2. Soldering is a crucial step in PCB production. Without soldering, various components cannot be attached to the board, and a functioning circuit board cannot be created.
**Common processes for soldering circuit boards**
1. **Arc soldering**
Arc soldering utilizes the heat from the arc to melt the workpiece for connection. This method features two basic types: melting electrode arc and non-melting electrode arc. In the melting electrode arc, the electrode melts from the arc’s heat, and the molten metal transfers to the workpiece. In the non-melting electrode arc, the electrode remains solid, and filler metal is added separately.
2. **Plasma soldering**
Plasma soldering, a form of flash arc welding, melts the base metal using a highly concentrated plasma arc. It offers high welding speed, no grooves, excellent weld quality, a small heat-affected zone, minimal soldering deformation, and can weld various metals effectively.
3. **High-frequency soldering**
High-frequency soldering includes high-frequency resistance soldering and induction welding, using 60-500KHz currents to heat and melt metal surfaces instantly. This method is efficient for soldering straight seam welded pipes and generates no soldering fumes if metal surfaces are clean.
4. **Gas soldering**
Gas soldering employs gas flames to melt workpieces for connection. Methods vary, including oxygen-acetylene and oxygen-hydrogen soldering, with acetylene often used as a combustible gas. Heat is generated through chemical reactions in the flame.
5. **Argon arc soldering**
Argon arc soldering, a type of flash soldering, produces strong ultraviolet radiation during welding. It includes non-consumable and consumable types, with mobile fume purifiers recommended and good local ventilation necessary for welder health.
6. **Resistance soldering**
Resistance soldering uses electrode pressure and resistance heat generated by soldering current to create joints. This includes spot, seam, projection soldering, and resistance butt welding. It is usually automated, with comprehensive electrical and mechanical control systems.
**Soldering process flow of circuit boards**
**Preparation**
1. **Soldering materials**
1) Common solder materials include Sn60, Sn63, or HL-SnPb39 tin-lead solder.
2) Fluxes like rosin or water-soluble flux are used, typically for wave soldering.
3) Cleaning agents should avoid corrosion and pollution; options include anhydrous ethanol, trichlorotrifluoroethane, isopropanol, aviation gasoline, and deionized water. Choose based on process requirements.
2. **Soldering tools and equipment**
1) Proper selection of electric soldering iron power and type is crucial for quality and efficiency. A low-voltage, temperature-controlled iron is recommended, with nickel-plated, iron-plated, or copper-plated tips as needed.
2) Wave soldering and reflow soldering machines are ideal for industrial mass production.
3. **Key operating points for circuit board soldering**
1) **Manual soldering**
① Check insulation materials before soldering to avoid damage. During soldering, prevent burning or damaging components.
② Maintain soldering temperature around 260°C to ensure quality.
③ Control soldering time within 3 seconds; for multi-layer boards or large components, up to 5 seconds. Re-soldering should follow the same quality standards. Adjust for specific conditions.
④ Prevent overheating of adjacent components and printed boards; use heat dissipation measures for sensitive components.
⑤ Ensure the soldered part is fixed without movement until cooled; use heat dissipation measures if needed.
2) **Wave soldering**
① Apply flux to ensure complete solder coverage; use rosin or water-soluble flux with a density of 0.81-0.87.
② Preheat the board to 90-110°C to avoid solder joint issues.
③ Control solder temperature to 250°C ± 5°C. Adjust wave crest angle to about 6° and welding line speed to 1-1.6 m/min. Maintain peak height at 1/2 to 2/3 of the board thickness to avoid “bridges”.
④ Cool the circuit board with strong wind after soldering.
⑤ Trim component leads after cooling.
3) **Reflow soldering**
① Ensure the solder and workpiece surfaces are clean to avoid defects.
② Proper solder application reduces defects and improves reliability.
③ Local heating sources can enable different soldering methods on the same substrate.
④ Use solder paste with the correct composition and no impurities.
4. **Board cleaning**
After soldering, clean the board thoroughly to remove flux residues, oils, and dust. Follow specific cleaning processes as required.
Circuit board soldering is vital for performance and reliability. With increasing demands for miniaturization and high performance in electronics, soldering technology will continue to evolve and innovate.
