Thermosonic bonding: an alternative to area-array solder connections

Thermosonic bondings for flip-chip, TAB, or surface mount technologies are potential alternatives to solder connections. They are dry processes having low-cost, simplicity, and fine-pitch advantages. The applications of these new connection technologies are expected to grow if their two major problems, assembly yield and reliability, are solved. The assembly problem is studied in this paper. It is well known that the use of ultrasonic energy can significantly simplify metal bonding processes. However, the changes of thermosonic process windows for area-array connections are not controllable; the progress of this technology development is not encouraging. Using flip-chip bonding cases with 30- and 1000-I/O chips, this work studies the effects on yields from tool configurations and masses. The yield is closely related to the ultrasonic amplitude of metal bumps. The amplitude associated with a good bonding process for a 30-I/O chip is about 1.30 μm. However, it could be reduced to 0.26 μm when the die collet is enlarged for a 1000-I/O chip. Fortunately, such a reduction can be overcome by a design that changes the mass of the collet and the length of the shank. This paper will address the understanding and the control of these effects with experimental and modeling studies