Conformal Coating, PCB Cleaner, Flux, and Hot Melt Adhesive – What Are the Health Hazards?

June 27, 2026

A Must-Read for SMT Operations: Safety Hazards and Protection Guide for PCB Cleaner, Flux, Conformal Coating, and Hot Melt Adhesive

In PCB repair, SMT assembly, and circuit board mass production, PCB cleaner (wash water), flux, conformal coating, and hot melt adhesive are the most frequently used auxiliary consumables for engineers and operators. Most people only focus on their process performance, while ignoring the health risks caused by uncured volatiles and long-term exposure.

These electronic chemical auxiliary materials are not absolutely safe. The toxicity, irritation levels, and hazard modes vary greatly among different types. This article provides a comprehensive analysis from four dimensions—composition characteristics, human health hazards, operational risks, and compliant protection—to offer the most practical safety reference for frontline operators.

I. PCB Cleaner (Trichloroethylene): High-Risk Volatile Hazardous Chemical

Conventional industrial PCB cleaner primarily consists of trichloroethylene (TCE), a universal circuit board cleaning agent widely used in the SMT industry. It is colorless, transparent, and has strong degreasing ability, capable of quickly removing flux residues, solder dross, and oil stains from PCBs. However, it is a toxic, flammable, and highly volatile chemical solvent.

✅ Core Physical and Chemical Properties: Low boiling point, fast evaporation rate, capable of generating large amounts of vapor at room temperature; insoluble in water, miscible with alcohols, ethers, and other organic solvents. Under humid and light-exposed conditions, it slowly decomposes to generate hydrochloric acid. When heated to high temperatures or in contact with metals such as iron, copper, and zinc, it produces highly toxic phosgene gas, presenting extremely high risks.

⚠️ Core Health Hazards to Humans:

• Acute Exposure: Short-term inhalation of high-concentration vapors causes rapid irritation to eyes and nose, tearing, nausea, dizziness, limb weakness, accompanied by an alcohol-like numbness. Severe cases may result in vomiting, confusion, limb convulsions, and in extreme cases, coma and respiratory distress.

• Long-term Chronic Exposure: Continuous inhalation of low-concentration volatiles impairs liver function, causing frequent fatigue, dizziness, and lethargy. Prolonged direct skin contact destroys the skin's natural oil barrier, leading to dryness, redness, allergic dermatitis, and recurrent eczema.

🛡️ Operational Protection Guidelines:

• Strictly prohibit operation in enclosed spaces; ensure strong ventilation at workstations.

• Wear nitrile protective gloves and activated carbon anti-toxic masks throughout the entire process; prevent direct skin contact and inhalation.

• Keep away from open flames and high-temperature equipment; avoid vapor combustion and decomposition that produce toxic fumes.

II. Flux: Essential for Soldering, with Hidden Chronic Irritation Risks

Flux is a core auxiliary material for soldering operations. The mainstream composition is rosin + isopropanol + active additives. Daily soldering, drag soldering, and rework operations continuously release fumes. Most people mistakenly believe that the mild odor means no harm, but long-term cumulative damage is significant.

⚠️ Core Health Hazards to Humans:

• High-concentration vapors irritate the eyes, nose, and throat mucous membranes, causing dryness, stinging, and frequent dry coughs.

• Short-term large-volume inhalation causes headaches, drowsiness, loss of balance, and lack of concentration.

• Long-term bare-hand contact: isopropanol continuously degreases the skin, leading to dry cracks, roughness, and peeling on hands.

• Additionally, during high-temperature soldering, flux combined with tin materials produces tin dioxide fumes. Long-term unprotected inhalation continuously irritates the respiratory tract, causing chronic discomfort.

🛡️ Operational Protection Guidelines:

• Workshops must be equipped with local exhaust systems to promptly remove soldering fumes.

• Strictly wear protective gloves and dedicated dust/mist respirators; avoid bare-hand operations.

• No eating or drinking at workstations; wash hands thoroughly after work and develop good hygiene habits.

• Under industry compliance standards, flux vapor concentration in workshops should be controlled within 400ppm; good ventilation significantly reduces risks.

III. Conformal Coating: Protecting the Circuit Board, Also Protect Yourself

Conformal coating is a core protective material for circuit boards against moisture, mold, and salt spray. The mainstream types are acrylic conformal coating and polyurethane conformal coating. Overall, polyurethane outperforms acrylic in performance, with low odor, low toxicity, better insulation, and stronger moisture resistance—making it the future industry trend.

The hazards of conformal coating come entirely from solvents and thinners. Once fully cured, it is basically non-toxic and harmless, and can be safely touched.

⚠️ Core Health Hazards to Humans:

• Low-end conformal coatings often contain benzene-based solvents such as toluene and xylene, which are highly volatile and moderately toxic. Acute exposure causes dizziness, chest tightness, limb weakness, conjunctival congestion, and unsteady gait. Long-term chronic exposure leads to skin cracking, recurrent dermatitis, endocrine disorders, and menstrual irregularities in women. High-concentration exposure can even cause agitation, convulsions, and coma.

• High-end benzene-free polyurethane conformal coatings use alcohol-based and ester-based environmentally friendly solvents, with extremely low odor and minimal irritation. Under standard operating conditions, their harm to humans is negligible.

🛡️ Operational Protection Guidelines:

• Coating and spraying operations must be performed at workstations with adequate ventilation and exhaust systems.

• Wear gas masks, chemical protective gloves, and goggles throughout the process.

• Prioritize benzene-free, environmentally friendly polyurethane conformal coatings to reduce toxicity risks at the source.

IV. Hot Melt Adhesive: Relatively Safe, But Not Entirely Risk-Free

Hot melt adhesive is a commonly used auxiliary material for electronic assembly, wire harness fixing, and structural reinforcement. The mainstream is EVA material—solvent-free, moisture-free, solid at room temperature, melting and curing upon heating, with stable physical properties. It is the safest among the four consumables.

⚠️ Potential Risks:

• Standard EVA hot melt adhesive is non-toxic and harmless, with basically no hidden risks in daily use.

• However, a small number of polyamide and polyester hot melt adhesives release trace amounts of irritating gases during high-temperature melting. Long-term operation in enclosed environments may cause mild respiratory discomfort.

• In addition, high-temperature molten adhesive can easily cause skin burns—the most common operational injury.

🛡️ Operational Protection Guidelines:

• Maintain regular ventilation during hot melt operations; no specialized anti-toxic equipment is required.

• Avoid direct contact with the hot glue nozzle and molten adhesive to prevent burns.

• Choose certified EVA environmentally friendly hot melt adhesives to avoid odors and harmful volatiles from inferior products.

V. Industry-Wide General Safety Operating Standards (Mandatory for All Personnel)

Zoned Operations: Cleaning, coating, and soldering workstations should be physically separated, each equipped with dedicated exhaust systems to prevent hazardous gas diffusion.

Proper Protection: Protective gloves and masks must be worn when handling chemical auxiliary materials. Goggles should be added in high-volatility scenarios. No bare-hand or unprotected-face operations.

Environmental Ventilation: All chemical operations are prohibited in enclosed spaces. Keep windows open and exhaust equipment running constantly to reduce vapor concentration.

Hygiene Standards: No eating or drinking during operations. Thoroughly clean hands and face after work to prevent residual substances from entering the body.

Regular Health Checkups: Long-term frontline operators should undergo regular respiratory and liver function examinations to prevent chronic damage.

Final Remarks

Most of the hazards of SMT electronic auxiliary materials result from long-term cumulative exposure and non-standard operations. PCB cleaner, flux, and conformal coating each have their specific risks, while hot melt adhesive is relatively safe but should not be taken lightly.

Process efficiency is certainly important, but the health of frontline operators is the core bottom line. Choosing environmentally friendly consumables, following standard procedures, and implementing basic protection measures are the only ways to fundamentally avoid occupational health risks.