||Thermosonic copper wire bonding process technology is one of the main IC packing process technologies. During this process, there is heat generation produced by friction resulted from relative sliding between the contact surface of copper ball and pad and the interface temperature is increased. This will affect the formation of intermetallic compound and bonding strength. Therefore, in the study of copper wire bonding process, temperature effect is an important factor on wire bonding strength. However, most of the existed research articles for studying these issues by using numerical simulation method usually considered the frictional resistance only and ignored the effect of heat generation caused by friction.|
In this study, the finite element method is used and a three-dimensional simulation model is established for studying thermosonic copper wire bonding process and not only the frictional resistance effects but only the frictional thermal effects are considered. This study makes discussion and analysis on three parts. The first part discusses the effects of frictional heat generation on contact surface stress field, strain field and temperature field of copper wire bonding surface. The second part discusses the effects of variation of ultrasonic frequency and amplitude on stress field, strain field and temperature field of copper ball and aluminum pad during the process operating time. The third part analyzes the effect of variation of ultrasonic frequency and amplitude on thickness of intermetallic compounds due to intermetallic compound thickness generation formulation.
The simulated results indicated that the maxima effective plastic strain of aluminum pad with considering frictional heat generation is 7.003 % lower than the values for which not considering frictional heat generation, the maxima temperature rises 20.47 %, and the maxima effective stress drops 41.53 %. The variation of ultrasonic frequency and amplitude on the temperature field is unobvious while the simulation time is 22 μs. But if the simulation time reaches 955 μs , the temperature will be raised 25.74 % to 34.45 %. Also, when simulation time is 22 μs, ultrasonic amplitude is 1 μm and the frequency varies from 60 kHz to 240 kHz, the thickness of intermetallic increases 37.58 %. If the frequency is 120 kHz and the amplitude varies from 0.5 μm to 1.5 μm, the intermetallic thickness increases 26.98 %.