Sapphire, as a material with a hardness second only to diamond, occupies an important position in the field of mobile phone mirror manufacturing. Its scratch resistance can effectively protect the phone screen from daily wear and tear, but its high hardness also poses challenges for processing. This article will analyze the process of grinding technology in the production of sapphire mobile phone mirrors, revealing the entire precision machining process from raw materials to finished products.

1、 Raw material selection and pretreatment

The quality of sapphire crystal directly affects the transmittance and mechanical strength of the product. Cylindrical ingots grown by methods such as bubble growth or heat exchange typically have a diameter of 150-200mm. The ingots need to be processed into 0.5-1.2mm thick wafers through inner circle cutting or wire cutting, with a surface roughness (Ra) of about 3-5 μ m and obvious cutting patterns and subsurface damage layers. In the preprocessing stage, an 800 # diamond grinding wheel is used for preliminary leveling to remove macroscopic defects, laying the foundation for subsequent precision grinding.

2、 Multi level grinding process system

The sapphire mobile phone mirror grinding adopts a three-level progressive system of "coarse grinding fine grinding polishing", and each stage requires strict control of process parameters:

1. Rough grinding stage: Use diamond grinding fluid with a particle size of 15-30 μ m in combination with cast iron grinding discs, with pressure controlled at 0.1-0.3 MPa and a speed of 200-300 rpm. At this stage, the main goal is to eliminate the waviness caused by cutting and reduce the surface roughness to below 0.5 μ m. The key technology is to maintain uniform distribution of the grinding fluid and avoid the occurrence of "hot spots" that can cause local stress concentration.

2. Fine grinding stage: switch to diamond micro powder with a particle size of 3-9 μ m, and use tin alloy grinding discs to achieve finer material removal. By adjusting the pH value in an alkaline environment of 9-11, the material removal rate (MRR) can be improved by about 20%. Real time monitoring of surface temperature is required during this stage, as exceeding 80 ℃ will cause lattice distortion.

3. Transition polishing: Pre polishing is carried out using alumina or silica suspension to fill the micro depressions left by the previous process. It is particularly noteworthy that the anisotropy of sapphire results in a removal rate of (0001) crystal plane that is 1.8 times faster than (1120) crystal plane, which requires fixture design to consider crystal orientation.

3、 Key Technologies of Chemical Mechanical Polishing (CMP)

As the ultimate precision machining method, CMP process directly determines the optical performance of the mirror surface:

1. Polishing solution formula: The mainstream uses a mixed system of nano-sized silica colloids (particle size 50-70nm) and oxidants (such as hydrogen peroxide), with a pH value accurately controlled in the range of 10.5-11.5.

2. Process parameter optimization: Maintain the downforce at 2-4 psi, rotate the polishing disc at 60-120 rpm, and control the temperature at 35 ± 2 ℃. A laboratory study found that using a periodic pressure oscillation mode can effectively reduce the incidence of "orange peel" defects.

3. Cleaning process: After polishing, the surface residue needs to be removed by ultrasonic cleaning, and the subsequent coating adhesion is enhanced by plasma activation treatment.

4、 Quality inspection

Seven major detection nodes are set up throughout the entire process:

1. Laser confocal microscopy for detecting subsurface damage depth

2. White light interferometer for measuring surface roughness (target Ra ≤ 0.3nm)

3. Polarization stress analyzer for residual stress analysis (requirement<50MPa)

4. Spectrophotometer test transmittance (≥ 85% @ 550nm when thickness 1mm)

5. X-ray diffraction detection of crystal integrity

6. Observation of atomic level surface morphology using atomic force microscopy

7. Sand drop test to evaluate wear resistance (# 9 Mohs hardness scratch to withstand 100g load)

In the process of transformation from ingots to lenses, every breakthrough in grinding technology embodies the wisdom of materials science and precision machinery. With the continuous improvement of mobile phone protection requirements in the 5G era, sapphire mobile phone mirror processing technology will continue to develop towards higher efficiency, precision, and environmental protection.