PCB News - Buried blind hole circuit board manufacturers explore the printing production process

With the rapid development of electronic information technology, the functions of electronic products have become more and more complex, their performances have become more and more superior, and their volume has become smaller and lighter. Therefore, the requirements for printed boards are getting higher and higher. As we all know, the wires of the printed board are getting thinner and thinner, the via holes are getting smaller and smaller, and the wiring density is getting higher and higher. For the current printed board industry, the production of printed boards with buried and blind holes has become quite common, and the types of buried and blind holes have become more and more complex. At present, the formation methods of buried and blind holes mainly include laser hole formation, photo-induced hole formation, plasma etching, chemical etching, mechanical drilling and other methods.

Among them, laser hole formation and photo hole formation are more typical. Laser hole formation has the advantages of good hole shape, small hole diameter, and wide application range. However, its equipment investment is large, and its environmental requirements are relatively high. Light-induced methods also require high environmental investment. For small and medium-sized enterprises, no matter which method they adopt, they cannot afford high environmental and equipment investment. Therefore, how to make use of existing equipment and rationally arrange the production process is the only way for small and medium-sized enterprises to produce printed boards with buried blind holes.

2. Comparison of Buried Blind Hole Formation Methods

2.1 Laser hole formation requires the purchase of expensive equipment, which has fast hole formation speed, good hole shape and a wide range of applicable materials. It is suitable for the production of large quantities of buried and blind hole printed boards.

2.2 The photo-induced hole formation process is long and slow. The process control is more complicated, is greatly affected by the material, and requires high environmental cleanliness.

2.3 Plasma etching requires the purchase of a more expensive plasma etching machine, which requires higher materials. The pore-forming speed is slow and the pore size range is large.

2.4 Chemical etching holes Poor hole type, strict process control.

2.5 Mechanical drilling The hole type is good and the hole diameter range is narrow, which is not suitable for small hole production. There are requirements for the conduction layer relationship of buried and blind vias.

3. Restrictions on the production of buried and blind vias
For small and medium-sized enterprises that cannot invest huge amounts of money to purchase special equipment, they can only make the best use of the company's existing equipment, rationally arrange the process sequence, and improve the key processes to realize the production of buried and blind holes. Even with the best performance of all equipment, the range of buried and blind-hole printed boards that can be produced is relatively narrow.

3.1 Because there is no laser hole forming machine, the aperture of the micro via is limited by the drilling machine. Under normal circumstances, high-precision drilling machines can only drill holes above 0.15mm. The ideal hole diameter is 0.2mm or more. In addition, due to the limitation of existing holeization and electroplating equipment, the metallization ability of via holes with high plate thickness to aperture ratio is limited. Therefore, the thickness of printed boards with small apertures is subject to certain restrictions.

3.2 Because it is impossible to use the build-up method for production, it can only rely on drilling and lamination methods to generate buried and blind holes. Therefore, the relationship between the layers connected by the buried and blind holes is limited. The same layer can only have through holes in the same direction, and there cannot be buried and blind holes that cross between two-way layers . The types of buried and blind holes that can be produced are shown in Figure 1 below (take a six-layer board as an example)

3.3 Affected by environmental temperature and humidity, and graphics transfer equipment, it is impossible to produce printed boards with too small pads.


3.4 The quality of the etching machine directly affects the line width and spacing of the buried blind hole printed board.

Fourth, the process

Negative film and drilling data preparation; inner layer blanking; drilling; hole metallization; pattern transfer; electroplating; etching; de-lead tin; black oxidation; lamination; drill the next layer of via holes to drill the top and bottom vias . This process is similar to the production of laminated printed boards, but it saves expensive equipment such as laser hole forming machines required by the laminated method. However, it is also limited by the type of buried and blind printed boards and the aperture of the vias. The production capacity and scope are far inferior to the laser hole-forming build-up method, and it is not suitable for mass production of printed boards with short cycle times.

5. Buried blind hole plate production process
5.1 Preparation of light drawing data The inner layer of ordinary multi-layer boards does not have the problem of drilling and holeization. In general, the production of the inner layer is mostly mask etching. The drilling data also has only one type of data for the top and bottom through holes. The production of the inner layer of the buried-blind hole printed board is different from that of the ordinary printed board. The inner layer containing the via hole must go through the holeization and electroplating process. Therefore, the positive and negative of the negative film is the opposite of the ordinary inner layer, and the relationship is mirror image. The opposite is also true. In addition, errors may occur during the data conversion process. For printed boards with a line width less than 0.15mm, the line width should be compensated when preparing the light drawing data.

5.2 Drilling Generally, the wiring density of buried and blind-hole printed boards is very high, and the via hole pads are relatively small, which requires the hole diameter to be as small as possible. As far as high-precision drilling machines are concerned, it is no problem to drill 0.2mm holes. When drilling holes, the error in the conversion between metric and inch systems should also be taken into account. For printed boards with larger ring widths and smaller sizes, this factor may not be considered. The general processing method is: For printed boards with too small ring width or too large size, a template should be drilled in advance to compare with the negative. If the error value is large, the error value and error direction should be noted, and the error should be compensated when drawing the negative The coefficient is added, so that the possibility of damage to the via hole with a small ring width can be reduced. The smaller the pore size, the more difficult it is for pore formation and pretreatment. Therefore, in order to reduce drilling pollution in the hole, the drilling machine parameters should be set reasonably. The choice of blind and buried hole diameters should not be too large. Excessive diameters will increase the difficulty of resin plugging. The preferred aperture range is 0.2-0.4mm.