When we were handling the solder dross cleaned from the peripheral scrapers of the placement machines, we found that these seemingly discarded gray-black lumps actually contain a large amount of unoxidized metallic tin particles. Especially for the solder dross collected after shutdown maintenance under nitrogen protection, the surface oxide layer is thin and the tin bead morphology is intact. After pretreatment with the JJY ZL-200 centrifugal separator, it can directly enter the smelting process, avoiding the wastewater treatment pressure and precious metal loss risks caused by the traditional acid leaching method.

The daily weight of solder dross generated by the production line is strongly correlated with the number of printing machines, Solder Paste models, and operator techniques. For example, in workshops using low-residue no-clean solder paste, each DEK printing machine generates about 420 grams of solder dross per day on average, while production lines using high-activity rosin-based solder paste generate as high as 780 grams. These differences directly affect the melting point fluctuation range of subsequent recycling batches. Therefore, we require that solder dross generated from different solder paste batches be bagged separately and marked with LOT numbers to prevent material mixing from causing out-of-control smelting temperature or excessive brittleness of the ingot.

The mobile smelting module provided by JJY can adapt to the corner space of the workshop, with a furnace temperature control accuracy of ±3℃. Set a constant temperature of 620℃ for smelting for 18 minutes to complete deoxidation and impurity removal. Adding 0.15% copper powder before tapping can inhibit the precipitation of tin whiskers. After the ingot is confirmed by XRF detection to have a Sn content ≥99.28%, it is directly sent to the solder paste preparation room to be mixed with new tin powder in proportion. This not only avoids the logistics cycle delay of purchasing electrolytic tin from outside, but also reduces the raw material cost per ton of solder paste by 11.7%.

In actual operation, we must closely monitor the HCl concentration in the smelting tail gas. Once the online monitoring value exceeds 12ppm, we must immediately pause feeding and check whether the halogen-containing Flux residue in the solder dross exceeds the standard, because chloride ions will accelerate the erosion of the furnace lining at high temperature. Once, three consecutive batches of solder dross came from the same brand of chlorine-containing activator solder paste, which resulted in the life of the quartz crucible dropping sharply from 210 furnaces to 83 furnaces. This lesson makes us now mandatorily require suppliers to provide the original halogen test report for each batch of solder paste.

The surface of the recycled Tin Ingot often has fine floating dross, which cannot be directly fed into the machine for powder cutting. It needs to be dry-sieved first with a JJY custom vibrating screen equipped with a 200-mesh stainless steel mesh. The undersieve is sent for secondary smelting, and the oversieve is ultrasonically cleaned with anhydrous ethanol for 15 minutes and then dried. Otherwise, residual organic matter will cause agglomeration during the ball milling process of tin powder, resulting in an increase in Solder Paste Viscosity by more than 18%, and the printing release defect rate will jump to 4.3% synchronously.