Authors: Vinod Mohan, Paul Morganelli, Ph.D., Bryon Stevens Company: Emerson and Cuming Date Published: 9/24/2006
Abstract: Alternative underfill solutions under development over the past five years (i.e. No-flow and Pre-applied underfills) have been met with limited approval because their use generally requires modifications to existing assembly processes. Whether pre-applied or board-applied, an advancing area in underfill technology is optimizing dispensing methods. Of all the techniques being explored, jet-dispensing of liquid underfills continues to grow as a way to increase capacity in the assembly of handheld electronics. In a capillary underfill process, jet dispensing has in some cases been shown to increase assembly throughput by more than 20 percent . The increased accuracy of jet dispensing makes this a valuable method by which to underfill package-on-package assemblies, and designs with very limited access to the package perimeter. As underfill suppliers develop new materials to meet the requirements of speed, reliability, and reworkabilty, there often is little or no consideration for how well the new materials will dispense via a jet. This paper will show the results of a jet-dispensing study of underfills with a wide range of rheological properties. Underfill flow properties and shear response will be correlated with dispense rate, volume, and accuracy of the jet. Critical process parameters will also be discussed in relation equipment capability.