Development of Anisotropic Conductive Film Using Pb-free Solder and Its Application to the Micro-joining of IC-chip

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The purpose of this study was to develop a quite new and unique anisotropic conductive film using Pb free solder which is necessary for a new micro-joining technology This anisotropic conductive film could be applicable to the IC chip with the electrode pitch less than 20〜30 micron. Besides, there is no restriction of the shape and arrangement of electrodes. Except for the development of anisotropic conductive film, fundamental information necessary for the design and development of Pb free solder was also obtained experimentally and theoretically.As the results, the technology for making the insulation film (polyimide film) which has fine and line up holes with a diameter of 10 micron was established by utilizing photolithography technique. In addition, it was demonstrated that the combination of this technique and the electroplating technique could make the process easy to fill solder particles up into fine holes on the insulation film. The optimum conditions for the electro-deposition (current density and time) of Sn-Pb and Pb free solders were determined in this study. By using the anisotropic conductive film developed in this study, the joining of electrodes on flexible printed board was tried by utilizing the bonding machine for practical IC chip micro-joining. It was confirmed that the good joining could be attained, and the possibility for the practical use of developed anisotropic conductive film. Moreover, a different type anisotropic conduction film contains solder particles dispersed in thermosetting resin was proposed, and the usefulness of it was shown by the practical bonding of the electrode on flexible printed board. Also in this study, the accumulation of information on melting temperature, strength, conductivity, wettability and phase stability of Sn alloys at extremely low temperature were carried out experimentally for the further design of new Pb-free solder alloys necessary for the new anisotropic conductive film.