Transfer Molding Wire Sweep Improvement in QFP Packages by Mold Plunger Tips Design

Transfer molding is a plastic encapsulation conventional method for electronic components, which can be seen such as in semiconductors, where the cavity is filled with melted resin by using a plunger. The multi plunger system was developed and used in more than a decade to supply resin from multiple holes when injecting resin into the cavity can greatly shorten the resin molding cycle and increase productivity. However, in QFP (Quad Flat Packages), wire sweep still the main challenge facing especially for the side gate transfer molding. After the plunger injected the EMC (Epoxy molding compound) into units on leadframe, there was flashes remain inside pot and plunger. These excess flashes remained was sticky and stubborn, which difficult to remove by mold vacuum cleaning system. If these flashes keep remain, it will potentially block the mold gate and disturb the mold flow into cavity resulting in wire sweep. Simulation been done to compare the mold flow behavior, while the change of the plunger tips design from flat type to chamfer type had been studied in order to minimize these excess flashes remain at the end of transfer filling process and improve the wire sweep. Evaluation also been performed to confirm the workability and effectiveness on the chamfer plunger type design towards the wire sweep improvement. Wire looping optimization for critical wires also been performed to continue improve wire sweep in QFP side gate molding from above 11 percent to within 5 percent.