Self-assembly of microchips on substrates

We demonstrated a technique for self-assembly using a plurality of silicon microchips onto a silicon substrate and performing further self-alignment at a high temperature to form permanently electrical connection by the eutectic solder bumps. Self-assembly is presented by controlling the hydrophobic-hydrophilic surface property of patterned microchips and substrate, and then self-alignment is accomplished using solder-based surface tension for flip chip assembly. The substrate is patterned and printed with flux and solder paste on the binding sites during assembly process, while the uncoated areas are transferred into hydrophilicity by using ion plasma cleaning. On the microchips, self-assembled monolayers (SAMs) Ere developed onto the patterned gold surface of the chips using 0.1M alkanethiol precursor molecules. On the other hand, the substrate is dipped with hydrophobic 2-ethyl-1-hexanol liquids on the binding sites. As soon as the hydrophobic pattern on a chip comes into contact with a substrate-binding site, the patterned gold surfaces are selectively wet and adhered to the hydrophobic adhesives of the substrate. These components are self-assembled in water by minimization of the surface energy that provides the driving force for the assembly. Next, at a temperature above its, melting point of 183(0)C, the solder melts; self aligns, and connects electronically between self-assembled microchips and the substrate. This self-alignment process is compatible with the surface mount technique (SMT). Also, use of different bonding sizes and shapes help enhancing the self-assembly performance. Hundreds of silicon microchips with a size of 500 X 500 X 75um have been successfully assembled on substrates with essentially 100% yield. The presented technique could be applied to assembly of light emitting diodes, RFID tags, micro-integrated circuit devices, or other types of microstructures.