Shenzhen how to improve the quality of multi-layer flexible circuit board lamination?

In order to solve the problem of bubbles in the pressing of multilayer flexible circuit board and improve the adhesion between layers, vacuum lamination technology is an inevitable trend. Pin - free positioning technology has been widely used for 4-6 layers of plates (MASSI). AM), and X-ray positioning drilling is applied to improve the positioning accuracy of multi-layer flexible circuit board. In addition to electric heating and hot oil heating, Deli Technology (zhuhai) Co., Ltd. has introduced laminating technology using copper foil resistance for direct heating, which not only greatly reduces energy consumption, but also uniformly improves laminating quality.

Due to the rapid development of electronic technology, prompted the development of printed circuit technology. PCB board is developed by single-sided, double-sided and multi-layer flexible circuit board, and the proportion of multi-layer board is increasing year by year. Multi-layer flexible circuit board performance in the high * precision * dense * fine * large and small two extreme development. Lamination is an important process in the manufacture of multilayer board, and the control of lamination quality is becoming more and more important in the manufacture of multilayer board. Therefore, to ensure the laminating quality of multi-layer flexible circuit board, it is necessary to have a good understanding of the laminating process of multi-layer flexible circuit board. Therefore, I have made the following summary on the process technology of how to improve the laminating quality of multi-layer flexible circuit board based on years of laminating practice:

Design the inner core plate in accordance with 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 vacuum hot press now, the hot pressing process is in a closed system, can not see, can not touch. Therefore, it is necessary to design the inner laminate reasonably before lamination. Some reference requirements are provided here:

1, according to the multi-layer flexible PCB board total thickness requirements to core board thickness, core board thickness, small deviation, blanking warp/weft direction, especially over 6 layer sandwich plate, the inner core board warp/weft directions must be consistent, that is the direction and the direction of overlap, weft direction and weft direction overlap, prevent unnecessary bending.

2, there must be a certain distance between the shape size of the core plate and the effective unit, that is, the effective unit to the edge of the plate distance should be as far as possible under the premise of not wasting materials, the general four layer plate spacing is greater than 10mm, the six layer plate spacing is greater than 15mm, the higher the number of layers, the greater the spacing.

3, the design of the positioning hole, in order to reduce the deviation between the layers of the multi-layer board, so in the multi-layer board positioning hole design needs to pay attention to: 4 layers of the board only need to design the positioning hole with more than 3 holes can be. More than 6 layers of multi-layer flexible circuit board in addition to the need to design positioning holes for drilling also need to design layer and layer overlap positioning rivet holes more than 5 and rivet tool plate positioning holes more than 5. However, the higher the number of positioning holes, rivet holes and tool holes, the more the number of holes should be designed, and the position should be as far as possible to the side. The main purpose is to reduce the offset between layers and leave more room for manufacturing. The target shape design should meet the requirement of automatic target shape recognition of target machine as far as possible, and the general design is complete circle or concentric circle.

4, the inner core plate requires no open, short, open, no oxidation, clean board surface, no residual film.

Two, to meet the requirements of PCB users, choose the appropriate PP, CU foil configuration.

Customer requirements for PP are mainly reflected in the thickness of the dielectric layer, dielectric constant, characteristic impedance, voltage resistance, laminate surface smoothness and other requirements, so choose PP according to the following aspects to choose:

1, Resin can fill the gap of printed wire when laminating.

2. Air and volatiles between laminates can be fully eliminated during lamination.

3. It can provide the necessary medium layer thickness for multi-layer board.

4, can ensure the bond strength and smooth appearance.

Based on years of production experience, I personally think that PP can be 7628, 7630 or 7628+1080, 7628+2116 configuration when 4-ply laminating. More than 6 layers of flexible circuit board PP selection is mainly 1080 or 2116, 7628 is mainly used to increase the thickness of the medium layer PP. At the same time, PP requires symmetrical placement to ensure mirror effect and prevent plate bending.

5. CU foil is mainly configured with different models according to the requirements of PCB users, and the quality of CU foil meets IPC standards.

Three, the inner core board processing technology

When laminating multi-layer flexible circuit board, the inner core board should be processed. The inner layer of the treatment process includes black oxidation treatment process and brown treatment process, oxidation treatment process is formed on the inner layer of copper foil a black oxidation film, the thickness of the black oxidation film is 0.25-4). 50 mg/cm2. The Browning process (horizontal Browning) is to form an organic film on the inner copper foil. The inner layer board processing process functions are:

1. Increase the specific surface between the inner copper foil and the resin to enhance the binding force between the two.

2. Increase the effective wettability of copper foil when melting resin flows, so that the flowing resin has sufficient ability to stretch into the oxide film, and show strong grip after curing.

3, resist the decomposition of the curing agent dicyandiamide in the liquid resin at high temperature and the influence of water on the copper surface.

4, so that the multi-layer board in the wet process of the process to improve acid resistance, prevention of pink circle.

The control of laminating parameters of multi-layer flexible CIRCUIT board mainly refers to the organic matching of laminating "temperature, pressure and time".

1: Several temperature parameters are more important in the process of temperature and lamination. 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 speed of temperature rise. Melting temperature system when the temperature rises to 70℃, the resin begins to melt. It is due to the 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 easy to fluid, it is because of the fluidity of the resin, to ensure that the resin filling, wet. As the temperature gradually increases, the fluidity of the resin has experienced a from small to large, and then to small, and finally when the temperature reaches 160-170℃, the fluidity of the resin is 0, then the temperature is called the curing temperature. In order to make the resin can be better filling, wetting, it is very important to control the heating rate, the heating rate 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 laminating quality of multilayer laminates. The heating rate is generally controlled as 2-4℃ / MIN. The heating rate is closely related to different types and quantity of PP. For 7628PP, the heating rate can be faster, that is, 2-4℃ / min, and for 1080 and 2116PP, the heating rate should 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 fluidity of resin is large, and the time is short, it is easy to cause sliding plate and affect the lamination quality. The temperature of hot plate mainly depends on the heat transfer of steel plate, steel plate, leather cow paper, etc., generally 180-200℃.

2: pressure, laminating pressure of multi-layer flexible circuit board is based on whether the resin can fill the hole between layers, exhaust the gas and volatiles between layers as the basic principle. Because the hot press is divided into non-vacuum press and vacuum hot press, so there is a section of pressure from the pressure. Two - stage pressure and multi - stage pressure several ways. General non - vacuum press with general pressure and two - stage pressure. Vacuuming machine adopts two-stage pressure and multi-stage pressure. For high, fine and fine multi - layer boards usually adopt multi - stage pressure. The pressure is generally determined according to the pressure parameters provided by the P P supplier, which is generally 15-35kg/cm2.

3: Time and time parameters mainly include control of laminating and pressurizing timing, control of heating timing, gel time and so on. For two-stage lamination and multi-stage lamination, the key to control the quality of lamination is to control the timing of primary pressure and determine the transition time from primary pressure to primary pressure. If the main pressure is applied too early, it will lead to too much extrusion resin and glue flow, resulting in lack of glue, thin laminate, even slide plate and other undesirable phenomena. If the main pressure is applied too late, it will cause laminate bonding interface is not firm, hole, or bubble and other defects.

Polly peak flexible circuit board as a professional FPC flexible circuit board manufacturers, we are in the direction of the digital camera, car satellite positioning device, liquid crystal TV, notebook computer, medical instrument, intelligent robot, mobile phone and so on are involved in the communication field and research and development, thank you very much for support for polly peak, many customers are willing to work with us hand in hand, Welcome more customers to negotiate cooperation.