Overview of printed circuit board HDI high density technology, application of HDI circuit board manufacturing technology
(1) fine wire technology in the future high fine wire width/spacing will be 0.20mm-o.13mm-0.08mm-0.05mm, to meet the requirements of SMT and Multichip Package (MCP). The following techniques are therefore required.
(1) due to the thin wire width of the HDI circuit boards are now used in thin or ultra-thin copper foil (
(2) the current HDI circuit board has been made by thin dry film and wet film lamination process, thin and good quality dry film can reduce line width distortion and defects. Wet film can fill small air gap, increase interface adhesion, improve wire integrity and accuracy.
(3) HDI PCB circuit etched by electrodeposition photo imageable etching resist film (company – deposited Photoresist, ED). Its thickness can be controlled in the range of 5-30/um, which can produce more perfect fine wires. It is especially suitable for narrow ring width, no ring width and full plate electroplating. At present, there are more than 10 ED production lines in the world.
(4) HDI circuit board line imaging using parallel light exposure technology. Because the parallel light exposure can overcome the influence of the oblique rays of the “point” light source on the variation of line width, the fine wires with accurate line width size and smooth edges can be obtained. But parallel exposure equipment is expensive, expensive, and requires a high degree of cleanliness in the environment to work.
Automatic Optic Inspection (AOI) is adopted for HDI circuit board Inspection. This technology has become a necessary means of detection in fine wire production and is being rapidly popularized and developed. For example, AT&T has 11 AoI and}tADCo has 21 AoI specially used for detecting inner layer graphics.
HDI circuit board manufacturers specializing in the production of 6 -12 – layer high density HDI circuit boards
The functional holes of the printed circuit board for surface mounting are mainly electrical interconnections, which makes the application of microporous technology more important. The use of conventional drill material and CNC drilling machine to produce small holes has many faults and high cost. Therefore, PCB high density is mostly concentrated on wire and pad fine, although great achievements have been made, but its potential is limited, to further improve the fine (such as less than o.08mm wire), the cost of sharp rise, so turn to micro hole to improve the fine.
In recent years, numerical control drilling machine and micro-bit technology has made a breakthrough, so micro-hole technology has a rapid development. This is the main outstanding characteristic in the current printing electric board production. In the future, the micro-hole formation technology mainly depends on the advanced CNC drilling machine and excellent micro-head, and the laser technology of the formation of small holes, from the perspective of cost and hole quality is still inferior to the CNC drilling machine formed by the small holes.
At present, the technology of nc drilling machine has made a new breakthrough and progress. And formed a new generation of CNC drilling machine characterized by drilling small holes. The efficiency of micro-hole drilling machine in drilling holes (less than 0.50mm) is 1 times higher than that of conventional CNC drilling machine, with fewer faults and a rotating speed of 11-15r/min. O.1-0.2mm microhole can be drilled with a small quality drill with high cobalt content. Three plates (1.6mm/ block) can be stacked to drill. When the drill bit is broken, it can automatically stop and report its position, automatically change the drill bit and check the diameter (the tool bank can hold hundreds of pieces), automatically control the constant distance between the drill tip and the cover plate and drill depth, so that blind holes can be drilled without damaging the table. CNC drill table with air cushion and maglev, move faster, lighter, more accurate, will not scratch the table. Such drilling machines are in short supply, including the Mega 4600 from Italy’s Prurite, the ExcelIon 2000 series from the us, as well as new generation products from Switzerland and Germany.
There are a lot of problems with drills to drill tiny holes. It has hindered the development of micro-hole technology, so laser hole erosion has been paid attention to, studied and applied. However, there is a fatal disadvantage, that is, the formation of horn holes, and as the thickness of the plate increases and serious. In addition to the pollution of high temperature ablation (especially multi-layer plate), the life and maintenance of light source, the repeated accuracy of the etching hole and the cost, etc., the promotion and application of the micro hole in the production of printed circuit board are limited. However, laser etched holes are still used in thin and high density microporous plates, especially in McM-l HDI circuit board technology, such as the combination of mylar etched holes in m.c.ms and metal deposition (sputtering technology). Buried hole formation can also be used in high density interconnect multilayer plates with buried and blind hole structures. However, due to the development and technical breakthrough of nc drilling machine and micro drill, it has been popularized and applied rapidly. Therefore, the application of laser drilling in the surface mounting of HDI circuit board cannot form a dominant position. But it still has a place in a field.
Buried, blind, through hole combination technology is also an important way to improve the high density of printed circuit board. In general, buried and blind holes are micro holes. In addition to increasing the number of wiring on the PCB surface, buried and blind holes are all connected by “closest” interlayer interconnection, which greatly reduces the number of through-hole formation and the isolation disk setting, thus increasing the number of effective wiring and interlayer interconnection in the board and increasing the interconnection density.
Buried, blind hole structure of the HDI circuit board, are generally completed by the “sub-plate” production, which means that it has to go through a number of platen, drilling, hole plating to complete, so precise positioning is very important. Therefore, the interconnect density of embedded, blind and through-hole multilayer board is increased by at least three times compared with the conventional full-through-hole board structure at the same size and number of layers. If the printed board is combined with buried, blind and through-hole under the same technical specifications, its size will be greatly reduced or the number of layers will be significantly reduced. So on the surface of high density PCB installation, buried, blind hole technology have been applied more and more, not only in the large computers, communications equipment and other surface mount PCB using, but also in the field of civil and industrial has been widely used, and even in some thin plate has been applied, such as a variety of PCMCIA, Smard, IC card, etc more than six thin layer PCB.