Assembly of Copper Column Interconnect Flip Chip

Abstract

This paper addresses a new flip chip interconnection technology, flexible flip chip connection (F2C2) technology, for attaching silicon chips to a chip carrier using flexible copper wires. F2C2 is a novel approach to create area array flip chip interconnections using a matrix block of wires encapsulated with a heat-resistant, dissolvable substance. A slice from the wire matrix ingot is first attached to the chip using solder. The other end of the slice is then matched and soldered to the footprint of a substrate. Finally, the encapsulating, dissolvable substance is removed from the body of the slice, leaving the chip attached to the carrier by the inter- disposed, flexible copper wires. The compliant copper wire interconnections can accommodate the coefficient of thermal expansion (CTE) mismatch problem between die and substrate, thus eliminating the need for underfill.