During high-temperature equipment soldering, Solder Wires and bars frequently exhibit defects such as cold solder joints, insufficient wetting, and post-soldering blackening. The root cause is that the melting point of the selected alloy overlaps with the continuous operating temperature of the equipment, leading to joint remelting or thermal creep. The practical solution is to prioritize Sn96.5Ag3.0Cu0.5 (melting point 217°C) or Sn95Sb5 (melting point 235°C) as a replacement for conventional Sn63Pb37 (melting point 183°C). The key preventive measure is to mark the measured maximum temperature rise of the equipment enclosure in the BOM and ensure the distance from the solder joint to the heat source is greater than 8mm.

After reflow, dense micropores appear on the solder joint surface, and the thrust test value is 30% lower than the standard. The symptoms indicate that the Flux carrier volatilizes too quickly at high temperatures and the intermetallic compound (IMC) layer thickens abnormally. The cause is that the rosin-based flux in the solder wire and bar has a softening point below 150°C and lacks heat-resistant stabilizers. The practical solution is to switch to ROL0 grade solder wire containing a compound system of hydrogenated rosin + sebacic acid + benzotriazole, while adjusting the nitrogen protection concentration from 500ppm to within 100ppm. The key preventive measure is to conduct a 260°C/10s thermal stability test on each incoming batch to observe whether the solder wire surface blisters or flux splatters.

During wave soldering, the end face of the Solder Bar frequently forms dross, the solder wave is unstable, and solder dragging is severe, accompanied by temperature control fluctuations in the solder bath exceeding ±3°C. The cause is that low-silver solder bars experience accelerated Sn phase precipitation and sudden viscosity changes during long-term operation above 270°C. The practical solution is to discontinue Sn99.3Cu0.7 Solder Bars and switch to Sn95.5Ag4.0Cu0.5+0.05Ni composite microAlloy Solder bars, while locking the actual operating temperature of the solder bath at 265±1°C. The key preventive measure is to measure the specific gravity of the molten solder in the bath weekly; when the measured value falls below 6.85g/cm³, immediately perform a 10% fresh material replacement.

When repairing high-temperature sensor pins, pad peeling and copper foil lifting occur after repeated rework, with symptoms appearing as early as the third heating cycle. The cause is that ordinary solder wires experience excessive growth of the Cu6Sn5 phase after holding at 200°C for more than 45 seconds, which pierces the solder mask. The practical solution is to switch to Sn96.5Ag3.0Cu0.5Ge0.1 solder wire containing 0.1% Ge, and use a pulse hot air gun set to 320°C/2.5 seconds single impact during soldering. The key preventive measure is to confirm the local temperature rise on the back of the PCB with an infrared thermal imager before repair; if it exceeds 110°C, a heat dissipation copper sheet must be installed for isolation.

The pay-off tension of the solder wire winding machine fluctuates, causing automatic wire feeding jams and frequent wire breakage, with symptoms concentrated after 2 hours of continuous operation. The cause is that solder wire grains undergo recrystallization and softening after being stored in a high-temperature workshop (>35°C) for more than 4 hours. The practical solution is to control the constant-temperature storage temperature of solder wires and bars at 20±2°C and relative humidity at 45±5%RH, and measure the tensile force at a speed of 150mm/min with a tension meter before putting them into use to ensure it is maintained within the 180–220gf range. The key preventive measure is that opened solder wire packages must be used up within 48 hours, and any unused portion beyond this time must not be mixed into new batches.

After 72 hours of powered aging, the solder joint exhibits annular cracks accompanied by resistance fluctuations, and microcracks extending along the IMC boundary are visible under a microscope. The cause is that excessive Bi content (>0.05%) in the solder wire causes segregation of low-temperature brittle phases. The practical solution is to require suppliers to provide ICP-MS test reports for each batch, with a focus on verifying whether the total content of Bi, Zn, and Al impurities is below 0.12%. The key preventive measure is to add a DSC (differential scanning calorimetry) test during incoming inspection to confirm that the melting range width does not exceed 1.8°C.