Until recently, the mobile phone’s external coating primarily consists of a combination of anodized aluminum, stainless steel, and glass, depending on the specific model and version. Here's a breakdown of the coatings used in recent iPhone models:
Picture: courtesy of Apple
Aluminum
Mobile phone models with aluminum bodies, such as the iPhone, typically feature an anodized aluminum coating. Anodization is an electrochemical process that creates a protective layer on the surface of aluminum, making it more resistant to scratches and corrosion. The anodized coating also provides a smooth and sleek finish to the device.
Stainless Steel: The higher-end phone models use a stainless-steel frame. Stainless steel is generally more durable and resistant to scratches than aluminum. The stainless-steel frame undergoes various finishing processes, including polishing, to achieve its shiny appearance.
Glass
The front and back of phones are made of glass. The glass used is typically a strengthened variant, such as Corning's Gorilla Glass. This type of glass is designed to be more durable and resistant to scratches compared to regular glass. Additionally, it undergoes special treatments, such as ion exchange processes, to enhance its strength and durability.
HiPIMS technology
Now things are getting different. HiPIMS (High Power Impulse Magnetron Sputtering) is a coating technology that can be used to enhance the surface properties of various materials, including metals, ceramics, and polymers. Now they are specifically developed for mobile phone coloration. HiPIMS, multicathode-HiPIMS, and bipolar-HiPIMS methods are employed to achieve specific aesthetic finishes and provide durability to the phone's exterior.
HiPIMS applied to the mobile phone coloration delivers unique colors, textures, and even enhanced scratch resistance.
Picture : SEM cross-section of NiCr films. Left: conventional DC-sputtering (columnar growth); right: HIPIMS (dense, glassy structure). Courtesy of R. Bandorf, ... G. Bräuer, in Comprehensive Materials Processing, 2014
HiPIMS (High Power Impulse Magnetron Sputtering) can indeed be used for decorative coatings on various surfaces of mobile phones, including metals and glass. HiPIMS technology offers advantages such as
- improved coating adhesion
- enhanced film density, and
- precise control over film properties.
Decorative coatings and HiPIMS
When it comes to decorative coatings, HiPIMS can be utilized to create excellent functional effects, finishes, and colors. Here are a few examples:
Metallic Finishes on mobile phone frames: HiPIMS can be used to deposit thin metallic films onto a substrate, creating a metallic appearance. This can be particularly useful for achieving a high-quality finish on surfaces like stainless steel or aluminum.
Colored Coatings (selective surface area of mobile phone)
HiPIMS can deposit thin layers of various materials that exhibit different colors at different areas of mobile phone surfaces for tattooing effect. By selecting specific target materials and controlling the process parameters, it is possible to achieve a range of colors and shades, allowing for customization and aesthetic enhancement.
Anti-reflective Coatings
HiPIMS can be utilized to create anti-reflective coatings on surfaces, reducing glare and improving visibility. These coatings are commonly used on displays, lenses, and other optical components.
Wear-resistant Coatings
HiPIMS can deposit hard and durable coatings, such as diamond-like carbon (DLC), that provide wear resistance and protection against scratches, extending the lifespan of decorative surfaces.
It's important to note that the specific coating materials, process parameters, and techniques used in HiPIMS can vary based on the desired decorative effect and the substrate being coated.
Picture courtesy of: Sergei Bezborodov
Manufacturers and coating specialists often have their own proprietary formulations and methods to achieve specific decorative coatings using HiPIMS technology.
To achieve decorative colors using HiPIMS, a combination of specific target materials, such as metals or compounds, and precise control over the process parameters would be necessary. These parameters can include the type of target material, gas composition, pulse frequency, pulse power, and other variables.
Bipolar HiPIMS
Now, Bipolar HiPIMS are planned to be used in the new version of the mobile phone to be released. BiPolar HiPIMS provides far more superiority in bringing color uniformity, color coordinate controls on edges and areas shadowed to the target and coating non-conducting substrates or non-conducting protective layers on the conductive substrates.