Manfacturing PCB Board

Posted 2022-11-30 03:33:51

PCB (Printed Circuit Board), the Chinese name is printed circuit board, also known as printed circuit board, is an important electronic component, is the support body of electronic components. Because it is produced by electronic printing, it is called "printed" circuit board.

Before PCBS, circuits were made up of point-to-point wiring. The reliability of this method is very low, because with the aging of the circuit, the rupture of the line will lead to the break of the line node or short circuit. Winding is a major advance in circuit technology. This method improves the durability and replaceable ability of the circuit by winding small diameter wires around the posts at the connection points.

As the electronics industry evolved from vacuum tubes and relays to silicon semiconductors and integrated circuits, the size and price of electronic components also fell. The increasingly frequent appearance of electronic products in the consumer sector has prompted manufacturers to look for smaller and more cost-effective solutions. And so PCB was born.

PCB manufacturing process

The production of PCB is very complicated. Taking four-layer printed board as an example, the production process mainly includes PCB layout, core board production, inner PCB layout transfer, core board drilling and inspection, lamination, drilling, copper chemical precipitation of hole wall, outer PCB layout transfer, outer PCB etching and other steps.

1. PCB layout

The first step of PCB production is to arrange and check the PCB Layout. The PCB manufacturing factory receives CAD files from the PCB design company, and since each CAD software has its own unique file format, the PCB factory translates them to a unified format -- Extended Gerber RS-274X or Gerber X2. Then the engineer of the factory will check whether the PCB layout conforms to the production process and whether there are any defects and other problems.

2, the production of core board

Cleaning copper cladding, if there is dust may lead to the final circuit short circuit or open circuit.

The figure below is a legend of an 8-layer PCB, which is actually made up of 3 copper coated plates (core board) plus 2 copper films, and then bonded together with semi-cured sheets. The production sequence starts with the core board in the middle (four or five layers of wiring), which is continuously stacked together and then fixed. The production of 4-layer PCB is similar, but only one core board and two copper films are used.

3. Transfer of inner PCB layout

First, the two layers of the Core are made. A photosensitive film is placed on the surface of the copper-coated sheet after it is cleaned. The film solidifies when exposed to light, forming a protective film over the copper-coated copper foil.

The two-layer PCB layout film and the double-layer copper-coated plate are inserted into the PCB layout film on the upper layer to ensure the precise layering position of the two layers of PCB layout film.

The photosensitive machine irradiates the photosensitive film on the copper foil with a UV lamp. Under the transparent film, the photosensitive film is cured, and under the opaque film, there is no curing photosensitive film. The copper foil covered under the cured photosensitive film is the required PCB layout circuit, equivalent to the role of manual PCB laser printer ink.

Then the uncured photosensitive film is cleaned with lye, and the required copper foil line will be covered by the cured photosensitive film.

The unwanted copper foil is then etched away with a strong base, such as NaOH.

Tear off the cured photosensitive film to expose the required PCB layout circuit copper foil.

4, core plate drilling and inspection

The core board has been made successfully. Then make matching holes in the core plate for easy alignment with other raw materials.

Once the core board is pressed together with other layers of PCB, it cannot be modified, so the inspection is very important. The machine will automatically compare with the PCB layout drawing to check the error.

5. Lamination

A new material called semi-cured sheet is needed here, which is the adhesive between the core board and the core board (PCB layer number >4), as well as between the core board and the outer copper foil, and also plays the role of insulation.

The lower layer of copper foil and two layers of semi-cured sheet have been fixed through the alignment hole and the lower layer of iron plate in advance, and then the made core plate is also put into the alignment hole, and finally the two layers of semi-cured sheet, a layer of copper foil and a layer of pressured aluminum plate are covered on the core plate in turn.

PCB boards which are clamped by iron plates are placed on the bracket and then sent to the vacuum hot press for laminating. The heat of the vacuum press melts the epoxy in the semi-cured sheet, holding the core plates and the copper foil together under pressure.

After the lamination is complete, remove the top iron plate pressing the PCB. The pressurized aluminum plate is then removed. The aluminum plate also acts as a barrier between the different PCBS and keeps the copper foil on the PCB smooth. Both sides of the PCB are covered with a layer of smooth copper foil.

6. Drilling

To connect the four layers of non-touching copper foil in a PCB, a perforation is drilled through the PCB, and then the hole walls are metallized to conduct electricity.

The X-ray drilling machine is used to locate the inner core board. The machine will automatically find and locate the hole on the core board, and then drill the positioning hole on the PCB to ensure that the next drilling is through the center of the hole.

Place a sheet of aluminum on the punch machine and place the PCB on top of it. In order to improve efficiency, one to three identical PCB boards are stacked on top of each other for perforation, depending on the number of PCB layers. Finally, the top PCB is covered with a layer of aluminum. The upper and lower layers of aluminum are so that when the bit is drilling in and out, it won't tear the copper foil on the PCB.

During the previous lamination process, the melted epoxy was squeezed to the outside of the PCB, so it needed to be removed. A die milling machine is used to cut the periphery of the PCB according to the correct XY coordinates.

7, the hole wall copper chemical precipitation

Since almost all PCB designs use perforations to connect different layers of wiring, a good connection requires a 25 micron copper film on the hole wall. The thickness of the copper film is achieved by electroplating, but the walls are made of non-conductive epoxy resin and fiberglass board.

Therefore, the first step is to accumulate a layer of conductive material on the hole wall, and form a 1 micron copper film on the entire PCB surface, including the hole wall, through chemical deposition. The whole process such as chemical treatment and cleaning is controlled by machines.

Fixed PCB

Cleaning PCB

Shipping PCB

8. Transfer of outer PCB layout

Next, the PCB layout of the outer layer will be transferred to the copper foil. The process is similar to the previous PCB layout transfer principle of the inner core board, which uses photocopied film and sensitive film to transfer the PCB layout to the copper foil. The only difference is that the positive film will be used as the board.
The inner PCB layout transfer adopts the reduction method, and the negative film is used as the board. The PCB is covered by the solidified photosensitive film for the circuit, clean the unsolidified photosensitive film, exposed copper foil is etched, PCB layout circuit is protected by the solidified photosensitive film.

The transfer of the outer PCB layout adopts the normal method, using positive plate as the board. The PCB is covered by the cured photosensitive film for the non - line area. The uncured photosensitive film is cleaned and then electroplated. There is a film can not be electroplated, and there is no film, first plated with copper and then plated with tin. After the film is removed, alkaline etching is carried out, and finally tin is removed. The line pattern is left on the board because it is protected by tin.

Clamp the PCB and electroplate the copper onto it. As mentioned earlier, in order for the hole to be conductive enough, the copper film plating on the hole wall must be 25 microns thick, so the whole system will be controlled automatically by computer to ensure accuracy.

9, outer PCB etching

The etching process is then completed by a complete automated pipeline. First of all, the cured photosensitive film on the PCB board is cleaned off. Then use a strong alkali to clean off the unwanted copper foil covered by it. Then the tin coating on PCB layout copper foil is removed with the tin solution. After cleaning, the 4-layer PCB layout is completed

PCB_Manufacturing

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