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Flip Chip Process using Mushroom Bumps and Interlocking Bumps
Keywords: flip chip, mushroom bump, interlocking bump
Flip chip process has been extensively investigated to attach IC chip directly to PCB circuit board, flexible substrate, and glass substrate of LCD panel. Recently, flip chip technology using non-conductive adhesive (NCA) has been proposed to overcome disadvantages of the flip-chip process using anisotropic conducting film (ACF) for fine pitch applications. In flip-chip process using NCA, prevention of NCA entrapment at the bonded chip/pad interface is of great importance to ensure the low contact resistance of the joints. Adoption of mushroom-type bumps instead of planar bumps may be a good solution to prevent the NCA entrapment. Surface smoothness and hardness of the mushroom bump may affect the plastic deformation behavior at the bonded interface and the contact resistance of the joint. In this study, two types of mushroom bumps were fabricated by electrodepositing; one is the Cu mushroom bump with Sn-3.5Ag capping layer and another is the Cu/Sn-Ag mushroom bump composed of the Cu column and the Sn-3.5Ag head. Contact resistances of the Cu and the Cu/Sn-Ag mushroom bumps were characterized with variations of the bonding temperature and the bonding stress. In this work, we also investigated a new flip chip process using interlocking bump structure fabricated by electrodeposition to accomplish improvement of electrical and mechanical properties of the bump joint with minimizing the bump shape change.
Tae-Sung Oh, Professor
Hongik University
Seoul 121-791,

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