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PCB Tech

PCB Tech

Special PCB circuit board manufacturing process
2021-09-12
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Author:Frank

Circuit board PCBprocessing special process As a person in the field of PCB industry, for PCB copy board, PCB design related process must be proficient. Through the analysis and summary of the company’s professional PCB copy board experts, our professional PCB copy board experts have The following special process for PCB processing of the circuit board, I hope it can be helpful to those in the PCB industry.
  Additive Process
   refers to the non-conductor substrate surface, with the assistance of an additional resist, the direct growth process of local conductor lines with an electroless copper layer (see Circuit Board Information Issue 47 P.62 for details). The addition method used in PCB copy board can be divided into different methods such as full addition, half addition and partial addition.
  Backpanels, Backplanes support plate
   is a thicker (such as 0.093", 0.125") circuit board, which is specially used to connect other boards. The method is to first insert the multi-pin connector (Connector) into the tight through hole without soldering, and then wire the wires one by one on the guide pins of the connector passing through the board. A general PCB copy board can be inserted into the connector. Because of this special board, the through hole cannot be soldered, but the hole wall and the guide pin are directly clamped for use, so its quality and aperture requirements are particularly strict, and its order quantity is not very large, and general circuit board manufacturers are not willing It is not easy to accept such orders, and it has almost become a high-grade specialized industry in the United States.

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  Build Up Process Build Up Process
This is a new field of thin multi-layer board practice. The earliest enlightenment originated from IBM's SLC process, which was started by its Yasu factory in Japan in 1989. The method is based on the traditional double-sided board. The outer panel surface is first fully coated with a liquid photosensitive precursor such as Probmer 52. After semi-hardening and photosensitive resolution, a shallow "photo-via" (Photo-Via) communicating with the next bottom layer is made, and then chemical copper and The electroplated copper adds a conductor layer to the entire surface, and after the circuit is imaged and etched, new-type wires and buried or blind holes interconnected with the bottom layer can be obtained. Such repeated layers will be able to obtain the required number of layers of multi-layer boards. This method not only eliminates the costly cost of mechanical drilling, but also reduces the hole diameter to less than 10 mils. In the past 5 to 6 years, various types of multi-layer board technologies that have broken the tradition and adopted successive layers have been continuously promoted by the U.S., Japan and European companies, making these Build Up Processes famous, and there are more than a dozen products on the market. There are so many kinds. In addition to the above-mentioned "photosensitive hole formation"; there are differences in alkaline chemical biting, laser ablation, and plasma etching for organic plates after removing the copper skin of the hole. Hole formation" approach. In addition, a new type of "Resin Coated Copper Foil" coated with semi-hardened resin can be used to make a thinner, denser, smaller, and thinner multilayer board by means of Sequential Lamination. In the future, diversified personal electronic products will become the world of such truly light, thin, short and small multilayer boards.
Cermet ceramic powder mixes ceramic powder and metal powder, and then adds adhesive as a kind of coating. It can be printed on the surface of the circuit board (or on the inner layer) in a thick film or thin film, as a "resistor" cloth. Placement to replace external resistors during assembly.
   Co-Firing
   is a process in which ceramic hybrid PCB circuit boards (Hybrid) are made. The circuits on which various types of precious metal thick film paste have been printed on the small board are fired at high temperature. The various organic carriers in the thick film paste are burned away, leaving noble metal conductor lines as interconnecting wires.
   Crossover is the three-dimensional cross of two wires that cross the board, and the gap between the intersections is filled with insulating medium. Generally, the addition of carbon film jumpers on the green paint surface of the single-sided board, or the wiring on the top and bottom of the build-up method are all such "crossovers".
  Discreate Wiring Board scattered wire PCB circuit board, double wire board
   is another term for Multi-Wiring Board, which is formed by attaching a round enameled wire to the board surface and adding through holes. The performance of this kind of multi-line board in terms of high-frequency transmission line is better than the flat square circuit formed by etching of general PCB.
   DYCOstrate plasma etch hole build-up method
   is a Build up Process developed by a Dyconex company located in Zurich, Switzerland. The copper foil at each hole of the board surface is etched first, and then placed in a closed vacuum environment, and filled with CF4, N2, and O2, so that the ionization is performed at a high voltage to form a highly active plasma (Plasma), The patented method for etching the substrate at the perforation position and the appearance of tiny via holes (below 10 mils), and its commercial process is called DYCOstrate.
   Electro-Deposited Photoresist
   is a new type of "photoresist" construction method. It was originally used for the "electro-painting" of complex-shaped metal objects. It has only recently been introduced to the application of "photoresist". The electroplating method is used to uniformly plate the charged colloidal particles of the optically sensitive charged resin on the copper surface of the PCB circuit board as an anti-etching resist. At present, it has been mass-produced and used in the direct copper etching process of the inner layer board. This kind of ED photoresist can be placed on the anode or cathode according to the different operation methods, which is called "anode type photoresist" and "cathode type photoresist". According to the different photosensitive principles, there are two types: "photopolymerization" (Negative Working) and "photolysis" (Positive Working). At present, the negative working ED photoresist has been commercialized, but it can only be used as a planar resist, and the through-hole cannot be used for image transfer on the outer layer board due to the difficulty of photosensitive. As for the "positive ED" that can be used as a photoresist for the outer layer plate (because it is a photosensitive decomposable film, the hole wall is insufficiently photosensitive but has no effect), Japanese companies are still stepping up their efforts and hoping to start commercialization Mass production use makes the production of thin circuits easier to achieve. This term is also called "Electrothoretic Photoresist" (Electrothoretic Photoresist).
   Flush Conductor Embedded circuit, flat conductor
   is a special PCB copy board with a flat surface and all conductor lines are pressed into the plate. The single-sided method is to first use the image transfer method to etch away part of the copper foil on the semi-cured substrate to obtain the circuit. Then, the board surface circuit is pressed into the semi-hardened plate by the high temperature and high pressure method, and at the same time, the hardening operation of the plate resin can be completed to become a circuit board in which the circuit is retracted into the surface and is completely flat. Usually this kind of board has been retracted on the circuit surface, and a thin copper layer needs to be etched away, so that another 0.3mil nickel layer, and 20 microinch rhodium layer, or 10 microinch gold layer, make When performing sliding contact, its contact resistance can be lower and it is easier to slide. However, this method is not suitable for PTH to prevent the through hole from being squeezed during pressing, and it is not easy for this kind of board to achieve a completely smooth surface, and it cannot be used at high temperatures to prevent the resin from expanding and then pushing the circuit out of the surface. Come. This kind of technology is also called Etch and Push method, and its finished board is called Flush-Bonded Board, which can be used for special purposes such as RotarySwitch and Wiping Contacts.
In addition to precious metal chemicals, Frit glass frit is used in Poly Thick Film (PTF) printing pastes, so that glass frit must be added in order to achieve agglomeration and adhesion effects in high-temperature incineration, so that the blank ceramic substrate Printing paste can form a firm precious metal circuit system.
  Fully-Additive Process
   is the method of electroless deposition of metal (mostly chemical copper) on a completely insulated sheet surface to grow selective circuits, which is called the "full additive method". Another not-so-correct term is the "Fully Electroless" method.
  Hybrid Integrated Circuit
It is a circuit in which precious metal conductive ink is applied by printing on a small ceramic thin substrate, and then the organic matter in the ink is burned away at high temperature, leaving a conductor circuit on the board surface, and can be used for welding of surface-mounted parts . It is a circuit carrier of thick film technology between the printed circuit board and the semiconductor integrated circuit device. In the early days, it was used for military or high-frequency applications. In recent years, the price of the hybrid is very expensive and the military is declining, and it is not easy to automate production, coupled with the increasing miniaturization and precision of circuit boards, the growth of this type of Hybrid has been greatly lower than in the early years. .
  Interposer interconnect conductive objects
   refers to any two layers of conductors carried by an insulating object, and the place where it is to be connected is filled with some conductive fillers, which is called Interposer. For example, in the bare holes of the multilayer board, if the silver paste or copper paste is filled to replace the orthodox copper hole wall, or the material such as the vertical unidirectional conductive adhesive layer, it belongs to this type of Interposer.
  Laser Direct Imaging, LDI laser direct imaging
   is to take the board that has been pressed with the dry film, no longer use the negative film to expose for image transfer, and replace it with a computer to direct the laser beam to directly perform fast-scanning photosensitive imaging on the dry film. Since it emits a single beam of parallel light with concentrated energy, the sidewall of the dry film after development can be made more vertical. However, the method can only work on each board individually, so the mass production speed is far not as fast as the use of negative film and traditional exposure. LDI can only produce 30 medium-sized boards per hour, so it can only occasionally appear in prototypes or boards with high unit prices. Due to the inherent high cost, it is difficult to promote in the industry.
  Laser Maching
   There are many precision processing in the electronics industry, such as cutting, drilling, welding, welding, etc., which can also be performed with the energy of laser light, which is called laser processing. The so-called LASER refers to the abbreviation of "Light Amplification Stimulated Emission of Radiation", which is translated as "laser" by the mainland industry, which seems more relevant than transliteration. Laser was produced by the American physicist T.H. Maiman in 1959, using a single beam of light to hit the ruby to produce laser light. Years of research have created a new processing method. In addition to the electronics industry, it can also be used in medical and military applications.
  Micro Wire Board
The round cross-section enameled wire (glue-sealed wire) attached to the board surface is made into a special circuit board with PTH to complete the inter-layer interconnection. It is commonly called Multiwire Board "multi-wire board" in the industry. ), and the wire diameter is very small (below 25mil), also known as micro-sealed circuit board.
  Moulded Circuit molded three-dimensional circuit board
  Using three-dimensional molds, injection molding (Injection Moulding) or transformation method to complete the three-dimensional circuit board manufacturing process, called Moulded circuit or Moulded Interconnection Circuit. The left picture is a schematic diagram of the MIC completed by two shots.
  Multiwiring Board (or Discrete Wiring Board)
It refers to the use of ultra-fine enameled wires, three-dimensional cross wiring directly on the board surface without copper foil, and then fixed with glue, drilling and plating holes, the resulting multilayer interconnection circuit board is called "multi-wire plate". This is developed by American PCK, and is still in production by Hitachi. This kind of MWB can save design time and is suitable for a small number of models with complex circuits (the 60th issue of the Circuit Board Information Magazine has a special article).
   Noble Metal Paste
   is a conductive paste for thick film circuit printing. When it is printed on a porcelain substrate by a screen method, and then the organic carrier is burned away at a high temperature, a fixed precious metal circuit appears. The conductive metal particles added in this printing paste must be precious metals to avoid oxide formation at high temperatures. The users of the commodities are gold, platinum, rhodium, palladium or other precious metals.
  Pads Only Board
In the early through-hole insertion era, some high-reliability multi-layer boards, in order to ensure solderability and circuit safety, only left the through-holes and solder rings outside the board, and the interconnection lines are hidden on the next inner layer. . This kind of two-layer board will not be printed with solder resist green paint, it is very particular in appearance, and the quality inspection is extremely strict. At present, due to the increase in wiring density, many portable electronic products (such as mobile phones) have only SMT pads or a few lines left on the circuit board surface, and many dense interconnections are buried in the inner layer, and the layers are also changed. Difficult blind holes or "Pads On Hole" (Pads On Hole) are used as interconnections to reduce the damage of all-through holes to the ground and high-voltage copper surfaces. This type of SMT tightly mounted board is also only a backing board.
  Polymer Thick Film (PTF) thick film paste
   refers to the ceramic substrate thick film circuit board, the precious metal printing paste used to make the circuit, or the printing paste used to form the printed resistive film, the process includes screen printing and subsequent high-temperature incineration. After the organic carrier is burned away, a firmly attached circuit system will appear. This type of board is generally called hybrid circuit board(Hybrid Circuits).