Due to the rapid development of electronic technology, the printed circuit technology has been continuously developed. PCB board through single-sided - double-sided multi-layer development, and the proportion of multi-layer circuit board is increasing year by year. Multilayer board performance to high precision fine large and small two extreme development. Laminating is an important process in the manufacture of multilayer board, and the control of laminating quality becomes more and more important in the manufacture of multilayer board. Therefore, to ensure the lamination quality of multilayer circuit boards, it is necessary to have a good understanding of the lamination process of multilayer circuit boards. For this reason, years of laminating practice, how to improve the laminating quality of multi-layer board in the process technology is summarized as follows:
1. design the inner core plate that meets the requirements of lamination.
Due to the gradual development of laminating machine technology, the hot press from the previous non-vacuum hot press to the present vacuum hot press, the hot pressing process is in a closed system, which can not be seen and touched. Therefore, it is necessary to carry out a reasonable design of the inner laminate before laminating, and some reference requirements are provided here:
1.1. to choose the core board thickness according to the total thickness of the multi-layer circuit board requirements, the core board thickness is consistent, the deviation is small, the material longitude and latitude direction is consistent, especially more than 6 layers of multi-layer circuit boards, each inner layer of the core board longitude and latitude direction must be consistent, that is, the direction of the warp and longitude overlap, the latitude direction overlaps with the latitude direction, to prevent unnecessary plate bending.
1.2., there should be a certain distance between the outer size of the core plate and the effective unit, that is, the distance from the effective unit to the edge of the plate should be as large as possible under the premise of not wasting materials, generally four layers of plates require spacing greater than 10mm, six layers of plates require spacing greater than 15mm, the higher the number of layers, the greater the spacing.
1.3. the design of positioning holes, in order to reduce the deviation between the multi-layer board layer and layer, so in the design of multi-layer circuit board positioning holes need to pay attention: 4 layers of board only need to design more than 3 positioning holes for drilling. In addition to the design of positioning holes for drilling in multi-layer boards with more than 6 layers, more than 5 rivet holes and more than 5 positioning holes for tool boards used for rivet overlapping between layers are required. However, the design of positioning holes, rivet holes, and tool holes is generally the higher the number of layers, the number of designed holes is correspondingly more, and the position is as close as possible. The main purpose is to reduce the alignment deviation between layers and to leave a large space for manufacturing. The design of the target shape should meet the requirements of automatic recognition of the target shape by the target machine, and the general design is complete circle or concentric circle.
1.4. the inner core board requirements no open, short, open, no oxidation, clean surface, no residual film.
2. to meet the requirements of PCB board users, choose the appropriate PP, CU foil configuration.
Customer requirements for PP are mainly reflected in the dielectric layer thickness, dielectric constant, characteristic impedance, voltage resistance, laminate appearance smoothness and other requirements, so the selection of PP can be based on the following aspects to choose:
2.1. Resin can fill the gap of printed wire when laminating.
2.2. can ensure the bond strength and smooth appearance.
2.3. can provide the necessary dielectric layer thickness for multi-layer circuit board.
2.4. can fully exclude the air and volatiles between the laminates during lamination.
2.5. CU foil mainly according to PCB board user requirements respectively configuration of different models, CU foil quality in line with IPC standards.
According to years of production experience, I personally believe that PP can be configured with 7628, 7630 or 7628+1080, 7628+2116 when the 4-layer plate is laminated. More than 6 layers of multi-layer plate PP selection is mainly 1080 or 2116, 7628 is mainly used as PP to increase the thickness of the medium layer. At the same time, PP is required to be placed symmetrically to ensure mirror effect and prevent plate bending.
3. the inner core plate processing technology
When the multilayer circuit board is laminated, the inner core board should be treated. The treatment process of the inner plate includes black oxidation treatment process and brown treatment process. The oxidation treatment process is to form a black oxide film on the inner layer of copper foil, and the thickness of the black oxide film is 0.25-4). 50mg/cm2. The Browning process (horizontal Browning) is to form an organic film on the inner layer of copper foil. The inner plate processing process functions are:
3.1. increase the specific surface of the inner layer of copper foil and resin contact, so that the binding force between the two is enhanced.
3.2. increase the effective wettability of molten resin flow on copper foil, so that the flowing resin has sufficient ability to extend into the oxide film, and show a strong grip after curing.
3.3. to prevent the decomposition of curing agent dicyandiamide in liquid resin at high temperature, the influence of water on the copper surface.
3.4. the multi-layer circuit board in the wet process to improve acid resistance, prevent pink circle.
4. The control of laminating parameters mainly refers to the organic matching of laminating "temperature, pressure and time".
4.1. temperature, laminating process there are several temperature parameters are more important. That is, the melting temperature of the resin, the curing temperature of the resin, the set temperature of the hot pan, the actual temperature of the material and the speed of warming. Melting temperature means that the resin begins to melt when the temperature rises to 70℃. It is due to this further increase in temperature that the resin melts further and begins to flow. In the temperature of 70-140℃ this period of time, the resin is a fluid, it is due to the fluidity of the resin, to ensure that the resin filling, wetting. As the temperature gradually increases, the fluidity of the resin experiences a change from small to large, and then to small, and finally when the temperature reaches 160-170℃, the fluidity of the resin is 0, and the temperature is called the curing temperature. In order to make the resin can be better filled and moistened, it is important to control the heating rate, which is the embodiment of the lamination temperature, that is, to control when the temperature rises to how high. The control of heating rate is an important parameter of laminate quality, and the heating rate is generally controlled at 2-4℃ / MIN. The heating rate is closely related to the different types and quantities of PP. The heating rate of 7628PP can be faster, that is, 2-4℃ / min, and the heating rate of 1080 and 2116PP can be controlled at 1.5-2 ℃ / MIN. At the same time, the number of PP is large, and the heating rate cannot be too fast. Because the heating rate is too fast, the wettability of PP is poor, the resin fluidity is large, and the time is short, it is easy to cause skateboards and affect the lamination quality. The temperature of the hot plate mainly depends on the heat transfer of the steel plate, steel plate, leather paper, etc., which is generally 180-200℃.
4.2. Time and time parameters are mainly the control of laminating pressure timing, the control of heating timing, and the gel time. For two-stage laminating and multi-stage laminating, controlling the timing of main pressure and determining the transition time from initial pressure to main pressure is the key to controlling the quality of laminating. If the main pressure is applied too early, it will lead to the extrusion of resin, too much glue flow, resulting in laminate lack of glue, thin board, and even skateboard. If the main pressure is applied too late, the laminate bond interface will be weak, empty, or there are bubbles and other defects.
4.3. pressure, multilayer circuit board lamination pressure is based on whether the resin can fill the interlayer cavity, exhaust the interlayer gas and volatile matter as the basic principle. Since the hot press is divided into non-vacuum presses and vacuum hot presses, there is a period of pressure from the pressure. Two stage pressure and multiple stage pressure several ways. General non-vacuum press adopts general pressure and two-stage pressure. The vacuum pump adopts two-stage pressurization and multi-stage pressurization. High, fine and fine multilayer plates are usually pressurized in multiple stages. The pressure size is generally determined according to the pressure parameters provided by the PP supplier, generally 15-35kg/cm2.
Therefore, how to determine the laminate temperature, pressure, time software parameters is the key technology of multi-layer laminate processing, according to many years of laminate practical experience that laminate software parameters "temperature, pressure, time" organic match, only on the basis of the first test OK, can determine the most ideal "temperature, pressure, time" software parameters. However, the "temperature, pressure, time" parameters can be determined according to different PP combination structures, different PP suppliers, different PP models, and the characteristics of PP itself to determine the corresponding lamination parameters.
English
Chinese