In the field of electronic manufacturing, Flexible Printed Circuits (FPC) are widely used due to their bendable, lightweight, and thin characteristics. From smartphones and tablets to wearable devices, FPCs are ubiquitous, providing crucial support for the miniaturization and multi-functionality of electronic products. Soldering is an indispensable key process in the production of FPCs. However, the solder smoke generated during this process has quietly become a hidden killer threatening the health of workers.
1. Analysis of Solder Smoke Composition
Solder smoke produced during soldering is not a single substance but a complex mixture, whose components are closely related to solders, fluxes, and the materials being soldered. In FPC soldering, commonly used solders include tin-lead alloys and lead-free solders (e.g., tin-silver-copper alloys). When these solders melt at high temperatures, they release metal vapors, which quickly cool and condense in the air to form tiny metal particles. For instance, tin exists in the smoke in the form of tin oxide particles.
Flux plays roles in removing oxides and reducing surface tension during soldering, but its composition is also complex, mostly containing rosin, activators, solvents, etc. Among them, halides in activators decompose at high temperatures to produce irritant gases such as hydrogen chloride. In addition, the materials of FPCs themselves, such as polymer materials like polyimide, may decompose under the high temperature of soldering, generating harmful gases such as benzene and formaldehyde.
2. Harm of Solder Smoke to the Respiratory System
The respiratory system is the first to be harmed by solder smoke. These tiny smoke particles, mostly with diameters at the micron or even nanometer level, can easily penetrate deep into the lungs with breathing. Long-term inhalation of smoke containing metal particles (e.g., tin oxide, lead particles) can cause inflammatory reactions in lung tissues. Macrophages attempt to phagocytize these foreign bodies, but some particles are difficult to be completely cleared and gradually accumulate in the lungs. Over time, this may lead to pneumoconiosis, with symptoms such as cough, sputum production, and shortness of breath, seriously impairing respiratory function and reducing quality of life.
Irritant gases such as hydrogen chloride and formaldehyde can irritate the respiratory mucosa, triggering respiratory inflammation. In the early stage, this may manifest as sore throat and cough; long-term exposure may develop into chronic respiratory diseases such as chronic bronchitis and asthma. According to relevant occupational health research data, workers who have worked in poorly ventilated soldering workshops for more than 5 years have a risk of chronic respiratory diseases several times higher than that of the general population.
3. Potential Threat to the Nervous System
Certain components in solder smoke, such as heavy metals like lead and manganese, have toxic effects on the nervous system. After entering the human body, lead can reach the brain through blood circulation, interfering with the normal transmission of neurotransmitters and affecting the function of the nervous system. Long-term exposure to lead-contaminated solder smoke may cause workers to experience symptoms such as headache, dizziness, fatigue, and memory loss. In severe cases, it can damage the central nervous system, leading to problems such as cognitive impairment and slow reaction.
Manganese exists in the smoke in forms such as manganese oxide and also has neurotoxicity. In the early stage of chronic manganese poisoning, patients often present with neurasthenic syndrome, such as insomnia, dreaminess, and listlessness. As the poisoning worsens, symptoms of extrapyramidal nerve damage may appear, such as limb tremors, slow movements, and rigid expressions—similar to the manifestations of Parkinson's disease—seriously affecting the patient's ability to take care of themselves.
4. Irritating Damage to the Skin and Eyes
In FPC soldering sites, workers' skin and eyes are also frequently affected by solder smoke. Chemical substances in the smoke, such as organic solvents in flux and irritant gases, can damage the skin's barrier function after contacting the skin, leading to dryness, itching, redness, and contact dermatitis. If the skin is exposed repeatedly for a long time, problems such as skin keratinization and chapping may also occur.
As one of the most sensitive organs of the human body, the eyes are more sensitive to the irritation of solder smoke. Tiny particles and irritant gases in the smoke can cause symptoms such as eye stinging, tearing, and conjunctival congestion when contacting the eyes. Long-term exposure to such an environment can easily trigger eye diseases such as conjunctivitis and keratitis; in severe cases, it may affect eyesight, bringing great inconvenience to workers' daily life and work.
5. Unignorable Carcinogenic Risks
Some components of solder smoke have been classified as carcinogens by the International Agency for Research on Cancer (IARC). For example, polycyclic aromatic hydrocarbons produced during soldering, as well as certain heavy metal compounds (e.g., hexavalent chromium compounds), may increase the risk of cancer with long-term inhalation. In FPC soldering, due to the complexity of materials and processes used, the types of carcinogens generated may be more diverse. For workers engaged in soldering for a long time, the risk of developing cancers such as lung cancer and bladder cancer is significantly increased. A study that followed up the health status of a large number of soldering workers found that their incidence of lung cancer was significantly higher than that of the general population, which is closely related to long-term exposure to the solder smoke environment.
The harm of solder smoke to human health is comprehensive and serious. With the widespread application of FPC soldering technology, both enterprises and individual workers must attach great importance to the protection against solder smoke. Enterprises should optimize workshop ventilation systems, adopt advanced smoke purification equipment, and provide workers with high-quality personal protective equipment, such as professional protective masks and goggles. Workers themselves should also enhance their awareness of protection, strictly abide by safety operating procedures, and conduct regular occupational health examinations to detect potential health problems at an early stage. Only in this way can we promote the development of the electronic manufacturing industry while effectively safeguarding the health of workers.
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