Effect of substrate dimensions and boundary conditions on the heat spreading of LED package

Abstract

Thermal management is a critical issue for the packaging of light-emitting diodes (LED). With poor thermal management, the elevated junction temperature of the LED chip will result in shorter life, lower efficiency, and color shifting. As a common practice, people typically used the thermal resistance concept for thermal management. However, this highly simplified model is 1-D in nature. The heat spreading in the direction transverse to the main path of heat conduction in the LED package cannot be taken into account. The present study investigated the effect of substrate dimensions and boundary conditions on the transverse heat spreading of a high power LED package. It was found that the conventional concept of thermal resistance may not apply when the thickness of package substrate reaches a certain level. The heat spreading in the transverse direction may exhibit certain unexpected behaviors. In some cases, the trends of junction temperature of LED may be totally opposite to the engineering intuition. Some discussion on the transverse heat spreading effect is given in this paper.