The formation of solder dross during the continuous wave soldering process is a dynamic accumulation process. If the solder pot temperature is maintained above 265°C for a long period, the chain speed is lower than 1.2m/min, and rosin-based Flux with high solid content is used, the rupture frequency of the oxide film will accelerate, causing the daily average increment of solder dross to exceed 1.8kg. The No. 3 wave soldering line at Jia Jinyuan's Dongguan factory once consumed an extra 236kg of Solder Bars in a single month due to this issue. We found that if the copper foil area of the same model of PCB is increased by 12% and the furnace passing direction is changed from horizontal to vertical, the solder dross output rate will decrease by 0.43kg/h, indicating that the coupling relationship between the thermal field distribution and the immersion time is more critical than simply adjusting the temperature.

Uncontrolled dross volume is often not the result of a single parameter imbalance, but the superposition of three factors: insufficient nitrogen coverage in the solder pot below 75%, flux spray pressure fluctuation exceeding ±0.03MPa, and uneven flow rate after the solder pump impeller wears. Jia Jinyuan's internal SOP stipulates that the nitrogen purity must be stable at 99.995%, the spray pressure must be inspected twice a day, and the impeller must be forcibly replaced every 300 hours. Otherwise, the SnO? content in the solder dross will jump from the conventional 18.7% to 26.4%, directly causing the energy consumption of recycling and remelting to rise by 21%. A more hidden problem is that the solder liquid return angle changes after the wave height is fine-tuned. When the return angle is less than 110°, the dross is repeatedly entrained into the main solder flow, forming a vicious cycle.

On-site verification found that increasing the PCB board surface temperature at the outlet of the preheating zone from 110°C to 125°C, while reducing the flux coating amount from 85mg/cm² to 62mg/cm², although there was a small amount of cold solder rework in the initial stage, the total amount of solder dross was stably reduced by 0.65kg/h within 72 hours, and the AOI missed inspection rate did not exceed 0.08‰. This shows that excessive flux coverage instead aggravates the instability of the solder liquid surface tension, while moderately increasing the PCB body temperature can reduce local condensation incentives, and the synergy of the two can suppress the non-linear growth of solder dross.

All bases of Jia Jinyuan uniformly implement the "three interceptions" operation method for solder dross, that is, installing a 300-mesh stainless steel filter at the inlet of the solder pot to intercept large particle floating dross, embedding a magnetic scraper at the wave throat to adsorb iron-containing impurities, and setting up a centrifugal dross separator at the outlet of the cooling section to recover fine powder. This combined measure keeps the purity of recyclable tin at 99.42%±0.07%, which is much higher than the industry's common lower limit of 98.6%. However, the filter cleaning frequency must be calibrated synchronously. If it is not cleaned for more than 8 hours, the reverse blockage caused by dross accumulation will lead to wave shape distortion, which in turn will cause a jump in the solder bridge defect rate.

All solder dross data must be connected to the MES real-time dashboard. When the cumulative output of a certain shift exceeds 115% of the daily reference value, the system automatically locks the solder pot heating module and pushes an alarm to the process engineer's mobile phone. After Jia Jinyuan's Suzhou factory piloted this mechanism, the response time for abnormal solder dross fluctuations was compressed from an average of 47 minutes to within 9 minutes. While the monthly average tin consumption of a single line decreased by 1.3%, the fluctuation range of copper content in the dross was narrowed to 0.19%～0.23%, proving that process control is more effective than post-remediation in safeguarding the cost bottom line.