Common Faults of Vacuum Coating Machines and Maintenance Strategies 

Vacuum coating technology, as a core technology in the field of precision manufacturing, is widely applied in electronics, optics, automotive, aerospace and other industries. It deposits metals, non-metals and other materials onto the surface of substrates in a vacuum environment, forming films with wear resistance, corrosion prevention and optical properties. Vacuum coating machines are the key equipment for realizing this process, with complex structures and high precision requirements. They cover multiple core modules such as vacuum systems, coating systems, electrical control systems and auxiliary systems. During long-term high-load operation, affected by factors such as environment, operation and wear, the equipment is prone to various failures, which not only affect the coating quality and production efficiency but also may shorten the equipment's service life. Therefore, in-depth analysis of the common faults of vacuum coating machines and the formulation of scientific and standardized maintenance strategies are of great significance for ensuring stable production and reducing operation and maintenance costs.

This article, based on the working principle and practical application scenarios of vacuum coating machines, systematically analyzes the manifestations, causes and solutions of various common faults, and summarizes comprehensive maintenance points. It provides references for relevant operators and maintenance personnel, helping to enhance the stability of equipment operation and production efficiency.

The core working logic of the vacuum coating machine is to reduce the pressure inside the sealed vacuum chamber to the required vacuum level through the vacuum pump group. Then, using methods such as evaporation, sputtering, and ion plating, the coating material is transformed into gaseous or plasma state, allowing it to be uniformly deposited on the substrate surface and forming a dense film. The normal operation of the equipment relies on the sealing performance of the vacuum system, the stability of the coating system, the accuracy of the electrical control system, and the coordination of the auxiliary systems. Any abnormality in any module will lead to equipment failure or substandard coating quality.

The faults of the vacuum coating machine mainly occur in four major modules: the vacuum system, the coating system, the electrical control system, and the auxiliary system. Among them, the faults of the vacuum system and the coating system have the highest occurrence rate and directly affect the process effect. Therefore, they need to be given special attention.

The vacuum system is the core component of a vacuum coating machine. Its main function is to maintain a high vacuum environment within the chamber, ensuring the smooth deposition of the coating material and minimizing the impact of air impurities on the quality of the film layer. Common faults include failure to reach the set vacuum level, sudden drop in vacuum level, and inability to start the vacuum pump.

This is the most common fault in the vacuum system, manifested as the vacuum gauge showing a value consistently higher than the process requirements after the equipment starts, unable to achieve the high vacuum state required for coating. The main causes include:

• aging, cracking or improper installation of the sealing ring, resulting in poor cavity sealing and air leakage;
• loose pipe connections or minor cracks causing vacuum leakage;
• needle holes, welding defects or severe internal contamination on the vacuum chamber wall affecting the vacuum extraction efficiency;
• contamination, insufficient oil level or wear of pump body components in the vacuum pump, leading to a decrease in vacuum pumping capacity;
• contamination, damage or invalid calibration of the gauge tube, resulting in reading deviations.

Solution:

• First, check the sealing ring. Clean the sealing ring regularly and replace it every 6-12 months. Ensure a tight and undamaged fit during installation.
• Use a helium mass spectrometer leak detector to locate the leak points, tighten loose pipelines, repair cracks, pinholes, etc., and recheck for leaks after repair.
• Regularly clean the residual coating materials and impurities on the inner wall of the vacuum chamber. Conduct pressure tests when necessary.
• Check the oil level and quality of the vacuum pump. Replace the vacuum oil every 200-500 working hours, keeping the oil level above the scale line. If the pump body components are worn, repair or replace them in time.
• Clean the vacuum gauge tube regularly. Calibrate it once every 12 months. Replace it immediately if damaged.

This is manifested as a sharp decline in vacuum level during the operation of the equipment, which fails to meet the process requirements. It is often accompanied by defects such as pinholes and color spots in the coating layer. The main causes include:

• pump body failure, such as overheating of the diffusion pump or jamming of the rotor of the mechanical pump;
• severe contamination inside the vacuum chamber, with the volatilization of residual substances leading to an increase in gas;
• insufficient cooling water flow, causing the pump body to overheat and affecting the efficiency of vacuum extraction;
• damage to the sealing gaskets at the evaporation source water path and the high-voltage electrode sealing area, resulting in leakage;
• malfunction of high valves, pre-valves, etc., causing sealing failure.

Solution:

• Immediately shut off all heating sources, start nitrogen to break the vacuum, and wait for the chamber to cool down before troubleshooting;
• Check the operation status of the vacuum pump, clean the diffusion pump annually and replace the special oil. If the mechanical pump gets stuck or makes abnormal noises, disassemble and repair it in time;
• Regularly clean the vacuum chamber. After every 50 coating cycles, perform argon ion etching on the chamber to remove residual contaminants;
• Check the cooling water circuit to ensure the flow rate is not less than 5L/min, clear the blockages in the pipeline, and ensure the normal operation of the cooling system;
• Replace the damaged sealing gasket, inspect and maintain the valves to ensure reliable sealing.

This is manifested as no response from the pump body after pressing the start button, and it cannot enter the vacuum pumping state. The main causes include:

• power failure, such as unstable voltage, circuit short circuit, or fuse melting;
• motor damage or overheating protection triggered;
• severe contamination of the oil inside the pump or insufficient oil level, resulting in the pump body getting stuck;
• faults in relays and contactors, with burned-out or stuck contacts.

Solution:

• First, check the power lines and voltage stability. Ensure that the voltage fluctuation is within ±5%. Replace the blown fuses.
• If the motor is overheating, wait for the pump body to cool down and then restart it. If the motor is damaged, replace it promptly.
• Check the oil level and quality of the vacuum pump. Replace the contaminated vacuum oil and refill it to the standard level.
• Check the relays and contactors. Repair or replace faulty components to ensure normal circuit conduction.

The coating system is responsible for converting the coating material into gaseous or plasma state and depositing it onto the substrate surface. Its failures mainly manifest as non-compliance with the quality standards of the coating layer, such as the detachment of the coating layer, uneven thickness, and deterioration of the coating quality, which directly affect the qualification rate of the products.

This is manifested as the separation of the film layer from the substrate surface and the peeling off in large patches, with extremely poor adhesion. The main causes include:

• contamination of the substrate surface, such as the presence of oil stains, moisture, dust, and other impurities;
• insufficient baking and cleaning of the substrate before coating, resulting in an oxide layer on the substrate surface;
• excessive stress in the film layer, which does not match the thermal expansion coefficient of the substrate;
• deviation of the evaporation source and sputtering target position, leading to uneven film layer deposition;
• and non-normal operation of the ion source, with insufficient pre-coating bombardment cleaning.

Solution:

• Strengthen the pre-treatment of the substrate, using ultrasonic cleaning (deionized water + alcohol) combined with ion bombardment (bias - 800V to -1200V, duration 5-15 minutes) to ensure the cleanliness of the substrate surface reaches atomic level;
• Before coating, fully bake the substrate, heating the metal substrate to 150-200℃ to release internal stress, and controlling the plastic substrate below 80℃ to prevent deformation;
• Optimize process parameters, adjust the matching between the coating material and the substrate to reduce the stress of the film layer;
• Adjust the position of the evaporation source and the target, ensure alignment with the center of the substrate, use tooling fixtures to fix the substrate, avoid obstruction;
• Check the operation status of the ion source to ensure that the pre-bombardment cleaning before coating is complete.

This is manifested as a deviation of more than ±5% in the thickness of the membrane layer on the same substrate surface or on different substrate surfaces, which does not meet the process requirements. The main causes include:

• deviation of the deposition source or unstable rotation speed of the crucible;
• the substrate not being firmly fixed or being obstructed, malfunction of the rotating mechanism;
• interference from magnetic and electric fields causing beam deflection;
• failure of the thickness meter (crystal control instrument) calibration, deviation of the probe position or contamination;
• fluctuations in process parameters, such as unstable evaporation rate and uneven gas flow.

Solution:

• Adjust the position of the deposition source to align with the center of the substrate, check the rotation speed of the crucible, repair any faults in the rotating mechanism;
• Use tooling fixtures to secure the substrate, avoiding any obstructions, and ensure uniform rotation of the substrate;
• Check the parameters of the electromagnetic coils, optimize the beam trajectory, and reduce electromagnetic interference;
• Calibrate the crystal controller instrument quarterly using standard film thickness sheets, clean the probe surface, and adjust the probe to the optimal position of 5-10 cm from the substrate;
• Stabilize the power supply voltage to ensure stable evaporation rate and gas flow rate, and control the accuracy error of the gas flow meter within ±1%.

This is manifested as pinholes, color spots, fogging and other defects on the film layer, and the performance indicators such as glossiness, hardness, and wear resistance do not meet the standards. The main causes include:

• the vacuum chamber has not been fully evacuated, and there are residual impurities such as water vapor and oxygen;
• air leakage during the coating process leads to gas contamination;
• the film material absorbs moisture or contains impurities, and pollutants are generated during evaporation and sputtering;
• the filament and beam system is abnormal, resulting in insufficient ionization of the coating material;
• the heating system fails, causing the substrate temperature to fail to reach the set value or fluctuate excessively.

Solution:

• Before coating, evacuate the vacuum chamber to a pressure of ≤ 5*10⁻⁴ Pa and perform baking to remove the residual gas in the vacuum chamber;
• inspect all sealing interfaces, replace aged sealing components to prevent air leakage;
• pre-melt the coating material in the vacuum chamber before use to remove moisture and impurities, and select qualified pure coating materials;
• check the filament condition, replace burned-out or aged filaments, ensure the installation position is centered, reset the beam limiter to zero after pre-melting and then start;
• inspect the heating elements, temperature controller and thermocouple, repair any short circuits or poor contact issues, re-tune the PID parameters of the temperature controller, adjust the thermocouple to the center position of the substrate, and calibrate annually.

The electrical control system is the "brain" of the vacuum coating machine, responsible for coordinating the operation of various modules. Its failures mainly manifest as the operation panel not responding, abnormal parameter display, and program失控, resulting in the equipment being unable to operate normally.

If the operation panel does not respond or the parameter display is abnormal, it is usually caused by the control board getting damp or covered with dust, the sensor connection being loose or damaged, or the software program crashing. Solution: Regularly clean the control cabinet with dry compressed air to prevent the control board from getting damp and dusty; check the sensor lines, repair loose connectors, and replace faulty sensors; restart the system or reinstall the control software to restore normal program operation. When the program is out of control and the process parameters cannot be adjusted, it is usually caused by PLC industrial computer failure, communication interruption, or inverter failure. Solution: Check the PLC operation status, troubleshoot communication lines, repair communication interruption problems; check the inverter, investigate overload, overvoltage, overcurrent and other alarm information, and repair or replace faulty components.

The auxiliary systems include the cooling system, gas supply system, etc. Although they do not directly participate in the core process of coating, they are crucial for the normal operation of the equipment and the quality of the coating. Common faults are as follows:

This is manifested as overheating of the pump body, target material, and heating components during equipment operation, and even triggering overheating protection and stopping the machine. The main causes include:

• too low water level in the cooling water, poor water quality leading to decreased cooling efficiency;
• blockage or bending of the cooling pipeline, poor water flow;
• pump failure, blocked heat exchanger;
• improper valve opening or accidental closure.

Solutions:

• Regularly check the water level of the cooling water, replenish the cooling water, and replace the cooling water regularly to prevent algae growth and scaling;
• remove the blockages in the cooling pipeline, straighten the bent pipelines to ensure smooth water flow;
• check the operating status of the pump, repair or replace the faulty pump, and clean the blockages in the heat exchanger;
• check the opening degree of the valves to ensure they are fully open.

This manifests as unstable process gas flow and inability to supply, resulting in interruption of the coating process or deviation in the composition of the film layer. The main causes include:

• failure or damage of the mass flow controller (MFC) calibration;
• blockage or leakage of the gas path;
• insufficient gas purity and malfunction of the pressure reducing valve.

Solutions:

• Regularly calibrate the mass flow controller, repair or replace faulty components;
• inspect the gas path, remove blockages, identify and tighten leakage points;
• select process gas with qualified purity, check the pressure reducing valve, and ensure stable pressure.

The maintenance of vacuum coating machines should follow the principle of "prevention first, combination of prevention and treatment". Through daily maintenance, regular maintenance and special maintenance, potential faults can be detected in time, extending the service life of the equipment and ensuring stable production. The maintenance work should cover all modules of the equipment, with a particular focus on wear-prone components and core systems.

1. Pre-commissioning inspection:
   • Check whether the power supply and wiring of the equipment are normal, and whether there are any damages or looseness;
   • Check the oil level and quality of the vacuum pump, ensuring that the oil level is within the standard scale and the oil is clear without turbidity;
   • Check whether the sealing rings are intact and clean, and whether there is any aging or damage;
   • Check the cooling system to ensure that the cooling water is sufficient and the water flow is smooth;
   • Check the gas supply system to ensure that the gas pressure is stable and there is no leakage in the gas path;
   • Check the operation panel parameters to confirm that the equipment is in a normal standby state.
2. Post-shutdown maintenance:
   • Shut off all power supplies, gas valves, and cooling water valves of the equipment;
   • Clean the inner walls of the vacuum chamber, the workpiece holder, and the observation window, using a lint-free cloth dipped in isopropyl alcohol to remove any remaining coating materials and impurities;
   • Clean the dust on the equipment surface, organize the circuits and pipelines;
   • Record the equipment's operating status, faults, and process parameters, and establish an operation file.

1. Weekly Maintenance:
   • Check the operating condition of the vacuum pump, listen for any abnormal sounds or vibrations from the pump body, and clean the surface dust of the pump body;
   • Inspect the seals, clean the sealing rings with anhydrous ethanol, apply special lubricating grease to enhance the sealing performance;
   • Check the cooling pipeline, clear the blockages in the filter;
   • Inspect the base fixtures to ensure they are securely fixed and without deformation.
2. Monthly Maintenance:
   • Replace the vacuum pump oil and clean the internal impurities of the pump body;
   • inspect the vacuum gauge tube, clean and calibrate it;
   • check the heating elements and thermocouples to ensure secure connections and normal operation;
   • clean the gas pipelines and identify any leakage points;
   • conduct a comprehensive cleaning of the vacuum chamber, and perform argon ion etching if necessary.
3. Quarterly Maintenance:
   • Inspect the evaporation source and target material condition, replace worn-out or depleted target materials and evaporation vessels;
   • Calibrate the film thickness meter and mass flow controller to ensure accuracy;
   • Check the electrical control system, clean the control boards and sensors, and tighten the wiring connections;
   • Check the cooling system, clean the internal deposits in the heat exchanger, and replace the aged cooling water pipes.
4. Annual Maintenance:
   • Conduct a comprehensive disassembly inspection of the equipment, replace worn-out seals, bearings, filament and other easily-damaged components;
   • inspect the internal rotors and blades of the vacuum pump, repair worn-out parts;
   • calibrate all instruments and meters to ensure accurate parameters;
   • perform no-load operation tests and process validations on the equipment to ensure it meets performance standards;
   • provide professional training to operators to standardize operation procedures.

1. Special maintenance for wear-prone components:
   • Components prone to wear, such as sealing rings, filament, target material, evaporation boat, etc., should be pre-stored with spare parts according to the usage frequency and wear condition, and replaced in time to avoid equipment shutdown due to component damage;
   • Regularly check the installation conditions of the components to ensure proper installation and avoid faults caused by improper installation.
2. Special Condition Maintenance:
   • For equipment operating in high-temperature, high-humidity, and dusty environments, the maintenance cycle should be shortened, and enhanced sealing protection and cleaning work should be carried out;
   • the inspection frequency of cooling systems and vacuum systems should be increased to prevent equipment failures caused by environmental factors;
   • regular moisture-proof and dust-proof treatments should be conducted on the equipment to ensure its internal dryness and cleanliness.

1. Before maintenance,

   all power supplies of the equipment must be disconnected, gas valves must be closed, and the pressure inside the vacuum chamber must be released to ensure that the equipment is in a safe state. Wait for the high-temperature components to cool down before proceeding with the operation to avoid burns.

2. During the maintenance process,

   operators must wear protective gloves, goggles and other protective equipment to prevent the splashing of coating fragments and the contact of chemical reagents.