BGA balling often encounters defects such as under-soldering, misalignment of
solder balls, missing solder balls and insufficient solder volume, which are usually caused by insufficient fixing force or insufficient self-centering force to the ball during reflow. Insufficient holding force can be caused by low viscosity, high barrier thickness or high outgassing speed; while insufficient self-setting force is generally caused by weak solder flux activity or too low solder volume.
BGA balling can be achieved by using solder paste alone or using solder balls with solder paste and solder balls with solder flux; the correct way to do it is to use an integral preform with solder flux or solder paste. The most common method appears to be to use solder balls with solder paste, and the balling process using tin 62 or tin 63 ball soldering produces excellent results.
In the case of tin 62 or tin 63 ball soldering with solder flux, the defect rate increases with solder flux viscosity, solvent volatility and pitch size decrease, as well as solder flux deposition thickness, solder flux activity and solder The dot diameter increases with the increase of the point diameter, and no leakage of solder balls is observed in the ball bonding system using solder paste for high temperature melting.
And its alignment accuracy increases with the thickness and solvent volatility of the solder paste, the activity of the solder flux, the size and solderability of the solder joint, and the increase in metal loading. When using tin 63 solder paste, the viscosity of the solder paste, Spacing and reflow cross section have little effect on spheroidization at high melting temperatures.
Easy-to-release solder paste is critical to individual solder paste balling where conventional printing and release processes are required. The overall preformed spheroidization process is also very promising. Reducing the thickness and width of the solder links is also important to improve the success rate of ball formation.
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