The activity requirements of Solder Paste for sensor soldering are far higher than those for conventional consumer electronics. Because MEMS chip pads have thin plating, small surface area, and low heat capacity, even a slight oxide film on the pad surface can easily cause poor wetting, trailing, and excessive solder joint void rate with ordinary medium-to-low activity solder paste. JJY high-activity solder paste optimizes the ratio of the organic acid system to the halogen activator, continuously decomposing copper oxide and nickel oxide above 150°C. Combined with a lower thixotropic index and narrower particle size distribution (D50=25±2μm), it provides better ductility at the stencil aperture edge and more complete printing release, enabling continuous, full solder bridging even on 0.3mm×0.3mm micro pads.

During verification on an automotive-grade pressure sensor production line, we found that when PCBs were stored in an SMT workshop with insufficient nitrogen protection for over 48 hours, the oxygen content on the OSP pad surface rose to 8.7at%. At this point, the first-pass soldering yield using conventional solder paste dropped to 91.3%, but after switching to JJY high-activity solder paste, the yield recovered to 99.6%. X-ray inspection showed that the solder joint void area ratio decreased from 12.4% to 3.1%. This was not achieved simply by increasing the reflow peak temperature; rather, its Flux completed all oxide removal within 30 seconds before the 183°C eutectic point, allowing the liquid tin alloy to fully spread and displace adsorbed water and residual sulfides at the pad interface.

The rosin-based carrier of this solder paste carbonizes rapidly above 217°C without coking, avoiding residue buildup at the root of 0201-sized sensor terminals. Meanwhile, its metal content is strictly controlled at 89.8±0.3wt%, ensuring consistent solder joint height while preventing adjacent pad bridging caused by excess solder. It is especially suitable for QFN package sensor modules with 0.4mm pitch. We once used the same stencil to print conventional solder paste and this high-activity solder paste separately. Under the same squeegee pressure and speed, the latter had an 11.2% higher filling rate on a 300-mesh stencil, and the coefficient of variation (CV value) of solder paste volume after release was only 4.3%, significantly better than the 7.9% fluctuation level of the former.

It should be noted that this solder paste has increased sensitivity to environmental humidity. It is recommended to use it up within 24 hours after opening, and it must be used with a nitrogen reflow oven. Otherwise, if the soaking zone exceeds 90 seconds in an air environment, it is easy to cause premature carbonization of the flux, which instead hinders wetting. We once conducted trial production in an old reflow oven without nitrogen supply; although the peak temperature met the standard, the solder joints were dull and the thrust decreased by 18%. The problem disappeared immediately after replacing the nitrogen supply, indicating that high activity is not a universal solution and must be matched with coordinated control of the entire process chain.