Wire sweep characterization of multi-tier copper wire bonding on thermally-enhanced plastic ball grid array packages

Copper (Cu) wire bonding is the most viable alternative interconnection technology to gold (Au) wire bonding when cost is considered. Recent developments in bonding technology and capability has resulted in copper wire bonding being targeted at high pin count and high performance applications such as ball grid array packages. Wire sweep performance is extremely important in high I/O products as slight increase in wire sweep may result in wire shorting and eventually losing the functionality of the devices. The gap is especially apparent in multi-tier high pin count ultra fine pitch (40μm) copper wire bonding packages. In this study, wire sweep characterization was performed using two types of 4N 18μm copper wires from two different suppliers. Existing 18μm Au wire from production was used as control. The test vehicle used in this study was a high pin count thermally enhanced plastic ball grid array (TEPBGA) 31mm×31mm package with 689 ball counts. The wire sweep performance of the different Cu wire types at various wire locations using the current production molding compound were also investigated. Wire sweep results showed that Cu wire type A had significant lower wire sweep (approximately 0.5%) compared to current Au wire. However, Cu wire type B showed comparable wire sweep performance as current production Au wire. In summary, wire sweeping resistance of copper wires are strongly dependent on the fabrication processes and heat treatments of the respective wire suppliers. Moreover, it was found that wire sweep percentage was very much influenced by wire locations during transfer molding process.