IC BSP 77 HITFET Failure Analysis

Gideon Analytical Labs received two BSP 77 HITFET devices with resistive shorts. The HITFET is a highly integrated temperature protected FET low-side switch which provides protection from short circuits, overloads, voltage surges, open circuits, excessive temperature, and ESD. These low-side switches are versatile power transistors specially designed for automotive and industrial applications. Their built-in intelligence and protective features offer improved performance and reliability over discrete components.

The die is covered with a polyimide over glassivation on top of the trace lines. The polyimide is destroyed. The yellow arrow is melted glass at the failure site. There are two circuits off the gate wire: the EDS protection and the drive unit. The failures occurred in the region adjacent to the gate pad. There are several junctions where over current is observed. The temperature on this device had to get hot in order to melt the polyimide.

Overload and short circuit are clearly the most damaging conditions in an application and it can take a few forms, depending on the input and load conditions: i.e., the short could be across the load (Vbb and Drain), or device (Drain-Source) for different input conditions (Vgs= LOW or Vgs= HIGH). Additionally, the short could be intermittent, significantly worsening the situation especially when the circuit contains inductive loads. In this case, the self-induced (fly-back) voltage and/or the clamped energy could be significantly higher than specified values for the device, thus irreversibly damaging the device.

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