Moldability improvements in thin quad flat packages (TQFPs)

Experience has shown that in thin packages (20×20×1.4 mm), molding defects occur somewhat more frequently with large devices (12.7×12.7 mm), and devices molded in the die-down configuration. For these unique conditions, the mold compound flow front advanced slowly over the top surface of the die and rapidly over the back of the die exposed by the X-flag leadframe design. The most frequent defect observed in evaluations of die-up and die-down molding was exposed silicon after molding, caused by the uneven mold compound flow. To develop a robust molding process window, designed experiments were used to evaluate leadframe downset, mold gate design, molding compound, and molding parameters. Results showed that the leadframe downset was the most significant variable to improve moldability, and a deeper downset produced the best results. The molding process was optimized with two molding compounds, and the manufacturing process window is robust over a large variety of device sizes in both die-up and die-down molding configurations. All 112 lead and 144 lead packages from this line are qualified at JEDEC Level 1 for moisture sensitivity