How to do the precision of PCB circuit board "extreme"?

High precision of circuit board refers to the use of fine line width/spacing, tiny hole, narrow ring width (or no ring width) and buried, blind hole and other technologies to achieve high density.

And high precision means the result of "thin, small, narrow and thin" will inevitably bring high precision requirements. Take line width as an example:

0.20mm line width, according to the regulations produced 0.16 ~ 0.24mm is qualified, its error is (0.20 soil 0.04) mm; And 0.10mm line width, the same error is (0.1±0.02) mm, obviously the latter accuracy is increased by 1 times, so it is not difficult to understand, so the high precision requirements are no longer discussed separately. But it is a prominent problem in production technology.

Fine wire technology

In the future, the linewidth/spacing of high fine litichip Package will range from 0.20mm to 0.13mm to 0.08mm to 0.005mm to meet the requirements of SMT and Mulitichip Package (MCP). Therefore, the following techniques are required.

① substrate

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

② Technology

Using thin dry film and wet film process thin and good quality dry film can reduce line width distortion and defects. Wet film can fill small air gaps, increase interface adhesion, improve wire integrity and accuracy.

③ Electrodeposition photoresist film

Electro-deposited Photoresist (ED) film was adopted. Its thickness can be controlled in the range of 5 ~ 30 / um, which can produce more perfect fine wire, especially for narrow ring width, no ring width and full plate plating. At present, there are more than ten ED production lines in the world.

④ Parallel light exposure technology

Using parallel light exposure technology. Because parallel light exposure can overcome the influence of line width variation caused by oblique rays of "point" light source, fine wire with precise line width size and clean edge can be obtained. But parallel exposure equipment is expensive, expensive, and requires a high degree of cleanliness.

(5) Automatic optical detection technology

Adopt automatic optical detection technology. This technology has become a necessary means of detection in fine wire production, and is being rapidly popularized, applied and developed.

Microporous technique

The function holes of the printed board for surface mounting mainly play the role of electrical interconnection, so the application of the microhole technology is more important. The use of conventional drill materials and CNC drilling machines to produce small holes has many faults and high costs.

Therefore, printed board density is mostly in the wire and pad fineness efforts, although great achievements have been made, but its potential is limited, to further improve the fineness (such as less than 0.08mm wire), the cost rises sharply, so turn to the use of microholes to improve the fineness.

In recent years, the technology of NC drilling machine and micro drill has made a breakthrough, so the micro hole technology has a rapid development. This is the main outstanding feature of current PCB production.

In the future, the micro-hole formation technology mainly depends on advanced CNC drilling machine and excellent micro-head, and the small hole formed by laser technology, from the point of view of cost and hole quality is still inferior to the small hole formed by CNC drilling machine.

① Numerical control drilling machine

At present, the technology of NC drilling machine has made new breakthrough and progress. And formed a new generation of NC drilling machine which is characterized by drilling tiny holes.

The efficiency of microhole drilling (less than 0.50mm) is 1 times higher than that of conventional CNC drilling machine, less failure, rotation speed of 11 ~ 15r/min; It can drill 0.1 ~ 0.2mm micro holes, using high quality cobalt drill bit, three plates (1.6mm/piece) can be stacked for drilling. When the bit is broken, it can automatically stop the machine and report the position, automatically change the bit and check the diameter (the tool library can accommodate hundreds of pieces), and automatically control the constant distance between the drilling point and the cover plate and the drilling depth, so it can drill blind holes and won't drill the mesa. CNC drilling machine table using air cushion and maglev, moving faster, lighter, more accurate, will not scratch the table.

Such drill presses are currently in high demand, such as the Mega 4600 from Prurite of Italy, Excellon 2000 series of USA, and the new generation products from Switzerland and Germany.

② Laser drilling

There are a lot of problems with conventional CNC drilling presses and drills to drill tiny holes. It has hindered the progress of micro hole technology, so laser etching has been paid more attention, studied and applied.

But there is a fatal disadvantage, that is, the formation of horn holes, and with the increase of plate thickness. In addition to the pollution caused by high temperature ablation (especially for multilayer boards), the life and maintenance of light sources, the repetition accuracy of etching holes and the cost, etc., the popularization and application in the production of tiny holes in printed boards are limited. However, laser etching is still applied in thin and high density microporous plates, especially in the high density interconnection (HDI) technology of MCM-L, such as the combination of mylar etching and metal deposition (sputtering technology) in M.C.Ms.

The buried hole formation can also be used in high density interconnected multilayer plates with buried and blind hole structures. However, due to the development and technological breakthrough of NC drill press and micro drill, it has been rapidly popularized and applied. So laser drilling in the application of surface mounted circuit board can not form a dominant position. But it still has a place in something.