They, in effect, use the board as a large heat sink. If you choose the right package and your design is still running too hot, there are still a few things that you can do. The first is to use airflow in your system via a fan. Vendors typically specify a Theta JA value as a function of airflow. The higher the airflow the lower the value of Theta JA , because more cool air comes into contact with the hot package.
Heat sinks can also be a big help.
Heat sinks lower the effective value of Theta JA by increasing the package's surface area. Using a heat sink in tandem with airflow and a package with low thermal resistance provides the best scenario to meet your thermal requirements. Copyright 1998 EDN Magazine, EDN Access . EDN is a registered trademark of Reed Properties Inc, used under license. EDN is published by Cahners Business Information , a unit of Reed Elsevier Inc.