Different types of PCB have different manufacturing methods, and the same type of PCB also has different processing methods.
Although there are many manufacturing processes, they can be classified into the following three basic methods:
Additive process: Through screen printing or exposure to form patterns, drilling, copper deposition, transfer lamination and other processing, the conductive patterns are directly made on the insulating substrate.
Subtraction method: selectively remove part of the copper foil on the copper-clad substrate by drilling, hole metallization, pattern transfer, electroplating, etching or engraving, and form conductive patterns.
Semi-additive process: additive process combined with subtractive method, skillfully using the processing characteristics of the two methods to form conductive patterns on the insulating substrate. The BUM board in HDI board adopts this process method.
At present, the most widely used and mature production technology is subtractive method. Of course, with the progress of science and technology, some new technological methods and technologies are constantly emerging and developing, such as the manufacturing technology of laminated multilayer board and rigid-flexible laminated board, which is different from the general subtraction method or adding layer method. The following will give a brief introduction to the manufacturing process of three kinds of printed boards.
1 subtraction method
The subtractive method for manufacturing printed boards is a process of selectively removing unnecessary conductive copper foils on the laminate coated with copper foils to form conductive patterns, so subtractive method is also called copper foil etching method.
Schematic diagram of substrate and final product used in subtractive method is as follows:
1) Typical process of single-sided printed circuit board The typical process flow of single-sided printed circuit board manufacturing is as follows:
Process: Two processes, punching and contour machining, can also be completed by one process with a pair of stamping dies.
2) Typical technological process of manufacturing double-sided printed boards with metallized holes. According to the different structures of printed boards, the technological process of copper foil etching is also different. Typical technological process of double-sided boards with plated holes (metallized holes) is as follows:
Note: 1) Anti-oxidation treatment refers to coating anti-oxidation solder flux (OSP) on bare copper pads without hot air leveling. 2) For the flexible board, the process of printing solder resist is changed to hot pressing the cover film (the pad window has been opened in advance), and the other processes are the same. 3) Typical process flow of rigid multilayer printed board manufacturing. The process flow of multilayer printed board is more complicated than that of double-panel manufacturing, mainly adding the manufacturing, processing, lamination and lamination of inner conductive patterns. The process of hole metallization is also more complicated than that of double-panel and requires high reliability. The process after pattern electroplating is the same as that of the plate with metallized holes on both sides, so it will not be introduced item by item. See the following figure for the specific process flow:
4) Flexible printing process: board manufacturing.
Printed boards are divided into five types: single-sided flexible board (type 1), double-sided flexible board (type 2), multi-layer flexible board (type 3), rigid-flexible multi-layer board with metallized holes (type 4) and flexible or multi-layer flexible combined printed board with rigid and non-metallized holes (type 5). These five types can be divided into two categories according to their different requirements for deflection:
Class a: can withstand the deflection during installation;
Class B: It can withstand the specified continuous bending and deflection for many times, (generally, it is a flexible board with two conductor layers or less, i.e. Type 1,
Type 2 plate). Such as printed boards of foldable parts on mobile phones and notebook computers.
Different types of flexible printed boards have different processing technologies. Except rigid and flexible substrates are needed for rigid and flexible printed boards of Type 4 and Type 5, all other types are processed by flexible substrates. Its processing method is similar to that of rigid board, which reduces the process of printing solder resist film and increases the process of laminating covering film. The main difference in equipment is that, because the flexible substrate is soft, it is easy to bend and damage the substrate in the process of transmission. Therefore, the arrangement density of conveying rollers of the equipment used is high, and the distance between rotating shafts is small. The etching process needs to be pulled by a hard plate, and special pumice powder cleaning equipment or chemical cleaning equipment is used for cleaning.
The manufacture of rigid-flexible printed circuit board is to make the flexible part according to the process of single-sided and double-sided flexible board at first, and then laminate the rigid-flexible laminated layer, drill holes and metallize the holes according to the process of rigid multilayer board. The key lies in the matching of the quality of the rigid-flexible laminated part and the thermal expansion coefficient of the material. Metallized holes can’t be set at the bent part, because this will affect the bending and destroy the metallized holes during bending. The typical manufacturing process of type I and type 2 flexible boards is as follows:
Note: 1. The covering layer is the insulating protective layer on the surface of the flexible circuit board, and its function is to protect the flexible circuit from moisture, dust and other chemical attacks and improve the bending performance.
2. The process route (I) is to remove Sn-Pb locally, then hot melt and then press or print the covering layer; Route (II) is to remove Sn-Pb from the whole plate, then press or print the covering layer, and finally carry out hot air leveling.
2 additive process
Additive process directly prints conductive materials on insulating materials by screen printing or chemical deposition to form conductive patterns.
Shape. The following two kinds of additive process are widely used:
1) Printing conductive materials on insulating substrates, such as ceramics or polymers, by screen printing. If metal conductive paste is printed on ceramic substrate, and then sintered and fused at high temperature, ceramic thick film printed board (CTF) will be formed. If conductive ink is printed on polymer insulation material, it will be heated and quickly dried and cured, and then polymer thick film circuit (PTF) will be formed.
2) On the insulating base material containing catalyst, after activation treatment, the pattern of electroplating resist layer which is opposite to the required conductive pattern is made, and selective electroless copper plating is carried out in the window (exposed activation surface) of the resist until the required copper layer thickness. This method has the advantages of long time, slow speed, low efficiency, low elongation rate of electroless copper deposition layer, difficult control of coating thickness, and not wide application. On this basis, the semi-additive process process was developed, that is, the deposited thin copper layer was used as the seed layer, and then the hole wall and the printed wire coating were thickened by pattern electroplating, and then etched. Because the etched copper layer is thin and the side erosion is small, the precision of the manufactured wire is high. Thereby accelerating the production speed, improving the quality of the copper plating layer and becoming the original semi-additive process. After years of research and improvement, this method has developed into a new semi-addition technology which is increasingly widely used.
Schematic diagram of additive process process (see Figure 1-2).
Note: Generally, the ceramic substrate is single-sided, and the polymer film substrate has single and double panels that can be drilled, which are mostly used for flexible boards.
Note: The board to be drilled should be drilled on the base material first, then coated with a resist layer, then selectively electroless copper plated, and finally removed. 3 Half additive process
Semi-additive process is a method for manufacturing printed boards by skillfully using the characteristics of subtractive method and additive process process. A new technology derived from the original semi-additive process technology. The typical process is to press the adhesive-free resin-coated thin copper foil (RCC) on the rigid core board, and use this copper foil as the conductive “seed” layer. On the top of the thin copper foil, a plating resist pattern is made by photolithography, and then the pattern plating is carried out. After the required thickness of the copper layer is reached, the plating resist layer is removed, and then etching is carried out to remove the very thin “seed” copper foil, and at the same time, a small amount of electroplated copper on the conductor is also removed (equivalent to At present, fine wires with a line width of 0.025mm and a line spacing of 0.05mm can be made, and even wires with a width of 12μm can be made by some processes. This technology has been widely used in the manufacturing process of high-density interconnected printed boards (HDI boards).
HDI printed board is a printed board characterized by fine wires, high wiring density, and via holes with small aperture (blind holes and buried holes with aperture less than 0.25mm). Now, it has been widely used in communication electronic products such as medium and high-end mobile phones, meeting the requirements of 2G/2.5G mobile phones and entry-level 3G mobile phones on printed boards, such as small, thin, dense and flat. If HDI board is combined with rigid-flexible knot technology, it can be the main way to reduce the thickness of 3G mobile phone. HDI printed circuit board has become the development trend of printed circuit board in the current period.
There are many manufacturing methods of HDI printed boards, and they are developing rapidly. There are mainly traditional mechanical drilling of micropores and blind holes, followed by successive pressing; With the emergence of resin-coated copper foil RCC and the development of laser processing technology such as smaller aperture, RCC process, printing thermosetting resin process and photosensitive resin process have come into being. According to the structure of HDI printed boards reported in the literature, the American Institute of Electronic Circuits and Packaging tried to classify and identify them in a certain order. So far, six structures have been identified, which are briefly described as follows:
(1) Type 1 structure
Type 1 HDI printed board is a typical structure with rigid double-sided or multi-layered core board. It adds one or more layers of micropores on the upper and lower sides of the rigid core board, one layer of micropores is called 1st-order (1+N+1)HDI board, and the layer of two micropores is called 2nd-order (2+N+2)HDI board, and there are 3rd-order, 4th-order …… multi-stage HDI boards in turn, and the micropores and through holes on the layers are electroplated at the same time. Schematic diagram of the structure of type 1 HDI board and blind hole structure (see Figure 1-3)
(2) Type 2 HDI PCB is a typical structure of rigid double or multi-layer core board with plated through holes. The through holes on the core board are filled with resin before lamination, and these holes become blind holes (or semi-blind holes) after the manufacturing process is completed. Micro holes (blind holes) are made on one or both sides of the core board.
(3) Type 3 structure
The typical structure of 3-type HDI printed board is that one side of rigid multilayer core board with blind holes has one or more layers of micropores, and the other side has two or more layers, and plated through holes run through the whole board to realize interlayer connection. Its structure (Figure 1-5)
(4) Type 4 structure
The typical structure of 4-type HDI board is a core board with rigid insulation layer and metal core, with a layer or
More layers are stacked layer by layer, with vias running through both sides of the PCB. (See Figure 1-6) The metal core board can adjust the printed circuit board’s
The heat dissipation effect is beneficial to the high-density assembly of high-power devices.
(5) Type 5 structure
The typical structure of 5-type HDI board is that it has plug holes with conductive ink or electroplating, and the interconnection structure with vertical connection is formed by successive pressing. There are many forms according to the number of blind holes superimposed and the materials and methods of plug holes. For resin plug holes, electroplating must be carried out first, then plug holes, after grinding, hole surface isolation electroplating, and then another layer is pressed together. However, when resin plug holes with smaller hole diameter are carried out by this method, it is difficult to remove the air bubbles in the holes, which reduces the reliability of connection. Electroplating plug hole method is an ideal hole filling method with simple process and high reliability. At present, it is widely used to make HDI boards with multi-step blind holes. Schematic diagram (see Figure 1-7).
Manufacturing process of type 5 HDI board:
(6) Type 6 structure
The typical structure of 6-type HDI board is a board with a multi-step HDI interconnection structure (see Figure 1-8), in which the conductive polymer is printed by the electroplating column or template on the whole copper foil, the adhesive sheet and the copper foil are superimposed, the thin insulating material is pierced in the lamination process to form vertical interconnection, and then the conductive bumps are imaged, etched and patterned to form new bumps, and then laminated. The manufacturing method of this structure is also called B2it method.
In addition, there are photosensitive resin laminated multilayer boards, transfer laminated multilayer boards, etc. Although the methods are different, the structure of the final HDI board is similar to one of the above structures, so it will not be introduced one by one.
HDI board is a high-end product of modern printed circuit board. Because of the small diameter of through holes and the small occupied space, the wiring density is improved, and the thin dielectric layer between conductor layers makes the signal transmission path in conductors short and fast, which is very beneficial to the transmission of high-frequency and high-speed signals. HDI board can provide very thin board thickness and multilayer printed boards with multilayer wiring. It is an indispensable basic component of modern communication equipment that needs light, thin, small and high reliability. At present, it is mainly used in mobile phones and modern mobile communication equipment. The spacing between layers and wires of HDI board is small, the withstand voltage between layers and lines is lower than that of ordinary printed boards, the aperture of through holes and blind (or buried) holes is small, and the coating in holes is generally 12~15μm, so it is more reliable to use ordinary multilayer boards for printed boards with high working current and voltage.
The manufacturing technology of HDI board concentrates on many modern scientific and technological achievements, such as: laser imaging, laser drilling, high-precision CNC drilling machine, high-precision parallel light exposure, automatic optical inspection (AOI), horizontal pulse electroplating technology, high-tech equipment and materials such as photosensitive resin and RCC copper foil, etc.
