Thermal Design Considerations for Surface Mount Power ICs

The focus of this paper is to present the techniques that are effective in removing the heat from the surface mounted power ICs and transferring it to the cooler surroundings. In the past the thermal design was as simple as adding the theta values (°C/W) of the power component, the thermal pad and the heat sink together and multiplying by the power dissipated in that component to arrive at the temperature rise between the ambient and the junction of the IC. Today, with surface mount technology and ICs with power pads the Printed Circuit Board (PCB) has become an integral part for removing the heat. The basic concepts of what makes a good thermally conductive PCB, some first order modeling examples and evaluations of an existing evaluation module (EVM) will help the designer understand the techniques in producing a good thermally conductive PCB.