Previously, when the production line was soldering 0.4mm pitch QFN packages, issues such as solder recession at pad edges and insufficient side fillet climb frequently occurred. Troubleshooting revealed that neither stencil aperture offset nor abnormal reflow profiles were the cause; instead, the original Japanese SMT solder paste exhibited significantly reduced wetting force on OSP boards with thick PCB surface oxide films. Especially when pad copper surface roughness Ra > 0.8μm, the solder spreading distance was more than 0.12mm shorter than the standard value. After switching to the Domestic Solder Paste LFP-JJY5RTS-0307, under the same conditions, the solder joint bridging rate decreased by 63%, and the average side solder climb height increased from 0.08mm to 0.13mm. Moreover, microscopic observation revealed transparent Flux residues without whitening, indicating that its ROL0 low-halogen design effectively prevents halogen ions from passivating the copper surface.

The core advantage of this Solder Paste lies in its precise matching of the melting point stability (221–227℃) of 0307 alloy powder with T4-grade particle size (15–25μm). This ensures that printing is not obstructed by overly coarse particles clogging stencil apertures below 38μm, while avoiding the excessive oxidation risk associated with T5 powder. Combined with a specific proportion of organic acid activator in the rosin-based vehicle, it achieves targeted removal of pad oxide layers during the preheat zone stage of 150℃ holding for 90 seconds. Therefore, on the same DEK printer, after reducing the squeegee pressure from 4.2kg to 3.5kg, the solder paste release rate actually increased from 91.3% to 96.7%, demonstrating that the rheological properties of this Domestic Solder paste are better adapted to the surface energy state of domestic stencils.

Compared to the LFP-JJY5RQ-305 series, the 5RTS model has a slightly lower solder climb rate by approximately 10 percentage points, but its residue ion chromatography test shows Cl? < 0.05μg/cm2 and Br? < 0.03μg/cm2. It is particularly suitable for compact structures such as fingerprint lock motherboards that cannot undergo water-washing post-treatment. Furthermore, it is more friendly to stencil lifespan: after continuous printing of 2500 pieces, the 38μm aperture area attenuation is only 4.1%, which is 2.7 percentage points lower than a certain Korean competitor. This means the production line only needs to perform stencil nano-coating regeneration once every two weeks, significantly reducing downtime frequency.

Actual cross-sectional analysis shows that for 0.3mm-thick nickel-palladium-gold pads soldered with LFP-JJY5RTS-0307, the average IMC layer thickness reaches 2.3μm with good continuity, and no island-like discontinuous growth of Cu?Sn? commonly seen in low-activity solder pastes is observed. This verifies the catalytic efficiency of its flux system for intermetallic compound formation. Meanwhile, the void rate of this solder paste under nitrogen protection is controlled within 8.2%, fully meeting the thermal cycle reliability requirements of automotive-grade LED driver modules.

For old batches of PCBs with solder recession, attempts to rework using LFP-JJY5RTS-0307 with a reflow profile featuring a peak temperature of 248℃ revealed that the solder joint wetting angle decreased from the original 58° to 32° after remelting. This indicates that this domestic solder paste not only has excellent initial solderability but also superior re-wetting ability during secondary heating compared to most similar products. This characteristic is particularly critical when handling urgent customer rush orders for repair soldering, avoiding the risk of pad detachment caused by repeated heating.