Low cost flip chip bumping

Abstract

Flip chip (FC) technology is a driving force for increased speed and performance along with higher I/O count, and has therefore a high level of importance for a variety of applications. A breakthrough, however, will be the use of flip chip due to cost reduction. To achieve this aim, it is essential to use low cost bumping techniques. However, to provide FC technologies for devices with high I/O count and high pin density applications like microcontrollers, RAMBUS devices, etc., it is necessary to redistribute the historically peripheral bond pads with ultra fine pad pitch into a wafer level CSP. This paper describes a low cost electroless Ni/Au under bump metallization (UBM), a wafer level redistribution process based on electroless copper circuitization and different methods of single and multiple solder ball placement.