Applying Taguchi Method to Optimize Vacuum Printing Encapsulation Process

Under the prosperity of the global electronics industry, the current market requires consumer products, such as smartphones, notebook computers, tablet computers, and other portable electronic products, to become lighter, thinner, shorter, and smaller. The miniaturized design of the system-in-package (SiP) technology integrates multiple different chips, such as an array package [ball grid array/chip-scale package (BGA/CSP)] or a peripheral package [quad flat package/thin small outline package (QFP/TSOP)], as well as passive components, such as resistors and capacitors, into a single package module. The vacuum printing encapsulation system (VPES) features cost-efficiency and flexibility advantages, compared with traditional transfer molding and compression molding, and thus improves product reliability. However, as VPES is an emerging process, the impact of relevant VPES parameters has not yet been determined. Moreover, it has been discovered that there are still air bubbles in the cured epoxy molding compound (EMC). In this study, the Taguchi experimental design is applied to propose the optimal process parameter combination, including the squeegee moving speed: 20 mm/s, the printing delay time: 20 s, the number of squeegee printings: three, and the inner chamber vacuum: 3 kPa. The results of variance analysis show that the contributions of the number of squeegee printings and the inner chamber vacuum to the air bubble rate of the EMC adhesive material are 76.38% and 17.75%, respectively, which indicates that they have a significant impact. The results of confirmation testing show that the above optimal VPES process parameters can minimize the air bubble rate occurring in the EMC adhesive material and avoid the risks of short circuits in the tin bridge during the reflow process of the SiP module.