Materials Merging Mechanism of Microfluidic Electroless Interconnection Process

Abstract

A low-temperature, pressureless bonding process, referred to as the microfluidic electroless interconnection process, has been developed for chip-stacking applications, in which electroless Ni plating is employed to bond copper pillars in an attempt to reduce the risk of thermo-mechanical damage during the assembly process. Copper pillar joints with a low standoff height were used to assess the bonding performance of the microfluidic electroless interconnection process on a smaller scale. The results showed that a striking lamellar structure formed in the deposits when electroless Ni solution was fed into a microfluidic platform intermittently, and through this visible structure, the bonding mechanism of the process can be characterized fully. Preliminary results showed that a high level of plating uniformity across the die could be obtained using the microfluidic interconnection process, and that the copper pillars were joined completely by electroless Ni plating without voids or seams. Further, it was found that the process is able to compensate not only for non-uniform copper surfaces, but also for the misalignment of copper pillars, which provides a competitive edge over other bonding methods. In addition, the direct shear test showed that the bond strength of the electroless Ni bonds was quite strong.