Application of the hottest nanotechnology in PCB m

2022-10-16
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Application of nanotechnology in micro drilling of printed circuit board

Abstract: with the development of printed circuit board (PCB) towards high-density interconnection, PCB through holes are rapidly miniaturized with a diameter of 0.1mm, and the requirements for drill bits are higher and higher. This paper introduces the development prospect and domestic and foreign trends of micro drill for nanotechnology road plate, as well as the principle of nanotechnology to improve the performance of drill bit

key words: nanotechnology; PCB; bit; Overview of cemented carbide

1

with the rapid development of mobile communication in the telecommunications industry and the entry of personal computers into thousands of households, it is required that the drill diameter of the through hole of printed circuit board (PCB) is becoming smaller and smaller. The development law of PCB through hole is as follows: 0.80mm → 0.50 mm → 0.40 mm → 0.30mm → 0.25mm → 0.20mm → 0.10mm → 0.05mm. The aperture of laser etching hole is mostly about 0.10mm. In 1997, the diameter of the smallest drill bit produced in large quantities in the world was 0.35 mm. In Japan, for example, the consumption rate of drill bits with a diameter of less than 0.25 mm increased from 12% in 1998 to 21% in 1999, and to 43% in 2002. Demand for bits in other diameter ranges was flat. A similar situation will also occur in some parts of Asia, especially Taiwan, China. For holes with diameter less than 0.15mm, the newly developed laser drilling technology has certain advantages. The future PCB bits are facing greater technical challenges, such as obtaining greater accuracy in geometry, core taper and helix angle, improving coating technology to prolong the service life of the bits, and improving the spindle to obtain higher speed

in the IT industry, the pursuit of miniaturization and high integration has become a trend. The miniaturization and high integration of electronic devices put forward higher requirements for cemented carbide micro machining tools. With the ultra-fine grain size of cemented carbide, the machinability of (PCB) cemented carbide micro drill continues to improve, requiring the finer the grain size of the alloy, the better [1]

nano materials usually refer to single crystal materials or polycrystalline materials with grain size less than 100nm. Due to the small grain size, the number of atoms on the crystal surface is significantly increased, even more than the number of atoms in the crystal, and the density of grain boundaries is extremely high, which shows a series of excellent properties of materials (micron materials) that are different from coarse grains, which determine the size of fixture structure and the labor intensity of fixture operation, such as high hardness and strength, low density, low elastic modulus, superplasticity, etc. Since the German scientist H. Gleiter successfully developed nanocrystalline materials for the first time in 1984, scientists around the world have competed to carry out a lot of research on this "new material in the 21st century". At present, nano ceramic materials, nano magnetic materials, nano metal materials, nano semiconductors, nano composites and nano catalyst materials have been successfully prepared, and have achieved industrial applications in nano catalyst materials. Nanoscale cemented carbide was first developed by the Rutgers University of the United States in 1989, and applied for a patent in the same year. Based on this technology, American nanodyne company produced nano WC Co cemented carbide composite powder on an industrial scale by spray conversion synthesis. Since then, large companies in Sweden, Germany, Japan and other countries have introduced their own ultra-fine cemented carbides close to nanostructures. Among them, the particle size of Sandvik T002 is the smallest, and its alloy grain size has reached 200nm. Two cemented carbide plants in China have also launched their own ultra-fine cemented carbide close to the nanometer level, with grain size less than 500nm, hardness and strength indexes of hra93 and 4000mpa respectively [2]

since the advent of nano materials, because of their unique properties, they have penetrated into almost all disciplines and engineering technology fields, causing a worldwide development boom. The United States, Japan, Britain, Germany and other countries have national nano material research programs and experimental centers. Cemented carbide is known as "the tooth of industry". In recent decades, the performance of materials used in aerospace, automotive and other industries has been continuously improved, the use of light and strong materials is increasing, and the processing difficulty is increasing. At the same time, in order to reduce costs and protect the environment, the machining industry gradually promotes dry cutting technology, which also makes the processing of some materials more difficult. Tungsten carbide is the main raw material for the preparation of cemented carbide. Nanocrystalline cemented carbide is a tool material developed in recent years. It is a cemented carbide material with high hardness, high wear resistance and high toughness, which is based on nano WC powder and added with appropriate binder and grain growth inhibitor. Its performance is significantly higher than that of conventional cemented carbide, and it has been used more and more widely in the fields of difficult to machine metal cutting tools, micro drills in the electronic industry, precision molds, medicine and so on [3]

union tool company of Japan recently decided to significantly increase the output of cemented carbide bits for PCB. The company has invested a lot of money to expand its union branches in Taiwan, China and the United States, add new equipment and improve production capacity. In recent years, the demand for PCBs for personal computers and information machines in European and American countries and Taiwan has surged, and the demand for drill bits for processing circuit boards has also increased. Union decided to expand the production workshop of its Taiwan branch to expand the production capacity of its branch

2 the requirements of the rapid development of PCB industry on the drill bit

2.1 the breaking mechanism of PCB drill bit

the processing technology of copper clad laminate, such as resin content, curing degree, filler type and addition ratio, has a certain impact on drilling. It can be said that the cause and effect relationship to the drill bit is formed at the same time of the formulation of copper clad laminate. In the composition of the plate, reinforcement materials such as glass fiber are closely connected with the drill hole. One of the reasons why CEM series came out is that it meets the requirements of drilling

improving the drilling performance of electronic cloth has become an important research topic for foreign electronic cloth manufacturers. The influence of electronic cloth on drilling can be summarized as follows: firstly, the structure of cloth (such as yarn design, density, etc.), secondly, surface treatment, thirdly, glass composition and physical processing, and finally, reducing bubbles in glass fiber to improve the quality of hole wall

their main methods are to make the surface of electronic cloth and resin more ductile (treated with new coupling agent), appropriately reduce the SiO2 content in glass fiber components or adopt new processing technology. Foreign countries have successfully developed a new processing technology, which is called "burnt cloth" or "brittle cloth". It uses higher temperature and longer time to burn the electronic cloth during thermal cleaning in the post-treatment process of the electronic cloth, so as to appropriately reduce the tensile strength of the electronic cloth and make the cloth brittle. Its strength is about 20% - 80% lower than that of ordinary cloth. The PCB made of this kind of "over burnt cloth" has good properties such as bit wear, hole wall roughness and small hole curvature when drilling with a fine drill, and can increase the number of overlapping pieces when drilling, which is conducive to improving production efficiency and reducing production costs, and realizing the micromorphization and high density of PCB. According to the introduction, the fiber opening cloth and wool raising cloth made by Toyo Textile Co., Ltd. of Japan have relatively good drilling processability. The drilling properties (mm) of E glass, D glass and NE glass are 0.010, 0.050 and 0.012 respectively. Its drillability is evaluated by measuring the wear amount (mm) of the drill bit after 8000 holes are drilled on the 1.6mm thick FR-4 plate with a 0.4mm diameter drill bit at a drilling rate of 60000r/min and a drilling rate of 1600mm/min [4]

with the progress of manufacturing technology of laser drilling machine centered on CO2 gas laser and the continuous progress of micro aperture processing technology, the laser processing technology of epoxy resin/glass cloth substrate is also under continuous development and research. The problems encountered are the poor shape quality of the through hole, the low accuracy of the aperture size, and the machining quality of the electroplated through hole can not meet the requirements. The emergence of these problems also makes it difficult to make progress in this development work. On the other hand, in the development of small-scale and light-weight electronic products, the inner core board of laminated multilayer board and high multilayer board (the substrate made of epoxy/glass cloth) also puts forward higher requirements for the machinability of micro aperture in mechanical drilling processing. Originally, the minimum drilling hole diameter of multilayer boards was 0.35mm, but now it is developing towards 0.25mm, and some PCB manufacturers are developing new technologies with a drilling hole diameter of 0.10mm. With the development of laser and mechanical drilling technology, the uneven distribution of glass fibers in substrate materials has become a prominent problem affecting micro aperture processing. At present, the voice for improving the performance of glass cloth is rising. Under this background, a Japanese company has successfully developed a new type of glass cloth with the goal of improving the machinability of laser and mechanical drilling of micro holes

especially in the case of laser processing, due to the different thermal characteristics (including thermal decomposition temperature, heat conduction, etc.) of glass fiber and resin, it will cause deviations in different positions of through-hole aperture size and opening aperture size. Especially in PCBs with high-density installation requirements, they all use extremely thin glass cloth as the reinforced insulation layer. These extremely thin glass cloths are woven with very fine yarn. "Cage shaped pores" exist in thin substrates, which further reduces the machinability of micro through holes. It can be concluded that the glass cloth used in the substrate material must improve the uneven distribution of glass fibers in the manufacture of PCB with high density wiring. This is the key to improve the machinability of micro aperture. In order to solve the problem of uneven fiber distribution in its weaving structure, this new glass cloth adopts uniform flattening fiber opening processing (MS processing for short) [5]

in the process of PCB micro hole machining, the axial force and torque increase with the increase of feed rate and drilling depth, and the main reason is related to the chip removal state. With the increase of drilling depth, it is difficult to discharge the chips. In this case, the cutting temperature rises, the resin material melts and firmly binds the glass fiber and copper foil fragments to form a tough cutting body. This cutting body has affinity with PCB parent material. Once this cutting body is produced, the discharge of chips will stop, the axial force will increase sharply, and the torque will also increase sharply, resulting in the fracture of microporous drill bit

the fracture mechanism of micro hole drill for PCB is as follows: the fracture forms of micro hole drill for PCB include crimp fracture, torsion fracture and crimp torsion fracture. Generally speaking, crimp fracture and torsion fracture coexist; The breaking mechanism of microporous bit is mainly chip blockage, which is the key factor causing the increase of drilling torque

2.2 wear mechanism of PCB microdrill

the results show that the wear of PCB microdrill is mainly caused by the chemical erosion of the Co binder in the microdrill material WC Co cemented carbide by the high-temperature decomposition products released by brominated epoxy resin in PCB material. At about 300 ℃, this erosion reaction is obvious. Reducing the CO content in cemented carbide can effectively reduce this chemical wear. When the drilling speed is lower than 150mm/min, chemical wear is no longer the main form of wear, but friction wear (that is, the peeling of alloy grains) has become the main form of wear

2.3 basic requirements for PCB micro drill materials

through the above analysis, we can comprehensively draw the basic requirements of PCB production technology for PCB micro drill materials:

1) high wear resistance and fracture toughness

2) high thermal conductivity

3) the finer the WC grain in cemented carbide, the better

4) it has good chemical erosion resistance

5) good processability, etc

among them, alloy crystal

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