PCB spraying process flow

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.