Accelerated characterization of bonding wire materials

Trends in the microelectronics industry are driving the development of novel materials for microelectronic wire bonding. The wire bonding industry is looking towards extending the use of Cu as a new wire material to replace Au. The development of Cu wires that overcome oxidation issues can be too time consuming. One reason for this is that the effects of shielding gas on the electrical flame off (EFO) process and the free air ball (FAB) formation are not fully understood. In this study an online method for characterizing FABs using in-situ thermosonic wire bonding is used to study the effects of shielding gas flow rate. The FAB heights before deformation (HFAB) and after deformation (Hdef) are measured using online z-position measurements for various wires. Effects such as large variation in HFAB at a single flow rate, abrupt changes in HFAB with increasing flow rate, or discrepancies between the trends in HFAB and Hdef indicate undesirable EFO processes. Using this online method the EFO process and the performance of novel wires can be determined quickly and efficiently. Ninety FABs can be characterized in 2 minutes for a specific set of EFO parameters. A complete characterization of a novel Cu wire with respect to FAB consistency can be done in less than 4 hours which includes determining process windows for different shielding gas flow rates. Traditional sample preparation, optical microscopy and manual measurement methods can take many days to obtain the same results.