The application and trend of 3D ceramics on mobile phones

First, what is ceramic

Ceramic material is a kind of inorganic non-metallic material made of natural or synthetic compounds by forming and sintering at high temperature. Its main properties are as follows:

Mechanical properties: high strength, hardness and plasticity, toughness is poor, as hard and brittle;

Physical properties: low thermal conductivity, manifested as poor heat dissipation;

Chemical properties: corrosion resistance, stable chemical properties, showing strong environmental adaptability.

Metal, ceramic tensile curve

Two, what is the 3D ceramic mobile phone back shell

The so-called ceramic mobile phone back shell is the mobile phone back shell made of ceramic materials, and 3D is relative to 2D and 2.5D, the mobile phone back shell must have a certain thickness, the upper and lower surface is a plane and parallel to each other is called 2D, the upper and lower surface is a plane, but the plane edge is polished into a radian, the radian from one surface to the other side is called 2.5D, Instead of a flat surface, 3D glass usually has a large arc at the edge, with the overall U-shaped shape.

Third, why use 3D ceramic back shell on mobile phone

Why use ceramic material to make the back case of mobile phone? First of all, ceramic material has unique advantages, high strength and hardness for bending resistance, scratch resistance, and these are the current materials used on mobile phones, especially aluminum pain points; The second is the unique texture of ceramic material after surface treatment. It feels delicate and gentle like jade, showing a high sense of quality and beauty. Why make it in 3D? Firstly, 3D is visually more beautiful and rich than 2D and 2.5D. The second is to cooperate with the 3D screen, so that the whole body is more coordinated; In addition, compared to the square edge, the arc shape also gives a better grip. Therefore, in the popularity of aluminum 2D, 2.5D mobile phone back cases and resulting in aesthetic fatigue, 3D ceramic mobile phone back cases have a strong appeal to mobile phone designers and consumers.

Four, why is there no scale application

Since the 3D ceramic mobile phone back case is so charming, why has not seen scale use on the market, even the released Xiaomi 5 Zun out of print is rarely seen in practice? It is good to reflect the 3D ceramic mobile phone back shell, but there are still a lot of problems to be solved, from the perspective of personal understanding, can be analyzed from the 3D ceramic mobile phone back shell technology itself and the choice of the product to the technology.

1. 3D ceramic mobile phone back case technology itself

Basic processing technology of 3D ceramics

3D ceramic mobile phone back shell basically needs to go through the above 6 steps to be processed and prepared, regardless of the specific process parameters, only from the preparation of ceramic material and performance characteristics analysis:

A. Raw material -- molding -- dispensing -- sintering

(1) Raw materials: ceramic raw materials are made by adding thermoplastic resin, thermosetting resin, plasticizer and antifriction agent to ceramic powder, so that the ceramic powder becomes a viscous elastic body, and then shooting the heated mixed slurry into the metal mold from the nozzle, cooling and curing. Commonly used thermoplastic resins are polyethylene, polystyrene, polypropylene, the amount of 10-30%. This technique has greatly improved the accuracy and reliability of forming products with complex shapes.

Die materials are generally made of alloy steel with high cleanliness, wear resistance and corrosion resistance. Mold design should conform to the flow characteristics of ceramic polymer system. In order to reduce the shrinkage of the form and avoid the involvement of the air in the mold, the mold should be considered to control the release outlet. In addition, there should be a cooling groove on the mold, which can be cooled and heated. The temperature of the mold is kept constant by the temperature regulator, which is very effective for improving the accuracy of the form. Due to the large amount of organic materials used in raw materials, in order to avoid hot cracking of the blank, degreasing without carbon residue is also an important subject.

Ceramics are sintered at high temperature, and once they become ceramics, their performance characteristics are hard and brittle. In order to shape extremely hard and brittle materials into the shape of the 3D mobile phone back shell we want, there is no other way except to use CNC to cut the whole piece of ceramic into the shape we want. Therefore, only when the raw material is soft, it is shaped as the target shape, and then sintered and hardened after forming. It is this process characteristic that inevitably causes the following problems:

Size problem: when forming the material has not been cured, after forming the glue, sintering, will inevitably lead to shrinkage changes in size, size accuracy can not be effectively controlled, unable to meet the requirements of the product, even if can meet the requirements, yield will be reduced;

Bubble problem: The essence of the glue discharge process is the volatilization of various organic compounds in ceramic raw materials, which inevitably leads to the existence of bubbles.

b, processing - table

Cracking problem: ceramic materials are hard and brittle materials, and no matter the processing or polishing in the surface, the essence is the removal of local materials. Apart from the easy loss of processing tools and grinding materials, hard and brittle ceramic structures are also prone to crack in the process of processing, resulting in low yield and high cost;

Surface quality problems: due to the ceramic sintering process produced bubbles, bubbles may be exposed in the subsequent processing and grinding process, as a level of the mobile phone back shell is not allowed to expose these bubbles, the result is the surface of the low yield;

2. Selection of products and technologies

In addition to the fact that the technology itself does not have problems, the product pays great attention to the following problems in the selection of technology:

(2) Injection molding

The injection molding principle of ceramic is basically the same as that of plastic. It's just plastic mixed with a lot of ceramic powder. In order to improve injection molding conditions, it is necessary to choose the organic material that matches the raw material used, and to choose the amount of addition. In order to obtain a dense and uniform injection molded form, the concentration of ceramic powder is higher. But too high will make the formability worse. In order to improve the fluidity of mixing stock, the viscosity of polymer system of dispersant should be reduced. As a pretreatment, it is very important to improve the dispersion of ceramic powder. In order to improve the fluidity of polymer, appropriate plasticizers and lubricants should be added. The particle size of ceramic raw materials is generally 1μm, adding binder (or called additive), after full mixing, stirring. In the stirring process, the ceramic powder is moistened and coated by the binder, and all of them become a uniform compound. After cooling, drying and crushing, the particles suitable for injection molding machine funnel feed can be obtained.

Die materials are generally made of alloy steel with high cleanliness, wear resistance and corrosion resistance. Mold design should conform to the flow characteristics of ceramic polymer system. In order to reduce the shrinkage of the form and avoid the involvement of the air in the mold, the mold should be considered to control the release outlet. In addition, there should be a cooling groove on the mold, which can be cooled and heated. The temperature of the mold is kept constant by the temperature regulator, which is very effective for improving the accuracy of the form. Due to the large amount of organic materials used in raw materials, in order to avoid hot cracking of the blank, degreasing without carbon residue is also an important subject.

(3) degreasing

This process mainly removes the adhesive mixed in the product. It is mainly divided into three stages. 1. The low temperature range from room temperature to 200℃ is mainly the melting and decomposition of components with relatively small molecular weight, such as paraffin and stearic acid; 2. The intermediate temperature range of 2,200-400 degrees is mainly the oxidation decomposition and removal of polypropylene with relatively large molecular weight. In the high temperature range of 3,400-600 degrees, a small amount of residual binder is completely removed. The degreasing stage has little effect on product size.

(4) sintering

Because the ceramic powder is mixed as a binder, the size of the product will shrink after sintering, and the shrinkage rate is about 20%, depending on the product. Sintering process is also easy to produce internal stress, affect the product performance.

Ceramics are sintered at high temperature, and once they become ceramics, their performance characteristics are hard and brittle. In order to shape extremely hard and brittle materials into the shape of the 3D mobile phone back shell we want, there is no other way except to use CNC to cut the whole piece of ceramic into the shape we want. Therefore, only when the raw material is soft, it is shaped as the target shape, and then sintered and hardened after forming. It is this process characteristic that inevitably causes the following problems:

Size problem: when forming the material has not been cured, after forming the glue, sintering, will inevitably lead to shrinkage changes in size, size accuracy can not be effectively controlled, unable to meet the requirements of the product, even if can meet the requirements, yield will be reduced;

Bubble problem: The essence of the glue discharge process is the volatilization of various organic compounds in ceramic raw materials, which inevitably leads to the existence of bubbles.

b, processing - table

Cracking problem: ceramic materials are hard and brittle materials, and no matter the processing or polishing in the surface, the essence is the removal of local materials. Apart from the easy loss of processing tools and grinding materials, hard and brittle ceramic structures are also prone to crack in the process of processing, resulting in low yield and high cost;

Surface quality problems: due to the ceramic sintering process produced bubbles, bubbles may be exposed in the subsequent processing and grinding process, as a level of the mobile phone back shell is not allowed to expose these bubbles, the result is the surface of the low yield;

2. Selection of products and technologies

In addition to the fact that the technology itself does not have problems, the product pays great attention to the following problems in the selection of technology:

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A. Reliability

After ceramic materials are prepared to meet the specifications of the back shell of the mobile phone, the reliability of the product needs to be tested. For ceramic materials, the most severe test is the roller drop and directional drop in the mechanical reliability test. At present, it is generally required to assemble the whole machine. The structural parts of the mobile phone do not break in the two drop tests of 1m*100 times and 1m*12 times (two rounds for each of the six faces) of the roller. However, these two tests just poke the soft ribs of the brittle ceramic material, so the mechanical reliability of the back shell of the 3D ceramic mobile phone is worrying.

B. Yield and cost

Both the dimensional deformation in the sintering process and the cracking and bubble exposure in the processing process of the surface have a serious impact on the yield of the product. The direct result of the low yield is a sharp rise in the cost, plus the high and fast consumption of the consumables in the processing and surface, resulting in the cost of the product is overwhelmed.

C. Technology maturity

How many problems still exist in a technology that has not been verified in mass production, although it has not been encountered at present, will it be exposed in mass production? Will it lead to timely delivery of the product if it is used at risk? If the product feels too risky at this point, it must not dare to use it. At present, the back shell of 3D ceramic mobile phone is facing this situation;

D. Availability

Generally speaking, mobile phones are large-scale products. If the product yield is too low or the industrial supply capacity cannot keep up, the products will inevitably fail to be delivered in time. Even if the production capacity is sufficient, under the current condition of low yield, mobile phone manufacturers will inevitably maintain a cautious attitude towards the large-scale use of 3D ceramic mobile phone back shell.

Five, the future will be scale application

Everything has advantages and disadvantages. If the advantages are attractive enough, it will inevitably attract a lot of continuous energy to overcome its disadvantages. Once the technological progress and the disadvantages are overcome, the large-scale use of the natural course will come.