| Budget Amount *help |
¥5,200,000 (Direct Cost: ¥5,200,000)
Fiscal Year 2001: ¥1,500,000 (Direct Cost: ¥1,500,000)
Fiscal Year 2000: ¥3,700,000 (Direct Cost: ¥3,700,000)
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| Research Abstract |
To investigate the formation and morphology of fine bump formed by the relatively simple dip method was investigated by the immersion of printed circuit board into molten solder. Among the various factors influencing on the aspect ratio of solder bump, wettability was found to have great influence. To secure the good wettability of environmentally conscious lead-free solders, the control of the electrode potential of solders and base metal was found to be important. In Sn-Ag system lead-free solder, the electrode potential is extremely close to the potential of copper base metal. The surface oxide of lead-free solder could not be removed by contacting with copper. On the other hand, the conventional Sn-Pb eutectic has adequate electrode potential. It becomes anode when contact with copper, this effectively removes the surface oxide of solder giving excellent wettability.
To suppress the intermetallic formation between solder and copper is also important to secure good wettability. The addition of various elements on the intermetallic formation was investigated, however, there was no elements for effective suppression of the formation rate of intermetallic compound.
To enhance to aspect ratio of solder bump, various factors such as immersion direction, lifting speed, solder land spacing and size, solder bath temperature, and solder composition were investigated. The most important point was to immerse the printed circuit board horizontally. For the further enhancement of aspect ratio, the new pressurized process was developed. The process could make solder bump having larger aspect ratio by enhancing the internal pressure of solder to be supplied.
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