| Use of flip chip electronic packages is increasing because they offer better electrical performance than standard wire bonded packages. Currently, their use is limited mainly to expensive products such as microprocessors because of their high cost. One reason for the high cost is the die-level application of underfill adhesive.; A process for screen printing underfill directly onto a wafer before dicing was investigated. After a preliminary study of nine potential underfill materials, one was selected for detailed investigation of the printing process. Process parameters studied included screen thickness, snap-off height, and squeegee speed. The response parameters were film thickness and average surface roughness. The film thickness was found to be directly proportional to the screen thickness. It was also observed that the underfill materials tended to shear from the screen rather than flow from the screen as suggested by earlier theoretical studies. |
