What Is DirectFET Technology?

The schematic in Figure 3 shows the construction of International Rectifier's DirectFET source mounted power-MOSFET technology. As the diagram illustrates, the device is based on a power MOSFET die housed in a copper clip assembly. This MOSFET die has solderable area array gate and source electrode connections on its front surface. The rear surface of the die, which forms the MOSFET drain electrode, is connected to the clip using an electrically conductive adhesive. The clip extends over the edge of the MOSFET die so that drain connections can be made to the circuit board.

Use of the copper clip to house the power MOSFET die delivers significant thermal advantages when compared to conventional package technologies, such as the SO-8. The main thermal advantage is that the top of the package (i.e. the metal clip) offers a lowresistance thermal connection to the power MOSFET die. Exploitation of this low-resistance thermal path to remove heat from the power die can result in less heat being transferred to the circuit board. Alternatively, heat may be transferred from the power die for dissipation through both the circuit board and the top of the package. Known as "dual sided cooling," this last technique offers the circuit designer significant flexibility in implementing effective thermal management schemes.