I. Core Definition and Principle of Wave Soldering
Wave soldering is an automated process that sprays molten solder (currently the mainstream is lead-free solder SAC305) into a wave through a wave generator. The PCB board passes through the wave at a specific angle and speed, and firm solder joints are formed between pins and pads through capillary action and metallurgical reactions. The core principle is "contact-infiltration-bonding". The waves are mainly divided into turbulent waves (preventing missing soldering) and laminar waves (finishing solder joints), which cooperate with flux (mainstream no-clean type) to achieve deoxidation and assist infiltration.
II. Complete Process Flow of PCBA Wave Soldering
Wave soldering is an assembly line operation, and the core process can be simplified into 7 steps. The parameters of each link directly affect the soldering quality:
(1) PCB Preparation and Component Insertion
Complete PCB preprocessing and THT component insertion. For mixed assembly, SMT soldering must be completed first, and components can be fixed with glue if necessary.
(2) Flux Application
Apply flux evenly on the PCB soldering surface by spraying or other methods. Its core functions are deoxidation, assisting infiltration and preventing reoxidation, and the application amount must be precisely controlled.
(3) Preheating
Use infrared or hot air heating to uniformly heat the PCB and components (90°C-130°C), activate the flux, evaporate the solvent, and reduce thermal shock.
(4) Wave Soldering
As the core link, the molten solder is heated to 250°C-270°C, and the PCB passes through the wave at an inclination angle of 5°-7° with a contact time of 2-6 seconds. Double waves are suitable for complex PCBs.
(5) Cooling
Rapid cooling by forced air cooling or water cooling to solidify the solder, avoid defects, and ensure the solder joint strength and PCB flatness.
(6) Pin Cutting and Cleaning
Trim the protruding pins and clean the solder dross and flux residues. Cleaning can be omitted if the no-clean flux meets the standard.
(7) Inspection and Touch-Up Soldering
Check for defects such as cold solder joints and bridging, touch up unqualified solder joints, and the qualified products enter the next link.
III. Common Defects and Countermeasures
Common defects of wave soldering and simple countermeasures: 1. Cold solder joint: Optimize preheating and soldering temperature, adjust the conveyor speed; 2. Bridging: Reduce soldering temperature and standardize flux application; 3. Solder spike: Control temperature and clean the solder pot impurities; 4. Solder ball: Optimize the flux process and increase the preheating temperature.
IV. Application Value and Development Trend
The core value of wave soldering lies in high efficiency, stable quality and controllable cost, which is suitable for mass production. In the future, it will upgrade towards lead-free and intelligence. The double-wave and triple-wave technologies will be continuously improved to adapt to the soldering needs of high-density PCBs and help the development of the electronic manufacturing industry.
