PCB Tech - Professional PCB multilayer board pressing process description

Professional PCB multilayer board pressing process description

Professional PCB multilayer board pressing process description: 1. High pressure

It is a high temperature and high pressure vessel filled with saturated steam. The laminated sample after lamination can be placed in a container for a period of time to allow water vapor to enter the board, and then the sample is taken out and placed on the surface of high-temperature molten tin to measure its "delamination resistance" characteristics. This term is also synonymous with pressure cooker and is more commonly used in industry. Another type of autoclave press is the "chamber pressure method", in which carbon dioxide is used in the laminator under high temperature and pressure.

2. Cover laminate cover pressure

It refers to the traditional laminating method of early multilayer boards. At that time, the "outer layer" of the MLB was made of a single-sided thin copper plate for assembly and compression. Until the end of 1984, the production of MLB increased significantly, and large-scale or large-scale copper laminates (Mss Lam) were used. This early MBB compression method, called cap lamination, used a single copper sheet substrate.

3. Folds

In laminates, copper sheets are often used to deal with wrinkles that appeared at that time. This defect is likely to occur when thin copper sheets of 0.5 ounces or less are laminated in multiple layers.

4. Affect depression

It refers to the slight uniform settlement of the copper surface, possibly due to the slight local bulging of the steel plate used for compression. If the edge of the steel plate falls neatly along the fault, it is called a plate. However, if the copper is still on the wire after corrosion, these shortcomings will lead to instability and noise in the high-speed transmission signal impedance. Therefore, such defects should be avoided as much as possible on the surface of the copper substrate.

5. Film distribution

During the lamination process, multiple sheets (for example, 8-10 groups) are often overlapped at each opening of the press. Each group of plates (such as 8-10 groups) must be separated by flat, smooth and hard stainless steel plates. This mirror-finished stainless steel plate is called a cutting plate or partition. Currently commonly used is AISI 430 or AISI 630.

6. Method for laminating copper foil with aluminum foil

Mass Lam (premium sheet) is a mass-produced multi-layer sheet, in which the outer and inner layers of copper foil and the film are directly pressed, replacing the traditional pressing method of early single-sided panels.

7. Kraft paper

Kraft paper is often used as a heat transfer buffer material during lamination. It is placed between the plate and steel plate of the press to adjust and approximate the heating curve of the bulk material. Make some boards between boards or laminates for compression. Try to turn off the temperature difference of each layer. The general specification is 90 to 150 pounds. Because the fibers in the paper are crushed under high temperature and pressure, they are no longer tough and difficult to function, so we must try to update them. This kind of kraft paper is made by mixing pine tree and various strong alkali liquids. After boiling, the volatile substances escape, and after the acid is removed, the precipitate is washed immediately and made into pulp, which is then pressed into rough and cheap paper.

8. High pressure

When the laminates are pressed, when the plates in the opening are positioned, they are heated and rolled up by the lowest thermal layer, and then lifted by a powerful hydraulic jack (ram) to compress the large pieces in the opening. The materials are glued together. At this time, the composite film (prepreg) begins to soften or even flow gradually, so the pressure used in the extrusion process should not be too large to prevent sheet slippage or excessive rubber flow. The lower pressure (15-50psi) used at the beginning is called the "kissing pressure". However, when the resin in the film body is heated, softened, cemented and hardened, the total pressure (300-500 psi) needs to be increased to tightly bond the film body to form a strong multilayer board.

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