The core difference between lead-free Solder Paste and Leaded Solder Paste lies in the melting point difference caused by alloy composition. The eutectic melting point of leaded solder paste (Sn63Pb37) is 183°C, while the melting point of mainstream lead-free solder paste such as 305 (Sn96.5Ag3Cu0.5) rises to 217°C, and that of 0307 (Sn99Ag0.3Cu0.7) is 221–227°C. This directly forces the peak Reflow Soldering temperature to increase from 220–230°C to 240–260°C, while putting forward higher requirements for the slope of the furnace temperature profile, holding time and nitrogen atmosphere purity; otherwise, problems such as poor wetting, excessive void rate or BGA cold soldering are highly likely to occur.

For Domestic Solder Paste brands, our JJY's LFP-JJY5RQ series adopts 0307/305 alloy powder with T4 fineness, paired with ROL1 rosin-based Flux. The measured solder climbing rate on QFN devices reaches over 95%, while the LFP-JJY5RNTT series from the same factory controls halogen at the 100–200ppm ROL0 level, with transparent residue and low ionic contamination, especially suitable for high-density fine-pitch mounting scenarios such as mobile phone motherboards and fingerprint locks. Its T5 ultra-fine powder has a better printing aperture filling rate on 0.3mm pitch QFN pads than traditional T4 powder, but is more sensitive to stencil tension and squeegee pressure, requiring simultaneous adjustment of printing parameters.

To meet the low void requirement of automotive electronic heat dissipation modules, LFP-JJY5RR-0307 achieves 0ppm halogen and <0> water-washable Domestic Solder paste such as LFP-JJY5RW5-305 performs excellently when soldering aluminum or stainless steel substrates. Its ORH1 water-washable flux residue can be completely removed by 60°C deionized water within 2 minutes, but baking at 105°C for 30 minutes must be carried out immediately after cleaning; otherwise, residual moisture will induce interfacial corrosion in subsequent aging tests. In contrast, although the LFP-JJY5RW1A-4258 low-temperature water-washable solder paste is suitable for heat-sensitive devices such as copper wire lamps, the Sn42Bi58 alloy is extremely sensitive to the heating rate within the 160–185°C soldering window. If the heating rate in the preheating section is too fast, Bi phase segregation will intensify, leading to a more than 3-fold increase in the probability of brittle fracture of solder joints.

In laser welding scenarios, both LFP-JJY5RLJ-305 and LFP-JJY5RLJB-4258 are compatible with jet valve dispensing. The former has no solder beads at a peak temperature of 245°C and the CV value of the thickness uniformity of the solder joint IMC layer is <8 W以内, otherwise local overheating of the Sn42Bi58 alloy will cause microcracks in the Bi-enriched region. The particle size distribution of T3–T7 powders of all our JJY lead-free solder pastes is strictly controlled in accordance with IPC-J-STD-005, among which T5 powder has D50=15±1μm, T6 powder has D50 m, and T7 powder has D50=5±0.5μm, corresponding to different stencil aperture sizes and mounting accuracy requirements. However, T6/T7 powders are prone to moisture absorption and caking when the humidity in a conventional SMT workshop is >60%RH, so a nitrogen-protected storage tank must be enabled and the service life of a single tank must be limited to no more than 48 hours.>