Thermal characterization of multi-chip light emitting diodes with thermal resistance matrix

The junction temperature of LEDs is important for its life, reliability and efficacy. The thermal resistance measurement can be implemented to obtain the junction temperature of a single-chip LED in different power consumptions and different environment temperatures. However, for the multichip applications such as Chip-on-Board (COB), multi-color and high-voltage LED packaging etc., only the average junction temperature can be obtained by the traditional steady thermal resistance measurement. In this paper, a thermal resistance matrix with thermal coupling factor is proposed to obtain the junction temperature of each chip in a multi-chip LED with different chip powers. In the case study, each element of the 4×4 thermal resistance matrix of a Red-Green-Blue-White (RGBW) four-chip LED is tested by a transient thermal tester (T3ster) to investigate the thermal coupling of chips one another. In addition, the thermal distribution of the LED package was analyzed by finite element analysis (FEA) simulation for comparison. It is shown that the thermal resistance matrix is effective for evaluation of junction temperature of each chip in the multi-chip LED package with a discrepancy less than 2.5% from measurement.