Multilayer Lamination Technology (1)

In order to completely solve the problem of air bubbles in the pressing of multi-layer boards and improve the adhesion between layers, it is an inevitable trend to use vacuum lamination technology. In terms of positioning technology, pin-free positioning technology (MASSI. AM) has been widely used for 4 to 6-layer boards, and X-ray positioning drilling is used to improve the positioning accuracy of multi-layer boards. In terms of heating method, in addition to the commonly used electric heating and hot oil heating, we have introduced the lamination technology using copper foil resistance direct heating, which not only greatly reduces energy consumption, but also improves the lamination quality by uniform heating.

PCB vacuum lamination unit:

Due to the rapid development of electronic technology, the continuous development of printed circuit technology has been promoted. PCB boards are developed through single-sided, double-sided and multi-layer development, and the proportion of multi-layer boards is increasing year by year. The performance of multi-layer boards is developing to the extremes of high precision, fine, large and tiny. An important process in the manufacture of multi-layer boards is lamination, and the control of lamination quality is becoming more and more important in the manufacture of multi-layer boards. Therefore, to ensure the quality of multi-layer board lamination, it is necessary to have a better understanding of the multi-layer board lamination process. For this reason, based on my years of lamination practice, I make the following summary on how to improve the lamination quality of multi-layer boards in terms of process technology.

A. Design the inner core board that meets the lamination requirements.

Due to the gradual development of lamination machine technology, the hot press has changed from the previous non-vacuum hot press to the current vacuum hot press. The hot pressing process is in a closed system, which cannot be seen or touched. Therefore, a reasonable design of the inner layer should be carried out before lamination. Here are some reference requirements:

1. The thickness of the core board should be selected according to the total thickness of the multi-layer board. The thickness of the core board is consistent, the deviation is small, and the warp and weft directions of the blanking materials are consistent, especially for multi-layer boards with more than 6 layers. The warp direction overlaps with the warp direction, and the weft direction overlaps with the weft direction, preventing unnecessary board bending.

2. There must be a certain distance between the external dimensions of the core board and the effective unit, that is, the distance from the effective unit to the edge of the board should be as large as possible without wasting materials. Generally, the four-layer board requires a spacing greater than 10mm, and the six-layer board requires a spacing greater than 15mm, and the higher the number of layers, the larger the spacing.

3. The design of the positioning holes: in order to reduce the deviation between the layers of the multi-layer board, it is necessary to pay attention to the design of the positioning holes of the multi-layer board. The 4-layer board only needs to design more than 3 positioning holes for drilling. For multi-layer boards with more than 6 layers, in addition to the positioning holes for drilling, it is necessary to design more than 5 positioning holes for overlapping positioning rivets and more than 5 positioning holes for tool plates for rivets. However, the designed positioning holes, rivet holes and tool holes are generally higher in layers. The number of designed holes should be correspondingly larger. The positions should be as close to the side as possible. The main purpose is to reduce the misalignment between layers and leave a larger space for manufacturing. The design of the target shape should meet the requirements of the automatic identification of the target shape of the target machine as much as possible, and it is generally designed as a complete circle or a concentric circle.

4. The inner core board requires no open circuit, short circuit, no oxidation, clean board surface, and no residual film.

B. To meet the requirements of PCB users, select the appropriate PP, CU foil configuration.

The customer’s requirements for PP are mainly reflected in the requirements of the thickness of the dielectric layer, dielectric constant, characteristic impedance, withstand voltage, and the smoothness of the laminate surface. Therefore, when choosing PP, you can choose according to the following aspects:

1. Resin can fill the gaps of printed wires during lamination.
2. It can fully remove the air and volatiles between the laminations during lamination.
3. It can provide the necessary dielectric layer thickness for multi-layer boards.
4. It can ensure bond strength and smooth appearance.

Based on years of production experience, I think that PP can be configured in 7628, 7630 or 7628+1080, 7628+2116 when 4-layer laminates are laminated. The choice of PP for multi-layer boards with more than 6 layers is mainly 1080 or 2116, and 7628 is mainly used as PP to increase the thickness of the dielectric layer. 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 PCB user requirements, and the quality of CU foil conforms to IPC standards.