C. Treatment Process of Inner Core Board
When the multi-layer board is laminated, the inner core board needs to be treated. The treatment process of the inner layer board 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 copper foil. The PCB inner layer board treatment process has the following functions:
1. Increase the specific surface of the contact between the inner copper foil and the resin to enhance the bonding force between the two.
2. Increase the effective wettability of the molten resin to the copper foil when it flows, so that the flowing resin has sufficient ability to extend into the oxide film, and shows a strong grip after curing.
3. Prevent the decomposition of the curing agent dicyandiamide in the liquid resin at high temperature and the influence of moisture on the copper surface.
4. Make the multi-layer board improve the acid resistance and prevent the pink circle in the wet process.
D. The organic matching of the lamination parameters: The control of the multi-layer board lamination parameters mainly refers to the organic matching of the “temperature, pressure and time” of the lamination.
There are several temperature parameters that are more important in the temperature and lamination process. That is, the melting temperature of the resin, the curing temperature of the resin, the set temperature of the hot plate, the actual temperature of the material, and the rate of temperature increase. The melting temperature is when the temperature rises to 70°C and the resin begins to melt. It is due to the further increase in temperature that the resin melts further and begins to flow. During the temperature of 70-140°C, the resin is easy to fluid. It is precise because of the fluidity of the resin that the resin can be filled and wetted. As the temperature gradually increases, the fluidity of the resin undergoes a change from small to large, then to small, and finally when the temperature reaches 160-170 ° C, the fluidity of the resin is 0, and the temperature at this time is called the curing temperature. In order to enable the resin to be filled and wetted well, it is very important to control the heating rate. The heating rate is the embodiment of the lamination temperature, that is, when the temperature rises to how high. The control of the heating rate is an important parameter for the lamination quality of the multi-layer board, 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. For 7628PP, the heating rate can be a little faster, that is, 2-4°C/min. For 1080 and 2116PP, the heating rate can be controlled at 1.5-2°C/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, PP The wettability is poor, the resin fluidity is large, and the time is short, which is easy to cause slippage and affect the lamination quality. The temperature of the hot plate mainly depends on the heat transfer of the steel plate, steel plate, kraft paper, etc., and is generally 180-200 °C.
Pressure, the lamination pressure of multi-layer boards is based on whether the resin can fill the voids between the layers and exhaust the gas and volatiles between the layers as the basic principle. Since the hot press is divided into a non-vacuum press and a vacuum hot press, there is a section of pressurization starting from the pressure. There are several ways of two-stage pressurization and multi-stage pressurization. General non-vacuum presses use general pressurization and two-stage pressurization. The vacuum pump adopts two-stage pressurization and multi-stage pressurization. Multi-stage pressure is usually used for high and fine multilayer boards. The pressure is generally determined according to the pressure parameters provided by the PP supplier, generally 15-35kg/cm2.
Time and time parameters are mainly the control of the timing of lamination and pressure, the control of the timing of heating, and the gelation time. For two-stage lamination and multi-stage lamination, controlling the timing of the main pressure and determining the transition time from the initial pressure to the main pressure are the keys to controlling the quality of the lamination. If the main pressure is applied too early, too much resin will be extruded and glue will flow out, resulting in the lack of glue, thin board, and even slippage of the laminate. If the main pressure is applied too late, it will cause defects such as weak lamination bonding interface, voids, or bubbles.
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