The hottest laser cutting helps the flexibility of

Laser cutting helps greatly increase the flexibility of ultra-thin glass substrates

under the trend of pursuing lightness and thinness in electronic products, glass substrates, as a key material, are also moving towards the goals of continuously adjustable thin experimental speed, automatic shutdown of specimen breaking and flexibility. Due to the hard and brittle physical properties of glass, how to not damage the glass substrate during cutting and how to eliminate the edge defects of glass after cutting have been the breakthrough parts of all circles. This paper will focus on the existing laser glass cutting process and laser edge strengthening technology, as well as the laser related technology currently developed in the industry

evolution of glass substrates

in recent years, the liquid crystal display (LCD) and touchpanel of various electronic devices are moving towards the goal of thin and flexible. In order to achieve the thin target, the thickness of glass substrate is gradually reduced from 1.1 mm (mm) to 0.4 mm, which is popular today, and will develop towards 0.2 and 0.1 mm in the future; In terms of flexible soft electronics, plastic materials have become one of the best substrates at present in order to achieve flexibility, impact resistance and easy to carry. Originally, the industry expected that plastic materials would gradually replace glass substrates. However, plastic materials cannot withstand the high-temperature process, which limits the possibility of their application. Therefore, there are still great challenges to achieve the ultimate flexible electronic products

in 2012, international glass substrate factories Corning, Asahi, neg and Schott have successively successfully developed and produced ultra-thin glass with a thickness of less than 0.1 mm, breaking through the limitation of the non bending characteristics of glass, and adding to the small range of glass steel enterprises and deep-processing enterprises, excellent optical properties, temperature and geometric stability, Make the glass substrate full of strong competitiveness again

under the condition of few defects and ultra-thin thickness, the ultra-thin glass substrate has a considerable degree of flexibility, but it still has the physical property of hard and brittle glass. In the process of treatment, it is easy to produce defects or extend and expand existing defects due to deformation and stress, and finally lead to the fracture of the substrate. Therefore, in the process of process conversion, the ultra-thin glass flexible substrate must have sufficient mechanical reliability and impact resistance, and it is required that fragments are not easy to occur in the process of transfer and transmission, so as to ensure the production yield of manufacturing. Therefore, how to improve the mechanical strength requirements of ultra-thin glass will be the most important key technology in the real application of ultra-thin glass in the future

after mechanical or laser cutting, the glass will form micro cracks on the edge of the glass, and the existence of micro cracks will make the glass edge have strong internal stress. Therefore, in the process of process conversion, it is possible to produce fragments due to the growth of micro cracks caused by human handling or improper external force, Therefore, the low damage glass cutting technology and the edge grinding technology to reduce or even eliminate the damage after cutting are the key to the success of the manufacturing process

glass cutting process

traditional glass cutting is to directly machine the wheel cutter to achieve the desired size. However, the biggest problem of wheel cutter cutting is the loss of tools, especially in the cutting of reinforced glass with high hardness; In addition, the mechanical cutting method will produce mechanical stress, which will cause edge damage. With the thickness of the substrate becoming thinner and thinner, all kinds of cracks caused by cutting will increase rapidly, which will seriously affect the quality and yield of the cutting process. Therefore, subsequent edge grinding must be combined after cutting to reduce edge cracks; However, when the thickness of ultra-thin glass is less than 0.2 mm, due to the relative fragility of the material, the use of machinery to cut or grind the edge will be too narrow and difficult to effectively control with the application of force. Therefore, it is necessary to gradually introduce the laser process to solve the related problems

the common types of laser sources used for glass cutting are CO2 laser, UV laser and ultrafast laser. The comparison of their characteristics is shown in Table 1; Among them, at present, the mainstream of mass production is CO2 laser, while ultrafast laser cutting is of good quality, but the cost is relatively high. At present, some manufacturers have begun to introduce mass production applications

co2 laser cutting technology has good cutting edge quality and low equipment cost, so it is highly accepted in the industry. However, it must make an initial crack before the edge by mechanical or other means to achieve the cutting effect, and its function principle is to cut by hot and cold cracks plus cracks. The processing path is not easy to be applied to the cutting of special shapes (such as arcs), and the arc angle must be modified with a long grinding time, In addition, the path will be offset during asymmetric cutting, which is the part to be improved

uv laser and ultrafast laser in the processing mechanism, both belong to the photochemical mechanism to cut and cut materials, and can directly process special-shaped tracks. Its processing quality depends on the accumulated heat energy of materials. Therefore, the processing effect of ultrafast laser is better than that of nanosecond laser. The difference in effect can be clearly observed from the profile of processing results in Figure 1, The edge quality of UV laser cutting is significantly worse than that of CO2 laser and ultrafast laser

as mentioned in the previous paragraph, although the quality of laser cutting is better than that of wheel knife cutting, obvious defects can be observed by observing its profile, which will increase the possibility of fracture in subsequent application. Therefore, whether traditional wheel knife cutting or various laser cutting technologies, after cutting, they will be combined with subsequent edge grinding technology to reduce edge defects, so as to reduce the probability of fragments in subsequent application. At present, the glass edging technology in the industry is mainly mechanical edging machines, which use grinding wheels to process the glass edges. However, due to the high hardness of the glass itself and the high brittleness of the material, mechanical edging is quite time-consuming, which will also make the grinding wheels wear rapidly and increase the process cost; In addition, when the glass substrate is thin to the size of ultra-thin glass, although the ultra-thin glass has a considerable degree of flexibility, it still cooperates to build coal to olefins and high value-added downstream projects; In November 2016, it has the physical property of hard and brittle glass. During the treatment process, it is easy to produce defects or extend and expand existing defects due to deformation and stress, and finally lead to the fracture of the substrate. Therefore, it is impossible to process it by mechanical edging

in view of this, major glass factories around the world have tried to develop various glass edge defect reinforcement technologies. In order to strengthen the edge of ultra-thin glass, Corning proposes to fill the edge defects with fillers to inhibit the generation of defects along the edge of the substrate and protect the bending strength of the edge. It mainly uses materials such as silicone and epoxy resin to cover the edge of the glass. After curing, the reinforcement effect can be achieved. Because the material itself is not defect free after reinforcement, the degree of reinforcement is limited; Asahi of Japan proposed the concept of remelting the defective part to achieve the strengthening effect. The process method is to irradiate the cut glass edge defect part with CO2 laser with strong thermal effect, and at the same time, use cooling gas to supply air to achieve the effect of temperature control, so that the edge defect is melted and then solidified and reshaped, and the defect is removed by melting the material itself to achieve the strengthening effect. Although the defect can be removed, However, there will still be strong residual stress at the edge, which will affect the degree of strengthening

in the part of eliminating edge defects, different from Corning's repair and Asahi's melting concept, the lamination manufacturing and laser application center of the South Branch of the Industrial Research Institute has developed the technology of edgehealing directly to the outermost defective part, that is, the edge defect is directly illuminated by the laser, and the edge defect part is separated from the glass body through the laser energy, and the substrate edge of the removed glass presents a perfect surface, The section after UV laser cutting and the results of laser treatment of the test piece after UV laser cutting are shown respectively. The glass substrate after laser treatment presents a perfect smooth surface, and there are no obvious defects when magnified with a microscope. The test pieces before and after laser treatment are bent respectively. As shown in Figure 3, it can be observed that the bending radius is significantly improved, and the experimental process is all incorporated into the computer control, which can be up to about 15 mm or less, After calculation, it can be obtained that the bending strength before and after laser treatment increases from about 100MPa to more than 350Mpa, mainly because this process directly removes the defective parts in the cutting process and retains the complete structure of the glass substrate itself, so a high-strength glass substrate can be obtained

the laser composite cutting and edge repair process technology currently developed by the lamination manufacturing and laser application center of the South Branch of the Industrial Research Institute, in addition to linear processing, can also directly carry out special-shaped trajectory processing, and at the same time, it can repair the edge defects, so that the edge presents a smooth surface shape. Through bending test, the bending radius of thin glass substrate can be less than 15 mm

in the future, the application of thin glass will gradually introduce smart handheld products. Major glass manufacturers and panel related industries in the world are also actively looking for solutions to improve the strength of glass substrates, reduce the probability of glass substrate damage in subsequent applications, and help to improve the process yield. The use of laser for composite cutting and edging technology has become a trend in the future, which will replace the traditional mechanical edging technology. In addition, the advantages of laser non-contact processing will have more opportunities to integrate the rolltoroll production line, and also provide more effective production solutions for domestic panel manufacturers. Zhonghua glass () Department