During routine maintenance of wave soldering, we found that even when a dedicated antioxidant is added to Solder Bars at a ratio of 0.15%, a noticeable dross layer still forms on the solder bath surface after 8 hours of continuous operation. This is because the antioxidant can only inhibit the slow reaction between Sn and O? on the static liquid surface, but cannot prevent turbulent entrainment caused by the solder circulation pump, nor can it prevent the complexation of thermal decomposition products from residual Flux on the PCB at 260°C with tin ions to form insoluble tin salts.

The purity and impurity content of the solder bars themselves have a decisive impact on the rate of dross formation. When the copper content exceeds 0.08%, even with sufficient antioxidant added, Cu?Sn? intermetallic compound particles will still accelerate precipitation at the bottom of the solder bath. These particles continuously float upward under solder disturbance and agglomerate with other oxides, eventually forming stubborn dross blocks that are difficult to remove.

On-site measured data shows that the average daily dross output decreased from 420g to 190g after using solder bars containing antioxidant, a reduction of approximately 55%. However, if the nitrogen protection flow is increased from 15L/min to 25L/min, the dross amount can be further reduced to 85g. This indicates that solder oxidation resistance is only one part of multi-factor control, and can never replace atmosphere control, solder temperature gradient optimization, and regular copper removal processes.

We once compared the performance of three batches of solder bars of the same model under identical operating conditions, and found that batch A had excessive humidity in the storage environment, resulting in a slight grayish-white oxide film visible immediately after opening the package. After being put into the bath, the dross amount surged by 37% within 2 hours, while batches B and C remained stable. This proves that the sealing performance of solder bars before leaving the factory and transportation/storage conditions have a pre-constraining effect on the subsequent release of antioxidant effectiveness.

The selection of flux type is equally important. Rosin-based flux produces little carbonized residue at high temperatures, and can maintain stable solder surface tension when used with antioxidants. However, if water-soluble no-clean flux is not thoroughly cleaned, its organic acid salt residues will continuously catalyze the conversion of Sn2? to Sn?? in the solder, increasing the antioxidant consumption rate by 2.3 times, thereby greatly shortening the effective protection period.

In actual operation, the fluctuation range of solder wave height, chain speed matching accuracy, and fixture immersion angle must be monitored simultaneously. Any deviation will aggravate solder splashing and local overheating. In such cases, even if the antioxidant concentration meets the standard, it cannot cover the instantaneous oxidation outbreak points caused by physical disturbance.