Systematic Investigation and Characterization of Ag Paste for LED Die Attach

In this paper, the bonding parameters of Ag paste are optimized for LED die attach. The Ag paste is characterized for its shear strength, hermeticity and morphology. It is found that a bonding strength of $\sim 6.87\text{MPa}$ is achieved and the hermeticity is at least $ 10\times$ below the rejection limit $(5\times 10^{-8}.atm.cc/s)$. The experimental results demonstrate that a high-quality bonding is achieved. Moreover, LEDs are fabricated and bonded onto substrate with Ag paste. The IV and EL of the un-bonded and bonded LEDs are obtained. The results show that Ag paste does not have a big impact on IV but has a positive effect on EL of LEDs. In addition, this study can be further used to optimize the process parameters, to characterize the material properties of Ag paste (e.g. optical reflectance, thermal conductivity, volume resistivity, porosity, etc.), and to study the effect of temperature on luminous efficacy and optical spectra (e.g. PL spectra and EL spectra) and reliability of the packaged LEDs.