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Zhaowei Zhong: School of Mechanical and Production Engineering, Nanyang Technological University, Singapore
ACKNOWLEDGMENT: The author would like to thank the Electronics Packaging Group of Gintic Institute of Manufacturing Technology for the cooperation he received.
Introduction
Flip chip technology is not new. It has been used for over 30 years since the C4 (controlled collapse chip connection) process was invented. However, three or four years ago, only a few companies in Singapore were doing research and development (R&D) on flip chip technology and tried to implement the technology to their daily manufacturing activities. Recently, a number of companies, both large multinational corporations (MNCs) and local small-medium-sized enterprises (SMEs) in Singapore, are preparing to implement flip chip technology in their products. This number will definitely increase in the near future. In other words, flip chip applications are expected to increase significantly in the next few years. One of the reasons is the increasing demands for miniaturization, high electrical performance, high I/O pin count, etc. Another reason is the increased availability of the lower-cost bonding and encapsulation materials, bumped bare dies, substrate, and equipment. Also, besides the C4 process, other processes have been developed (Lau, 1995; Zhong et al., 1997; Boustedt and Vardaman, 1997; Lyn et al., 1997; Kloeser et al., 1997; Johnson et al., 1997; Neiro et al., 1997; Beddingfield, 1997; Jimarez et al., 1997; Schiebel, 1997; Riley, 1997; Savolainen, 1998).
Flip chip on board (FCOB) assembly is a process for attaching bare die directly on printed circuit board (PCB). It requires minimum board space, has the lowest form factor and the direct interconnection between die and board improves electrical performance. With the push towards miniaturisation in electronic products, FCOB is an emerging technology in PCB assembly.
In FCOB assembly, anisotropic conductive adhesives (ACAs) and solder alloys can be used for die attachment. Gold bumps attachment with ACF (anisotropic conductive film) or ACP (anisotropic conductive paste), and eutectic solder bumps attachment with underfill are promising low cost flip chip mounting processes.
Flip chip assemblies on FR-4 and ceramics using ACF, ACP, or eutectic solder with underfill are discussed in this paper. Several types of ACF and ACP with different types of conductive particles and adhesives were investigated. Design of experiments (DOE) using the Taguchi techniques was carried...