Immobilization of metal coated polymer spheres on Indium pads

This paper investigates an approach for creating a metallurgic bond between Ø5 μm metal (Au)-coated polymer spheres (MPS) and Indium (In) pads. MPS were positioned onto In pads where the metal coating reacted with the In. The MPS were deposited by dry dispensing. The adhesion force between the MPS and the In pads was measured by acceleration/centrifugal testing. Under a centrifugal force of 34 nN, the percentage of remaining MPS increased from 10 % for samples without heat treatment to more than 90 % for samples exposed to 200 °C annealing. This is a strong indication that a metallurgic bond had formed between the metal coating on the MPS and the In on the pads.