The replenishment cycle for wave soldering bars cannot be set as a one-size-fits-all fixed schedule; it must be dynamically determined based on the daily PCB volume, solder joint density per board, Flux residue level, and changes in copper content in the solder pot. For example, when continuously producing high-density double-sided boards, the specific gravity of the molten solder may drop by 0.02 within 6 hours, and dross thickness may exceed 3mm. In such cases, immediate replenishment is required even if the shift handover time has not yet arrived. Our production line tests show that when the solder pot temperature is maintained at 255℃±2℃ and the throughput exceeds 120 boards per hour, the natural consumption rate of Solder Bars rises to 1.8～2.3kg/h. If the regular 12-hour replenishment schedule is still followed, the fluidity of the molten solder will deteriorate in the latter half of the shift, leading to an increase in solder joint spikes.

Before replenishing solder bars, the surface dross must be completely removed using a stainless steel skimmer. Unremoved tin oxide dross will trap air bubbles and carry them into the main solder pool the moment the new solder bar melts, causing subsequent clogging of the wave solder nozzle. At the same time, check whether the actual molten solder level is more than 5mm below the scale line; otherwise, overflow or pump cavity cavitation may occur after replenishment. New solder bars must not be dropped whole into the high-temperature zone. Instead, they should be slowly slid along the side wall of the solder pot into the preheating zone, allowed to stay in the 180～200℃ transition zone for no less than 90 seconds, and then pushed into the main heating zone after the surface oxide film softens. Otherwise, the sudden introduction of cold material will cause a local temperature drop of 3～5℃, inducing solder crystal precipitation and adhesion to the pump impeller.

It is strictly prohibited to mix solder bars of different brands or batches in the same solder pot. Even if all are SAC305 composition, differences in the proportion of trace elements such as copper, silver, and bismuth among manufacturers are at the ±0.015% level. After mixing, melting point shift is highly likely to occur after 72 hours of continuous operation, manifested as an automatic attenuation of wave height by 8%～12% during low-temperature nighttime periods. The amount of replenishment is not "the more the better"; a single addition is recommended to be controlled at 8%～12% of the original solder volume. If it exceeds 15%, the machine must be shut down for a complete spectral analysis of the molten Solder Composition. Otherwise, the dross generation rate will double within 4 hours, ultimately leading to reduced clamping force of the chain claws and causing board drop.

We once encountered a problem of excessive solder joint void rate for three consecutive days on a customer's production line in Dongguan. The root cause was found to be that the preheating step was skipped during solder bar replenishment. Repeated impacts from cold material formed a microcrystalline deposition layer at the bottom of the solder pot, which was found to be 0.4mm thick during cleaning. After direct scraping, the void rate immediately fell back to below 0.3%. Therefore, the replenishment action itself is not the goal; the core is to maintain continuous stability of the physical and chemical parameters of the molten solder, including a specific gravity maintained at 7.25～7.35g/cm3, copper content controlled between 0.08%～0.12%, and liquid level fluctuation amplitude less than ±1.5mm. Any deviation of these indicators will be reflected in the appearance of solder joints within 2～3 hours.