Chip on paper technology utilizing anisotropically conductive adhesive for smart label applications

Smart labels are a new generation of low cost transponders consisting of a transponder chip and a flexible type of antenna. Applying a flip chip assembly technology yields a new generation of low cost radio frequency identification (RFID) system that is a paper-thin smart label. Anisotropically conductive adhesive (ACA) is utilized to attach a flip chip onto a paper substrate to form the BiStatix RFID tag. Unlike bar codes, which are passive tags, smart labels can dynamically transmit and receive information to help identify, track and route packages remotely. The concept of flipping or inverting a silicon chip to be mounted on a paper substrate offers distinct advantages and enables achieving the cost and performance goals of this new product technology. Significant process development and reliability assessment was required to develop this smart label application. This paper discusses the process development and reliability assessment that was completed to achieve a low cost flip chip on paper assembly process. The various characteristics of ACA made it an enabling technology for this smart label application. A bare (unbumped) flip chip-without a dielectric layer and conductive polymer bumps-was aligned and placed on the paper substrate with compressive force. A thin layer of anisotropically conductive adhesive was used to attach the IC chip to the conductive ink antenna on the paper substrate. The conductive adhesive underfills and cures in only seconds. Advantages of this environmentally preferred process include the elimination of additional curing processes and reduced equipment requirements as well as the reduction of total IC packaging thickness. (C) 2003 Elsevier Ltd. All rights reserved.