Solder Mobility for High-Yield Self-Aligned Flip-Chip Assembly

Self-aligned flip-chip assembly with sub-micron accuracy is of particular importance to low-cost manufacturing of single-mode opto-electronic components. The concept of alignment via surface tension force of melted solder has been proposed over two decades ago and appears simple. Yet, its effective working into manufacturing requires solving a few fundamental issues. In prior work, we introduced the concept of solder reservoirs which provide a solder volume self-balancing mechanism to notably enhance self-alignment yield. In this paper, we show that the effectiveness of reservoirs is impeded when the solder wetting of pads or the solder mobility between pads and reservoirs is limited. We therefore studied a wide variety of metal stacks and identified candidates for substantial wetting and solder mobility improvement. We ranked the metal stacks for solder mobility using traditional wetting angles as well as speed of wetting along narrow tracks. First test parts, manufactured with the improved metal stacks, show the expected benefit in increased yield for chip alignment.

[1]  Tymon Barwicz,et al.  Toward High-Yield 3D Self-Alignment of Flip-Chip Assemblies via Solder Surface Tension , 2016, 2016 IEEE 66th Electronic Components and Technology Conference (ECTC).

[2]  Tymon Barwicz,et al.  Flip chip assembly with sub-micron 3D re-alignment via solder surface tension , 2015, 2015 IEEE 65th Electronic Components and Technology Conference (ECTC).

[3]  P. J. Nasiatka,et al.  Determination of optimal solder volume for precision self-alignment of BGA using flip-chip bonding , 1995, Proceedings 1995 IEEE Hong Kong Electron Devices Meeting.

[4]  J. Raymond,et al.  Fluxless Chip Join Process Using Formic Acid Atmosphere in a Continuous Mass Reflow Furnace , 2016, 2016 IEEE 66th Electronic Components and Technology Conference (ECTC).

[5]  H. Reichl,et al.  Precise flip chip assembly using electroplated AuSn20 and SnAg3.5 solder , 2006, 56th Electronic Components and Technology Conference 2006.

[6]  P. Buchmann,et al.  A high-density, four-channel, OEIC transceiver module utilizing planar-processed optical waveguides and flip-chip, solder-bump technology , 1994 .

[7]  Tymon Barwicz,et al.  Demonstration of self-aligned flip-chip photonic assembly with 1.1dB loss and > 120nm bandwidth , 2016 .

[8]  Y.C. Lee,et al.  Soldering technology for optoelectronic packaging , 1996, 1996 Proceedings 46th Electronic Components and Technology Conference.