What are the lamination methods of PCB multilayer circuit boards?

PCB circuit boards are classified according to the number of circuit layers: they can be divided into single-sided, double-sided and multi-layer boards. Common multi-layer boards are generally 4-layer boards or 6-layer boards, and complex multi-layer boards can reach dozens of layers. So, what are the lamination methods of PCB multilayer circuit boards?

1. Kraft paper

When the multi-layer board is pressed (laminated), kraft paper is mostly used as a heat transfer buffer; it is placed between the hot plate and the steel plate of the pressing machine to ease the heating curve closest to the bulk material, so that multiple sheets The temperature difference of each layer of the substrate or multi-layer board to be pressed should be as close as possible, and the common specification is 90 pounds to 150 pounds.

2, kiss pressure, low pressure

When the multi-layer boards are pressed together, when the boards in each opening are positioned, they start to heat up and lift up from the bottom layer with a strong hydraulic top column to compress the bulk materials in each opening for bonding. At this time, the combined film begins to soften or even flow gradually, so the pressure used for the top extrusion should not be too large. This method initially used a lower pressure (15 to 50 PSI) called "kiss pressure". However, when the resin in each film is softened and gelled by heat and is about to harden, it needs to be increased to the full pressure (300-500 PSI), which is called "low pressure".

3. Copper foil pressing method

Refers to mass-produced multi-layer boards. The outer layer is made of copper foil and film directly laminated with the inner layer to replace the traditional pressing method of single-sided thin substrates in the early days.

4. Cap pressing method

In the traditional lamination method of early multi-layer PCB boards, at that time, the "outer layer" of MLB mostly used thin substrates with single-sided copper skin for lamination and lamination. It was not until the end of 1984 that the output of MLB increased significantly, and the current copper was used. Leather-style large or bulk presses.

5. Pressure cooker

It is a container filled with high-temperature saturated water vapor and can be applied with high pressure. The laminated substrate sample can be placed in it for a period of time to force the water vapor into the plate, and then the plate sample can be taken out and placed at high temperature. The tin surface was melted and its "anti-delamination" properties were measured.

6. Large platen (lamination)

This is a new construction method that abandons the "alignment pin" in the multi-layer board lamination process and adopts multiple rows of boards on the same side. The specific method is to cancel the registration pins of various loose materials (such as inner layer sheet, film, outer layer single-sided sheet, etc.); and change the outer layer to copper foil, and pre-fabricate the "target" on the inner layer plate. After pressing, the target is "sweeped" out, and the tool hole is drilled from the center, which can be set on the drilling machine for drilling.

7. Superposition

Before lamination of multilayer circuit boards or substrates, it is necessary to align various loose materials such as inner layers, films and copper sheets with steel plates, kraft paper pads, etc. It can then be carefully fed into the press for hot pressing. For the speed and quality of mass production, the "automatic" stacking method is generally required for the eight-layer structure; most factories combine "stacking" and "folding" into a comprehensive processing unit. The engineering of automation is quite complex.

The above is the lamination method of PCB multilayer circuit board. The specific situation should be based on the customer's product needs and the comprehensive utilization of its own resources to make high-quality products.