How to remove the three-proof paint?

Complete Guide to Conformal Coating Removal: From Principles to Operational Standards

In the precision-driven fields of electronics manufacturing and electrical maintenance, conformal coating removal is akin to "precision surgery" – requiring complete stripping of the protective coating while ensuring the integrity of the PCB substrate and components. This seemingly simple operation actually involves the cross-application of materials science, chemical engineering, and electronic processes. As an innovative enterprise with over a decade of deep expertise in the electronic adhesive sector, and based on accumulated research on thousands of conformal coating formulations, Noble has systematically established a scientific and comprehensive removal technology system, providing the industry with full guidance from theory to practice.

 I. Technical Prerequisites and Decision Logic for Conformal Coating Removal

 Conformal coating removal is not a blind operation; it is based on accurate judgment of coating characteristics and substrate condition. With the ongoing miniaturization of electronic components (e.g., the widespread use of 01005 packages), removal precision requirements have escalated to the 0.1mm level. Any operational error can lead to solder joint detachment or circuit corrosion. Therefore, before selecting a removal method, the following three fundamental assessments must be completed:

 (I) Coating Characteristic Analysis

 -   Physical Parameter Measurement: Use a film thickness gauge to measure coating thickness (typically 50–150Мm), a Shore durometer to determine coating hardness (typically in the D60–D80 range), and an adhesion tester to evaluate the bond strength between the coating and substrate (≥5N/cm indicates strong adhesion). These data directly influence the choice of removal method – thick coatings (>100Мm) are more suitable for chemical dissolution, whereas thin coatings (<50Мm) can be removed mechanically.

 -   Chemical Type Identification: Process according to the base material composition of the conformal coating:

-   Acrylics: Easily dissolved by ketone-based solvents, suitable for chemical cleaning.

-   Silicone Rubbers: Heat resistant but low mechanical strength, suitable for thermal peeling.

-   Polyurethanes: Strong adhesion and solvent resistance, require a combination of heat and chemical action.

-   Epoxy Resins: High hardness, typically require abrasion combined with solvent treatment.

(II) Substrate Sensitivity Testing

Develop differentiated plans based on the protection needs of different materials:

-   Copper Traces: Avoid acidic cleaners (pH<5) to prevent etching.

-   Aluminum Heat Sinks: Prohibit strong alkaline solutions (pH>12) to prevent damage to the oxide layer.

-   Plastic Components (e.g., ABS housings): Test solvent compatibility to avoid swelling.

-   Precision Chips: Strictly prohibit high temperatures (>120°C) and mechanical shock.

 (III) Scenario Adaptation Principles

 Select the optimal solution based on the working environment:

-   Mass Production Line Processing: Prioritize automated chemical cleaning (coupled with ultrasonic equipment).

-   Field Maintenance Operations: Suitable for portable hot air guns + localized solvent treatment.

-   Laboratory Precision Operations: Recommend micro-abrasion coupled with optical inspection.

-   Explosion-Proof Environments (e.g., gas station equipment): Must use spark-free mechanical tools and explosion-proof solvents.

 II. Physical Removal Technology System and Operational Standards

 Physical removal techniques rely on mechanical force or thermal energy to achieve coating剥离, with the core advantage of avoiding chemical pollution, but they demand extremely high operational precision.

 (I) Mechanical Removal Techniques

 -   Precision Scraping Method

-   Tool Selection: Select scrapers of different specifications based on coating thickness – 0.1mm thin-blade plastic scraper (for <50Мm coatings), 0.3mm stainless steel scraper (for 50–100Мm coatings), combined with a 30° sharp angle design for precise.

-   Operational Key Points: Maintain a 15°–30° angle between the scraper and the board surface, use a "pushing scrape" method rather than a "pulling scrape" method, keep each scraping stroke under 5mm to avoid stressing the circuits.

-   Typical Application: Localized coating removal around chips on mobile phone motherboards, performed under a magnifying glass (10x).

 -   Brush Cleaning Method

-   Tool Characteristics: Nylon brush (hardness 600–800 grit) suitable for preliminary cleaning, hog bristle brush (hardness 1000–1200 grit) for fine treatment, anti-static brush (surface resistance <10⁹Ω) for sensitive electronic areas.

-   Operational Standards: Use a "spiral sweeping" technique, spreading out from the center, apply pressure ≤50g, coupled with simultaneous vacuuming to remove debris.

 -   High-Pressure Airflow Method

-   Equipment Parameters: Use an adjustable pressure air source (0.2–0.5MPa), fitted with a 0.3mm nozzle, maintain a distance of 10–15cm from the board surface, airflow angle 45°.

-   Applicable Scenarios: Removing loose coating debris, especially suitable for crevice areas like connectors and sockets.

 (II) Thermodynamic Removal Techniques

 -   Localized Heating Method

-   Soldering Iron Application: 30W temperature-controlled soldering iron (set to 250–300°C), iron tip covered with a high-temperature silicone sleeve, single point heating time ≤3 seconds to prevent pad overheating.

-   Hot Air Gun Operation: Use a digital hot air gun (accuracy ±5°C), set to 300–350°C (for acrylics) or 400–450°C (for silicone rubbers), airspeed level 3–5, movement speed 5–10mm/s, use metal baffles to control the heating area.

 -   Low-Temperature Embrittlement Method

-   Technical Principle: Utilize dry ice (-78.5°C) to rapidly embrittle the coating, coupled with a micro pneumatic hammer (impact force 5–10N) for剥离.

-   Operational Process: Dry ice blast for 3–5 seconds → pause for 2 seconds → light tapping with pneumatic hammer → vacuum removal of debris. Suitable for thick coatings (>150Мm).

 (III) Micro-Abrasion Technology System

 -   Electric Abrasive Tools

-   Equipment Configuration: Variable speed abrasive pen (3000–10000 rpm), fitted with diamond burrs (diameter 0.5–2mm), equipped with vacuum dust extraction.

-   Parameter Control: Use low speed (3000–5000 rpm) + light pressure (10–20g) for thin coatings; use high speed (8000–10000 rpm) + medium pressure (30–50g) for thick coatings.

 -   Laser Removal Technology

-   High-End Solution: 1064nm fiber laser (power 5–20W), pulse width 10–50ns, spot diameter 50–100Мm, removes coating through non-contact vaporization. Suitable for areas around ultra-small components like 0201.

 III. Chemical Removal Technology and Safety Control

 Chemical removal relies on the solvent's dissolving, swelling, or saponifying action to剥离 the coating. It is efficient but requires strict control of safety risks.

 (I) Solvent System Classification and Application

 -   Polar Solvents

-   Acetone-based solvents: Suitable for acrylic conformal coatings, dissolution time 3–5 minutes, can be reduced to 1 minute with ultrasound (40kHz).

-   Cyclohexanone solution: For polyurethane coatings, requires immersion for 5–10 minutes, temperature controlled at 25–35°C to accelerate the reaction.

 -   Non-Polar Solvents

-   Toluene-ethanol mixture (ratio 3:1): Used for removing epoxy coatings, forms a paste-like residue after dissolution, requires secondary cleaning with isopropyl alcohol.

-   Fluorocarbon solvents: Eco-friendly option (ODP value 0), strong dissolving power for silicone rubber conformal coatings, suitable for precision electronic components.

 -   Specialized Debonders

-   Nuofeer NF-801 Type: Designed for composite coatings, contains special chelating agents, can dissolve multi-layer conformal coatings within 5 minutes, non-corrosive to PCB substrates.

-   Safety Characteristics: LD50 (oral, rat) >5000mg/kg, classified as low toxicity, Volatile Organic Compound (VOC) content <100g/L.

 (II) Operational Process Standards

 -   Pre-treatment Stage

-   Masking Protection: Use high-temperature resistant tape (withstand temp ≥150°C) to cover areas not requiring removal, especially corrosion-prone parts like connectors and sockets.

-   Test Verification: Perform a small area test on a non-critical area at the edge of the PCB, observe for 10 minutes to confirm no substrate damage.

 -   Main Treatment Stage

-   Application Method: Use a micropipette for precise droplet application (for small areas) or immersion treatment (for large areas), liquid level should just cover the coating.

-   Reaction Control: Judge the degree of dissolution through timed observation, avoid over-immersion (maximum not exceeding 30 minutes).

 -   Post-treatment Stage

-   Residue Removal: Use a lint-free cloth moistened with isopropyl alcohol for wiping, coupled with a soft brush for cleaning crevices, followed by rinsing 2–3 times with deionized water.

-   Drying Process: Oven dry at 60°C for 30 minutes, or air dry at room temperature for 2 hours, ensuring no solvent residue remains.

 (III) Safety Protection System

 -   Personal Protective Equipment (PPE)

-   Respiratory System: Half-mask respirator (fitted with organic vapor cartridges), use supplied-air respirators in confined spaces.

-   Hand Protection: Nitrile rubber gloves (thickness ≥0.1mm), change every hour or immediately upon contamination.

-   Eye Protection: Chemical splash goggles (with side shields), use face shields for splash risk scenarios.

 -   Environmental Control

-   Ventilation Requirements: Local exhaust ventilation system air volume ≥1000m³/h, ensure solvent concentration in the work area is below 10% of the Lower Explosive Limit (LEL).

-   Electrostatic Protection: Floor resistance 10⁶–10⁹Ω, operators wear anti-static wrist straps (grounding resistance 1MΩ).

-   Waste Disposal: Solvent-containing waste liquid must be placed in explosion-proof containers and handled by qualified units; must not be discharged arbitrarily.

 IV. Quality Verification and Subsequent Processing

 Evaluation of removal effectiveness requires multi-dimensional inspection:

 -   Visual Inspection: Under 200 lux illumination, observe with a 10x magnifier, requirements:

-   No residual coating (≤5%in non-critical areas is permissible).

-   No circuit scratches (copper foil loss ≤0.01mm²).

-   No solder joint damage (solder joint pull-off force maintained at ≥80% of original).

 -   Functional Testing:

-   Insulation Resistance: Resistance between test points ≥10¹⁰Ω (500V DC).

-   Continuity Test: Change in conduction resistance for all circuits ≤10%.

-   Temperature Resistance Test: No failure after 10 cycles of thermal shock from -40°C to 125°C.

 -   Subsequent Processing:

-   Localized Recoating: Apply the same type of conformal coating to the removed area, control thickness to 30–50Мm.

-   Overall Inspection: Perform 100% visual and functional re-test after the recoating has cured, ensuring consistency with the original state.

           Nuofeer's validation through numerous practical cases shows that scientific removal technology not only restores the repairability of circuit boards but also maximally preserves their original protective performance. In 5G base station repair projects, using the combined "localized heating + specialized debonder" solution reduced single-board repair time from 4 hours to 1.5 hours, with post-repair equipment operational stability reaching 99.8%. In the future, with the development of conformal coating materials (such as self-healing coatings), removal technology will also evolve towards greater precision and environmental friendliness. Nuofeer will continue to invest in R&D to provide the industry with more advanced solutions.

          Against the backdrop of the intelligent transformation in electronics manufacturing, conformal coating removal has evolved from a mere repair process to a crucial link in process optimization. Simulating the removal process through digital twin technology, combined with machine vision for automated operation, can elevate removal precision to the 0.05mm level. This requires practitioners not only to master traditional techniques but also to understand the synergistic application of new material properties and intelligent equipment, thereby promoting the industry's advancement towards efficient, green, and precision manufacturing while ensuring the reliability of electronic devices.