Developing underfill process in screening of no-flow underfill and wafer-applied underfill materials for 3D stacking

The demands and challenges in pushing the limits of Moore´s Law made the 3D IC stacking radiate the pressure for MPTs (materials, processes and tools) in keeping up with the technology. The 3D IC architecture design built around the TSVs, micro-bumps and thinned wafers/dies is the center of the show, of which the MPTs must conform and be viable to be part of the supporting cast. Underfilling´s main objectives is to provide the mechanical stability for micro-bumps and prevents moisture between the resulting gap between dies before the 3D stack is sent for packaging. With several complexities in 3D stacking had to be considered and addressed in applying the underfill materials. Complexities such as the stacking options Die-to-Die (D2D) or Die-to-Wafer (D2W), the thicknesses of the dies to be stacked (~50 um die thickness), the thermo-compression bonding parameters to be used and the behavior of the underfill materials to the different process parameters had to considered during the characterization process of underfills.