Flow Modeling of Wire Sweep in Transfer Molding

Transfer molding is one of the most widely used process for encapsulating integrated circuits. Wire sweep is becoming a critical process defect in the era of miniaturization of electronic products. This is because wire sweep can cause electrical short as integrated circuit lead count increases which leads to reducing wire pitches. Common practices in predicting wire sweeps in encapsulation calculate first the flow in the cavity without wires. The drag force on the wires is then calculated based on the local velocity using the flow drag relationship of flow in an infinite medium. Recent experimental result has shown that wire density had a strong influence on wire sweep. This paper describes both an empirical prediction and a stokes flow analysis of flow wire interaction on wire sweep. The analysis determined the flow induced loads on the wires for different wire shapes, spacing, and locations from the wall.