The high precision of circuit boards refers to the use of technologies such as fine line width/spacing, micro holes, narrow ring width (or no ring width), and buried and blind holes to achieve high density. And high precision refers to the requirement for high precision that results from being "thin, small, narrow, and thin". Taking line width as an example: for a line width of 0.20mm, producing a line width of 0.16-0.24mm according to regulations is qualified, with an error of (0.20mm ± 0.04) mm; And for a line width of 0.1mm, the same error is (0.10 ± O.02) mm. Obviously, the accuracy of the latter is doubled, and so on, which is not difficult to understand. Therefore, the requirement for high accuracy will not be discussed separately. But it is a prominent challenge in production technology.

(1) The future high-density wire width/spacing of fine wire technology will be 0.20mm-0.13mm-0.08mm -0.005mm to meet the requirements of SMT and Multichip Package (MCP). Therefore, the following technologies are required to be adopted.

① Using thin or ultra-thin copper foil (<18um) substrate and fine surface treatment technology.

② By using thinner dry film and wet film sticking processes, thin and high-quality dry films can reduce line width distortion and defects. Wet film coating can fill small air gaps, increase interface adhesion, and improve wire integrity and accuracy.

③ Using electro deposited photoresist (ED) film. Its thickness can be controlled within the range of 5-30/um, which can produce more perfect fine wires. It is particularly suitable for narrow ring widths, no ring widths, and full board electroplating. Currently, there are more than ten ED production lines worldwide.

④ Adopting parallel light exposure technology. Due to the ability of parallel light exposure to overcome the effects of line width variations caused by the oblique rays of "point" light sources, fine wires with precise line width dimensions and smooth edges can be obtained. But parallel exposure equipment is expensive, requires high investment, and requires working in a high cleanliness environment.

⑤ Adopting Automatic Optical Inspection (AOI) technology. This technology has become an essential means of detection in fine wire production and is rapidly being promoted, applied, and developed. AT&T has 11 AoIs, and Tadco has 21 AoIs specifically designed to detect inner layer patterns.

(2) The functional holes of printed boards used for surface mounting of microporous technology are mainly for electrical interconnection, making the application of microporous technology more important. The use of conventional drill materials and CNC drilling machines to produce micro holes has many faults and high costs. So the high-density development of printed boards mostly focuses on the refinement of wires and solder pads. Although great achievements have been made, its potential is limited. To further improve the refinement (such as wires smaller than 0.08mm), the cost has sharply increased, so we have turned to using micropores to improve the refinement.

In recent years, breakthrough progress has been made in CNC drilling machines and micro drill bit technology, resulting in rapid development of micro hole technology. This is the main prominent feature in current PCB production. In the future, the formation technology of micro holes will mainly rely on advanced CNC drilling machines and excellent micro heads, while the small holes formed by laser technology are still inferior to those formed by CNC drilling machines in terms of cost and hole quality.

① At present, the technology of CNC drilling machines has made new breakthroughs and progress. And a new generation of CNC drilling machines characterized by drilling tiny holes has been formed. The efficiency of drilling small holes (less than 0.50mm) with a micro hole drilling machine is twice as high as that of a conventional CNC drilling machine, with fewer faults and a speed of 11-15 r/min; It can drill 0.1-0.2mm micropores, using high-quality small drill bits with high cobalt content, and can stack three plates (1.6mm/block) for drilling. The drill bit can automatically stop and notify the position when it breaks, automatically replace the drill bit and check the diameter (the tool library can accommodate up to hundreds of pieces), and automatically control the constant distance and drilling depth between the drill tip and the cover plate, so it can drill blind holes without damaging the table. The CNC drilling machine table adopts air cushion and magnetic levitation, which move faster, lighter, and more accurately without scratching the table. Such drilling machines are currently in high demand, such as Prurite's Mega4600 from Italy, ExcelIon2000 series from the United States, as well as new generation products from Switzerland, Germany, and other countries.

② There are indeed many problems with using conventional CNC drilling machines and drill bits for laser drilling to drill small holes. Laser etching has been recognized, researched, and applied due to its hindrance to the progress of micro hole technology. But there is a fatal drawback, which is the formation of horn holes and their severity increases with the increase of plate thickness. In addition, the pollution caused by high-temperature ablation (especially on multi-layer boards), the lifespan and maintenance of light sources, the repeatability and accuracy of etching holes, and cost issues have limited the promotion and application of micro holes in printed circuit board production. However, laser etching has still been applied in thin and high-density microporous plates, especially in the high-density interconnect (HDI) technology of MCM-L, such as the high-density interconnect combining polyester film etching and metal deposition (sputtering technology) in M.C.Ms. The formation of buried holes in high-density interconnected multilayer boards with buried and blind hole structures can also be applied. However, due to the development and technological breakthroughs of CNC drilling machines and micro drills, they have quickly been promoted and applied. Therefore, laser drilling is performed on the surface

The application in installing circuit boards cannot form a dominant position. But it still holds a place in a certain field.

③ The combination of buried, blind, and through-hole technology is also an important way to improve the high-density of printed circuits. Generally, buried and blind holes are small holes. In addition to increasing the number of wiring on the board, buried and blind holes use the "nearest" interlayer interconnection, greatly reducing the number of through holes formed. The setting of isolation disks will also be greatly reduced, thereby increasing the number of effective wiring and interlayer interconnection inside the board and improving the density of interconnection. Therefore, the multi-layer board with buried, blind, and through-hole combination has at least three times higher interconnect density than the conventional full through-hole board structure under the same size and number of layers. If the printed board with buried, blind, and through-hole combination has the same technical specifications, its size will be greatly reduced or the number of layers will be significantly reduced. Therefore, buried and blind hole technology has been increasingly applied in high-density surface mounted printed boards. It is not only used in surface mounted printed boards for large computers, communication equipment, etc., but also widely used in civilian and industrial fields. It has even been applied in some thin boards, such as various PCMCIA, Smard, IC card and other thin six layer or more boards.

Printed circuit boards with buried and blind hole structures are generally produced using a "split board" production method, which means that they need to go through multiple pressing plates, drilling, hole electroplating, etc. to complete. Therefore, precise positioning is very important.