The PCB spraying process mainly consists of two core processes: anti-corrosion paint coating and tin spraying, which are respectively used for protection and enhanced welding. The specific process involves key steps such as pre-treatment, spraying operation, curing, and post-treatment. 

Three-anti-corrosion paint coating process flow 

Preprocessing. 

Cleaning: Use a dedicated cleaning agent or ultrasonic waves to remove oil, dust and ionic contamination from the PCB surface (standard requirement: ≤ 1.56 μg/cm²). 2

Baking the board: Preheat at 60℃ for 10-20 minutes to remove moisture and enhance the adhesion of the coating. 3 4

Shading: The non-coated areas (such as connectors) are protected using tape or a laser mask (with an accuracy of 50 μm). 2 4

Application implementation. 

Method Selection:

Brush coating / Dip coating: Suitable for simple board shapes, but with low material utilization rate (dip coating loss reaches 40%). 2

Selective Spraying: Accuracy ± 0.1mm, suitable for components below 0402 or high-density boards. 2 5

Parameter Control: The spraying thickness is usually 25-75 μm. Be sure to avoid run-off or bubbles. 4 6

Solidification and Inspection. 

Curing method: UV curing (dries within 3-5 seconds), thermal curing (gradually heated to 120℃), or moisture curing (humidity 40-60% RH). 2

Quality verification: Through X-ray thickness measurement (with an accuracy of ±1 μm) and salt spray test (no corrosion after 72 hours), etc. 2

Soldering process (HASL) 

Preprocessing. 

Micro-etching: Sodium peroxide solution corrodes the copper surface by 0.5 - 1 μm, enhancing the adhesion of the tin layer. 7 8

Soldering agent application: Uniform spraying to enhance the wetting property of the solder solution. 7

Soldering operation. 

Immersion in tin: Immerse in tin solution at 265 ± 5℃ for 3 to 5 seconds (for lead-free process, it is a Sn96.5/Ag3/Cu0.5 alloy). 8

Hot air leveling: Using a high-pressure air knife at 280-300℃ to level the tin layer, with a thickness controlled at 1-3 μm. 8 9

Post-processing. 

Cooling: Rapid cooling (> 4°C/second) is performed to stabilize the structure of the tin layer. 8

Cleaning: Remove residual soldering flux to prevent corrosion. 7

Process Selection Suggestions 

Protection requirements: In high-reliability scenarios (such as automotive electronics), polyurethane or silicone three-layer anti-corrosion paint (with a temperature resistance range of 150-200°C) should be preferred. 2

Welding requirements: The tin spraying process has low cost and excellent welding performance, but for high-precision boards, it needs to be combined with processes such as gold plating.