The design and manufacture of PCB copy board is moving from the subtractive method to the additive method. This article mainly explains the concepts and manufacturing processes of the PCB subtractive method and the additive method, for your reference and study!
1. Brief introduction of PCB subtraction method
The subtractive process is a method of selectively removing part of the copper foil on the surface of the copper clad laminate to obtain a conductive pattern. The subtractive method is the main method of printed circuit manufacturing today, and its biggest advantage is that the process is mature, stable and reliable.
Printed circuits manufactured by the subtractive process can be divided into the following two categories.
1.1. Non-porous printed board (.Non-plating-thr’ough-hole Board)
This type of printed board is produced by screen printing and then etching the printed board, or it can be produced by photochemical methods. Non-perforated plated printed boards are mainly single-sided boards, and there are also a small amount of double-sided boards, which are mainly used in televisions and radios. The following is the single panel production process:
Single-sided copper clad board laying-photochemical method/screen printing image transfer-removal of anti-corrosion printing material-cleaning and drying-hole processing-shape processing-cleaning and drying-printing of solder resist coating-curing-printing of markings- Curing—cleaning and drying—pre-coating flux—drying—finished product.
1.2. Plating-through-hole Board
On the copper-clad laminates that have been drilled, chemical plating and electroplating are used to make the holes between two or more layers of conductive patterns change from electrical insulation to electrical connection. This type of printed board is called perforated plating. PCB. Perforated printed circuit boards are mainly used in computers, program-controlled switches, mobile phones, etc. According to different electroplating methods, it can be divided into graphic electroplating and full board electroplating.
a. Pattern electroplating (Patter.n, P'I'N) On the double-sided copper clad laminate, a conductive pattern is formed by screen printing or photochemical method, and lead-tin, tin-cerium is plated on the conductive pattern, Anti-corrosion metals such as tin-nickel or gold, and then remove the resist other than the circuit pattern, and then etched. The pattern electroplating method is further divided into pattern electroplating and etching process (Pattern PlATIngAnd Etching Process) and bare copper clad solder mask process (Solder Mask OnBare Copper, SMOBC). The process of making double-sided printed boards with bare copper-clad solder mask process is as follows.
Double-sided copper clad board blanking, punching positioning hole, CNC drilling, inspection, hair removal, chemical thin copper plating, electroplating thin copper, inspection, brushing, film (or screen printing) exposure and development (or curing) Inspection and revision—graphic copper plating—graphic tin-lead alloy plating—film removal (or removal of printing material)—inspection and revision—etching—lead tin stripping—open circuit test—cleaning—solder resist pattern—nickel/gold plug plug sticker Adhesive tape—hot air leveling—cleaning—screen printing mark symbol—shape processing—cleaning and drying—inspection—packaging—finished product.
b. Full board electroplating (Panel, PNL) On double-sided copper-clad laminates, copper is electroplated to a specified thickness, and then the image is transferred by screen printing or photochemical methods to obtain a corrosion-resistant positive-phase circuit image. Remove the resist to make a printed board.
The full plate plating method can be subdivided into the plugging method and the masking method. The process flow of making double-sided printed boards with masking method (TenTIng) is as follows.
Double-sided copper-clad board, cutting material, drilling, hole metallization, full board electroplating thickening, surface treatment, glazing, photomasking dry film, normal phase wire pattern making, etching, film removal, plug electroplating, shape Processing—inspection—printing of solder resist coating—solder coating with hot air leveling—printing of marking symbols—finished product.
The above method has the advantages of simple process and good coating thickness uniformity. The disadvantage is that energy is wasted, and it is difficult to manufacture through-hole printed boards without lands.
2. Introduction of PCB addition process
The method of selectively depositing conductive metal on the surface of an insulating substrate to form a conductive pattern is called an additive method.
2.1. Advantages of the additive method
The printed board is manufactured by the additive process, which has the following advantages:
a. Since the addition method avoids a large amount of etching copper and the resulting large amount of etching solution processing costs, the production cost of printed boards is greatly reduced.
b. Compared with the subtractive method, the process of additive process is reduced by about 1/3, which simplifies the production process and improves the production efficiency. In particular, the vicious circle in which the higher the product grade is, the more complicated the process is avoided.
c. The additive process can achieve flush wires and flush surfaces, so that SMT and other high-precision printed boards can be manufactured.
d. In the additive process, since the hole wall and the wire are electroless copper plated at the same time, the thickness of the copper plating layer on the hole wall and the conductive pattern on the board surface is uniform, which improves the reliability of the metallized hole and can also meet the high-thickness diameter. Compared with printed boards, copper plating requirements in small holes.
2.2. Classification of additive methods
The additive manufacturing process of printed boards can be divided into the following three categories:
a. Full Additive Process (Full Additive Process) is an additive process that only uses chemical copper deposition to form conductive patterns. Take the CC-4 method as an example: drilling-imaging-adhesion-increasing treatment (negative phase)-electroless copper plating-removal of resist. The process uses catalytic laminates as the substrate.
b. Semi-additive Process (Semi-additive Process) On the surface of the insulating substrate, chemical deposition of metal, combined with electroplating and etching, or the addition of the three to form conductive patterns is used. Its technological process is: drilling-catalytic treatment and adhesion-enhancing treatment-electroless copper plating-imaging (electroplating resist)-pattern copper plating (negative phase)-removal of resist-differential etching. The base material used for manufacture is ordinary laminate.
c. Partial Additive Process (Partial Additive Process) is to manufacture printed boards by additive method on catalytic copper clad laminates. Process flow: Imaging (anti-etching)—etching copper (normal phase)—removing the resist layer—coating the entire board with electroplating resist—drilling—electroless copper plating in the hole—removing the electroplating resist.
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