Enhancing Hydrophilicity of Electroplated Ag Metallization by Ar/O2 Plasma Treatment to Promote Ag Sintering Reaction

초록

Wide-bandgap (WBG) power modules require robust die attach for high-temperature applications. Ag is attracting attention as a die attach bonding material for WBG power semiconductors due to its advantages such as high thermal/electrical conductivities and high operable temperature. The robustness and reliability of the bonding joint are generally influenced by the chemical and physical state of the surface. Some module manufacturers recommend plasma pre-cleaning of the substrate surface during the Ag sintering process. However, there is insufficient information regarding the effect of plasma pre-cleaning on the sintering characteristics between the Ag plating and Ag powder, and its contribution to improving joint quality. This study investigates the effect of Ar/O2 plasma pre-cleaning on Ag sintering behavior on the electroplated Ag metallization. We compared three conditions for Cu dies/substrates with electroplated Ag metallization: (1) no cleaning, (2) ethanol ultrasonic cleaning, and (3) ethanol ultrasonic cleaning + Ar/O2 plasma treatment pressure-assisted Ag sintering. Plasma-treated samples exhibited the highest shear strength (49.38 MPa), a 37.5% increase over non-cleaned samples. The plasma pre-cleaned sample exhibited the best interfacial connection ratio (63.34%) between the Ag sintered layer and Ag metallization and the lowest porosity. These enhancements are attributed to the effective removal of surface contaminants and a significant increase in surface energy, which improved the hydrophilicity of the Ag surface. Ar/O2 plasma pre-cleaning thus effectively removes contaminants and activates the surface, significantly enhancing the microstructural, mechanical, and thermal properties of Ag sintered joints.

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