Au hollow pyramidal bumps for low-temperature low-pressure bonding fabricated via Au film transfer method

Low-temperature, low-pressure bonding is crucial for fabricating highly functional microsystems. This study presents the development of Au hollow pyramidal bumps (height: 4 μm, width: 6 μm, pitch: 12 μm) that plastically deform under low bonding pressure and facilitate low-temperature Au–Au bonding. The bump arrays were fabricated using the Au film transfer method. A strong bond reaching the fracture strength of bulk Si was formed between the Si chip with Au hollow pyramidal bumps and the Si substrate with Au film at 150 °C in ambient air. Furthermore, finite element method simulations reveal that hollow pyramidal bumps reduce stress concentration on the devices during bonding. The study findings confirm that the proposed method enables bonding of device chips at low temperatures with reduced stress concentrations, thereby contributing to the fabrication of microsystems. • Au hollow pyramidal bumps were fabricated via Au film transfer. • Hollow pyramidal bumps suppress stress concentration on devices during bonding. • Strong bonding was achieved using the bumps in ambient air at 150 °C.