Issue link: https://iconnect007.uberflip.com/i/1533904
APRIL 2025 I SMT007 MAGAZINE 75 e surface of manually re-tinned pins oen appears to have a rough finish as seen in Figure 2. is is indicative of an uncon- trolled lead tinning process due to impuri- ties such as excessive dross, flux residues, and non-optimized immersion dwell and extrac- tion speed. Figure 3 shows an example of random surface anomalies on the resulting solder joints. ese irregularities can be described as alligator skinning, voids, and blow-holes which are more likely to occur with a man- ual tinning process and are considered solder defects per IPC J-STD-001. e ideal method to facilitate re-tinning of surface mount or through-hole components is to use the robotic hot solder dip (RHSD) process. It is recommended that this re-tin- ning operation be carried out using a lead tinning machine utilizing precise flux applica- tion, controlled preheating, dual solder pots, nitrogen inerting, and defined process control. A defined process of this type is highly recommended in lieu of manually dipping components into a single static solder pot to reduce solder contamination, minimize non-wetting issues, and enhance solderability. e RHSD component lead tinning process utilizes two separate solder pots. e first is a cleansing bath of molten solder to remove the original solder coating, unwanted plat- ing, and any residual contam- inants. Next, the component leads are preheated and fluxed, followed by a final immersion in a clean solder bath of pure eutectic solder. is provides a homogeneous intermetal- lic layer with the base metal of the component leads, which increases the overall solderability, thus facil- itating improved reliability of printed circuit board assemblies. All types of through-hole and surface mount components can be re-tinned using the robotic hot solder dip process. Sur- face mount components with terminations or pads without leads, such as chip compo- nents, SOTs, SOICs, LCCs, and PLCCs can be re-tinned using the solder drag process. In many cases fixturing may be required when automatically re-tinning surface mount com- ponents to ensure consistency is maintained during the re-tinning process. Formed multi-side components such as FP and QFP devices, have very delicate leads that can be easily damaged. ese are typi- cally re-tinned using a side wave process with Figure 2: The surface of manually re-tinned pins often appears to have a rough finish. Figure 3 Figure 2: The surface of manually re-tinned pins often appears to have a rough finish.