Multi Row QFN Wire Gap Clearance Improvement Using Improved Mold Compound

The Multi row quad flat no lead (MRQFN) package is known to be a low-cost package that offers high pin count similar to the ball grid array (BGA) package [1]. Augmented with exposed pad, it can offer both improved thermal dissipation and electrical grounding effect, rendering it suitable for compact design in high-power and high-frequency applications including both automotive and non-automotive products. In many occasions, due to intricate wire layout, multi-tiered wire bond looping and long wire span are required. Hence, the primary challenge is to optimize wire gap clearance to prevent wire short after molding, and any latent reliability failure such as leakage due to inadequate wire gap. To achieve optimal wire gap, the crucial factors to be considered are like wire configuration, wire location, bond pad pitch, mold gate design and mold flow direction. In addition, epoxy molding compound (EMC) properties particularly mold spiral flow is also equally important, which will affect the mold flow during transfer molding. In this paper, the importance of longer spiral flow in EMC was studied in detailed, underscoring its role and characterizing its viscosity behavior. In summary, through a series of wire gap improvements by wire loop profile and molding process optimization, a remarkable improvement in term of wire gap clearance and wire sweep performance were achieved, particularly for wires at die corners. Wire gap post molding of more than 2x wire diameter was accomplished while wire sweep was reduced to less than 10%. The final solution also passed electrical test after temperature cycle (TC) and biased high accelerated stress test (HAST) that proved the effectiveness of the solution