热超声倒装键合振动传递与键合强度形成研究

采用多普勒激光振动测量系统，获得了热超声倒装键合过程中工具末端及芯片的振动速度曲线。通过比较分析两条曲线，揭示了热超声倒装键合强度的生成过程：在键合初始阶段，键合界面的相对运动主要发生在芯片金凸点与基板焊盘表面之间，并使其接触表面氧化层和污染层被破坏，裸露出新鲜原子，为金凸点与焊盘间的原子扩散并最终形成键合强度提供条件；随着键合的进行，芯片振动速度开始下降，而工具末端振动速度继续增大（即出现速度分离现象），工具末端和芯片间产生明显相对运动，表明键合强度已产生，芯片金凸点／基板焊盘间的结合力超过工具末端／芯片间的摩擦力；速度分离后芯片与工具末端的振动速度和位移曲线表明了超声振动能量部分耗散在芯片／工具的摩擦上。

Study on Vibration Transformation and Bonding Strength Formation of Thermosonic Flip Chip

With the Doppler laser vibration measurement system,the vibration velocity curves of the flip chip and tool tip were obtained during thermo-sonic flip chip bonding.Comparing and analyzing the two curves,the generation process of bonding force for thermosonic flip chip was understood.At the beginning,the relative movement of the bonding interface mainly occurs between golden bumps of the chip and pads of the substrate,which breaks the oxide and the contamination layer of the interface surface and exposes fresh atom.This is necessary conditions for atom diffuse and bonding strength formation.After a period of time,the vibration velocity of the chip decreases,and velocity of tool increases,which causes "velocity separation".It indicates that the tool tip and chip have relative movement and bonding strength forms on the bumps and pads interface.The displacement and velocity curves after "velocity separation" are the evidence that ultrasonic vibration energy is consumption by friction of tool and chip interface.