Low-temperature, pressureless Cu-to-Cu bonding by electroless Ni plating

Abstract

A novel low-temperature, pressureless bonding approach by electroless plating with controlled flow through a microfluidic device, in which a laminar forced convection flow of electroless solution was passing through a microchannel between dies and to gaps between copper pillars, was developed to metallically interconnect copper pillars together. Previous study had been demonstrated that, with the help of generating a forced convection flow of electroless solution using a microfluidic device, not only did the uniformity across the entire die improve, but intimate, void-free joints also could be achieved. This paper will make further investigations into electroless bonding on lower die standoff heights (15 and 35 μm). For both small joints, void-free joints of copper pillars have been demonstrated achieved by electroless Ni plating at a flow rate of 0.113 mL/min. Furthermore, Cu-to-Cu bonding using electroless plating approach has been shown to possess the capability to accommodate large non-copalanarity and misalignment of copper pillars.