Ultra low loop conversion from gold to copper wire

It has been a trend to convert gold wire to copper wire in manufacturing of semiconductor chip due to cost effectiveness. Another motivation for the conversion comes from the physical properties of copper wire. Copper wire offers the advantages of presenting higher mechanical strength, lower electrical resistance and slower intermetallic growth. Aside from the differences in term of chemical stability, copper is a stiffer material as compared to gold. It has been determined that copper wire requires new process optimization in comparison to gold wire. Parameter adjustments for ball bond formation, stitch bond formation, and looping profile are needed during conversion from gold to copper. It is challenging to convert a loop profile from gold to copper wire, especially for the case of ultra low loops with a loop height of 3 mils and lower. Wire humping is the main challenge to be faced on copper wire. Loop profile configurations are determined physically by die thickness, wire length, and other package requirements. Total conversion of loop shape and loop height from gold wire to copper wire involves complex processes. It may not be realistic, nor functionally required, to replicate the exact loop shape in actual implementation. However, the aim is to retain the same loop height while not significantly changing the loop shape. Copper wire also seems to have a higher tolerance than gold in terms of neck damage. This allows users to have a wider setting of parameters related to the wire neck. In term of process application, ultra low loop copper wire is comparable to gold wire after optimization.