In SMT circuit board assembly process,do you know the PCB craft process?（2）

First let's take a look at a few concepts:

4. Lamination

Lamination is a process in which the layers of the wires are bonded together by means of the adhesion of the pp sheet. This bonding is achieved by interdiffusion, permeation, and interweaving of macromolecules on the interface, and the discrete multilayer board is pressed together with the pp sheet to form a desired number of layers and thickness of the multilayer board. In actual operation, the copper foil, the bonding sheet (prepreg), the inner layer board, the stainless steel, the separator board, the kraft paper, the outer layer steel sheet are laminated according to the craft requirements in smt circuit board assembly.

For designers, the first thing to consider about lamination is symmetry. Since the board is subjected to pressure and temperature during lamination, there is still stress in the board after lamination is completed. Therefore, if the laminated boards are not uniform on both sides, the stress on the two sides will be different, causing the board to bend to one side, which greatly affects the performance of the PCB.

In addition, even in the same plane, if the copper distribution is uneven, the resin flow speed will be different at each point, so the thickness of the place where the copper is less will be slightly thinner, and the thickness of the copper will be slightly thicker.

In order to avoid these problems, various factors such as the uniformity of the copper layout, the symmetry of the laminate, and the design and arrangement of the blind buried holes must be considered in detail.

5. Drilling

A through hole is formed between the layers of the circuit board to achieve the purpose of connecting the layers.

6. Plated copper plating

(1).Plating Copper

Also called chemical copper, the PCB board after drilling has a redox reaction in the copper sink tank,a copper layer is formed to metallize the hole, so that copper is deposited on the surface of the original insulated substrate to achieve electrical communication between the layers.

(2). Plate plating

The PCB board which is just sinking copper is thickened to 5-8um in the surface of the board and the hole, so that the thin copper in the hole is oxidized and slightly etched and the substrate is leaked before the pattern plating.

7. Outer layer dry film

The same process as the inner dry film.

8. Outer graphic plating, SES

Holes and copper layers are plated to a certain thickness (20-25um) to meet the copper thickness requirements of the final PCB board. The unused copper on the board surface is etched away to reveal useful line patterns.

9. Solder mask