Low Temperature Fine Pitch Au-In Solid Liquid Inter Diffusion Bonding for Wafer Level Packaging

A low temperature fine pitch wafer scale bonding process through Au-In solid liquid inter diffusion bonding is discussed in this paper. 20 μm fine pitch gold and indium miro-bumps with 10 μm diameter are fabricated on two oxidized silicon wafers. Then the wafer bonding process is accomplished at 180 °C with less than 2 μm alignment accuracy. Daisy chains of nearly 2500 interconnects with a fixed contact size of 10×10 μm² connected successfully. Besides, there is no significant change of the daisy chain resistance after temperature cycling test. An average die shear strength of more than 20 MPa is also achieved. This work shows great potential of Au-In solid liquid inter diffusion bonding for future high density wafer level packaging and heterogeneous integration.