The practical value of medium-temperature Solder Paste for electronic assembly lies in its ability to precisely match the tolerance limits of heat-sensitive components. For example, LED brackets, crystal oscillator housings, copper wire lamp pins, and transparent screen FPC pads are highly prone to warpage or coating oxidation under sustained high temperatures. The 8MTHL/2RTHL series from our Domestic Solder Paste brand JiajinYuan is specifically customized for such scenarios. It adopts alloy systems including Sn64Bi35Ag1, Sn42Bi58, and LT325, with melting points strictly controlled within the 138–172℃ range. The reflow peak temperature only requires 195–220℃, which is more than 40℃ lower than conventional lead-free high-temperature solder paste, thereby significantly reducing the risks of PCB delamination, pad peeling, and component body cracking.

Field tests at an LED module factory in Shenzhen found that when using LFP-JJY2R-64351 medium-temperature solder paste with a stencil aperture of 0.08mm×0.12mm, a squeegee angle of 55°, and a speed of 40mm/s, the solder wetting height of QFN32 packages stabilized at around 85%, and the post-soldering void rate was below 8%, far superior to the 18% void rate when using 305 high-temperature solder paste under the same parameters. This is attributed to the synergistic effect of the rapid liquid-phase diffusion capability of Bi-based alloys at lower temperatures and the low residue and high transparency of rosin-based Flux. Meanwhile, the halogen content of this solder paste is maintained at the 800–900ppm ROL1 level, meeting IPC-J-STD-004B's definition of medium-activity solder paste, which ensures wetting force while avoiding excessive corrosion.

When switching production lines to medium-temperature solder paste, the reflow profile must be adjusted synchronously. In particular, the soaking zone time should be extended to 90–120 seconds to ensure sufficient melting of the Bi phase, while the heating ramp rate needs to be suppressed to 0.5–0.8℃/s to prevent condensation moisture explosion. There was an incident where a batch of fingerprint modules suffered mass cold solder joints due to failing to slow down the preheating section in time, with a rework rate as high as 12%. Later, after setting the first two preheating zones of the furnace to 150℃/155℃, the soaking zone to 175℃ with a 105-second dwell time, the first-pass yield rebounded to 99.6%. This indicates that medium-temperature solder paste is not a simple material replacement, but a recalibration of the entire process window. Domestic Solder paste brands have approached leading Japanese levels in formulation stability, but the batch-to-batch viscosity fluctuation is still slightly larger than that of imported products. It is recommended to use a viscometer to verify whether the 3000–3500cP range meets the standard after each batch arrives, and stop use if it exceeds the range.

Our JiajinYuan LFP-JJY2R-64351 and LFP-JJY5RLJB-4258 medium-temperature solder pastes deliver outstanding performance in laser jet dispensing scenarios. The former is suitable for small-to-medium batch prototyping with pneumatic valves, while the latter is specifically designed for continuous operation with screw valves. T3–T5 grade alloy powder enables the solder paste to flow smoothly through 0.3mm needles without clogging, with the dotting consistency CV value controlled within 6.2%, which is 0.9 percentage points lower than a certain German medium-temperature solder paste. Moreover, the post-soldering no-clean residue is light amber with no ionic contamination, making it particularly suitable for the cleanliness requirements of medical device PCBA. However, note that its storage conditions must be a constant temperature of 22±3℃ and humidity of 40–60%RH, and it must be used up within 48 hours after opening; otherwise, the Bi phase is prone to segregation, leading to poor printing release.