Integration of capillary self-alignment for face to face micro bump bonding

This paper reports a face to face microbump bonding process using capillary self-alignment. The process uses water as a self-alignment medium. A SAM (self-assembled monolayers) coating was performed on the surface of the chip to create a hydophobic/hydrophilic area. A thin (150nm) Cu ring is formed on the surface of the chip, which can confine the alignment medium during the chip positioning process. Test chips have been flip-chip bonded with the self-alignment. The alignment and bonding result have been demonstrated via the resistance measurement of daisy chain 20 and 40μm pitch. 100% yield on 40μm pitch and almost full connectivity on 20 μm pitch chains have been obtained.