Conformity Magazine - September 2008 - (Page 35)

Early measurements indicated that the PPV is a real world issue. PPV was measured when a charged person touched a Zener diode mounted on a current probe. In fact, the measured voltage across the Zener diode touched by a charged person was even higher than observed on the HBM simulator.[4] The explanation of the PPV for a real world situation is the same as in the simulator. The charged human has a capacitance to their surrounding, about 100pF, and forms a small, variable, capacitance between their finger and anything he or she touches as the finger approaches the object. However, the original real world measurements did not represent the real world in one significant way. The geometry did not accurately replicate a person touching an integrated circuit. In the “real world” events, the Zener was housed in a flat surfaced fixture. The capacitance between the person and the Zener was therefore a flat surface to a rounded finger. This creates a much larger capacitor than would occur between a finger and the small pins of a modern integrated circuit. To investigate this, a more realistic real world simulation was needed. Several simulated packaged integrated circuits were built from circuit board material and Zener diodes. A schematic is shown in Figure 6 and photographs are shown in Figure 7. The Zener diodes simulate the protection circuitry on an integrated circuit. They have high input impedance between 0 and 10 V and low resistance below and above those voltages. Wires attached to the cathode end of the diodes allowed measurement of the voltage on the solder balls or pins of the simulated packages. The simulated packages were fitted with a 3mm threaded screw that could fit into the center of an IEC 61000-4-2 compliant current sensor. The current sensing target was used solely to trigger an oscilloscope and provide a ground point. The remaining 3 channels of the oscilloscope could be used to monitor the voltage on the package pins. Rather than use a charged person’s finger, an ESD gun in air discharge mode with a round tip was used. To make measurements the ESD gun was set to a voltage, the ESD gun’s trigger was pulled, charging the tip of the gun, and the gun was moved toward the package pins until an arc occurred, triggering the oscilloscope. Measurements on the simulated ball grid array (BGA) packages showed that the PPV was indeed much lower than for the geometry with a person’s finger touching a flat surface. The resulting PPV September 2008 Conformity 35 Figure 4: Schematic for model of PPV due to relay capacitance change Figure 5: Schematic of a typical dynamic ESD clamp http://www.fair-rite.com http://www.fair-rite.com http://www.fair-rite.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - September 2008

Conformity Magazine - September 2008 Contents Editor’s Note Commission Adopts Regulations for Internet-Based TRS Services Another Company Fined for Non-Compliance with HAC Requirements FCC Extends “Do-Not-Call” Registry Compliance Requirements Marketing Company Gets $1.4 Million Fine for Junk Faxes EU Commission Codifies Directive on TTE Market Competition EU Commission Releases Updated Standards List for the R&TTE Directive Updated Standards List for the “New” Low Voltage Directive Released New Standards List Released for the EU’s Machinery Directive The ESD Association: Voluntary Standards in Action ESD Open Forum Medical EMC Standards: Towards the 4th Edition of IEC 60601-1-2 iNARTE Informer Pre-Pulse Voltage in the HBM ESD Model Digital Interfaces and EMC Performance ESD Design Buyer’s Guide Product News Commission Publishes Updated Standards List for the EU’s Personal Protective Equipment Directive FDA Links “Human Factors” to Adverse Events with Medical Devices CPSC Actions in the 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 - September 2008

For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.