Head-in-pillow (H-l-P) is one of the common defects encountered during soldering of BGA components, wherein the flux plays a critical role to clean the surface oxide of solder powder and solder balls throughout the processing window. The main root causes for HIP can be categorized into material issue and process issue. The mostly defect is that non-wetting between ball and solder paste due to the warpage of BGA component and poor solder paste properties. Therefore, reflow steps like preheat, soaking zone and temperature above melting point also play an important role in process issue. This research represents a solder paste flux re-design which enables a more robust wettability of all elements in the solder joint and eliminate the poor-wetting soldering defects. Aiming to eradicate the H-l-P manufacturing defects, the new flux design focuses on the improvement of basic flux characteristics in terms of activity, fluidity, and thermal resistance. The results have shown that the redesigned solder paste has indeed many beneficial effects on the HIP issue. High activity formula imparts better surface oxide cleaning capability and results in excellent solderability. In addition, the anti-oxidation property of solder paste and solder balls is enhanced via improving the flux fluidity and thermal resistance.
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