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70 SMT007 MAGAZINE I MAY 2025 erefore, the recommendation is to remove the gold to ensure that the solder establishes an electromechanical and metallurgical bond with the base metal beneath the gold—typi- cally nickel or copper. e ideal method for removing gold plat- ing from surface mount and through-hole components is a robotic hot solder dip pro- cess. is re-tinning operation should be performed using a lead tinning machine that incorporates controlled flux applica- tion, convection preheating, dual dynamic solder pots with a built-in dross skimmer, nitrogen inerting, and defined process con- trols. is approach is preferable to manu- ally dipping components into a static sol- der pot, as it helps reduce solder contami- nation, minimize non-wetting issues, and enhance solderability. Re-tinned pins processed via robotic hot solder dipping typically exhibit a smooth, gold-free finish, as shown in Figure 3. is finish indicates a fully controlled lead-tin- ning process, free from impurities, exces- sive dross, or flux residues, with optimized parameters for immersion dwell time and extraction speed. When evaluating a gold removal or tin- ning process, consider the type of solder pots being used. Dynamic solder pots are supe- rior to static pots because they can circulate molten sol- der, resulting in minimal dross accumulation. Additionally, the number of solder pots mat- ters; using two pots is typically recommended over one. e dynamic action in the first pot effectively removes gold plat- ing, oxidation, and other res- idues, while the second pot is used to apply the new finish to the leads. ere is usually a nitrogen shroud surround- ing the solder pot, which mini- mizes icicles and dross buildup, resulting in a smooth finish. Consistent results with the re-tinning pro- cess rely heavily on precise control of speed, time, depth, and temperature. Without con- trol of these factors, issues with contami- nation, termination coverage, inconsistent solder thickness, and component damage become more prevalent. GEIA-STD-0006— Requirements for Using Solder Dip to Replace the Finish on Electronic Piece Parts— states that a robotic hot solder dip apparatus shall have: • Dynamic solder waves or other method, which removes dross before solder dipping • Controlled dwell time in preheat and sol- der pot within ±0.1 sec • Controlled depth of immersion to within ±0.1 mm • Controlled exit speed out of solder pot to within ±0.3 cm/sec • Piece parts shall be preheated to less than 71°C prior to solder dipping • Total immersion time shall be less than 5 seconds per component side Solder pot contamination can occur eas- ily, especially if using a single solder pot sys- tem. Tinning component leads with con- Figure 3: Re-tinned pins processed via robotic hot solder dipping typically exhibit a smooth, gold-free finish.