer Challenges in Testing - Field-Induced Charged Device Model: What Really Happens Design Fundamentals - EMI Shielding Technologies for Consumer Electronics Equipment Focus On...Compliance Software Buyer's Guide Additional Standards Published for the EU's ATEX Directive Additional Standards for the EU's Medical Devices Directive Also Published China to Require Bar Codes to Enhance Product Safety CPSC Releases 2007 Self-Assessment CPSC Actions in News IEC Standards Update UL Standards Update Product Reviews Telcordia Standards Update From Our "You Can't Make This Stuff Up" Department Looking Back: Items from Past Issues of Conformity Advertisers

Conformity Magazine - March 2008

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