How to produce pcb board?

1. Produce Pcb Board-Cutting (CUT)

How to produce pcb board?Slicing is the process of cutting the original CCL into boards that can  make on the production line,

First, let’s understand a few concepts:

(1) UNIT: UNIT refers to the unit graphics designed by PCB design engineers.

(2) SET: SET refers to an overall graphic that engineers put together multiple UNITs in order to improve production efficiency and facilitate production. That is, we often say puzzle, which includes unit graphics, craft edges and so on.

(3) PANEL: PANEL refers to a board formed by combining multiple SETs and adding tool board edges in order to improve efficiency and facilitate production during the production of PCB manufacturers.

PCB stack-up

2. INNER DRY FILM

The inner layer dry film is the process of transferring the inner layer circuit pattern to the PCB board.

In PCB production, we will mention the concept of pattern transfer, because the production of conductive patterns is the foundation of PCB production. Therefore, the graphics transfer process is very important for PCB production.

The inner layer dry film includes multiple processes such as inner layer filming, exposure and development, and inner layer etching. The inner film is to paste a special photosensitive film on the surface of the copper plate, which is what we call dry film. The film cures when exposed to light, forming a protective film on the board. Exposure and development is to expose the board with the film attached. And the light-transmitting part is cured, and the non-light-transmitting part is still a dry film. After developing, the uncured dry film removed, and the board with the cured protective film is etched. After the film removal process, the circuit pattern of the inner layer is transferred to the board.

 

For designers, our main consideration is the minimum line width of the wiring, the control of the spacing and the uniformity of the wiring. Because the spacing is too small, the film will  sandwiche, and the film will not be able to fade away, resulting in a short circuit. If the line width is too small, the adhesion of the film is insufficient, resulting in an open circuit. Therefore, the safe spacing in circuit design (including wire and wire, wire and pad, pad and pad, wire and copper surface, etc.) must considere in production.

 

(1) Pre-treatment: grinding board

The main function of the grinding board: the basic pretreatment is mainly to solve the problems of surface cleanliness and surface roughness. Remove oxidation and increase the roughness of the copper surface, so that the film can  attachto the copper surface.

(2) Film

The treated substrate is pasted with dry or wet film by hot pressing or coating to facilitate subsequent exposure production.

(3) Exposure

Align the negative film with the substrate on which the dry film has been pressed. And transfer the pattern of the negative film to the photosensitive dry film by irradiating with ultraviolet light on the exposure machine.

 

(4) Development

Use the weak alkaline of the developer (sodium carbonate) to dissolve. And wash away the unexposed dry/wet film, and the exposed part remains.

(5) Etching

After the unexposed dry film/wet film is remove by the developer, the copper surface will expose. And the exposed copper surface will  dissolve and corroded with acid copper chloride to obtain the desired circuit.

(6) Stripping

The exposed dry film protecting the copper surface is peele off with sodium hydroxide solution to expose the circuit pattern.

 

3. Browning

Purpose: to form a microscopic rough and organic metal layer on the inner copper surface to enhance the adhesion between layers.

 

Process principle:

A uniform organic metal layer structure with good adhesion properties can produce by chemical treatment. which enables the surface of the copper layer can  controlle and roughene before the inner layer is bonded. And can use to enhance the adhesion strength between the inner layer copper layer and the prepreg after pressing.

 

 

4. Lamination

Lamination is the process of bonding each layer of circuits into a whole by means of the adhesiveness of the pp sheet. This bonding is achieved through the interdiffusion and penetration of macromolecules on the interface. And then interweaving. In actual operation, the copper foil, adhesive sheet (prepreg), inner layer plate, stainless steel, isolation plate, kraft paper, outer layer steel plate and other materials are stacked according to the process requirements.

 

For designers, the first thing to consider in lamination is symmetry. Because the board will  affecte pressure and temperature during the lamination process, there is still stress in the board after the lamination czn complete. Therefore, if the two sides of the laminated board are not uniform, 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 on the same plane, if the distribution of copper is not uniform, the resin flow speed at each point will be different, so that the thickness of the place with less copper will be slightly thinner, and the thickness of the place with more copper will be slightly thicker. Some.

In order to avoid these problems, the uniformity of copper distribution, the symmetry of the stack, the design and layout of blind and buried vias and other factors must considere in detail in the design.

 

5. Drilling

Through holes can generate between the layers of the circuit board to achieve the purpose of connecting the layers.

6. Immersion copper plate plating

(1).Immersed copper

It is also calls chemical copper. After drilling, the PCB board undergoes a redox reaction in the copper sink to form a copper layer to metallize the hole, so that copper can deposite on the surface of the original insulating substrate to achieve electrical communication between the layers.

(2). Plate plating

Thicken the surface of the PCB board and the copper in the hole to 5-8um to prevent the thin copper in the hole from being oxidized and micro-etched before the pattern plating and leaking the substrate.

 

7. produce pcb board Outer dry film

The same process as the inner layer dry film.

8. Outer layer pattern plating, SES

The hole and circuit copper layer can  plate to a certain thickness (20-25um) to meet the copper thickness requirements of the final PCB board. And etch away the unused copper on the board to expose useful circuit patterns.

 

9. Solder mask

Solder mask, also know as solder mask and green oil, is one of the most critical processes in the production of printed boards. It is mainly through screen printing or coating solder mask ink, coating a layer of solder mask on the board surface, and developing through exposure. , Expose the plate and hole can soldere, and cover other places with a solder mask to prevent short circuit during soldering.

 

10. Silkscreen characters

The required text, trademark or part symbol  printed on the board by screen printing. And then exposed on the board by ultraviolet radiation.

 

11. Surface treatment

The solderability of bare copper itself is very good. But it is easy to  oxidize by moisture when exposed to the air for a long time. The most basic purpose of surface treatment is to ensure good solderability or electrical properties.

 

12. produce pcb board-Molding

The PCB  cut to the desired external dimensions with a CNC molding machine.

 

13. produce pcb board-Electrical measurement

Simulate the state of the board, check the electrical performance when it powered on, and check whether there is open or short circuit.

 

14. Final inspection, random test, packaging

produce pcb board Check the appearance, size, hole diameter, plate thickness, marking, etc. of the board to meet customer requirements. The qualified products  packaged in bundles for easy storage and shipping.