Polymeric adhesive materials for optoelectronic device & packaging

Abstract

Due to the increasing high demand of optoelectronic components for handling the demand of increasingly networked society, tremendous effort have been made to open the door for noble technologies that meet the economic criterion, technical requirements and high yield manufacturing without sacrificing high performance. To develop such components, polymeric materials are particularly attractive. Because of their structural flexibility, easy processing and fabrication capabilities at low cost with high yields, polymers are being increasingly used for a variety of optical applications in optoelectronic devices. For joining components and materials, the adhesive also replaces the laser welding or soldering methods of optoelectronic packaging and offers the advantages in terms of mass-production at low-cost. Electrically conductive polymeric adhesives again provide an environmentally friendly solution to replace the solder for electrical interconnections of flip chip bonding. It offers several potential advantages over conventional solder interconnection technology including finer pitch printing, more flexibility, lower temperature and simpler processing. However, as a relatively new technology, polymer and adhesive does have some limitations and drawbacks in this application. It is important to understand their limitations and how to use them optimally. Some reliability issues including processing induced lower curing speed, limited thermal and chemical stability, weakened mechanical strength, interfacial delamination, surface contamination and increased contact resistance at higher temperature are several major obstacles currently preventing polymeric adhesive from becoming a vital part of optoelectronic devices and packaging. Therefore, fundamental studies are necessary to develop a better understanding of the mechanisms underlying these problems, and to improve the performance of polymeric adhesives in this application. This study mainly aims at improving the understanding of polymeric thin film as lower cladding of optical waveguide, packaging material of fiber array and anisotropic conductive adhesive film (ACF) as an interconnection of flip chip on flex packages. During the fabrication of polymeric thin film by spin coating, the behavior of material properties should be understood under the conditions of rapid fluid flow and convectively-driven evaporation that occur during the spinning. The effect of spinning process on the cure speed, degradation and failure mechanisms were evaluated that can greatly aid the appropriate selection of adhesive material & process parameters in the fabrication and extend the outdoor longevity of the product. Curing of adhesives was found as one of the primary concerns in the fabrication and package designs, and affects the stability, adhesion, interfacial delamination and electrical & optical properties of polymeric adhesive joints. Therefore, great efforts also have been done mainly to evaluate the curing of UV adhesive during the fabrication of fiber array, curing effect on the adhesion strength, and contact resistance of anisotropic conductive adhesive joints for flip chip technology. Lastly, the effect of other related process parameters during the fabrication or operating life of the devices were also investigated. This includes the plasma cleaning of the flex and silicon substrate, and temperature ramp of adhesive joints to evaluate the adhesion strength and contact resistance. The results generated in this study should provide very useful information in adhesive development for this application.

Date of Award	4 Oct 2004
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Hau Ping Andy CHAN (Supervisor) & Yan Cheong CHAN (Co-supervisor)