This specification should be used in conjunction with the overview document JESD51, Methodology for the Thermal Measurement of Component Packages (Single Semiconductor Device) [1] and the electrical test procedures described in JESD51-1, 'Integrated Circuit Thermal Measurement Method (Single Semiconductor Device' [2. The environmental conditions described in this document are specifically designed for testing of integrated circuit devices that are mounted on standard test boards with two internal copper planes [3]. This standard is not applicable to packages that have asymmetric heat flow paths to the printed board caused by such thermal enhancements as fused leads (leads connected to the die pad) or power style packages with the exposed heat slug on one side of the package.