The performance of power MOSFET devices encapsulated with green and non-green mold compounds

The green initiative has driven semiconductor manufacturers to eliminate the use of environmentally unfriendly substances such as antimony oxide, flame retardant and halogenated compounds in their microelectronics packages. Nevertheless, there may be concern that the new chemistries in green package may alter the properties of semiconductor devices. We have evaluated the performance of power transistors encapsulated with green and non-green epoxy mold compound (EMC) via autoclave stress. We have proven that green device indeed possesses superior electrical and physical properties than non-green device. Our research result reveals that device with non-green EMC exhibits relatively higher gate-to-source leakage current (I_GSS) and drain-to-source on-resistance (R_DS[on]) as compared to device with green EMC. The non-steady electrical characteristic of non-green device is attributed to its higher level content of bromide ions released from flame retardant. Under moist environment, bromide ions form electrolytic solutions and trigger the corrosion process. We found that copper ball bonds in non-green device are extremely susceptible to electrolytic corrosion. The corrosion begins from the ball periphery and gradually extends toward the ball base. The corrosive ions accelerate dissolution of aluminum pad underneath copper ball, leading to separation gap formation between intermetallic and bond pad, thus isolating the pad away from the intermetallic layer. Moreover, the gap size is gradually enlarged when the autoclave stress period is extended, resulting in the rise of R_DS[on] over time. In contrast, green device is more impervious to corrosion induced bond damage. As a result, green device demonstrates more stable R_DS[on] and lesser leakage current of IGSS even operating under high humidity, pressure, and temperature conditions.