This article mainly deals with UV laser processing technology. Through experiments, the UV/IR laser equipment was compared with the processing results of the materials. It was found that in the processing of special materials, the UV laser is more smooth and efficient than the infrared laser. For infrared devices that are processed with materials with higher infrared transmittance, UV lasers have significant advantages in processing.
1 Introduction
Laser technology is one of the four major inventions in the 20th century that are famous for atomic energy, semiconductors, and computers. For more than forty years, with the increasing demand for small electronic products and microelectronic components, precision processing of process materials (especially polymer materials and high-melting point materials) has become the fastest-growing laser in industrial applications. One of the fields.
Laser processing is an important application of the laser industry. Compared with conventional machining, laser processing is more precise, more accurate, and more rapid. This technology utilizes the characteristics of interaction of laser beams and substances to process various materials including metals and non-metals, involving various processes such as welding, cutting, marking, punching, heat treatment, and molding. The unique characteristics of the laser make it an ideal tool for microprocessing, and is currently widely used in three areas of microelectronics, micro-mechanics and micro-optics processing.
Laser processing technology is a processing technology that uses the characteristics of laser beam and material interaction to cut, weld, surface treat, punch and micro-machin materials (including metals and non-metals).
Laser processing has its unique features:
(1) Extensive range: almost any material can be carved and cut.
(2) Safe and reliable: Non-contact processing will not cause mechanical extrusion or mechanical stress on the material.
(3) precise and detailed; processing accuracy up to 0.01mm.
(4) The effect is the same: to ensure the same batch of processing results.
(5) High speed and high speed: The high-speed engraving and cutting can be performed immediately according to the pattern output by the computer, and the speed of the laser cutting is much faster than the speed of the wire cutting.
(6) Low cost: Not limited by the amount of processing, laser processing is cheaper for small batch processing services.
(7) Cutting gap is small: laser cutting kerf is generally 0.02mm-0.05mm.
(8) Smooth cutting surface: The laser-cut cutting surface has no burr.
(9) Heat distortion is small; laser processing laser slits fine, fast, and energy concentrated, so the heat transferred to the material being cut is small, causing the deformation of the material to be very small.
Materials used in infrared device technology (gems, etc.), processing conditions (accuracy, deformation, etc.) require laser processing. Given the many types of lasers, we mainly deal with infrared laser devices and UV laser processing systems. Therefore, we hope to compare the processing results of the same kind of materials between the two UV/IR laser systems through experiments to understand their characteristics and differences, and to determine their respective scope of application and superiority, so as to better develop special materials for the future. Plus work pave the way.
2 Experimental Equipment Introduction
The experimental equipment used in this paper is JHM-1GY-300B YAG laser equipment and PSV-6001 355nm all-solid-state UV laser drilling machine.
2.1 YAG laser equipment
The YAG laser device has a laser wavelength of 1.06 μm, a maximum single-pulse laser energy output of 60 J, and a pulse frequency of 1 Hz to 100 Hz (continuously adjustable). It focuses the laser to a point where the power density in the focal plane can reach 105-1013 W/cm2. The device can also be used for laser welding, laser welding is the use of laser beams with excellent directionality and high power density characteristics to work. Through the optical system, the laser beam is focused to a very small area, and in a very short time, a locally concentrated heat source area where the energy is highly concentrated is formed at the portion to be welded, so that the object to be welded is melted to form a firm solder joint and a weld seam. Figure 1 shows an example of a welded joint of stainless steel and titanium alloy welded by YAG laser.
2.2 Ultraviolet Laser Drilling Machine
The PSV-6001 UV laser drilling machine is based on a diode-pumped solid-state laser with a high power tripled frequency (DPSS) laser, a wavelength of 355nm, an average power of 2.3W, a maximum frequency of 100kHz, and a spot diameter on the workpiece. Can be as small as 20μm or less. The machine applies drawing software and performs reasonable parameter settings, which can perform a series of operations such as drilling, engraving, cutting, and so on. In the experiments that have been done, organic materials processed using the ultraviolet laser drilling machine include polymers, paper products, and the like. Inorganic materials include metals, precious stones, glass, ceramics, etc.
2.3 Comparison of UV/IR Lasers
Infrared YAG lasers (wavelength 1.06 μm) are the most widely used laser sources for material handling. However, many plastics and some special polymers (such as polyimides) used in large quantities as flexible circuit board base materials cannot be finely processed by infrared or "hot" processes. As "hot" deforms the plastic, a carbonized form of damage occurs at the edges of the cut or drilled hole, which may lead to structural weakening and parasitic conduction paths, and some subsequent processing steps have to be added to improve the quality of the process. Therefore, infrared lasers are not suitable for the processing of some flexible circuits. In addition, the infrared laser wavelength cannot be absorbed by copper even at high energy densities, which severely limits its use.
However, the output wavelength of the UV laser is below 0.4 μm, which is a major advantage of processing polymer materials.
Unlike infrared processing, UV microprocessing is not a heat treatment by nature, and most materials absorb ultraviolet light more easily than infrared light. High-energy ultraviolet photons directly destroy the molecular bonds on the surface of many non-metallic materials. Parts processed by this “cold†photo-etching process have smooth edges and minimal charring. Moreover, the characteristics of the short ultraviolet wavelength itself are superior to the mechanical microprocessing of metals and polymers. It can be focused to sub-micron orders of magnitude, so that fine parts can be processed, and even at low pulse energy levels, high energy densities can be obtained and materials can be effectively processed.
The application of micro-holes in the industry has been quite extensive, and there are two main ways to form micro-holes:
One is the use of infrared lasers: the material on the surface of the material is heated and vaporized (vaporized) to remove the material. This method is often referred to as thermal processing. YAG laser (wavelength 1.06 μm) is mainly used.
The second is the use of UV lasers: high-energy UV photons directly destroy the molecular bonds on the surface of many non-metallic materials, the molecules from the object, this method does not produce high heat, it is called cold processing, the main use of UV laser (wavelength 355nm).
Table 1 compares these two processing methods.
3 experimental results and discussion
3.1 Drilling experiment
Fig. 2 shows the coffee beans 2 holes punched on a ceramic sheet with the same thickness of 1 mm using JHM-1GY-300B YAG laser equipment and PSV-6001 355nm ultraviolet laser drilling machine, respectively.
The results show that the holes made with infrared lasers have poor roundness and the edges are "burned" black. With ceramic chips processed by ultraviolet lasers, the small holes have good roundness and smooth edges. From the experimental results and the data in Table 1, it is not difficult to find that the UV laser is more than a few orders of magnitude higher in processing speed and drilling accuracy than the infrared laser, and the quality effect is also obvious.
3.2 cutting experiment
Laser cutting is the use of focused high-power laser irradiation processing material surface, when the laser exceeds the threshold power density, causing the irradiation point material temperature rose sharply, the temperature reaches the boiling point, the material gasification and the formation of holes, with the laser beam and the workpiece With relative movement, a slit is finally formed on the surface of the material. Cutting quality (including slit width, edge straightness, and finish) is determined by laser power, laser beam mode, assist gas pressure, and cutting speed. The laser power needed for cutting is directly proportional to the thickness of the material, which is a typical straight line for ferrous metals. The maximum cut thickness is a function of power, focal length of the converging lens, laser wavelength, and cutting speed. Focal length and convergence angle are important parameters for cutting quality, thickness, and speed.
In theory, the thickness of the cut is determined by the Rayleigh region of the laser Gaussian beam, which is known in the industry as the depth of focus (DOF). Its physical expression is
In the formula, λ is the wavelength, f and D are the focal length and diameter of the converging lens, respectively, and the depth of focus gives the upper limit of the cutting thickness. FIG. 3 is an SEM image of a 0.1 mm thick high-melting-point metal molybdenum sheet cut by an ultraviolet laser drill. It can be seen from the SEM image that the high-melting-point metal has a flat cutting edge due to its high absorption of ultraviolet light.
Laser cutting has the advantages of narrow slits, small heat-affected zone, high efficiency, no mechanical stress on the cutting edge, and can be applied to the processing of many different thin film materials, and has a small limitation on the aperture and feature size.
FIG. 4 shows the comparison between the ultraviolet laser scribing and the mechanical scribing. The components of the cut filter dielectric film are mainly zinc sulfide, tin zinc, and the like. The UV laser drilling machine has a processing frequency of 100 kHz and a cutting speed of 10 mm/s.
As can be seen from Figure 4, the edge of the filter with the ultraviolet laser is smooth and the damage is small. The use of mechanical dicing machine is easy to produce "collapse", the stress generated by the cutting is easy to fall off the dielectric film, damage the filter. We know that infrared laser cutting vaporizes the material on the surface of the material, and the filter dielectric film is easily oxidized and degraded when the temperature exceeds 130°C. Therefore, the dicing process of the filter cannot be formed with an infrared laser. Currently, filters cut with ultraviolet lasers have been used for certain types of infrared devices. The use of high-power ultraviolet laser cutting of some metals, such as copper films, molybdenum films, etc., with the advantages of narrow slits, small heat affected zone, high cutting efficiency, suitable for the development of a variety of different high-precision micro thin film devices. Research on high-power ultraviolet laser cutting technology has greatly promoted the application and development of laser as a universal processing tool.
3.3 Experimental Comparison
(1) Copper has good thermal conductivity (thermal diffusivity is 1.19cm2/s, thermal conductivity is 4.01W/cm°C), conductivity (conductivity is 6×103s/m) and ductility, and it is comparable in air Stability [quote. Therefore, these excellent properties make copper thin film materials widely used in the manufacture of thin film devices. However, copper is a hard-to-process material in the processing of laser materials because copper has a high thermal reflectivity and a low absorption rate for laser light. Therefore, even at high energy densities, it is difficult to finely cut copper using ordinary C02 lasers and Nd:YAG lasers.
However, copper has a high absorption rate for a triple-frequency solid-state ultraviolet laser having a wavelength of 355 nm. Since the wavelength of the ultraviolet laser is short, the focal point can be as small as sub-micron, so the copper laser film is cut by the ultraviolet laser. It will be an effective method to develop this kind of high precision micro thin film device. The use of ultraviolet laser drilling machine in the thickness of 0.05mm copper drill hole, the goal is small hole diameter, roundness and edge quality.
After repeated experiments, the processing frequency of the ultraviolet laser drilling machine is 25KHz, and the cutting speed is 0.3mm/s. Figure 5 is the use of ultraviolet laser drilling machine coffee beans 10μm hole.
(2) Processing experiments on 0.1 mm thick green ceramics In Guo Dong et al.'s "Aluminum Ceramic Substrate Through Hole New Laser Drilling Process", the author chose a common alumina ceramic as a research object, and the laser is Nd:YAG. Lighter. Figure 6 is the hole that it machined.
In Figure 6, when the hole is drilled to the trailing edge of the laser pulse, the liquid phase that will be carried away in the future will re-agglomerate at the entrance of the hole wall and hole due to the sharp reduction of light intensity and vapor pressure and beam divergence. Recast layers and deposits, when the ceramic body is processed directly, a large amount of irregular deposits will form around the hole. On the other hand, there is almost no deposit in FIG. 7 and the surface is cleaner and smoother.
4 Conclusion
A comparison of several experiments found that:
(1) Laser processing is more precise, more accurate and more rapid than conventional machining.
(2) It can be seen through the drilling experiment that: UV laser has more obvious advantages than infrared laser in processing speed, drilling precision and quality effect. Therefore, in some occasions with high aperture precision, high surface quality of holes, and high melting point of processing materials, ultraviolet laser can be used instead of infrared laser.
(3) From the cutting experiment, it is not difficult to find that cutting some metals such as copper thin films and molybdenum sheets with ultraviolet lasers has the advantages of narrow slits, small heat affected zone, and high cutting efficiency, and is suitable for many kinds of high precision micro thin films. Device development. Although the solid-state semiconductor pump ultraviolet laser has many advantages, how to better use the solid-state semiconductor pump ultraviolet laser for precision machining through optimization and adjustment of processing parameters is a problem that needs further exploration at this stage.
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