PCB Blog - PCB board processing special process

PCB board processing special process

1. Additive Process
Refers to the surface of the non-conductor substrate, with the help of an additional resister, the direct growth process of the local conductor circuit is carried out with the chemical copper layer (see P.62 of the 47th issue of the Circuit Board Information Magazine for details). The addition method used by the circuit board can be divided into different methods such as full addition, half addition and partial addition.

2. Backpanels, Backplanes
It is a circuit board with a thicker thickness (such as 0.093", 0.125"), which is specially used to connect to other boards. The method is to insert the multi-pin connector (Connector) into the tight through hole first, but do not solder it, and then wire it one by one in a winding method on each guide pin of the connector passing through the board. A general circuit board can be inserted into the connector. Because of this special board, the through holes cannot be soldered, but the hole wall and the guide pins are directly clamped for use, so the quality and aperture requirements are very strict, and the order quantity is not many, and general circuit board manufacturers are reluctant It is not easy to receive such orders, and it has almost become a high-grade specialized industry in the United States.

3. Build Up Process
This is a new field of thin multi-layer board practice. The early enlightenment originated from IBM's SLC process, which was started in its Yasu factory in Japan in 1989. The method is based on traditional double-sided boards. The outer surface of the board 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) that communicates with the next bottom layer is made. The conductor layer of electroplating copper is comprehensively increased, and after line imaging and etching, new wires and buried or blind holes interconnected with the bottom layer can be obtained. Repeatedly adding layers in this way will obtain a multi-layer board with the required number of layers. This method not only eliminates the cost of expensive mechanical drilling, but also the hole diameter can be reduced to less than 10mil. In the past 5-6 years, various types of multi-layer board technologies that break the tradition and gradually add layers, under the continuous promotion of the US, Japan and Europe, have made these Build Up Processes famous, and more than ten products have been listed. so many species. In addition to the above-mentioned "photosensitive hole forming", there are still differences such as alkaline chemical bite hole, Laser Ablation, and Plasma Etching for organic plates after removing the copper skin of the hole." "hole" approach. In addition, the new "Resin Coated Copper Foil" coated with semi-hardening resin can also be used to make a finer, denser, smaller and thinner multilayer board by means of Sequential Lamination. In the future, diversified personal electronic products will become the world of this kind of truly thin, short, and multi-layer boards.

4. Cermet
Mix the ceramic powder with the metal powder, and then add the adhesive as a kind of coating, which can be printed on the circuit board surface (or on the inner layer) as a "resistor" cloth by printing a thick film or a thin film. Replaces external resistors during assembly.

5. Co-Firing
It is a process for the hybrid circuit board (Hybrid) of porcelain. The circuit with various kinds of precious metal thick film paste (Thick Film Paste) printed on the small board is fired at high temperature. The various organic carriers in the thick film paste are burned off, and the lines of precious metal conductors are left as interconnecting wires.

6. Crossover
The three-dimensional intersection of the two wires vertically and horizontally on the board surface, and the gap between the intersection points is filled with insulating medium. Generally, a carbon film jumper is added to the surface of the single-panel green paint, or the wiring above and below the build-up method is such a "crossover".

7. Discreate Wiring Board
That is to say, the Multi-Wiring Board is made by attaching circular enameled wires to the board surface and adding through holes. The performance of this kind of multi-wire board in high-frequency transmission line is better than that of the flat square circuit etched from general PCB.

8. DYCOstrate plasma etching hole buildup method
The copper foil at each hole on the board surface is etched first, then placed in a closed vacuum environment, and filled with CF4, N2, O2, so that ionization at high voltage forms a highly active plasma (Plasma), A method used to etch through-hole substrates to produce tiny vias (below 10 mil).

9. Electro-Deposited Photoresist
It is a new type of "photoresist" construction method, which was originally used for "electric paint" on metal objects with complex shapes, but was recently introduced to the application of "photoresist". The system adopts the electroplating method to uniformly plate the charged colloidal particles of the photosensitive charged resin on the copper surface of the circuit board as an anti-etching agent. 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 the cathode respectively according to the operation method, which is called "anodic electric photoresist" and "cathode electric photoresist". There are two types of "photopolymerization" (negative working Negative Working) and "photosensitive decomposition" (positive working) according to their different photosensitive principles. At present, the ED photoresist for negative working has been commercialized, but it can only be used as a planar resist, and the through-hole cannot be used for image transfer of the outer layer due to the difficulty of photosensitive. As for the "positive-type ED" that can be used as photoresist for the outer layer (because it is a photosensitive film, so the photosensitive on the hole wall is insufficient but has no effect), the Japanese industry is still stepping up efforts, hoping to start commercialization For mass production purposes, the production of thin lines is easier to achieve. This term is also known as "electrophoretic photoresist" (Electrothoretic Photoresist).

10. Flush Conductor
It is a special circuit board with a flat surface and all conductor lines are pressed into the board. The single-panel method is to use the image transfer method to etch away part of the copper foil on the semi-cured substrate to obtain the circuit. Then, the circuit board is pressed into the semi-hardened board by means of high temperature and high pressure, and at the same time, the hardening of the board resin can be completed, and the circuit board can be formed into a fully flat circuit board with the lines shrunk into the surface. Usually, on the surface of the circuit where the board has been shrunk, a thin copper layer needs to be micro-etched, so that another 0.3 mil nickel layer, 20 micro inch rhodium layer, or 10 micro inch gold layer, so that the When performing sliding contact, the contact resistance is lower and sliding is easier. However, this method is not suitable for PTH, to prevent the through hole from being squeezed when pressing in, and it is not easy to achieve a completely smooth surface of this board, and it cannot be used at high temperatures to prevent the resin from expanding before pushing the circuit out of the surface. Come. This technology is also known as Etch and Push method, and the finished board is called Flush-Bonded Board, which can be used for special purposes such as RotarySwitch and Wiping Contacts.

11. Frit
In the Poly Thick Film (PTF) printing paste, in addition to precious metal chemicals, glass powder should be added in order to exert the cohesion and adhesion effect in high temperature incineration, so that the printing paste on the blank ceramic substrate can be Form a solid precious metal circuit system.

12. Fully-Additive Process
It is a method of growing selective circuits on the surface of a completely insulated plate by electroless metal deposition (mostly chemical copper), which is called "full addition method". Another less correct term is the "Fully Electroless" method.

13. Hybrid Integrated Circuit
It is a circuit in which precious metal conductive ink is applied by printing on a small porcelain 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 surface-mounted parts. . It is a circuit carrier between the printed circuit board and the semiconductor integrated circuit, which belongs to the thick film technology. In the early days, it was used for military or high-frequency purposes. In recent years, due to the high price and declining military use, and it is not easy to automate production, coupled with the increasing miniaturization and precision of circuit boards, the growth of this Hybrid has been greatly inferior to that in the early years. .

14. Interposer
Refers to any two layers of conductors carried by an insulating object, and the place to be connected is filled with some conductive fillers to be connected, which is called Interposer. For example, in the bare holes of multilayer PCB board, if they are filled with silver paste or copper paste instead of the orthodox copper hole wall, or materials such as vertical unidirectional conductive adhesive layer, they belong to this type of Interposer.