Flux-free process for placement and attach of solder balls to wafers, flip chips and all BGA packages

The current method used by industry for solder ball placement and attachment on wafers and BGA packages produces unacceptable production yields, as the existing process requires the use of flux. When flux liquefies during reflow soldering, the bonds between the flux, balls and pads are destroyed and the balls are free to move. Defects such as vacancies, adjacent ball bridging, loss of positional accuracy and voids are created. Also, flux residues are not always completely removed during post-solder cleaning processes due to these voids, and high resistance shorts and/or corrosion may result. Demand for flip chip technology and BGA devices has steadily increased and more efficient high volume manufacturing assembly methods must be developed to keep pace. Ball attachment production yields also must be improved so that manufacturing costs can be reduced. In response, SST has developed a new and more cost-effective method of solder ball placement and attachment to wafers and to plastic and ceramic packages for BGA applications. The new method virtually eliminates the problems associated with the current methods. The SST process uses specially designed tooling for loading and precise holding of solder balls in the required position during processing. The soldering operation is performed without flux in a controlled atmosphere. As a result, pre-solder paste screening and post-solder cleaning operations are not required. The SST ball attachment process for wafers is performed at the wafer level prior to singulation, thereby maximizing production capability. The ball attachment process for BGA packages is also very efficient.