Application of the hottest solid-state UV laser in

The application of solid-state UV lasers in microelectronic industry

with the increasing demand for small electronic products and microelectronic components, the precision processing of polymer materials has increasingly become one of the fastest-growing application fields of lasers in industrial applications. UV laser is an ideal tool for processing plastic (such as polyimide) and metal (such as copper) materials widely used in microelectronic component industry. The latest technology of solid-state lasers has promoted the development of a new generation of compact, all solid-state UV exciters. The most natural way is to "input what you need to query", which makes it an economic and effective processing means for a large number of dynamic scientific and technological leaders in this field. Wiring, drilling and cutting circuit in the production process of laminated circuit boards made of insulators and copper materials, it is required to carry out fine processing of small functional components, such as processing micro through holes, slots and path auxiliary holes on flexible circuit boards, and the final cutting of formed circuit boards

in the past mass production, many small parts were pressed by mechanical hard stamping molds. However, the large loss and long lead time of the hard die method are not practical and costly for the processing and forming of small parts. Similar processing methods, such as drilling and wiring with program-controlled mechanical drilling machine, or punching with low-cost steel ruler or arbor die, also have their own limitations; In the drilling of rectangular, triangular or D-shaped holes and the fine machining of complex curves, these traditional methods are more powerless; At the same time, tool wear, glue overflow and material breakage caused by drilling also limit the size, accuracy and qualification rate of components. Microchannel technology for interconnecting multilayer is becoming more and more important for today's high-density interconnect circuits (HDI), but they are particularly strict with small size requirements. The diameter of the channel usually ranges from 1 to 10 mils (microns), while the traditional mechanical drilling and punching are not suitable for mass production of through holes with a diameter of less than mils (microns), because fine drills and molds are very expensive and have a very short life. In addition, it is almost impossible to use these methods to produce blind channel holes and cut and bury conductive gaskets. Laser microprocessing the unique characteristics of laser make it an ideal tool for microprocessing Laser is a non-contact zero wear tool, which can transfer a very large energy density to the precise machining position for drilling, cutting and welding by focusing. The type of interaction between the two depends on the characteristics of the material to be treated and the wavelength and energy of the laser. Pulsed CO2 laser and infrared YAG laser are common infrared laser sources in material processing

however, many plastics and some special polymers (such as polyimide) widely used in the matrix materials of flexible circuit boards cannot be finely processed by infrared treatment or "heat" treatment. Heat will deform the plastic and cause carbonization damage on the cutting edge or drilling edge, which may lead to the structural weakening of the circuit board and parasitic conductive paths, so the subsequent processing procedures have to be increased to improve the processing results. Therefore, infrared lasers are not suitable for the processing of some flexible circuits. In addition, even at high energy density, the wavelength of CO2 laser cannot be absorbed by copper, which further severely limits its scope of use. In contrast, the output wavelength of UV laser is less than 0.4 μ m, which is the main advantage suitable for processing polymer materials. Unlike infrared processing, UV microprocessing is not a "heat" process in essence. 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. This "cold" processed part has smooth edges and minimal carbonization effect. Due to the advantages of ultraviolet light in focusing, the focus can be as small as submicron, so it has more advantages in the micro processing of metals and polymers, and can process small parts; Even at a low pulse energy level, a high energy density can be obtained to effectively process materials. The advantages of solid-state devices have always been that excimer lasers play a leading role in the application field of UV "cold processing". However, excimer technology has many inherent shortcomings: all excimer lasers use toxic gases, and the replacement, storage and adjustment of special gases are very troublesome At the same time, they are huge, expensive, and expensive to operate and maintain; Moreover, the biggest problem is that the output beam of excimer laser is large and square, and the space quality is poor, which seriously limits the focusing of the beam, making it necessary to use masks in the process of microprocessing. Excimer lasers are good for drilling holes with the same shape and repeatability in one step (such as processing holes on the drum nozzle of inkjet printers), but in general, the efficiency is not high. Only 1% of the pulse energy acts on the machined surface, while about 99% of the other light energy is lost to the template. In addition, the flexibility of the mask method is limited. If the pattern changes and the mask needs to be replaced, the whole processing process must be stopped

the application of solid-state UV lasers has been limited by the insufficient output power, which can not meet the processing needs. With the development of more reliable semiconductor pumped solid-state technology and more reliable frequency tripling mechanism, the situation has changed. The new tripled frequency semiconductor pumped solid-state laser has become a competitor of excimer lasers. The energy density level is the same, but the repetition rate is higher and the beam quality is better. Avia semiconductor pumped solid-state laser produced by coherent company has an output wavelength of 355nm, an average power of 1.5W, a maximum repetition frequency of 100kHz, and good beam quality, which is very suitable for microprocessing applications. Good beam quality and excellent focusing ability enable you to get rid of the mask for processing, transmit the beam to any position on the workbench through the computer-controlled scanning galvanometer system), and use cad/cam software to perform drilling, marking or cutting through direct writing; When the pattern changes, there is no need to replace the hardware. Drilling experiments show that drilling and cutting of any size and shape larger than the focal point can be carried out through repeated carving. High repetition rate is another outstanding advantage of modern DP, so the strain gauge is connected to the SS laser in the measuring circuit. The repetition rate of excimer lasers is usually several hundred hertz The repetition frequency of Avia can reach 100kHz. The high repetition rate can greatly improve the production in the application of low-density hole distribution and wiring or cutting processing. For example, drilling a 30 micron diameter hole in a 2 mil (50 micron) thick kaptontm polyimide material requires approximately 200 pulses with an energy density of 0.2j/cm2. Avia can drill about 250 holes in one second when working at 50KHz repetition frequency, while it takes one second for excimer laser working at 200Hz repetition frequency to drill a hole with the same parameters. The Avia pulse repetition rate is adjustable from single pulse to 100kHz, enabling you to control the pulse energy and average power very quickly and flexibly. With these methods, important processing parameters can be actively changed in highly demanding processing processes, such as selective removal of polymer coated metals, and vice versa. This function is very useful in many applications, such as drilling blind channel holes, cutting polymer insulating materials to expose buried conductive gaskets, cutting circuit boards, etc. In the mass production environment with high processing requirements, excessive maintenance or shutdown is not allowed. The progressiveness of UV semiconductor pumped solid-state laser in design and production technology makes it an ideal choice for system integration The all solid-state sealed off design, compact in structure and durable, makes this kind of laser very easy to match with the efficient production environment; At the same time, the advantages of high reliability, simple operation and low requirements for hydropower facilities make them increasingly widely used in the field of industrial production. (end)