BGA packages classification to reach ESD CDM standards

Almost every electronic device is sensitive to electrostatic discharges. The charged device model (CDM) is today used by the industry to characterize the electrostatic discharge events that occurs in an automated industrial environment. Based on this model, the JEDEC and ESDA give some standards that, with specific test equipment, rank the electronic device by their ability to withstand different level of electrostatic discharges. To ensure the compatibility of its products with those standards, the company designs some dedicated protections at the silicon level. The counterpart of those protections is that they take additional area on the silicon. Therefore a particular attention is given to fit the standard constraints without oversizing the protections. In ESDA and JEDEC standards, the rating is directly determined by the voltage level applied between positive and negative electrodes of the tester. If this voltage level contributes to the amplitude of current peak that will happen during the discharge, it is also highly dependent on the package under test, whose dimensions are a major contributor to the resulting current peak for a known voltage. This article shows first, the limitation of the JEDEC and ESDA standards approach on today BGA packages. Secondly, it presents a simple way to determine the capacitance between the package and the tester, thus predicting the shape of the electrostatic discharge crossing the product. Among the different BGA packages developed in the company, it also shows which packages are reaching the standard limits.