热超声倒装键合工具和芯片振动的频率特征

采用激光多普勒振动测量系统,监测了热超声倒装键合过程工具末端和芯片的振动速度。由工具和芯片的振动速度有效值曲线,发现了“速度分离”现象,即键合启动数毫秒后,芯片的振动速度突然下降而工具的振动速度继续增大;“速度分离”表明金凸点／焊盘界面已初步形成键合强度。研究了工具和芯片振动速度信号的频率特征,发现芯片振动信号的3倍频成分的产生时刻就是“速度分离”发生的时刻,小键合力有利于“速度分离”发生,也就是有利于初始键合强度的形成,提出了以3倍频产生时刻为临界点的变键合力加载思路。

Vibration frequency characters of chip and bonding on thermosonic flip chip bonding

The vibration velocity of tool tip and chip on thermosonic flip chip (TSFC) bonding was monitored with a laser Doppler vibrometer, and the "stall" phenomena was observed from the virtual value curve of vibration velocity, i.e., after the TSFC bonding started a fever milliseconds, the chip velocity decreases suddenly, while the tool tip velocity still increases.Stall indicated that the bump pad interface has formed initial bonding strength.And the frequency characters of the vibration velocity signals were also obtained.It is found that the 3rd harmonics of chip vibration velocity signal indicates the stall phenomena, i.e., when the 3rd harmonics appeared, the stall happens.Experiment results show that little bonding force is good for produce stall.