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Applications and Trends of 3D Ceramics in Mobile Phones

Release time:

2016-11-01 14:26

Applications and Trends of 3D Ceramics in Mobile Phones

I. What is ceramics?

Ceramic materials are a class of inorganic nonmetallic materials made from natural or synthetic compounds through shaping and high-temperature sintering. Their main performance characteristics are:

Mechanical properties: High strength and hardness, but poor ductility and toughness, exhibiting a hard and brittle behavior.

Physical properties: Low thermal conductivity, resulting in poor heat dissipation.

Chemical Properties: Corrosion-resistant and chemically stable, demonstrating strong environmental adaptability.

II. What is a 3D ceramic phone back cover?

A ceramic phone back cover is a phone back cover made from ceramic material. As for 3D versus 2D and 2.5D, all phone back covers have a certain thickness. When the top and bottom surfaces are flat and parallel to each other, it’s referred to as 2D. If the top and bottom surfaces remain flat but the edges are polished into rounded curves that smoothly transition from one surface to the other, it’s called 2.5D. In contrast, a 3D glass back cover no longer has flat top and bottom surfaces; typically, the edges feature a significant curvature, giving the entire back cover a U-shaped profile.

3. Why is a 3D ceramic back cover used on mobile phones?

Why use ceramic materials for phone back covers? First, ceramics possess unique advantages: they are highly strong and hard, offering excellent resistance to bending and scratch resistance—precisely the weaknesses of current phone materials, especially aluminum. Second, after surface treatment, ceramic materials exhibit a distinctive texture that feels smooth and delicate, warm and soft like jade, conveying an exceptionally high-quality and aesthetically pleasing impression. Why make them in 3D form? First, because 3D designs offer superior visual appeal and greater richness compared to 2D or 2.5D designs. Second, when paired with 3D screens, 3D back covers create a more harmonious overall device appearance. Moreover, compared to sharp square edges, rounded curves provide a better grip and feel in the hand. Thus, at a time when 2D and 2.5D aluminum back covers have become ubiquitous and are starting to cause aesthetic fatigue, 3D ceramic back covers have become irresistibly appealing to both phone designers and consumers.

Four, why hasn't it been scaled up yet?

Given how appealing 3D ceramic back covers for mobile phones are, why aren’t they yet widely adopted in the market? Even the now-discontinued Xiaomi 5 Supreme Edition is rarely seen in actual use. This highlights that while 3D ceramic back covers for mobile phones certainly have their merits, they still face numerous challenges that need to be addressed. From my personal perspective, we can analyze this issue from two angles: the 3D ceramic back-cover technology itself and the product’s choice of technological approach.

1. The 3D ceramic phone back cover technology itself

Basic 3D ceramic manufacturing process: Raw material → Shaping → Degreasing → Sintering → Machining → Surface finishing

A 3D ceramic phone back cover basically requires the above six steps for processing and fabrication. Leaving aside specific process parameters for now, let’s analyze it solely from the perspective of the ceramic material’s preparation and performance characteristics:

(1) Raw Materials: Ceramic raw materials are prepared by adding thermoplastic resins, thermosetting resins, plasticizers, and friction-reducing agents to ceramic powders, thereby transforming the ceramic powder into a viscous elastomer. The heated and mixed slurry is then injected through a nozzle into a metal mold, where it cools and solidifies to form the final product. Commonly used thermoplastic resins include polyethylene, polystyrene, and polypropylene, with addition levels ranging from 10% to 30%. This technology significantly enhances the precision and reliability of shaping complex-shaped products.

(2) Injection Molding

The injection molding principle for ceramics is essentially the same as that for plastics—except that a large amount of ceramic powder is mixed into the plastic. To optimize the injection-molding conditions, it is essential to select organic materials that are well-matched to the raw materials being used and to carefully determine the appropriate addition levels. To obtain a dense and uniform injection-molded product, the concentration of ceramic powder should be relatively high; however, an excessively high concentration can degrade the molding performance. To improve the flowability of the compounded feedstock, the viscosity of the polymer-based dispersant should be reduced. As part of the pretreatment process, it is crucial to enhance the dispersibility of the ceramic powder. To further improve the flowability of the polymer matrix, suitable plasticizers and lubricants must be added. The particle size of ceramic raw materials typically ranges around 1 μm. After adding a binder (also referred to as an additive) and thoroughly mixing and stirring the components, the ceramic powder becomes wetted and coated by the binder during the stirring process, eventually forming a homogeneous composite ready for injection molding. Before injection molding, the material must undergo cooling, drying, and grinding to produce particles that are appropriately sized for feeding into the hopper of the injection-molding machine.

Mold materials typically employ alloy steels that exhibit excellent high cleanliness, wear resistance, and corrosion resistance. Mold design should be tailored to match the flow characteristics of ceramic-polymer systems. To minimize shrinkage in the molded parts and prevent air entrainment within the mold cavity, the mold must incorporate controlled venting channels. Additionally, the mold should be equipped with cooling and heating channels, and a temperature controller should be used to maintain a constant mold temperature, which is highly effective in improving the dimensional accuracy of the molded parts. Since the raw materials involve extensive use of organic substances, it is crucial to thoroughly degrease the green body without causing thermal cracking or leaving behind carbon residues, making degreasing an important issue to address.

(3) Degreasing

This process primarily removes the binder mixed into the product. It mainly consists of three stages:

a. In the low-temperature range from room temperature to 200℃, the main components are those with relatively low molecular weights—namely, the melting and decomposition of paraffin and stearic acid.

b. In the medium-temperature range of 200–400°C, the primary process is the oxidative decomposition and removal of polypropylene with relatively high molecular weight;

In the high-temperature range of approximately 400–600°C, the remaining binder is completely removed in small quantities. The degreasing stage essentially does not cause any changes in product dimensions.

(4) Sintering

Since the ceramic powder contains a binder, the dimensions of the product will shrink after sintering, with a shrinkage rate of approximately 20%, depending on the specific product. The sintering process can also easily generate internal stresses, which may affect the product’s performance.

Ceramics are produced through high-temperature sintering, and once they’ve become ceramics, they exhibit hard and brittle properties. To reshape this extremely hard and brittle material into the 3D phone backshell shape we desire, there’s no alternative but to use CNC machining to carve the entire ceramic block into the desired form. Therefore, the only feasible approach is to mold the material into its final shape while it’s still in a soft state; only after shaping can it be subjected to sintering and hardening. It’s precisely this process characteristic that inevitably leads to the following issues:

Dimensional Issues: During the molding process, the material has not yet fully cured. After molding, degreasing and sintering are carried out, inevitably leading to dimensional shrinkage and changes. As a result, dimensional accuracy cannot be effectively controlled, making it impossible to meet product requirements. Even if the requirements can be met, the yield rate will suffer accordingly.

Bubble issues: The degassing process essentially involves the volatilization of various organic substances in the ceramic raw materials, which inevitably leads to the formation of bubbles.

(5) Processing, surface treatment

Cracking Issues: Ceramic materials are hard and brittle. Whether during machining or surface finishing processes such as grinding and polishing, the underlying principle is the removal of material from localized areas. Besides the rapid wear and tear of machining tools and abrasive materials, the hard and brittle nature of ceramic structures also makes them prone to cracking during processing, resulting in low yield rates and high costs.

Surface quality issues: Bubbles formed during the ceramic sintering process may become exposed during subsequent machining and grinding operations. Since the back cover of a mobile phone, which serves as a primary surface, must not have any exposed bubbles, this results in a low yield rate for surface finishing.

2. Product’s choice of technology

In addition to the fact that the technology itself poses no issues, when making technology choices, products pay close attention to the following considerations:

Reliability → Yield → Cost → Technological Maturity → Availability

(1) Reliability

After ceramic materials are fabricated into the specifications and structural design required for mobile phone back covers, they must undergo product reliability testing. For ceramic materials, the most rigorous tests are undoubtedly the drum drop test and the directional drop test within mechanical reliability assessments. Currently, it is generally required that, after assembly into a complete device, none of the phone’s structural components should fracture when subjected to two drop tests: a 1-meter drum drop test performed 100 times and a 1-meter directional drop test performed 12 times (two drops per face, totaling six faces). These two tests precisely expose the inherent brittleness of ceramic materials, making the mechanical reliability of 3D ceramic phone back covers a serious concern.

(2) Yield and Cost

Whether it’s dimensional deformation during the sintering process or chipping and bubble exposure during the surface treatment and finishing processes, all these issues severely impact product yield. A low yield directly leads to a sharp increase in costs. Moreover, consumables used in machining and surface treatment are expensive and deplete rapidly, further driving up product costs to an unsustainable level.

(3) Technology Maturity

How many issues might still remain in a technology that hasn't been verified through mass production? Although we haven't encountered any problems yet, could they surface during actual mass production? And if we take the risk of using it anyway, could it lead to delays in delivering products on time? If the risks at this stage are deemed too high, companies will naturally hesitate to adopt the technology rashly. Right now, 3D ceramic phone back covers are facing precisely this situation.

(4) Availability

Generally speaking, mobile phones are mass-produced products. If the product yield rate is too low or the industry's supply capacity cannot keep up, it will inevitably lead to delays in shipments. Even if production capacity is sufficient, given the currently low yield rates, mobile phone manufacturers will naturally remain cautious about the large-scale adoption of 3D ceramic back covers for their devices.

V. Will it be scaled up for future applications?

Everything has its advantages and disadvantages. If the advantages are compelling enough, they will inevitably attract sustained and substantial effort to overcome the drawbacks. Once technological advancements enable these shortcomings to be addressed, large-scale adoption will naturally follow. We eagerly look forward to the day when 3D ceramic back covers for mobile phones become a reality.

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