Conformity Magazine - March 2008 - (Page 35)

ntegrated circuits are commonly tested for ESD robustness with 3 tests, Human Body Model (HBM), Machine Model (MM) and Charged Device Model (CDM). Most engineers quickly grasp the procedure for HBM and MM but CDM is often poorly understood. This is unfortunate because a large fraction of the ESD failures experienced in a modern board assembly operations are CDM type failures. This article will describe the events which occur during a CDM test conducted using the widely accepted field induced CDM (FCDM)1, 2 test and discuss some of the issues involved with the most widely used FCDM standards. All ESD events consist of a charged object discharging through a discharge path. Characterizing an ESD event requires understanding both the capacitance and the discharge path. ESD stress tests such as HBM and MM can be described with the simple circuit diagram in Figure 1. This procedure works well because these test standards emulate a person or machine becoming charged and discharging through the sample being tested. The capacitance is a person for HBM (100pF) or the machine for MM (200pF). The discharge path for a human includes skin and body resistance which is approximated by a 1500Ω resistor. For a machine the current is limited by the induction in a metallic discharge path, about 0.8µH for the specified waveform. I CDM is different. CDM emulates an integrated circuit that becomes charged during handling and discharges to a grounded metallic surface. The capacitance is the capacitance of the integrated circuit to its surroundings and the discharge path is a pin of the IC directly to a grounded surface. The test method for CDM must have a capacitance that scales with the device under test’s (DUT) capacitance and a discharge path with very little impedance other than the DUT’s own pin impedance. Figure 2 shows an FCDM simulator. The simulator consists of a metallic field plate that may or may not have a thin insulator on its surface. The presence, thickness and material of the Figure 1: Basic circuit diagram used to describe HBM and MM 901 Sheldon Dr., RTP (Cary), NC 27513 USA marCh 2008 Conformity 35 http://www.productsafet.com http://www.productsafet.com

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

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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