Bonding of copper pillars using electroless Au plating

Pressureless Cu-to-Cu bonding was achieved at 50 °C by electroless Au plating with controlled flow through a microchannel. Electroless plating process is attractive because of its low cost and low energy without voltage. Also, the low process temperature of electroless Au plating could avoid damages caused by thermal stress during fabrication. In this study, two kinds of copper pillars, dome-shaped and mushroom-shaped, were used to examine the basic properties of electroless Au plating in a microfluidic fixture. It was discovered that with controlled flow, electroless Au tended to filled gaps and deposited on regions with lower flow rates. Then, by controlling the gap height between copper pillars, dome-shaped copper pillars were bonded successfully by electroless Au plating in a microfluidic fixture without voids or seams between plated layers.