Comparative Study of Die-Attach Materials for LED Die Bonding

Abstract

In this work, the bonding conditions of different die-attach materials are optimized for LED die to substrate bonding. The die-attach materials are characterized for their mechanical bonding strength, hermeticity, and surface morphology. Among the investigated materials, it is found that SAC solder has the largest bonding strength of ~60 MPa. The hermeticity is at least 10× below the rejection limit of MIL-STD-883E standard (5×10−8 atm-cc/s) for all die-attach materials. The results show that high-quality bonding is achieved. Moreover, LEDs are fabricated and bonded onto substrate with die-attach materials. The electrical, electroluminescent, and photoluminescent properties of the un-bonded and bonded LEDs are investigated. The results reveal that non-conductive electrical adhesive has the least negative impact on the electrical property of LEDs, Ag paste has the largest positive effect on electroluminescent and photoluminescent properties. In addition, this comparative study can be used as guidelines to further optimize the process parameters, to characterize the material properties of die-attach materials (e.g. porosity, optical reflectance, volume resistivity, and thermal conductivity, etc.), and to study the effect of temperature on reliability luminous efficacy, and optical property of the packaged LEDs.