Flip-chip technology at room temperature: A new design of microtube-based interconnect for improved mechanical and electrical properties

Abstract

Flip-chip assembly of photonic components can be achieved at room temperature by using 10 µm pitch interconnects made of metallised oxide microtubes inserted into ductile reception pads. In order to reduce the electrical resistance of interconnects and the assembly force required, interconnect design in regard to geometry and materials used are optimised through electrical and mechanical finite elements (FEM) simulations. To reduce electrical resistance, one may increase the metallisation thickness or microtube inner diameter. To minimise the assembly force, reducing the reception pad diameter is recommended. Experiments on silicon (Si) test vehicles are conducted to validate these predictions; they indicate that there is no short circuit, with an effectiveness of 100 %. This is achieved first through the assembly of Al-0.5 %wCu metallised oxide microtubes into Al-0.5 %wCu reception pads, using a force less than 10 mN/interconnect and proved to have a resistance of 230 mΩ. Second, with gold (Au) metallised oxide microtubes in indium (In) pads assembled with a force less than 0.7 mN/interconnect. Last interconnects have a resistance of 670 mΩ/interconnect and can still be reduced to 500 mΩ by 2 h annealing at 100 °C.