Three Core Technologies of Vacuum Coating for Phone Cases: Evaporation Coating,Magnetron Sputtering Coating, Ion Coating

Three Core Technologies of Vacuum Coating for Phone Cases: Evaporation Coating, Magnetron Sputtering Coating, and Ion Coating

In the smartphone accessory market, the functions of phone cases have gone beyond simple protection. They also possess anti-scratch, wear-resistant, anti-fingerprint, and colorful decorative properties. The realization of these features is inseparable from the support of vacuum coating technology. Vacuum coating is a process carried out in a high-vacuum environment, where materials such as metals, ceramics, and polymers are deposited on the surface of the phone case through physical or chemical methods to form a film. Among these, vacuum evaporation coating, magnetron sputtering coating, and ion coating are the three most widely used methods. This article will provide a comprehensive understanding of the mysteries of these three core technologies from aspects such as technical principles, process flow, performance characteristics, and application scenarios.

1. Vacuum Evaporation Coating: The Entry-Level Choice with Low Cost and High Appearance Quality

Vacuum evaporation coating (Vacuum Evaporation Coating) is the earliest vacuum coating technology applied in phone case production. With advantages such as low equipment cost, simple operation, and fast coating speed, it is still the mainstream choice for mid-to-low-end colorful phone cases to this day.

1.1 Technical Principle: High Temperature Vaporization and Gas Phase Deposition

The core principle of vacuum evaporation coating is the "high-temperature vaporization - gas phase flight - low-temperature deposition" physical process. In a sealed vacuum chamber, through methods such as resistance heating and electron beam bombardment, the coating materials (such as aluminum, chromium), oxides (such as silicon dioxide, titanium dioxide) are heated above their melting points, causing them to rapidly vaporize or sublimate, forming a high-density gas state particles. These particles, almost unaffected by air molecules in the high-vacuum environment, move in a straight line and collide with the pre-cooled surface of the phone case. Due to the rapid temperature drop, they quickly condense, forming a uniform film layer.

This process is similar to hugging cold glass with water vapor in winter. The difference is that vacuum evaporation coating takes place in an environment without air interference, allowing the gas state particles to deposit orderly, avoiding defects such as air holes and impurities in the film layer.

1.2 Core Process Flow

The complete process of vacuum evaporation coating for phone cases can be divided into three stages: pre-treatment, evaporation coating, and post-treatment. The differences from other vacuum coating technologies lie mainly in the evaporation stage:

Pre-treatment stage: First, sort the phone cases and process them according to PC, TPU, glass, etc. materials; then, use ultrasonic cleaning to remove surface oil, dust, and release agents, with the cleaning temperature controlled at 40-60°C and time 10-20 minutes; after cleaning, place the phone cases in a vacuum drying oven and dry at 60-80°C for 15-30 minutes to ensure no moisture residue on the surface; for PC/TPU and other inert plastic materials, some manufacturers may add plasma activation steps to enhance the adhesion of the film layer.

Evaporation coating stage: Fix the dried phone cases on a rotatable fixture holder and send them into the vacuum chamber and close the door; start the vacuum pump to evacuate the vacuum chamber, reducing the pressure to 10⁻³-10⁻⁵Pa in a high-vacuum state; perform 50-80°C degassing in the vacuum chamber to remove residual water vapor in the chamber; place the evaporation material in the evaporation boat (resistance heating) or crucible (electron beam heating) and start the heating source; the heating temperature of the electron beam can reach 1000-2000°C, causing the evaporation material to rapidly vaporize; the fixture rotates at 5-10 r/min to ensure uniform film deposition, with the film thickness controlled at 50-200 nm; to achieve a colorful effect, different refractive index evaporation materials can be replaced successively to form rainbow colors, gradient colors, etc. visual effects.

Post-treatment stage: After the coating is completed, introduce dry nitrogen gas to break the vacuum in the vacuum chamber, wait for the temperature to drop to room temperature, and then remove the phone case. For some products, a post-curing process at 80-100°C for 30-60 minutes is carried out; finally, through tests such as the grid test and appearance inspection, qualified products can be packaged and shipped.

3. Performance Characteristics and Application Scenarios

The advantages of vacuum evaporation coating are very prominent: the equipment investment is low, and the price of a single small-scale evaporation coating machine is only several hundred thousand yuan; the coating speed is fast, and the single batch processing time is usually within 30 minutes; it can achieve rich decorative effects, such as metallic texture and colorful gradient, meeting the appearance needs of the general consumers for mobile phone cases.

However, this technology also has obvious shortcomings: the adhesion and density of the film layer are poor, and the wear resistance is average. Generally, it can only withstand 200-500 times of rubber friction tests; the film layer structure is relatively loose, and it is prone to peeling and scratches during long-term use.

Based on these characteristics, vacuum evaporation coating is mainly applied to mid-to-low-end decorative mobile phone cases, especially PC cases and TPU cases that emphasize "high appearance level and low price", common products include metal-colored mobile phone cases, rainbow gradient cases, etc., with prices usually below 50 yuan.

II. Magnetron Sputtering Coating: The Preferred Choice for High Wear Resistance and Anti-Fingerprint Performance

Magnetron Sputtering Coating (Magnetron Sputtering Coating) is a coating technology developed in the 1970s. It uses a magnetic field to confine electrons to bombard the target material, causing the target material atoms to be sputtered and deposited to form a film. Compared with vacuum evaporation coating, the adhesion, density, and wear resistance of the film layer have significantly improved, and it is the core implementation method for anti-scratch and anti-fingerprint functions of mid-to-high-end mobile phone cases.

1. Technical Principle: The Synergistic Effect of Magnetic Field and Electric Field

The core principle of magnetron sputtering is "plasma bombardment - atomic sputtering - film deposition". In the vacuum chamber, inert gases such as argon are introduced, and a high-voltage electric field is used to ionize the argon gas to form plasma (containing electrons and argon ions). At the same time, a magnetic field is set behind the target material to form a perpendicular composite field with the electric field. Electrons move in a spiral path under the action of the composite field and cannot directly bombard the anode but continuously collide with argon molecules, generating more plasma; argon ions are accelerated by the electric field force and collide with the surface of the target material, causing target material atoms to gain sufficient energy to break free from the lattice bond and form sputtered particles; these sputtered particles deposit on the surface of the mobile phone case in an unordered manner, due to the high energy of the particles, the deposited film layer is extremely dense and firmly bonded to the substrate.

Compared with vacuum evaporation coating, the particle deposition process of magnetron sputtering coating is more "violent", and the formed film layer is like "embedded" in the substrate surface, rather than simply adhering, which is also the key reason for its excellent wear resistance.

2. Core Process Flow

The pre-treatment and post-treatment of magnetron sputtering coating are basically the same as vacuum evaporation coating, with the core difference being the coating stage:

Coating stage: The mobile phone case is fixed on the holder and sent into the vacuum chamber. The vacuum is reduced to 10⁻³-10⁻⁵Pa; after degassing, argon gas is introduced into the vacuum chamber to maintain an air pressure of 0.1-1Pa; a high-voltage electric field is applied between the target material and the mobile phone case, and argon gas ionizes to form plasma; the magnetic field behind the target material confines electrons, causing the plasma to continuously bombard the target material, and target material atoms sputter and deposit on the surface of the mobile phone case; the holder rotates and applies a negative bias of 0-100V to further enhance the adhesion of the film layer; if anti-fingerprint function is required, after the metal film layer is deposited, a fluoropolymer target material is replaced to sputter a 10-30nm anti-fingerprint layer; the film thickness is usually controlled at 100-200nm, and the single batch processing time is about 40-60 minutes. Common types of target materials include stainless steel targets (wear-resistant layer), ceramic targets (high hardness layer), DLC-type diamond-like carbon targets (super wear-resistant layer), fluoropolymer targets (anti-fingerprint layer), etc. Different target materials can achieve different performance effects.

3. Performance Characteristics and Application Scenarios

The core advantage of magnetron sputtering coating lies in its excellent performance: the film layer has extremely strong adhesion, no peeling is observed in the scratch test; it has good density, outstanding wear resistance, and can withstand more than 1000 steel wool friction tests; it can achieve multiple functions such as scratch resistance, anti-fingerprint, and corrosion resistance. For some products using DLC targets, the surface hardness can reach HRC 50 or above, approaching the hardness of metal surfaces.

Its shortcomings mainly lie in the high equipment cost, with the price of a single magnetron sputtering coating machine usually exceeding 1 million yuan; the coating speed is slow, and the production efficiency is lower than that of vacuum evaporation coating; the decorative effect is relatively simple, mainly consisting of pure colors and metallic colors, and it is difficult to achieve complex iridescent effects.

Based on these characteristics, magnetron sputtering coating is mainly applied to mid-to-high-end functional phone cases, such as glass cases with "anti-scratch and wear-resistant" features, PC + TPU composite cases, and business phone cases requiring anti-fingerprint functions. The product prices are usually between 50 and 200 yuan, and are commonly found in the accessories of high-end models such as Huawei and Apple.

III. Ion Plating: The High-end Choice for Performance and Appearance Balance

Ion Plating is a composite technology that combines the advantages of vacuum evaporation coating and magnetron sputtering coating. By introducing ion bombardment during the coating process, the film layer has both high adhesion, high density, and excellent decorative effects. It is the preferred coating technology for high-end flagship phone cases.

1. Technical Principle: Synergistic Optimization of Evaporation and Ion Bombardment

The core principle of ion plating is "evaporation vaporization + ion bombardment + deposition formation". It retains the "high-temperature evaporation" coating method in vacuum evaporation coating while drawing on the strengthening means of "ion bombardment" in magnetron sputtering coating. In the vacuum chamber, the evaporation source is heated to vaporize the coating material, forming gaseous particles; at the same time, inert gases such as argon are introduced to ionize and generate plasma; the phone case is used as the cathode and a higher negative bias of 200-500V is applied to attract the ions bombarding the surface of the phone case and the deposited film layer.

The role of ion bombardment is mainly reflected in two aspects: one is to clean the surface of the phone case, removing residual trace impurities and oxide layers, further enhancing the adhesion of the film layer; the other is to refine the crystal grains of the film layer, making the film layer structure more dense, and at the same time improving the hardness and wear resistance of the film layer. This "first evaporation then bombardment" composite method allows the film layer formed by ion plating to have both the uniform appearance of evaporation coating and the excellent performance of magnetron sputtering coating.

2. Core Process Flow

The process flow of ion plating is similar to the previous two technologies, with the core difference lying in the ion bombardment stage during the coating process:

Coating stage: The phone case is fixed on the hanging frame and sent into the vacuum chamber; the vacuum is reduced to 10⁻³-10⁻⁵Pa; after baking to remove air, the evaporation source is heated to vaporize the coating material, forming gaseous particles; inert gases such as argon are introduced into the vacuum chamber to ionize and generate plasma; the phone case is applied with a 200-500V negative bias, and the ions are bombarded on the surface of the phone case and the deposited film layer under the electric field force; the hanging frame rotates to ensure the uniformity of the film layer, the deposition temperature is controlled at 100-150℃ to avoid damage to the phone case substrate due to high temperature; the film thickness is controlled at 100-300nm, and the single batch processing time is about 50-70 minutes; if a multi-functional composite effect is required, multiple target materials can be combined, depositing the wear-resistant layer, decorative layer, and anti-fingerprint layer in sequence. According to the differences in the evaporation source and ion source, ion plating can be divided into various sub-types such as arc ion plating and hollow cathode ion plating. Among them, arc ion plating is the most widely used in mobile phone shell coating, capable of producing high-hardness ceramic coatings and metal ceramic coatings.

3. Performance Characteristics and Application Scenarios

The comprehensive performance of ion plating is the most outstanding: the coating layer has extremely strong adhesion, far exceeding that of evaporation plating and sputtering plating, and can withstand more than 2000 wear tests; the coating layer has good density, high hardness, and outstanding scratch and corrosion resistance; it can simultaneously achieve decorative and functional effects, presenting delicate metallic texture and matte effect, and also having anti-fingerprint and anti-oil stain functions; it has strong adaptability to the substrate and can be used for mobile phone shells made of PC, TPU, glass, metal, etc.

The only drawback is that the equipment cost is extremely high. The price of a single ion plating equipment is usually several million yuan, and the production efficiency is slightly lower than evaporation plating, resulting in higher product costs.

Based on these characteristics, ion plating is mainly applied to high-end flagship mobile phone shells, such as luxury brand collaboration shells, professional anti-drop shells, and high-end business shells. The product prices are usually above 200 yuan, and are commonly found in high-end accessories of Samsung and Apple flagship models, as well as "military-grade anti-drop" and "super wear-resistant" high-end functional products.

Four. Technical Development Trends and Consumer Purchase Suggestions

1. Technical Development Trends

As consumers' requirements for the performance and appearance of mobile phone shells continue to increase, vacuum coating technology is developing in three directions: "multi-functional composite", "low cost high performance", and "environmental protection".

In the multi-functional composite aspect, future vacuum coating technology will more often adopt "multi-target material combination" and "multi-layer film deposition" methods, such as ion plating + magnetic control sputtering composite process, which can achieve super wear resistance while also providing rich decorative effects; at the same time, anti-fingerprint, anti-oil stain, and antibacterial functions will be further integrated to meet consumers' diversified needs.

In terms of low cost high performance, the price of magnetic control sputtering coating equipment is gradually decreasing, and some mid-to-low-end manufacturers have begun to introduce simplified equipment, making the prices of high-end performance mobile phone shells more affordable; at the same time, evaporation plating technology is optimizing the pre-treatment process and film layer structure, gradually improving the wear resistance.

In terms of environmental protection, coating materials are developing towards no chromium and no heavy metals, reducing environmental pollution; at the same time, the energy consumption in the vacuum coating process is continuously decreasing, and some equipment uses energy-saving vacuum pumps and heating sources to improve energy utilization efficiency.

2. Consumer Purchase Suggestions

When ordinary consumers purchase mobile phone shells, they can choose based on their own needs and budget, combining the characteristics of the three coating technologies:

If you focus on appearance and budget is limited, seeking cost-effectiveness, choose mobile phone shells with vacuum evaporation coating. These products have rich appearances and low prices, suitable for light daily use;

If you focus on practicality, need anti-scratch and wear-resistant functions, and have a medium budget, it is recommended to choose mobile phone shells with magnetic control sputtering coating. These products have balanced performance and can meet most people's daily usage needs, being the mainstream choice in the market;

If you pursue ultimate performance, need super wear resistance, anti-drop, and high-end texture, and have a sufficient budget, you can choose mobile phone shells with ion plating technology. These products usually mark "military-grade anti-drop" and "super wear-resistant" as selling points, suitable for users with high requirements for mobile phone protection.

In addition, when purchasing, you can also judge the quality of the coating layer through simple tests: use your fingernail to scratch the surface, no scratches indicate good hardness; drop a drop of water on the surface, the larger the water droplet angle, the better the anti-fingerprint effect; check the product description to understand the coating process type and wear resistance test data, which can also help make a more accurate choice.

Conclusion The three technologies - vacuum evaporation coating, magnetron sputtering coating, and ion coating - respectively meet the low, medium, and high-end demands of the mobile phone case market, jointly forming the technical system of vacuum coating for mobile phone cases. From a principle perspective, all three achieve film deposition in a high vacuum environment, but through different energy transfer methods, they have formed significantly different film layers; from an application perspective, they cover the entire price range from several dozen yuan to several hundred yuan, meeting consumers' diverse demands for appearance, performance, and price.
With the continuous advancement of technology, vacuum coating technology will be applied more widely in the mobile phone case field. In the future, mobile phone cases will have higher performance, more diverse appearances, and more affordable prices. For consumers, understanding the characteristics of different coating technologies can help us make more rational product choices; for the industry, continuous technological innovation and upgrading will drive the mobile phone case accessory market towards a more high-quality and diverse direction.