Predicting the process induced warpage of electronic packages using the P-V-T-C equation and the Taguchi method

A critical issue in the manufacturing of electronic packages is the warpage induced during the molding process as a result of differences in the shrinkage of the constituent materials. Package warpage causes serious problems such as the quality degradation of devices and yield loss in manufacturing processes. Loss of lead coplanarity happens due to package warpage and causes difficulty in device testing and surface mount assembly. Internal stresses associated with package warpage can also cause device failures such as die cracking, broken circuits and package cracking. Warpage in IC package has drawn intensive attention in the past. Although the effects of thermal shrinkage were extensively investigated in the literatures, the influence of the cure shrinkage on package warpage had received less attention. Accordingly, this study develops a numerical approach for generating more accurate predictions of the package warpage by taking the effects of both thermal shrinkage and cure shrinkage into account. A three-dimensional finite element model of the small outline package (TSOP) DBS-27P is constructed and the proposed numerical approach, which is based on the P-V-T-C (pressure-volume-temperature-conversion) equation and the CTEs (coefficients of thermal expansion) of the package materials, is employed to predict the warpage at each of its corners under various packaging processing conditions. Using the Taguchi method, the relative influences of the transfer pressure, the packing pressure, the mold temperature and the curing time on the degree of package warpage are identified and the optimal processing conditions are established. A series of experimental packaging trials are performed using the optimal processing conditions. It is found that the warpage of the actual package is in good agreement with that predicted numerically. Therefore, the accuracy of the proposed numerical approach is confirmed. Moreover, the results also demonstrate the capability of the Taguchi method to identify the optimal packaging processing parameters on the basis of a limited number of simulation runs.