Realization of a Circular Economy for Solder Pastes: Development of a Multi-Stage Separation and Recovery Process

The disposal of solder paste waste poses significant environmental and economic challenges for the electronics industry. Due to their limited shelf life, large volumes of solder pastes are incinerated after use or upon expiration, resulting in the permanent loss of valuable raw materials. To address the associated environmental and economic challenges, this work presents a purification and recycling approach for expired solder pastes within the framework of the Zero Waste Paste (ZWP) project. The focus lies on the non-destructive separation of the metallic solder powder from fluxes, additives, and other organic constituents while preserving particle morphology and material quality for reuse. Several solvent-based extraction procedures using non-aggressive organic solvents were systematically investigated and optimized for yield, purity, and processability. The most promising methods achieved recovery rates of up to 86.8 wt % of clean solder metal powder. Comprehensive material characterization was performed using scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), viscosity measurements, and thermogravimetric analysis (TGA), confirming high purity, intact spherical particle morphology, and minimal residual organic contamination. Furthermore, solder pastes containing recycled solder powder were produced and subjected to static and dynamic qualification tests, demonstrating performance comparable to conventional reference pastes. The results indicate that the proposed purification approach enables the effective recycling of solder paste waste and represents a viable step toward a circular economy in electronics manufacturing. Future work will address scalability, process automation, and validation under industrial production conditions.

Keywords: Reflow soldering process, Solder paste waste, Solder paste recycling, Solder paste purification, Circular economy, Zero Waste Paste, Reliability, Lead-free solder alloys, SEM/EDX material characterization, Thermogravimetric analysis (TGA), Recycled solder powder reliability, Solder paste qualification.