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54 SMT007 MAGAZINE I JULY 2025 also enhances the overall reliability of the solder joints during operational life. While re-tinning is a useful remedial step, it is important to verify the effectiveness of the process through visual inspection and, if necessary, addi- tional solderability testing, especially for critical or high-reliability applications. There is often confusion within the industry regarding solderability testing vs. component re- tinning. Solderability testing assesses how well molten solder will wet and adhere to a compo- nent's surface, with common methods being quali- tative (visual inspection after dipping) and quantita- tive (wetting balance measurements). Conversely, re-tinning involves physically applying a fresh layer of solder via immersion into a molten sol- der bath to create a highly solderable surface with a new intermetallic layer. This process restores and enhances the component's surface condition, especially when original finishes have degraded. Industry Applications of Component Re-tinning Companies actively engaged in component re- tinning include defense, military, and aerospace OEMs, as well as medical device manufacturers and other high-reliability OEMs. Contract elec- tronics manufacturers (CEMs) working within the defense, aerospace, medical, and high-reliability sectors frequently perform re-tinning, especially when dealing with legacy components or end-of- life builds. This process is critical for maintaining supply chain integrity and ensuring long-term reli- ability of critical assemblies. Re-tinning Best Practices To produce a high-quality intermetallic layer dur- ing re-tinning, it is essential to perform solderabil- ity testing both before and after the process— using tools like dip-and-look or wetting balance systems—to confirm that the surface is suitable for reliable solder joints. Proper pre-cleaning of com- ponents is also critical; organics and oxides must be removed to facilitate effective re-tinning. Technicians typically perform the re-tinning in a dual solder pot setup. The first bath removes unwanted plating and oxides, while the second applies a controlled, uniform solder alloy coating. Technicians should also carefully control parame- ters such as immersion speed, dwell time, depth, and extraction speed to ensure consistency across components. Flux Selection and Application Flux choice is vital in the re-tinning process. Since rosin-based fluxes are generally specified for sol- derability testing rather than re-tinning, the recommenda- tion is to use fluxes suited for the specific termination fin- ish. When post-tinning clean- ing is permitted, it is prefer- able to use water-based (low pH) fluxes, which help remove residual flux and oxides cleanly. For components that cannot undergo post-tinning cleaning, no-clean, alcohol- based fluxes are suitable. Min- imize flux volume in all cases. The goal is to fully coat the termination without leaving excess residue, which could interfere with subsequent assembly or reliability. K N O C K I N G D OW N T H E B O N E P I L E