Improved characteristics of electroless Cu deposition on Pt–Ag metallized Al2O3 substrates in microelectronics packaging

The employment of multilayer metallization is critical in microelectronic packaging, especially in the field of solder joint reliability. In this study, investigation of conductivity, solderability, electromigration resistance and adhesion strength of the multilayer metallization structure in the electroless Cu/Pt–Ag/Al2O3 assembly is conducted. The deposited electroless Cu layer exhibits a preferred (111) orientation. The particle size of electroless Cu deposit reaches 0.5 μm after 3 h of deposition, with a deposition rate or approximately 3.1 μm/h after appropriate modification of bath concentration, temperature, pH value and loading ratio. The resistivity of the electroless Cu/Pt–Ag/Al2O3 assembly is reduced from 4.1 to 3 μΩ cm when the thickness of Cu film reaches 10 μm. The employment of electroless Cu deposition onto the Pt–Ag metallized Al2O3 substrate improves the solder-leaching and electromigration resistance of the metallized assembly. The presence of electroless Cu deposit acts as a diffusion barrier to prevent the dissolution of Pt–Ag into the melted solder. No significant change in the resistance is observed for the electroless Cu/Pt–Ag/Al2O3 assembly after dc stressing for 150 h. After thermal aging tests, the adhesion strength between the electroless Cu and the Pt–Ag conductor is raised due to the Cu recrystallization reaction.