Reliability of AuGe Die Attach on DBC Substrates With Different Ni Surface Finishes

Abstract

Plated Ni is a commonly used barrier layer for direct bond copper (DBC) substrates used in high-temperature and high-power applications. The Ni plating method can be electrolytic or electroless, and the composition may be pure Ni, Ni:P, or Ni:B. With a melting point of 356 °C, eutectic Au88Ge12 (wt.%) solder preforms can be used for die attach in high-temperature applications up to 325 °C. The reactivity of these different Ni layers with the Ge in the AuGe solder preform has been compared. With Ni and Ni:B, the reaction was rapid during the reflow process, and initial shear strengths were low. With electroless and electrolytic Ni:P, the initial shear strengths were high and decreased ~30% after 3000 h aging at 300 °C and 325 °C. The formation of Ni–Ge intermetallic compounds (IMCs) during high-temperature storage was studied, and the growth kinetics of the Ni–Ge IMCs were calculated. A −55 °C to +300 °C thermal cycling test was conducted, in which the Cu-to-alumina DBC substrate interface failed before the die attach.