Special manufacturing process of PCB circuit board

As a person in the PCB industry, the special process of PCB processing must be skilled in PCB copying, PCB design related processes. Through the analysis and summary of our professional PCB copying personnel, our professional PCB copying experts have come to the following special processes of PCB processing, hoping to help people in the PCB industry.

Additive Process

It refers to the non-conductive substrate surface. With the help of adding resistance agent, the chemical copper layer is used for direct growth of local conductor lines (see P.62, Issue 47 of the Journal of Circuit Board Information for details). The addition methods used for PCB copying can be divided into full addition, half addition and partial addition.

Backplanes

It is a kind of circuit board with thick thickness (such as 0.093 ", 0.125"), which is specially used to connect other boards. The method is to insert the multi pin connector into the pressing through-hole without soldering, and then wire one by one in the way of winding on each guide pin where the connector passes through the board. The connector can also be inserted into the general PCB board. Because the through-hole of this special board cannot be soldered, but the hole wall and the guide pin can be directly clamped for use. Therefore, its quality and aperture requirements are particularly strict, and its order volume is not very large. Generally, circuit board manufacturers are reluctant to and difficult to accept such orders. In the United States, it has almost become a high-grade specialized industry.

Build Up Process

This is a new field of thin multilayer board practice. The first enlightenment came from the SLC process of IBM, which was trial produced in Yasu factory in Japan in 1989. This method is based on the traditional double-sided board. First, liquid photosensitive precursors such as Probmer 52 are fully coated on the two outer board surfaces. After semi hardening and photosensitive decomposition, shallow "Photo Via" which is connected with the next bottom layer is made, Then conduct chemical copper and electroplating copper to comprehensively increase the conductor layer, and after line imaging and etching, new type conductors and buried or blind holes interconnected with the bottom layer can be obtained. By adding layers repeatedly, the required number of layers can be obtained. This method can not only eliminate the expensive mechanical drilling cost, but also reduce the aperture to less than 10 mil. In the past five to six years, various types of multilayer board technologies that break the tradition and adopt layers by layers have made such Build Up Processes famous and more than ten kinds of products have been launched under the constant promotion of American, Japanese and European industries. In addition to the above "photosensitive hole forming"; After removing the copper skin at the hole location, there are different "pore forming" ways for organic plates, such as alkaline chemical biting, laser ablation, and plasma etching. In addition, a new type of "Resin Coated Copper Foil" coated with semi hardening resin can also be used to make thinner, denser, smaller and thinner multilayer boards by sequential lamination. In the future, diversified personal electronic products will become the world of such really thin, short and multi-layer boards.

Cermet ceramic gold mixes ceramic powder and metal powder, and then adds bonding agent as a kind of coating. It can be printed on the circuit board (or on the inner layer) in thick film or thin film as the cloth placement of "resistor" to replace the external resistor during assembly.

Co Firing

It is a manufacturing process of porcelain mixed PCB circuit board (Hybrid). The circuit printed with various kinds of precious metal thick film pastes on the small board is fired at high temperature. All kinds of organic carriers in the thick film paste are burned, leaving precious metal conductor lines for interconnection.

Crossover refers to the vertical crossing of two vertical and horizontal conductors on the overlapping plate, and the insulating medium is filled between the crossing point drops. Generally, carbon film jumper is added to the green paint surface of the single panel, or the wiring above and below the layer adding method belongs to this "crossover".

Discrete Wiring Board

Another term of Multi Wiring Board is that round enamelled wire is attached to the Board surface and a through hole is added. The performance of this kind of double line board in the aspect of high-frequency transmission line is better than that of the flat square circuit formed by etching of general PCB.

DYCOstrate plasma etching and layer adding method

It is a Build up Process developed by a Dyconex company located in Zurich, Switzerland. It is a patented method that first etches the copper foil at each hole position on the board surface, then places it in a closed vacuum environment, and fills it with CF4, N2, O2, so that it can be ionized under high voltage to form plasma with high activity, which can be used to etch the substrate at the hole position, and then micro pilot holes (below 10mil) appear. Its commercial process is called DYCOstrate.

Electrodeposited Photoresist

It is a new construction method of "photoresist", which was originally used in the "electro varnish" of metal articles with complex shapes, but recently introduced into the application of "photoresist". The system adopts the electroplating method to uniformly plate charged colloidal particles of optically active charged resin on the copper surface of PCB circuit board as the anti etching inhibitor. At present, it has been used in the direct copper etching process of inner laminates. According to different operation methods, this ED photoresist can be placed on the anode or cathode respectively, which is called "anode type electric photoresist" and "cathode type electric photoresist". According to the different photosensitive principles, there are two types: "Negative Working" and "Positive Working". At present, the negative ED photoresist has been commercialized, but it can only be used as a planar photoresist. Due to the difficulty of photosensitivity in the through-hole, it cannot be used for image transfer of the outer panel. As for the "positive ED" that can be used as the photoresist of the outer plate (because it is a photosensitive decomposition film, the hole wall is not sensitive enough, but it has no effect), the Japanese industry is still stepping up its efforts to develop commercial mass production applications, so that the production of fine lines can be easily achieved. This term is also known as "electrophoretic photoresist".

Flush Conductor embedded line, flat conductor

It is a special PCB board with a flat surface, and all conductor lines are pressed into the board. The method of single panel is to etch the copper foil on the semi cured substrate plate by image transfer method to obtain the circuit. Then, press the circuit on the board into the semi hardened plate in a high temperature and high pressure manner, and at the same time, complete the hardening operation of the plate resin, so as to become a circuit board that the circuit shrinks into the surface and is completely flat. Usually, a thin copper layer needs to be slightly etched off on the circuit surface into which the board has been shrunk, so that another 0.3mil nickel layer, a 20 microinch rhodium layer, or a 10 microinch gold layer can be plated, making the contact resistance lower and sliding easier when sliding contact is performed. However, this method should not be used for PTH to prevent the through-hole from being squeezed out during pressing. It is not easy for this board to achieve a completely smooth surface, and it cannot be used in high temperature to prevent the line from being pushed out of the surface after the resin expands. This technology is also known as the Etch and Push method, and the finished board is called the Flush Bonded Board, which can be used for special purposes such as RotarySwitch and Wiping Contacts.

In addition to precious metal chemicals, frit glass melts need to be added into the thick film paste (PolyThick Film, PTF) printing paste, so as to exert the effect of coagulation and adhesion in high temperature incineration, so that the printing paste on the blank ceramic substrate can form a solid precious metal circuit system.

Full Additive Process

It is the method of growing selective circuits on the surface of completely insulated plates by electroless metal deposition (mostly chemical copper), which is called "full addition method". Another incorrect statement is the "Fully Electroless" method.

Hybrid Integrated Circuit

It is a circuit that applies precious metal conductive ink to a small porcelain thin substrate by printing, and then burns the organic matter in the ink away at high temperature, leaving a conductive circuit on the surface of the plate, which can be used for welding surface bonded parts. The utility model relates to a circuit carrier between a printed circuit board and a semiconductor integrated circuit device, belonging to thick film technology. In the early days, it was used for military or high-frequency applications. In recent years, due to the high price and decreasing military use, and the difficulty in automatic production, coupled with the increasing miniaturization and precision of circuit boards, the growth of this kind of Hybrid has been much less than in the early years.

Interposer interconnection conductor

Interposer refers to any two layers of conductors carried by an insulating object that can be conducted by filling some conductive fillers at the place to be conducted. For example, if the bare holes of the multilayer board are filled with silver paste or copper paste to replace the traditional copper hole wall, or materials such as vertical unidirectional conductive adhesive layer, they belong to such interposer.

Laser Direct Imaging

Instead of exposing the plate with negative film for image transfer, the computer commands the laser beam to directly conduct rapid scanning photosensitive imaging on the dry film. As a single beam of concentrated parallel light is emitted, the side wall of the dry film after imaging can be more vertical. However, the method can only work on each plate separately, so the mass production speed is far faster than using negative film and traditional exposure. LDI can only produce 30 medium-sized boards per hour, so it can only occasionally appear in prototype proofing or high price boards. Due to the high congenital cost, it is difficult to promote in the industry.

Laser Machining

In the electronic industry, there are many precision processes, such as cutting, drilling, welding, welding, etc., which can also be carried out with the energy of laser light, called laser processing. The so-called LASER refers to the abbreviation of "Light Amplification Stimulated Emission of Radiation", which is translated by the mainland industry as "laser", which seems more relevant than transliteration. Laser was produced by T.H. Maiman, an American physicist, in 1959 by projecting a single beam of light onto a ruby. Over the years, research has created a new processing method. In addition to the electronic industry, it can also be used for medical and military purposes.

Micro Wire Board

The round section enamelled wire (sealant wire) attached to the board surface is made into a special circuit board with PTH to complete inter layer interconnection. It is commonly known in the industry as the Multiwire Board "double wire board". When the wiring density is very large (160~250 in/in2) and the wire diameter is very small (less than 25 mil), it is also called the micro sealed circuit board.

Moulded Circuit

The stereo die is used to complete the manufacturing process of the stereo circuit board by Injection Moulding or transformation, which is called Moulded Circuit or Moulded Interconnection circuit.

Multiwiring Board (or Discrete Wiring Board)

It refers to the multilayer interconnection circuit board, which is obtained by using extremely thin enamelled wires to directly cross connect the copper foil free board, then coating, fixing, drilling and plating holes. It was developed by PCK, an American company, and is still being produced by Hitachi, a Japanese company. This kind of MWB can save design time, and is suitable for a small number of models with complex circuits (there is a special article in the 60th issue of the Journal of Circuit Board Information).

Noble Metal Paste

It is conductive printing paste for thick film circuit printing. When it is printed on the porcelain substrate by screen printing, and the organic carrier is burned away at high temperature, a fixed precious metal circuit appears. The conductive metal powder added to the printing paste must be precious metal to avoid the formation of oxides at high temperatures. The commodities are used for gold, platinum, rhodium, palladium or other precious metals.

Pads Only Board

In the early through-hole insertion era, in order to ensure the solderability and circuit safety of some high reliability multilayer PCB boards, only the through-hole and the solder ring were left outside the board, while the interconnecting circuits were hidden on the next inner layer. This kind of board with two more layers will not be printed with solder proof green paint, and the appearance is particularly exquisite, and the quality inspection is extremely strict. At present, due to the increase of wiring density, many portable electronic products (such as cell phones) have only SMT pads or a few lines left on their PCB circuit boards, and many of the interconnecting dense wires are buried in the inner layer. The layers are also changed to use highly difficult blind holes or "Pads On Holes" as interconnections to reduce the damage of the full hole to the ground and the copper surface with high voltage. This SMT flush mounting board is also the only type of pad.

Polymer Thick Film (PTF) thick film paste

It refers to the precious metal printing paste used for manufacturing circuits of ceramic based thick film circuit boards, or printing paste used to form printed resistance films. Its manufacturing processes include screen printing and subsequent high-temperature incineration. After burning off the organic carrier, there will be a firmly attached circuit system, which is commonly referred to as Hybrid Circuits.

Semi Additive Process

It refers to the process of directly growing the required lines on the insulating substrate surface in the form of chemical copper, and then continuing to thicken them in the form of electroplated copper, which is called "half addition". If chemical copper method is adopted for all line thicknesses, it is called "full addition" process. Note that the above definition is from the latest specification IPC-T-50E issued in July 1992, which is different from the original IPC-T-50D (November 1988). The early "version D" and the industry's general statement refer to the bare non-conductive substrate or the substrate with thin copper foil (such as 1/4 oz or 1/8 oz). First prepare the image transfer of negative resistor, and then thicken the required circuit by chemical copper or copper electroplating method. The new 50E does not mention the word "thin copper skin". There is a big gap between the two statements, and the reader seems to have a similar idea