| Liquid-crystal-on-silicon(LCOS) spatial light modulator(SLM) is a critical component for optical information display and processing. One of the enabling technologies for the applications of LCOS SLMs is the manufacturable assembly process. The challenge for the assembly lies in that the gap between the VLSI and the cover glass must be controlled in a {dollar}mu{dollar}m level with sub-{dollar}mu{dollar}m uniformity.; This thesis work has developed a new assembly approach using a self-pulling soldering technology. During reflow, the molten solder provides a compliant, self-adjusting surface tension force that pulls down the cover glass against the VLSI chip with a gap defined by the pre-fabricated spacers. The developed assembly technology has very good manufacturability because (1) the solder technology is compatible with existing surface mount manufacturing systems, (2) the self-pulling assembly process eliminates manual operations, and (3) the fabrication and assembly can be batch processed. In order to develop the technology, we have conducted three in-depth studies: solder joint design, fluxless soldering, and process development for the fabrication and assembly.; The first study was for the solder joint design for precision assemblies. A public domain software, "Surface Evolver", has been modified as a numerical modeling tool. In addition, the numerical results have been non-dimensionalized and represented by a polynomial regression model, which established a relationship between the surface tension forces and the solder joint design parameters such as solder volume, pad size, joint height, misalignment level, and surface tension coefficient. The numerical and the regression models can design solder joints for different precision self-alignments. In particular, they have been used to define an optimum solder volume for the LCOS SLM assembly.; The second study of the thesis was for fluxless, contamination-free soldering using (1) FR-4 assisted forming gas, and (2) formic acid vapor. The reflow temperature for the forming gas soldering was around 350{dollar}spcirc{dollar}C, and that could be reduced to 230{dollar}spcirc{dollar}C by the organic outgases from FR-4. The fluxless soldering process using formic acid vapor has proven to be most efficient. At 220{dollar}spcirc{dollar}C, its measured self-alignment characteristics were as good as those using liquid flux. The 2-{dollar}mu{dollar}m alignment accuracy was achieved within 10 seconds. The most critical parameters for formic acid vapor soldering was the acid vapor concentration in the reflow chamber. The effective concentration window was above 0.7%. The concentration was affected acid by the acid temperature, the combination ratio of the nitrogen gas channel and the formic acid gas channel flow rates.; The third study of the thesis was to develop the fabrication and assembly procedure for a 128 x 128 LCOS SLM. Several critical technologies developed include glass machining, polyimide spacers, silicone die attachment. The assembly technology achieved excellent gap thickness and uniformity. A functional 128 x 128 LCOS spatial light modulator has been fabricated, assembled, and tested.; The technologies and research results of this thesis work will impact the advancements of LCOS SLM as well as other optoelectronic and microelectronic modules. |
