The double-sided circuit board is a medium layer in the middle, and both sides are wiring layers. PCB multilayer circuit board is a multilayer wiring layer, and there is a dielectric layer between every two layers, and the dielectric layer can be made very thin. A multilayer circuit board has at least three conductive layers, two of which are on the outer surface, while the remaining layer is synthesized inside the insulating board. The electrical connections between them are usually made through plated through holes in the cross-section of the board.
High assembly density, small size, and light weight Due to the high assembly density, the connections between components (including components) are reduced, thereby improving reliability; the number of wiring layers can be increased, thereby increasing design flexibility; A circuit with a certain impedance; it can form a high-speed transmission circuit; it can be equipped with a circuit, magnetic circuit shielding layer, and a metal core heat dissipation layer to meet the needs of special functions such as shielding and heat dissipation; simple installation and high reliability.
The cost is high; the cycle is long; the detection method with high reliability is required. Multi-layer circuit board is the product of the development of electronic technology in the direction of high speed, multi-function, large capacity and small volume. With the continuous development of electronic technology, especially the extensive and in-depth application of large-scale and ultra-large-scale integrated circuits, multi-layer printed circuits are rapidly developing towards high-density, high-precision, and high-level digitalization. Fine lines and small apertures have appeared. , Blind and buried holes, high thickness-to-aperture ratio and other technologies to meet the needs of the market.
A multilayer PCB circuit board is a printed circuit board formed by laminating and bonding alternating conductive pattern layers and insulating materials. The number of layers of the conductive pattern is more than three layers, and the electrical interconnection between layers is realized through metallized holes. If a double-sided circuit board is used as the inner layer, two single-sided boards are used as the outer layer, or two double-sided boards are used as the inner layer, and two single-sided boards are used as the outer layer, the positioning system and insulating bonding materials are laminated together, and the conductive The graphics are interconnected according to the design requirements to become four-layer, six-layer, and eight-layer circuit boards, also known as multi-layer PCB circuit boards.
Compared with the production process of general PCB multilayer boards and double-sided circuit boards, the main difference is that several unique process steps are added to PCB multilayer boards: inner layer imaging and blackening, lamination, etchback and desmearing. In most of the same process, some process parameters, equipment precision and complexity are also different. For example, the metallized connection of the inner layer of the multilayer board is the decisive factor for the reliability of the multilayer board, and the quality requirements for the hole wall are stricter than those of the double-layer board, so the requirements for drilling are even higher. In addition, the number of stacked boards per drilling of multi-layer boards, the speed and feed rate of drill bits during drilling are different from those of double-sided boards. The inspection of finished and semi-finished multi-layer boards is also more stringent and complicated than that of double-sided boards. Due to the complex structure of multi-layer boards, glycerin hot-melt technology with uniform temperature should be used instead of infrared hot-melt technology that may cause excessive local temperature rise.
①Remove surface oil, impurities and other pollutants;
②The oxidized surface is not affected by moisture at high temperature, reducing the chance of delamination between copper foil and resin.
③ Make the non-polar copper surface into a polar CuO and Cu2O surface, increase the polar bond between the copper foil and the resin; ④ increase the specific surface of the copper foil, thereby increasing the contact area with the resin, which is beneficial The resin is fully diffused to form a greater bonding force;
⑤The boards with the inner circuit must be blackened or browned before they can be laminated. It is to oxidize the copper surface of the inner board. Generally, the generated Cu20 is red and CuO is black, so the Cu20-dominated oxide layer is called browning, and the CuO-dominated one is called blackening.
1. Lamination is the process of bonding each layer of circuits into a whole with the help of B-stage prepreg. This bonding is achieved through interdiffusion and penetration of macromolecules on the interface, and then interweaving. The process of bonding the various layers of circuits into a whole with a prepreg. This bonding is achieved through interdiffusion and penetration of macromolecules on the interface, and then interweaving.
2. Purpose: To press discrete PCB multilayer boards together with adhesive sheets into PCB multilayer boards with required layers and thickness.
① Lamination process Send the stacked circuit board into the vacuum heat press. Using the heat energy provided by the machine, the resin in the resin sheet is melted, so as to bond the substrate and fill the gap.
②Lamination For designers, the first thing to consider in lamination is symmetry. Because the board will be affected by pressure and temperature during the lamination process, there will still be stress in the board after the lamination is completed. Therefore, if the two sides of the laminated board are uneven, the stress on the two sides will be different, causing the board to bend to one side, which greatly affects the performance of the PCB.
③Typesetting Copper foil, bonding sheet (prepreg), inner layer board, stainless steel, isolation board, kraft paper, outer layer steel plate and other materials are laminated according to the process requirements. If the board has more than six layers, pre-typesetting is required. Copper foil, adhesive sheet (prepreg), inner layer board, stainless steel, isolation board, kraft paper, outer layer steel plate and other materials are laminated according to the process requirements. If the board has more than six layers, pre-typesetting is required.
In addition, even on the same plane, if the distribution of copper is uneven, the flow rate of the resin at each point will be different, so that the thickness of the place with less copper will be slightly thinner, and the thickness of the place with more copper will be slightly thicker. Some. In order to avoid these problems, factors such as the uniformity of copper distribution, the symmetry of the stack, the design and layout of blind buried holes, etc. must be carefully considered during the design.
Purpose: to make the through hole golden.
①The base material of the circuit board is composed of copper foil, glass fiber and epoxy resin. In the production process, the section of the hole wall after the substrate is drilled is composed of the above three parts of the material.
② Hole metallization is to solve the problem of covering the section with a uniform layer of metal copper that is resistant to thermal shock. Hole metallization is to solve the problem of covering a uniform, thermal shock-resistant gold house copper on the cross section.
③The process is divided into three parts: 1. Decontamination process, 2. Electroless copper deposition process, 3. Thickened copper process (full board electroplating copper).
Hole metallization involves a concept of capability, thickness-to-diameter ratio. The aspect ratio refers to the ratio of the plate thickness to the hole diameter. , thickness-to-diameter ratio. The aspect ratio refers to the ratio of the plate thickness to the hole diameter. When the board keeps getting thicker and the hole diameter keeps decreasing, it becomes more and more difficult for the chemical water to enter the depth of the hole, although the electroplating equipment uses vibration, pressurization, etc. to allow the water to enter the center of the hole
