Bumping and stacking processes for 3D IC using fluxfree polymer

A novel, maskless, low-volume bumping material, called solder bump maker, which is composed of a resin and low-melting-point solder powder, has been developed to make solder bumps on TSVs. With the coining process, the standard deviation of bump heights became 1μm. Fluxing underfill which features an extremely low-weight loss with temperature, has been, also, developed to simplify the chip-to-chip and chip-to-wafer bonding processes and implement the mass reflow process for them. Therefore, these processes can be reduced to only three steps: dispensing fluxing underfill, pick and place of TSV chips, and reflow. With the fluxing underfill, a 4 × 4 array of 4 tier-stacked TSV chips on a Si wafer was, successfully, developed.