PCB Technical - How to make the difference between PCB and PCBA

Some people who are new to the electronics manufacturing industry may not be very clear about PCBA and PCB, and they may confuse the two. When I first came into contact with the electronics industry, I also encountered this problem. In order for everyone to identify them quickly and reduce unnecessary annoyance, the next editor will introduce the difference between PCB and PCBA.

Quickly recognize the difference between PCBA and PCB

One, recognize the PCB

PCB has many names, which can be called circuit board, circuit board, printed circuit board, etc. It is an important electronic component used to support electronic components and realize the connection of electronic components.

Second, recognize PCBA

PCBA is the abbreviation of Printed Cirruit Board Assembly in English, but in foreign countries, PCBA is generally translated into PCB Assembly. It is to form a finished product, referred to as PCBA, through the process of SMT patch, DIP plug-in and testing, etc. of the empty PCB board.

Third, the difference between PCBA and PCB

PCB is an empty board with nothing on the surface of the board; while PCBA is processed on an empty PCB, where resistors, capacitors, chips and other components are installed to form a board with certain functions. The core parts of all electronic products are It is composed of PCBA.

4. Core board punching and inspection

The core board has been successfully produced. Then punch alignment holes on the core board to facilitate alignment with other materials. Once the core board is pressed together with other layers of PCB, it cannot be modified, so inspection is very important. The machine will automatically compare with the PCB layout drawing to check for errors.

5. Laminating

A new raw material is needed here, called a prepreg, which is the adhesive between the core board and the core board (PCB layers>4), as well as the core board and the outer copper foil, and it also plays a role in insulation.

The lower copper foil and the two layers of prepreg have been fixed in advance through the alignment hole and the lower iron plate, and then the finished core board is also placed in the alignment hole, and finally the two layers of prepreg, a layer of copper foil and A layer of pressure-bearing aluminum plate covers the core plate.

The PCB boards clamped by the iron plates are placed on the support, and then sent to the vacuum heat press for laminating. The high temperature in the vacuum hot press can melt the epoxy resin in the prepreg and fix the core boards and copper foils together under pressure.

After the lamination is completed, remove the upper iron plate that presses the PCB. Then remove the pressure-bearing aluminum plate. The aluminum plate also has the responsibility of isolating different PCBs and ensuring the smoothness of the outer copper foil of the PCB. Both sides of the PCB taken out at this time will be covered by a layer of smooth copper foil.

6. Drilling

To connect 4 layers of non-contact copper foils in the PCB, first drill through the through holes to open the PCB, and then metalize the hole walls to conduct electricity.

Use the X-ray drilling machine to locate the inner core board. The machine will automatically find and locate the hole on the core board, and then punch the positioning hole on the PCB to ensure that the next hole is drilled from the center of the hole. pass.

Put a layer of aluminum plate on the punching machine machine, and then put the PCB on it. In order to improve efficiency, according to the number of PCB layers, 1 to 3 identical PCB boards are stacked together for perforation. Finally, cover the uppermost PCB with a layer of aluminum plate. The upper and lower layers of aluminum plate are used to prevent the copper foil on the PCB from tearing when the drill bit drills in and out.

In the previous lamination process, the molten epoxy was squeezed out of the PCB, so it needed to be cut off. The profiling milling machine cuts its periphery according to the correct XY coordinates of the PCB.

7. Copper chemical precipitation on the hole wall

Since almost all PCB designs use perforations to connect different layers of lines, a good connection requires a 25-micron copper film on the hole wall. The thickness of the copper film needs to be realized by electroplating, but the hole wall is composed of non-conductive epoxy resin and glass fiber board.

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

Fixed PCB

Cleaning the PCB

Shipping PCB

8. Outer PCB layout transfer

Next, the PCB layout of the outer layer will be transferred to the copper foil. The process is similar to the transfer principle of the previous PCB layout of the inner core board. The PCB layout is transferred to the copper foil by photocopying film and photosensitive film. The only difference is Yes, positive films will be used as the board.

The internal PCB layout transfer uses the subtractive method, and the negative film is used as the board. The PCB is covered by the cured photosensitive film as a circuit, and the uncured photosensitive film is cleaned. After the exposed copper foil is etched, the PCB layout circuit is protected by the cured photosensitive film.

The transfer of the outer PCB layout adopts the normal method, and the positive film is used as the board. The non-circuit area is covered by the cured photosensitive film on the PCB. After cleaning the uncured photosensitive film, electroplating is performed. Where there is a film, it cannot be electroplated, and where there is no film, copper is plated first and then tin is plated. After the film is removed, alkaline etching is performed, and finally the tin is removed. The circuit pattern remains on the board because it is protected by tin.

Clamp the PCB with clamps, and electroplate the copper. As mentioned earlier, in order to ensure that the holes have sufficient conductivity, the copper film plated on the hole walls must have a thickness of 25 microns, so the entire system will be automatically controlled by the computer to ensure its accuracy.

9. Outer PCB etching

Next, a complete automated assembly line completes the etching process. First, clean the cured photosensitive film on the PCB. Then use a strong alkali to clean the unnecessary copper foil covered by it. Then use the tin stripping solution to strip the tin plating on the PCB layout copper foil. After cleaning, the 4-layer PCB layout is complete.