An optimization study of underfill dispensing volume

The underfill dispensing volume has been modeled and verified through both experiments and application of statistical technique. The model established is capable of estimating the operating range of the dispensing volume of a defined flip chip assembly and is targeted to reduce wastage as well whilst fulfilling the reliability requirement. The model has taken into consideration the reliability factor, e.g., presence of fillet; manufacturing tolerance of bumps size and standoff variation. In this study, the actual volume for flip chip assemblies prepared in a controlled manner, so that fillets were seen on all sides, was compared with the recommended underfill volume. It was found that the model tended to yield a higher volume and it is concluded that this variation is related to the over estimation of the fillet element in the formulation. For reliability assessment, these flip chip assemblies were examined under C-mode SAM and no voids were found. These flip chip assemblies also passed electrical testing after 500 cycles of air to air thermal cycles and therefore are proven to meet the reliability requirement.