High precision of the printed circuit board technology overview

Printed circuit technology is the use of high-precision fine line width / spacing, small holes, narrow ring width (or no ring width), and buried, blind holes and other technologies to achieve higher density. The accuracy refers to the "small, small, narrow, thin," the result will bring high precision requirements in order to line width, for example: O.20mm width, required to produce O. 16-0.24mm for qualified, the error is (O.20 soil 0.04) mm; and O. 10mm in width, the same token the error is (0.10 ± O.02) mm, which obviously improve the accuracy of a fold, and so on is not difficult to understand, and therefore no separate discussion of high-precision requirements. But it is the production technology in a prominent problem.

(1) the future of high technology, fine wire fine line width / spacing will be 0.20mm-O. 13mm-0.08mm-0.005mm, in order to meet the SMT and multi-chip package (Multichip Package, MCP) requirements. Thus requiring the use of the following techniques.

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

② The dry and wet thin film technology, thin and good quality dry film can reduce the line width distortion and defects. Wet film could fill a small gap, increase the interface adhesion, improve the integrity and accuracy of wire.

③ The electrodeposition photoresist film (Electro-deposited Photoresist, ED). Its thickness can be controlled in 5-30/um range, can produce a more perfect fine line, for small ring width, no ring-width and full board is particularly applicable to plating, the world, over 10 production lines of ED.

④ parallel optical lithography. As the parallel light exposure can overcome the "point" to the oblique rays of light to bring the impact of width amplitude, etc., which can get exact size and width edges smooth fine line. But the parallel exposure, expensive equipment, high investment and high cleanliness requirements in the environment.

⑤ using automated optical inspection technology (Automatic Optic Inspection, AOI). This technology has become a fine line to detect the essential means of production, is the rapid popularization and application development. Companies such as AT & T has 11 sets of AoI,} tadco company has 21 sets of AoI designed to detect the inner graphics.

(2) porous surface mount technology printed circuit board with the function of the hole is mainly from the electrical interconnect function, thereby the application of micro-technology is more important. Using conventional materials and CNC drilling machine to drill a small hole production failures and more costly. Therefore, high density printed circuit board conductors and pads in most of the fine efforts, has made great achievements, but its potential is limited, to further enhance the close of (such as less than O.08mm wire), the cost surge, which turned with the micro-technology to increase the fine.

CNC drilling machine and a small drill bit in recent years, technology has made a breakthrough, micro-hole technology, which has developed rapidly. This is the current PCB production in the main outstanding features. Tiny holes to form the future technology mainly relies on advanced CNC drilling and excellent small head, and laser technology to form the holes, and holes from a cost point of view of quality is still inferior to the formation of CNC drilling holes.

① CNC Drilling CNC Drilling technology has now made new breakthroughs and progress. And formed a small drill hole is characterized by a new generation of CNC drilling machine. Micro-drilling drill holes (less than 0.50mm) is more efficient than conventional CNC drilling-fold higher, fewer failures, speed 11-15r/min; can drill O. 1-0.2mm micro-, cobalt-containing small amount of high quality drill bits can be three boards (1.6mm / block) stack up for drilling. Drill down and report broken automatically know the location, automatically replace the drill bit and check the diameter (the tool library that can accommodate as many as hundreds of branch), can automatically control the drill tip and the cover of a constant distance and drilling depth, which can be drilled blind hole will not drill a bad table. CNC drilling machine tops, air and magnetic levitation type, move faster, lighter, more accurate, will not scratch the surface. This drill is currently very tight, such as Italy Prurite the Mega 4600, the United States ExcelIon 2000 series, as well as Switzerland, Germany and other next-generation products.

② CNC laser drilling and conventional drilling bit to drill small holes do exist many problems. Has hindered the progress of micro-hole technology, which the laser pits attention, research and application. But there is a fatal flaw, namely the formation of speaker holes, and with the increasing seriousness of thickness. Ablation with high pollution (especially plywood), and maintenance of the life of light source, the repeatability of pits and cost, thus producing small holes in the PCB area promote the application has been limited. But the laser pits in the thin high-density microplates still been applied, especially in the MCM-L high-density interconnect (HDI) technology, such as M. C. Ms pits in the polyester film and metal deposition (sputtering) a combination of high-density interconnect has been applied. Buried in a blind hole structure in high-density multilayer interconnect to form the buried hole can also be applied. However, due to CNC drilling and micro-drill development and technological breakthroughs, spread rapidly and applications. Thus the surface-mount PCB laser drilling in the application can not form a dominant position. But the field is still in a place.

③ buried, blind, buried vias technology, blind, through-hole technology is also improved with high-density printed circuit is an important way. Generally buried, blind holes are small holes, in addition to improving the number of outside wiring board surface, buried, blind hole is a "recent" the interconnection between the inner layer, greatly reducing the number of vias formed, isolated disc set will greatly reduced, thereby increasing the effective wiring board and the number of interconnect layers, increased high-density interconnect. So buried, blind, via a combination of multilayer plates than conventional all-pass structure, the same size and number of layers, its interconnection density increased by at least three times, if under the same technical indicators, buried, blind, combination of through-hole PCB, its size will be greatly reduced or significantly reduced number of layers. Therefore, in high-density surface mount printed circuit board, buried and blind via technology increasingly has been applied, not only in mainframe computers, communications equipment, etc. used in surface-mount printed circuit board, and in civil, industrial The area has also been widely used, even in some of the thin plate has been applied, such as a variety of PCMCIA, Smard, IC card of six or more thin plates.

Buried, blind hole structure of the printed circuit board, generally a "sub-board" mode of production to complete, which means to go through several plate, drilling the hole of the plating to complete, so precise positioning is very important .