With the rapid development of science and technology, electronic products are constantly developing towards miniaturization, lightness and multi-function. Therefore, PCB, as the carrier of electronic components, is bound to develop towards miniaturization and high density. Traditional PCB board surface spread a large number of resistance components, so that a large number of board space is occupied. This is a serious violation of the new generation of high-speed transceiver digital information electronic products, portable small, light and high-performance, multi-functional development of the law, and from the reliability of PCB assembly, the stability of resistors and electrical performance considerations, the integration of resistors is very necessary. At present, it is more and more difficult to install a large number of components on the printed circuit board to meet these performance requirements. In order to continuously meet the needs of these development trends, the majority of electronic components are passive components, and the ratio of the number of passive components to the number of passive components is ( 15-20 ) ∶ With the increase of IC integration and I / O number, the number of passive components will continue to increase rapidly. Embedded resistance technology can well solve the above problems, which is one of the key technologies to realize the integration of resistors. Therefore, embedding a large number of embedded passive components into the printed circuit board of high-speed materials can shorten the line length between the components, improve the electrical characteristics, improve the effective packaging area of the printed circuit board, reduce the welding point of the printed circuit board surface, so as to improve the reliability of the packaging and reduce the cost.
Existence form of buried resistance
There are various buried resistance components, but there are mainly the following two forms : an embedded buried resistance technology is a technology that pastes various required resistance components into the inner layer of the finished line through SMT ( surface mounting technology ), and then embeds the resistance components pressed into the inner layer of the components. One is the special resistance material through printing, etching into graphics, forming the required resistance value of the internal ( external ) material, using the conventional multilayer PCB manufacturing process and other parts of the circuit connected. The following figure：
Advantages of buried resistance
The above embedded buried resistance and the two buried resistance forms etched into graphics have the following common advantages over the separated resistance : ( 1 ) Improving impedance matching of lines ( 2 ) Shortening the path of signal transmission and reducing parasitic inductance ( 3 ) Elimination of resistance in surface mounting or inserting processes ( 4 ) Reducing signal crosstalk, noise and electromagnetic interference ( 5 ) Reducing passive components and improving the mounting density of active components.
The embedded resistance plate process of 8-layer high transmission rate material is mainly based on the embedded technology of resistance components, and is completed by the high speed material of Panasonic Company in Japan. The main difficulty of the embedded technology of resistance components is that the resistance components are easy to be damaged during lamination. In view of this difficulty, it is necessary to measure the change coefficient of the resistance core plate before pressing. The corresponding position of the supporting PP and the light plate is taken to pre-drill the drill nozzle matching the pressing filler and the components (Figure 2), and the core plates and PP and light plates of each layer are riveted during pressing to prevent layer deviation, slide plate and reveal resistance (Figure 3) to prevent the resistance from being damaged during pressing.
figure1
figure2
The main processing difficulties are to control the alignment of the resistance and prevent the components from being crushed. There are a series of complex processes in the single side and multiple high-speed PP light plate structure, such as sliding plate layer deviation, high-speed PP resistance hole filling + resin plug hole saturation in the middle of the plate, small aperture metal half slot easy to expose copper, hole drape, and deep control backtracking.
3.1 According to the change of sheet after resistance sticking in 03 / 06, the actual actual size measurement of the resistance and the filling requirement, the corresponding coefficient and the pre-drilling aperture of the resistance layer PP are determined. The laminated structure of the secondary outer layer PP + bare sheet resistance without drilling + PP ( resistance drilling ) is adopted ( Fig. 7 ). The mixed pressure characteristics of high TG materials are used in the high-speed PP, sheet and one-time pressing, and the reasonable high-speed material parameters are confirmed to prevent the failure of the sheet due to the resistance damage caused by the heating change of the sheet, such as layer deviation, slide, filling and delamination, and the sheet that has been pasted cannot be over-browned.
3.2 Since the inner layer has been post-welded and then pasted, it is necessary to carry out the window-opening treatment of resistance welding in the edge of the effective plate of PCS unit ( Fig. 8 ) to prevent the risk of delamination of the printed resistance welding oil layer after heat treatment in the post-construction process.
3.3 Therefore, the pre-drilled PP hole filling has a certain impact on the flatness of the board, while the customer has strict requirements on the resin plug hole does not allow depression, it is necessary to adjust the height of the two plugs when the resin plug hole, adjust the pressure and speed to a certain extent, and fill the hole after the tree plug.
3.4 There are small-aperture metal half-holes after drawing electricity, and the board design should be carried out in the same direction. ( Fig. 9 ) The gong belt with matching coefficient should be used for the gong half-hole, and the tool hole sealed by dry film should be used for positioning, so as to reduce the deviation of the gong half-hole caused by the deviation of the plate hole. At the same time, the small knife pre-gong + the adjustment and compensation of the back and forth knife should be used for adding the gong, so as to prevent the deviation of the half-hole and the problem of hole plugging and short circuit caused by the failure of copper skin rewinding.
3.5 Deep control after half-hole drilling starts from the bottom, need to pay attention to control the depth can not be drilled to the L3 layer, test need to adjust the tester set resistance value after testing, other processes are normal production.
With the rapid development of electronic industry, people ' s demand for small, light, thin, high integration and high reliability electronic products is increasing. Passive device embedded technology will become one of the core competitiveness of PCB enterprises. Through the improvement and innovation of the original technology, it has evolved into a new technology, which has excellent applicability and promotional value. The development of the PCB industry is the coexistence of opportunities and challenges. Only by accumulating and precipitating, can it break through, meet the growing market demand and win more market opportunities.
