Influence of Molding Compound on Leakage Current in MOS Transistors

Leakage current in a metal-oxide-semiconductor (MOS) transistor can be a significant contributor to heat dissipation, resulting in higher power consumption. Leakage current can also be the cause of failure by some mechanisms such as latch-up or breakdown. In plastic-encapsulated transistors, molding compounds can have an effect on the magnitude of the leakage currents. This paper assesses the properties of molding compounds that can increase leakage current in MOS transistors. A fishbone diagram is developed to show the factors relating to molding compounds that can increase the leakage current directly or indirectly. Since passivation layer damage can be caused by improper selection and processing of molding compounds, the contributions of the passivation layer toward leakage current are also discussed. A case study is presented that demonstrates various experimental techniques for identifying the mechanism of an increase in leakage current. The experimental techniques can be used to evaluate the propensity of a molding compound to cause an increased leakage current. Recommendations are presented for molding compound and MOS transistor manufacturers regarding the selection and evaluation of molding compounds using a design-of-experiments approach.