Transient Contact Liquid-Solid Reaction Of Solder Droplet/Pad And Interfacial Microstructure Evolution

Solder bumping is the key step for high-density electronic packaging. Reliability of packaging was directly influenced by the quality of solder bump. Molten solder droplet bumping (MSDB) is adapted to the requirement of high-density packaging and has distinctive advantages. During MSDB, the sufficient heat provided by solder droplet heat substrate, forming interconnection between solder and pad. Through inspection of MSDB process, it can be found that initial temperature of solder droplet is the main influential factors for reliable bump. There exists a lowest temperature, reliable MSDB bump can be achieved only when initial temperature of solder droplet is above this temperature. For example, when MSDB bump was fabricated on Au/Ni/Cu pad with 0.76mm SnPb solder droplet, the molten droplet couldn't connect with the pad successfully when the initial temperature is below 300℃. Based on FEM analyses, it can be confirmed that the instant liquid-solid reaction time of MSDB is about 30ms. Compared with hot air and infrared reflow, liquid-solid reaction time of MSDB is short. The liquid-state reaction time of MSDB is more similar to laser reflow. However, it is a typical heat process in laser reflow while it is a purely temperature reduction process in MSDB. Liquid solder solidified before reaching temperature equilibrium. Based on MSDB, SnPb and SnAgCu solder bump on Au/Ni/Cu pad, SnPb solder bump on Cu pad were fabricated respectively in this thesis. Transient contact liquid-solid reaction between solder droplet and pad during MSDB was analyzed. At the same time, evolution of intermetallic compounds(IMC) at interface of MSDB bump and pad during a second reflow (liquid-solid reaction) as well as aging process (solid-state reaction) was systemically studied.With eutectic SnPb solder and Au/Ni/Cu pad, the influence of initial temperature on the transient contact liquid-state reaction between solder droplet and pad was studied. Morphology and distribution of interfacial Au-Sn compound was different with the increment of initial temperature of solder droplet. It can be seen that preheat pad had distinctive effect. When the pad was preheated, the interfacial reaction between pad and solder droplet was more intensive. Interfacial reaction between solder bump and pad was compared under...