Thermal management of high power LEDs: Impact of die attach materials

Thermal management plays an important role in high power light emitting diodes (LEDs). The physical properties, such as light output, dominate wavelength and life span of LEDs are affected adversely by the junction temperature. As the result, heat flow path in LEDs becomes more and more important with increasing input power. The packaging materials including the die attach materials can decide heat flow rate from junction to board. However, die attach materials have far lower thermal conductivities compared to other packaging materials. The thermal conductivity of die attach materials thus can be reflected by the thermal resistance from junction to board. We developed an in situ measurement method after LEDs packaged incorporated with the measurement of junction temperature, light output and input power to exactly determine thermal resistance from junction to board. The results provide a reference in the selection and development of die attach materials for high power LEDs.