Evaluation of chip-to-board interconnection using variable aspect ratio contact pad areas

This paper describes the evaluation of chip-to-board interconnection for low I/O sensor attachment. In particular the interconnections of different chip and printed circuit board (PCB) pad size ratios with offsets were investigated. Initial assemblies were made using lead-free, 99.3Sn0.7Cu solder. Solder joint shape prediction software, "surface evolver", has been used to simulate the solder joint shape formation for different ratio chip-to-board bond pad areas with different offsets between the two surfaces during the interconnection. The preliminary results show that depending on the solder volume and the aspect ratio of the chip-to-board pads, a convex or concave curvature of the solder joint is observed. Further simulation suggests the pad size plays a major role in the shape of the considered joints.