New Silver Paste for Die-Attaching Ceramic Light-Emitting Diode Packages

Micrometer-sized Ag particles adsorb substantial oxygen above 200°C and a dispersion of these particles in alcohol can be successfully used as a die-attach material by sintering to form a soft porous bonding layer. The characteristics of a light-emitting diode (LED) using this Ag paste as a die-attach material were evaluated. The LED was assembled on an alumina ceramic package, which did not degrade upon sintering, with a sapphire-based InGaN LED die. The bonding strength was twice as high to the ceramic package as to a copper alloy lead frame. Thus, the Ag paste is suitable for use with LED ceramic packages as a bonding material. In addition, a significant reduction of the thermal resistance and improvement of the reliability are achieved by using the Ag sintered layer for die-attaching the ceramic LED package. To improve the bond reliability between sapphire and alumina, both of which are low-thermal-expansion materials, the thermal expansion of the Ag sintered layer was reduced by the addition of Kovar particles. The addition of Kovar particles, with or without Ag plating, to Ag particles exhibited a desirable effect. The present mounting method for LEDs was proved to be useful for die-bonding electronic components, providing an alternative technique to high-temperature high-lead soldering.