In actual production lines, low-temperature solder is mainly used for MLCC chip capacitors with capacitance greater than 4.7μF and package size smaller than 0603, as these components are highly prone to delamination and cracking under the conventional reflow peak temperature of 240℃. After adopting Sn42/Bi58 low-temperature Solder Paste with a melting point of 138℃, reliable soldering can be completed by controlling the reflow peak at only 165±5℃, provided that the soak zone time must be extended to over 90 seconds to ensure full activation of the Flux; otherwise, the cold solder rate will surge by more than 12%.

LED beads, especially Mini-LEDs with flip-chip structures, often have solder joint void rates exceeding 35% when using traditional solder paste. Switching to Sn58/Bi42 low-temperature solder paste with a melting point of 150℃, combined with a furnace environment with nitrogen concentration above 95%, can reduce the void rate to within 8%. However, the cooling rate in the cooling zone must be simultaneously controlled to within 2.5℃ per second; otherwise, the brittleness of solder joints will increase significantly, and microcracks will appear after a single drop test.

If FPC connectors on flexible printed circuit boards are soldered with ordinary solder paste, the base PI film will shrink and deform significantly above 220℃, leading to PIN pin offset. After selecting Sn64/Bi35 low-temperature solder with a melting point of 170℃, the entire reflow process can be completed at a peak temperature of 195℃. At this point, not only is the solder joint wetting angle maintained within 30°, but also the FPC bending life is increased from 3000 cycles to over 8500 cycles. However, the stencil opening must be enlarged by 15% to compensate for the increased solder paste slump.

Type-C female connectors with PBT or LCP plastic housings are prone to softening and deformation during high-temperature reflow, leading to a 30% decrease in insertion force. After switching to low-temperature solder paste with a melting point of 138℃, the stability of insertion force is greatly improved. However, it should be noted that the stencil thickness must be strictly controlled at 0.1mm; otherwise, excessive solder paste volume after printing will easily cause bridging, especially between PIN pins with 0.4mm pitch. We have previously reworked 2700 motherboards due to this issue.

CMOS sensors in automotive camera modules are extremely sensitive to thermal shock; their silicon substrate will develop lattice dislocations if held above 200℃ for 3 seconds. Therefore, Sn48/Bi52 low-temperature solder paste must be used with a peak temperature of 155℃. At this point, the reflow time window has a tolerance of only ±2℃ and ±0.5 seconds; any fluctuation in conveyor speed will directly result in cold soldering. Therefore, it is recommended to pair it with a closed-loop temperature control module and a real-time infrared temperature measurement feedback system.