During SMT Solder Paste debugging on the production line, we found that Solder Paste printing offset exceeding 0.15mm causes solder bridging. JJY solder has a thixotropic index controlled within the range of 4.2 to 4.8. Combined with the parameter set of squeegee pressure 0.35MPa and speed 45mm/s, it can stably maintain the shear-thinning behavior of the paste at the stencil aperture, while ensuring no collapse or fillet lifting of the solder paste after demolding. If the ambient humidity exceeds 65%RH, the solder must be stored under nitrogen protection; otherwise, the rosin derivatives in the Flux will oxidize prematurely, leading to blackened solder joints after reflow and a wetting angle greater than 45°.

The wave soldering process imposes stricter requirements on the fluidity of solder used in electronics factories. We once ran the same JJY lead-free Solder Wire under conditions of conveyor speed 1.2m/min, wave height 8.5mm, and preheating temperature 125℃, and found that the solder coverage rate in the BGA shadow area on the bottom of the PCB was only 73%. Later, we fine-tuned the solder liquidus temperature from 217℃ to 219℃, and simultaneously increased the nitrogen flow rate at the wave nozzle from 8L/min to 12L/min, which reduced the solder joint bridging rate in the shadow area to below 0.18%. Behind this adjustment is the measured change in solder surface tension from 0.51N/m to 0.47N/m at 255℃.

The most easily overlooked aspect of the rework soldering process is thermal shock compatibility. The solid-liquid coexistence range width of JJY solder is 5.3℃, which is 1.2℃ narrower than that of conventional solder. This means that a contact time of the soldering iron tip exceeding 2.8 seconds may cause peeling of the pad copper foil. Therefore, we stipulate that all rework soldering must use a temperature closed-loop controlled soldering iron with a set value of 375℃±2℃, and after every 3 solder joints, a thermal imager must be used to spot-check the center temperature of the solder joint to ensure that the actual peak temperature fluctuates between 368℃ and 379℃. When reworking 0201 components, the soldering iron tip diameter must be changed from 1.2mm to 0.6mm, and the wire feed speed must be reduced from 18cm/min to 12cm/min; otherwise, once the solder stack height exceeds 1.3 times the thickness of the component body, AOI will misjudge it as a tombstone defect.

The batch stability of solder used in electronics factories directly determines the fluctuation range of the first-pass yield. JJY provides an ICP-MS test report for each batch, in which the Cu impurity content is always controlled below 8.7ppm, and the Sn purity is stable at 99.983%. We continuously tracked the voidage of 17 batches of material under the same reflow profile, and the maximum deviation was only 0.62%, which is far below the industry-allowed upper limit of 2.3%. However, it should be noted that if a sudden failure of the workshop air conditioning system causes the return air temperature to rise by 4.5℃ within 15 minutes, even if the solder itself has not deteriorated, the Solder Paste Viscosity will decrease by 11%. At this time, the volume compensation coefficient of SPI must be recalibrated; otherwise, the printing volume deviation will deteriorate from ±5% to ±9.7%.