High-toughness (111) nano-twinned copper lines for fan-out wafer-level packaging

Abstract

In the present paper, the nt-Cu were electroplated on the InFO test vehicles with 5 μm line width to compare the reliability with the normal electroplated copper. The temperature of the TCT ranges from -55 to 125°C. The microstructure of the copper traces after 200 cycles and 1000 cycles was shown in the results. The nt-Cu RDL is much stronger than the normal Cu in the thermal cycling test. In order to understand the mechanical property of the nt-Cu and the normal Cu, tensile tests of electroplated copper foils was employed. After annealing at 250°C for 3 hours, the toughness of nt-Cu (about 60MJ/m3) is much higher than normal copper (about 30MJ/m3). In addition, the simulation results shows that the maximum stress on the copper trace during the TCT is about 200MPa which is much lower than the yield point of nt-Cu. In other word, the nt-Cu would return to original size when the stress removed without strain accumulation. In summary, we observed that the nt-Cu performs much better than normal copper in TCT. From the tensile test and simulation, we can understand the mechanical behavior and the typical reason for the high reliability of nt-Cu.