Alternative Z-axis connector technologies for high-density 3-D packaging

This paper addresses the result of research on Z-axis interconnects suitable for 3-D processor modules. We discuss the advantages and disadvantages for the intended system. One selected interconnection medium, which is manufactured by Shin-Etsu, is based on metal wires embedded in a matrix of polymeric material. The wires protrude from the surface of the polymer film. By compressing this material between substrates, contact is made between metallized gold pads on the substrates via the embedded wires. The Shin-Etsu connector allows connections among multiple substrates at 0.5-mm pitch without the need for precision connector alignment because it contains redundant wires at very fine pitch. The second interconnection method, which is manufactured by FormFactor, uses a wire bonder to create gold wires with spring-like geometries on an array of metallized pads, fabricated on a test socket or interposer. This paper describes the testing program to determine connector performance and reliability.