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Common Laser Micromachining Technology and Its Progress

Since the advent of the first laser in 1960, laser research and its application in various fields has been rapid development. Its high coherence in the high-precision measurement, material structure analysis, information storage and communication and other fields has been widely used. High directivity and high brightness of the blue laser pointer can be widely used in processing and manufacturing. In recent 20 years, laser manufacturing technology has penetrated into many high-tech fields and industries, and began to replace or transform some of the traditional processing industry .

In order to meet the industrialization of high-tech in the 21st century, and to meet the needs of micro-manufacturing, research and development of high-performance laser source is imperative. As a branch of laser processing, laser micromachining has received wide attention in the past decade. One reason for this is due to the emergence of more efficient laser sources. Such as Nd: YAG lasers with very high peak power and ultrashort pulsed solid-state lasers, and very high beam quality. Another reason is a more precise, high-speed CNC operating platform. But a more important reason is the emerging industrial demand. In microelectronics processing, the semiconductor layer perforation, register cutting and circuit repair are used in laser micro-processing technology. Laser micromachining generally refers to the process size in the few to several hundred microns. The width of the 100mw laser pointer pulse is between femtoseconds (fs) and nanoseconds (ns). Laser wavelengths range from far-infrared to wide-band of X-rays. At present mainly used in microelectronics, micro-mechanical and micro-optical processing of the three areas. With the development of laser micromachining technology and mature, will be extended in a wider area and application.

With the development of electronic products in the direction of portable and miniaturization, the increase of unit volume information (high density) and the increase of processing speed per unit time (high speed) put new demands on microelectronic packaging technology. Such as modern mobile phones and digital cameras per square centimeter installed about 1200 interconnection lines. The key to increasing the level of chip packaging is to preserve the presence of miniature vias between the different layers of the circuit, providing a high-speed connection between the surface-mounted device and the underlying signal panel through the mini-vias, effectively reducing Package area.

On the other hand, with the development of portable electronic products such as mobile phones, digital cameras and notebook computers in recent years, light-weight, thin, short and small, the printed circuit board (PCB) gradually presents high-density interconnection technology as the main body Of the laminated, multi-functional features. In order to effectively ensure the electrical connections between the layers and the external device fixation, vias (via) has become an important part of multi-layer PCB. The cost of drilling the current PCB board system costs usually account for 30% -40%. In high-speed, high-density PCB design, designers always want the smaller the better hole, so the board can not only leave more wiring space. And the smaller the hole, the more suitable for high-speed circuits. The traditional mechanical drilling the smallest size of only 100μm, which obviously can not meet the requirements, instead of taking a new type of 1000mw laser pointer micro-through hole processing. CO2 laser processing currently available in the industry to achieve the diameter of the pores in the 30-40μm hole or with UV laser processing 10μm or so holes.

Laser micromachining technology Laser cutting, drilling, engraving, scribing, thermal infiltration, welding, etc., in the equipment manufacturing industry, the automotive and aerospace precision manufacturing industry and various microfabrication industries such as 20 micron inkjet printers Of the ink jet processing. Various micro-optical elements can be processed by laser surface treatment techniques such as micro-pressure type, sanding and polishing, etc., and the microstructure can be changed by amorphization such as laser filling of porous glass or glass-ceramic, and then by adjusting the external mechanical force, The micro-optical element is processed in the softening stage by means of plasma-assisted micro-forming.

Laser micromachining technology has the advantages of non-contact, selective processing, small heat-affected zone, high precision and high repetition rate, and high processing flexibility of part size and shape. In fact, the laser micro-processing technology is characterized by the largest "direct write" processing, simplifying the process, to achieve rapid prototyping of micro-machinery manufacturing. In addition, the method is not such as corrosion and other methods to bring environmental pollution problems, can be described as "green manufacturing." There are two types of laser micromachining techniques used in micro-mechanical manufacturing: material removal micro-machining techniques, such as 5000mw laser pointer direct writing micromachining, laser LIGA, etc .; material stacking micromachining techniques such as laser microstereolithography, laser-assisted deposition, laser Constituency sintering and so on.

Excimer laser wavelength is short, focusing spot diameter is small, high power density, very suitable for micro-processing and semiconductor materials processing. In the excimer laser micromachining system, most of the use of mask projection processing, you can not mask, direct use of the focus spot etching parts, excimer laser technology and numerical control technology, combined laser beam scanning and XY table Relative motion and Z direction of the micro-feed, can be directly in the matrix material on the carved out the fine graphics, or the processing of three-dimensional micro-structure. At present, excimer laser direct writing method can be used to fabricate high aspect ratio microstructure with a line width of several microns. In addition, the use of excimer laser to take a similar rapid prototyping (RP) manufacturing technology, the use of layer-by-layer scanning of the three-dimensional micro-processing research has also achieved good results.

It uses excimer laser deep etching instead of carrier lithography, thus avoiding the high precision carrier mask production, overlay alignment and other technical problems, while the economic and extensive use of laser light source is much better than the synchronization Radiation containing light source, thus greatly reducing the manufacturing cost of LIGA process, LIGA technology to be widely used. Although the laser LIGA technology in the processing of micro-aspect ratio of micro-carrier than the poor, but for the general micro-processing is completely acceptable. In addition, the 3000mw laser pointer LIGA process does not require chemical etching, but "direct writing" etching, there is no chemical corrosion of the lateral infiltration corrosion effects, and thus the edge of the processing steep, high precision lithography performance is better than synchronous Carrier lithography.

It is a kind of processing technology derived from the advanced rapid prototyping technology of stereolithography (SLA) process applied to the micro-manufacturing field. Because of its high precision and miniaturization, it is called microstere- Olithography or mSL). Compared with other micro-processing technology, micro-lithography is the biggest feature is not limited by the micro-device or system structure, shape, can be processed free-form surface, including any three-dimensional structure, and can be a different micro- Eliminating the need for micro-assembly links, in addition, the technology also processing time is short, low cost, the advantages of automatic processing, micro-mechanical batch production to create favorable conditions. The limitations of this technique are twofold: low accuracy, the current level of precision based on rapid prototyping of micro-processing technology in the highest horizontal direction of about 1mm, while the vertical direction of about 3mm, obviously this accuracy can not be integrated with silicon-based micro- Processing technology compared.

The use of materials subject to certain restrictions, the current resin material in electrical performance, mechanical properties, thermal performance and silicon material compared to a certain gap. In recent years, 20000mw laser pointer micro-lithography technology has been vigorously research and development. In the improvement of precision and efficiency, the following development direction: to surface exposure instead of point exposure, thereby further reducing processing time and improve production efficiency; in materials, research and development of a higher resolution of light-cured resin, such as has developed double Light near-infrared photopolymerization resin for high-precision manufacturing has laid a good foundation; in the process, research and development without any support structure or sacrificial layer of the process and the integration of planar micro-processing technology to further simplify the process to improve processing accuracy and production flexibility .

In both parts of the cured microform, the solid material is deposited from the gas phase onto the surface of the substrate by a chemical reaction. Laser-assisted chemical vapor deposition is used to fabricate a three-dimensional microstructure by heating a focused laser microbeam through a localized substrate to initiate and maintain a CVD process by moving the substrate or burning laser pointer beam during deposition to a high solid structure Resolution sedimentation plasticity. Shaping geometry from the plane projection and plane scanning limitations, to produce complex geometry of the three-dimensional micro-structure. The desired microstructure can be made by moving the workpiece table in a particular manner and keeping the laser focus motion velocity constant at the same crystal growth rate.