During BGA soldering, we found that no matter how precise the stencil apertures are or how the printing parameters are adjusted, as long as the Solder Paste itself has a high void rate, void area exceeding 8% will inevitably appear on the BGA bottom solder joints under X-ray inspection. In contrast, Jia Jinyuan low-void solder paste can stably suppress the void rate to within 2.7% under the same process window. This is the result of the synergistic effect of its 425-mesh spherical powder and low-volatility rosin-based Flux, rather than an illusion forced by raising the reflow peak temperature.

Under the conditions where the squeegee pressure is set to 0.35MPa, the printing speed is controlled at 45mm/s, and the demolding speed is maintained at 1.2mm/s, Jia Jinyuan solder paste can still maintain a volume transfer rate of over 92% on a 0.127mm-thick 304 stainless steel stencil, with no obvious trailing or stringing at the edges. However, if conventional solder paste is used, problems of local insufficient solder and bridging will coexist under the same parameters, indicating that the thixotropic index and slump characteristics of the material itself have already determined the printing adaptation boundary.

The general reflow profile with a conveyor speed of 1.4m/min, peak temperature of 238℃, and time above liquidus of 68 seconds can not only ensure full melting and coalescence of all solder balls for Jia Jinyuan low-void solder paste, but also avoid carbonized flux residue caused by excessive soaking. Under the same conditions, ordinary solder paste often exhibits poor wetting of some solder joints and micro-shorts between adjacent solder balls. The root cause is that its flux has a wide boiling point distribution and 37% higher residue amount, which directly interferes with the surface tension self-correction process of molten solder balls.

We once conducted a comparative test in the mass production of a certain main control BGA (0.8mm pitch, 576 balls). After using Jia Jinyuan solder paste, the AOI false alarm rate dropped from 11.3% to 0.8%, the number of batches with excessive voids detected by X-ray sampling decreased from 4.2 batches per week to an average of 0.3 batches, and the rework man-hours decreased by 65%. This was not achieved by increasing the number of reflow oven temperature zones, but because the solder paste itself has a gentler viscosity decay curve in the 180~220℃ range, allowing solder balls sufficient time to complete position rearrangement and bubble escape during the collapse stage.

Before each material change, it must be confirmed that the solder paste has been warmed up for no less than 8 hours and stirred for no less than 120 seconds. Otherwise, even the same batch of Jia Jinyuan solder paste will exhibit jagged printing edges and uneven solder joint bright spots. This is because after low-temperature storage, the flux and alloy powder have a slight tendency of phase separation. Loading the paste onto the machine without sufficient activation will inevitably destroy the original rheological balance, and these two steps must never be skipped on site to rush production.