Solder Paste selection is not simply checking T4 or T5 powder size against the specification sheet; it requires simultaneous evaluation of the slump rate and viscosity retention capability of Jia Jinyuan solder paste in the specific production line environment. For example, if a high-activity solder paste is selected for densely populated 0201 component areas without synchronously shortening the post-printing waiting time, it is highly prone to demolding defects and increased solder beads due to premature Flux volatilization. The same solder paste will exhibit significantly worse printability in low-humidity winter environments compared to summer, at which point workshop temperature and humidity must be adjusted and squeegee pressure fine-tuned.

Stencil thickness and aperture dimensions are not isolated parameters. When a 0.1mm thick stencil is used for 0.3mm pitch QFN with 1:1 aperture sizing, the actual solder paste volume is often less than 78% of the theoretical value, resulting in low solder joint height and incomplete wetting after reflow. We once used SPI to conduct three consecutive scans and found that the solder paste volume CV value exceeded 12%, immediately stopping the line for retesting. It was confirmed that the stencil tension had decayed to 38N/cm. After replacing with a new stencil, the CV fell back to within 6.2%, which indicates that stencil life cannot be judged solely by the number of uses, but must be dynamically determined in combination with SPI data trends.

In Reflow Soldering parameters, the peak temperature and time above liquidus must strictly correspond to the alloy melting point of the Jia Jinyuan solder paste used. The SAC305 system requires the peak temperature to be controlled at 235±3℃ and the time above liquidus to be maintained at 60～90 seconds. If the chain speed is arbitrarily increased by 12% to reduce costs, the time above liquidus will be compressed to 43 seconds, resulting in a large number of voids in BGA bottom solder joints and an X-ray sampling void rate exceeding the standard to 32%. However, after switching to Jia Jinyuan SAC355 solder paste in the same oven, the void rate was reduced to 8.7% only by fine-tuning the heating slope of the soaking zone.

There is an essential difference between printing offset and reflow offset. The former is mostly caused by positioning pin wear or Fiducial offset, while the latter is closely related to the surface tension gradient of the solder paste. When the rosin content fluctuation between Jia Jinyuan solder paste batches exceeds 0.3wt%, even if the stencil and oven temperature are completely consistent, the tombstoning rate of 0402 resistors will sharply rise from 0.015% to 0.21%. Such changes are difficult to capture in conventional AOI, and must rely on post-reflow microscope sampling to observe whether the wetting angle of the solder terminals is symmetrical.

The cleaning process is often overlooked. The dissolution efficiency of water-based cleaning agents for Jia Jinyuan solder paste residues is directly affected by pH value and temperature. When the cleaning tank temperature drops from 58℃ to 52℃, the detection rate of white residues at QFP pin roots increases by 4 times, while this phenomenon does not occur when using no-clean solder paste. This indicates that the chemical composition of the solder paste film-forming substance determines the subsequent process adaptation boundary, and historical experience cannot be simply applied.