Robust loop parameters for ball neck strength enhancement [package wire bonding]

A fractional factorial designed experiment was carried out to study the wire neck strength of gold ball bonding for the QFP160L package. Five wire loop parameters, reverse length (RL), reverse height (RH), loop height (LH), ball security height (BSH) and loop factor A (A), were evaluated. The wire neck strength of the gold ball was measured by the wire pull test. In addition, temperature cycling was used as a means to study the reliability of wire neck formation. Analysis of the results shows the following conclusions: (1) RL should be set at a low level to prevent violent bending on the wire neck area; (2) high settings of A and RH can provide stronger wire neck strength; (3) BSH should be set lower than RH; (4) LH did not have much effect on the wire neck strength. The fractional factorial design proved to be extremely useful in optimization of the wire bonding operation and made future fire-fighting for line issues easier