Electroless Cu plating on glass substrates via repeated Sn-sensitization and Pd-activation cycles without adhesion promoter layers

• Strong adhesion between glass and Cu is achieved by electroless plating. • The conventional method of Sn sensitization and Pd activation is applied. • Optimizing the number of alternating sensitization and activation cycles is key. • A dense single-particle layer is favorable for strong adhesion. • The process is cheap and highly productive without an adhesion promotor. In recent years, glass substrates have gained significant attention as packaging materials for semiconductor chips and high-frequency devices, owing to their rigidity, dimensional stability, and surface smoothness. These substrates often incorporate through-glass vias formed perpendicular to the surface. Various fundamental studies have been conducted to meet the growing demand for increased computing power. However, ensuring strong adhesion between the deposited Cu layer and glass surface remains a major challenge. In this study, a Cu metallization process was investigated that achieves strong adhesion without the need for an adhesion promoter layer (APL) prior to electroless plating (ELP). The experimental conditions in the traditional ELP process, which involves repeated sensitization and activation cycles using Sn²⁺ and Pd²⁺, were optimized, and a peel strength of 6 N·cm⁻ 1 between the deposited Cu layer and surface of the glass substrate was achieved by optimizing the number of sensitization and activation cycles. Increasing the number of sensitization and activation cycles enhanced the coverage of the glass surface with particulate Sn-Pd mixtures, leading to nearly full coverage and optimal Cu adhesion. However, excessive cycling caused the accumulation of Sn–Pd catalyst particles, which diminished the adhesion of the Cu layer. The developed method circumvents the limitations associated with conventional APLs and offers cost-effective, high throughput processing suitable for industrial application.