High Thermal Performance Package with Anisotropic Thermal Conductive Material

The development of high power and compact size semiconductor packages lead to the challenge in the need of high thermal dissipation design. For package level thermal solution, metal (especially copper) heat spreader and metal/metal-oxide filler thermal interface material are widely adopted. However, the thermal performance of packages is limited by isotropic conductive behavior of most of these materials. The thermal conducting performance could be further improved by directing the heat transportation in the direction desired, for instances the in-plane dissipation for heat spreader and the out-of-plane dissipation for thermal interface material. This present study reported the successful adoption of anisotropic thermal conductive pyrolytic graphite sheet as heat spreader and vertically aligned graphite sheet as thermal interface material in semiconductor package, individually. The Joint Electron Device Engineering Council standard still air junction to ambient measurement experiment shows that a flip chip ball grid array package incorporated with a pyrolytic graphite sheet as heat spreader improved thermal resistance of the module by 20%. The thermal dissipation behavior of the module was simulated with a well validated computational thermal dynamics model based on the experimental results. The anisotropic thermal conductive vertically aligned graphite sheet was also adopted as thermal interface material to replace the nowadays grease type thermal interface material. A thermal test chip assembled large size high performance flip chip ball grid array package mounted on a Joint Electron Device Engineering Council defined 4 layers thermal test printed circuit board was chosen as the test vehicle for thermal interface material performance test. The junction to case measurement experiment shows that the package with the anisotropic conductive thermal interface material improved the thermal resistance by 40%. Some novel designs were proposed basing on the application of this anisotropic thermal conductive material as validated by thermal simulation study. Package design guideline basing on the implementation of the anisotropic thermal conductive material will be discussed in this paper.