Ultra-fast lasers such as nanoseconds and picoseconds are mainly reflected in differences in pulse width. As shown on the right side of the PPT, the pulse width of the picosecond laser is shorter, while the pulse width of the nanosecond laser on the left is longer. Due to the pulse width characteristics of these two lasers, picosecond lasers can directly convert materials from solid to gas during material processing, while nanosecond lasers need to be first converted to liquid and then to gas. The picosecond laser can be basically ignored in electron-lattice heat conduction. Compared with other nanosecond lasers and millisecond lasers, a "cold" process is realized.
Next, we mainly talk about the application of ultrafast lasers in brittle materials. According to the difference of the pulse energy, it can be divided into three types: modification, crack, and removal. Cracks are mainly used in cutting, and removal is mainly used in melting of materials.
In terms of application of modification, it is currently a business of mass production of Huagong, mainly used for the processing of two-dimensional code inside glass. Utilize a very small pulse energy to change the refractive index in the processing area to form a small spot, and in the process, it will not have any impact on the performance and strength of the material of the QR code itself. Because the QR code is relatively small, it is about 0.2 × 0.2mm in area, which is invisible to the naked eye during the application process. The supporting equipment can be used to trace the production process of the product.
The application of cracks is divided into two parts. One is hidden cutting. By making the laser perpendicular to the surface of the material, a light spot is formed inside the material. Later, mechanical or other methods can be used to crack the material along the processing path to obtain a chip. This hidden cutting is mainly used in LED light bar. The other is silk. In simple terms, a circular light spot is formed into a filament shape by DOE (Diffractive Optical Elements, Diffractive Optical Elements), which is used for continuous cutting and can penetrate through objects at once. The thickness of the material can be selected between 0.2-2mm. The lower right corner of the PPT shows a cutting effect of 2mm glass.
The pulse energy used for the removal is different from the previous one. The pulse energy used in the aforementioned crack application is not high, it will only generate some melting points at the point of cutting, and will not affect the entire material. The most commonly used is galvanometer, which is equivalent to ablating the material, and the pulse energy used is relatively large. It is a process from solid to gasification. The main applications are the removal of plating inks, the removal of PVD on sapphire, lettering, with grooves on glass and sapphire, punching of sapphire and glass, and cutting of sapphire and glass.
Let's look at application examples. The sheet on the back of our phone is mainly divided into two types: sapphire or glass, and iPhones mostly use sapphire. As shown in the PPT, after a whole sapphire wafer is clamped in a hanging basket, it enters the next removal application, and the corresponding hole is produced at the corresponding position. The chipping can be less than 20 μm, and the taper can be less than two degrees. In vertical. At the same time, in order to improve the unit efficiency, we will use the double-headed crack light for the existing cutting. The speed can be cut in two seconds, the chipping can be less than 10 μm, and the taper can be two degrees. In addition, the strength of 4pd (4 point bend) can be more than 600MPa.
The processing of the sapphire camera window is slightly different from that of the mobile phone sheet. The main difference is whether the wafer has ink. The cutting process of the mobile phone sheet does not have the problem of damaging the ink, and the camera window is plated with ink before cutting, which requires higher technology and technology, and may cause light leakage after the ink is burned. Therefore, we will use a new generation of application technology for sapphire window processing, and adjust it on the optical path to achieve the same chipping and taper as before, and the ink damage is less than 50μm.