Protection against secondary ESD effects

Protection against ESD has become key issue in electronic circuit design both from regulatory specifications and to reduce the probability of the damages it can cause to semiconductor devices. Semiconductor devices are normally manufactured with varying level of on-chip protections depending on the type of the device and the manufacturer. The damage caused by ESD depends on this level of on-chip ESD protection and the amount of the transient energy transferred on to the device pins. One of the easiest methods of limiting the amount of transient energy transferred is the usage of series resistance. However in the era of high-density packaging this method is inadequate because the transient energy can get transferred to the closer by adjacent tracks on the high density PCBs due to secondary discharges and can cause damage to the device connected to it. Incorporation of additional off-chip protection devices can take care of this problem. Use of TranZorb, Transient voltage suppression Zener as the off-chip protection device is one of the remedial action. The usage of the TranZorb at various locations in the circuitry as secondary level protection or as board level protection is discussed in this paper. The various aspects related to the usage of TranZorb and the effectiveness of the same is supported by appropriate ESD tests.