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How is a PCB Made Step by Step? Video Explained

Author: Apogeeweb
Date: 16 Aug 2021
 360
how are pcbs made

Introduction

Printed Circuit Board(PCB) is a board of most modern electronic devices that has lines and pads that connect various points together. Even if it is a small board, its manufacturing process is very cumbersome and exquisite. Here will introduce the PCB manufacturing process steps by steps with pictures and video.

How is PCB made?

The following are the detailed PCB producing processes:

Introduction

Step 1. PCB CAD File

Step 2. Plate Production

Step 3. PCB Inner Layers

Step 4. Board Punching and Checking

Step 5. Lamination

Step 6. Drill

Step 7. Copper Chemical Precipitation on the Holes

Step 8. PCB Outer Layers

Step 9. Computer Control and Copper Electroplating


Step 1. PCB CAD File

The first step in PCB production is to organize and check the PCB layout. The PCB manufacturers get the CAD files from the PCB design company, and they will convert them into a unified format-Extended Gerber RS-274X or Gerber X2, because each CAD software has its own unique file format. Then the electronic engineers will check whether the PCB layout conforms to the manufacturing process, and whether there are any defects and other issues.

pcb cad file

Figure 1. PCB CAD File

When making a PCB at home, the PCB layout can be printed on paper with a laser printer, and then transferred to the copper clad laminate. During the printing process, because the printer is prone to lack of ink and breakpoints, it is necessary to manually fill up the ink with an oil-based pen.

PCB Laser Printing

Figure 2. PCB Laser Printing

However, the factory generally uses photocopying to print the PCB layout on the film. If it is a multi-layer PCB, the layout film photocopied on each layer will be arranged in order.

PCB Film Arranged in Order

Figure 3. PCB Film Arranged in Order

Then the film will be punched with alignment holes. Alignment holes are very important, which is essential to align the materials of each layer of the PCB.

Step 2. Plate Production

Clean the copper plate. If there is dust, it may cause the final circuit to be short-circuited or broken.

Clean the Copper Plate

Figure 4. Clean the Copper Plate

The figure below is an example of an 8-layer PCB, which is actually made up of 3 copper clad laminates plus 2 copper films, and then glued them together with prepregs. The production sequence is to start with the middle board (4th- and 5th-layer of circuits), continuously stack together, and then fix. The production of 4-layer PCB is similar, including one core board and two copper films.

8-layer PCB Plate Display

Figure 5. 8-layer PCB Plate Display

Step 3. PCB Inner Layers

First, make the two-layer circuit of the middle core board. After the copper clad laminate is cleaned, it will be covered with a photosensitive film on the surface. This film will solidify when exposed to light, forming a protective film on the copper foil.

PCB Core

Figure 6. PCB Core

Insert the two-layer PCB layout film and the double-layer copper clad laminate into the upper PCB layout film to ensure that the upper and lower PCB layout films are stacked accurately.

PCB Layout Film Placing

Figure 7. PCB Layout Film Placing

The machine irradiates the photosensitive film on the copper foil with a UV lamp. The transparent film is cured under the light, and there is still no cured photosensitive film. The copper foil covered under the cured film is the required PCB layout, which is equivalent to the function of the laser printer ink of the manual PCB. In addition, the copper foil covered by the black film will be corroded away, and the cured transparent film will be preserved.

Cured Photosensitive Film

Figure 8. Cured Photosensitive Film

Clean the uncured photosensitive film with lye, and the required copper foil circuit will be covered by the cured film.

Clean Uncured Photosensitive Film

Figure 9. Clean Uncured Photosensitive Film

Then use a strong base, such as NaOH, to etch away the unnecessary copper foil.

Copper Foil Etching

Figure 10. Copper Foil Etching

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

Tear Off the Cured Photosensitive Film

Figure 11. Tear Off the Cured Photosensitive Film

Step 4. Board Punching and Checking

The core board has been successfully produced. Then punch alignment holes on it to facilitate with other materials.

Punch Alignment Holes on PCB

Figure 12. Punch Alignment Holes on PCB

Once the core board is pressed together with other layers, it cannot be modified. So PCB checking is very important. The machine will automatically compare with the PCB layout drawing to find out the error.

PCB Layout Drawing Comparison

Figure 13. PCB Layout Drawing Comparison

The first two layers of PCB boards have been made.

Step 5. Lamination

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

PCB Prepreg and Copper

Figure 14. PCB Prepreg and Copper

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.

Fixed PCB Prepreg and Copper

Figure 15. Fixed PCB Prepreg and Copper

In order to improve work efficiency, this factory will stack three different PCB boards together before fixing them. The upper iron plate is magnetically attracted to facilitate alignment with the lower iron plate. After the two layers of iron plates are successfully aligned by inserting the alignment pins, the machine compresses the space between the iron plates as much as possible, and then fixes them with nails.

Fixed PCB Layers

Figure 16. Fixed PCB Layers

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

PCB Layers Lamination

PCB Layers Lamination

Figure 17. PCB Layers Lamination

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

Remove the Upper Iron Plate and Aluminum Plate

Figure 18. Remove the Upper Iron Plate and Aluminum Plate

Step 6. Drill

So how to connect 4 layers of copper foils that are not in contact with each other in the PCB? First, make the through-hole through the PCB, and then metalize the hole wall to conduct electricity.

PCB Drill

Figure 19. PCB Drill

Put a layer of aluminum plate on the punching machine, and then put the PCB on it. Since drilling is a relatively slow process, in order to improve efficiency, according to the number of layers of the PCB, 1 to 3 identical boards are stacked for drilling together. Finally, cover the uppermost PCB with a layer of aluminum plate. The upper and lower of aluminum plates are used to prevent the copper foil on the PCB from tearing when drilling.

PCB Drill

Figure 20. PCB Drill

Next, you only need to select the correct drilling program on the computer, and the rest is done automatically by the drilling machine. The drill bit is driven by air pressure, and the maximum rotation speed can reach 150,000 revolutions per minute. Because such a high rotation speed is sufficient to ensure the smoothness of the hole wall.

Drill Program

Figure 21. Drill Program

The replacement of the drill bit is also automatically completed by the machine according to the program. The smallest drill bit can reach a diameter of 100 microns, while the diameter of a human hair is 150 microns.

Drill Replace

Figure 22. Drill Replace

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

Cuts PCB Periphery

Figure 23. Cuts PCB Periphery

Step 7. Copper Chemical Precipitation on the Holes

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. The entire process such as chemical treatment and cleaning is controlled by the machine.

Step 8. PCB Outer Layers

Next, the PCB outer layer is transferred to the copper foil. The process is similar to the transfer principle of the previous PCB inner core board. The PCB layout is transferred to the copper foil by photocopying film and photosensitive film. The only difference is positive films will be used as boards.
The transfer of the internal PCB layout described above 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 film is cleaned. After the exposed copper foil is etched, the PCB layout circuit is protected by the cured 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 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. So the circuit pattern remains on the board because it is protected by tin.
Put the cleaned PCB on both sides of the copper foil into the laminating machine, and the photosensitive mold will be pressed onto the copper foil.

Laminator

Figure 24. Laminator

Fix the printed PCB layout film of the upper and lower layers through the holes, and put the PCB board in the middle. Then, the photosensitive film under the light-transmitting film is cured by the irradiation of the UV lamp, which is the circuit that needs to be reserved.

PCB Expose to the UV Light

PCB Expose to the UV Light

Figure 25. PCB Expose to the UV Light

After cleaning off the unnecessary and uncured photosensitive film, inspect the PCB board.

PCB Checking

PCB Checking

Figure 26. PCB Checking

Clamp the PCB with clips, 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.

PCB Copper Plating

PCB Copper Plating

Figure 27. PCB Copper Plating

Step 9. Computer Control and Copper Electroplating

After the copper film is electroplated, the computer gives instructions to electroplate a thin layer of tin. Then, check to ensure that the thickness of the plated copper and tin is correct.

Electroplated Copper and Tin Inspection

Figure 28. Electroplated Copper and Tin Inspection

Next, a complete automated assembly line completes the etching process. Then, clean the cured photosensitive film on the PCB.

Clean Cured Photosensitive Film

Figure 29. Clean Cured Photosensitive Film

Then use a strong alkali to clean the unnecessary copper foil covered by it.

Clean the Unnecessary Copper Foil

Figure 30. Clean the Unnecessary Copper Foil

Finally, 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.

 

Frequently Asked Questions about PCB Manufacturing Process

1. Which are the techniques of PCB manufacturing?
There are several PCB manufacturing methods that a PCB can be submitted to before reaching the final product. These methods include preparing the board's surface, placing components, soldering, cleaning, and inspection and testing.

 

2. What is PCB design process?
Step 1 – The Design
Step 2 – Printing the Design
Step 3 – Creating the Substrate
Step 4 – Printing the Inner Layers
Step 5 – Ultraviolet Light
Step 6 – Removing Unwanted Copper
Step 7 – Inspection.
Step 8 – Laminating the Layers

 

3. Which software is best for PCB design?
Top 8 Best PCB Design Software of 2021
PROTEL (Altium Designer)
PADS (PowerPCB)
ORCAD
Allegro
Eagle (Easily Applicable Graphical Layout Editor)
Kicad
EasyEda
Fritzing

 

4. What is a PCB layer?
A PCB is defined as a number of copper layers in a well defined sequence. Copper layers of a PCB are usually just named layers or also called SIGNAL layer. However, to define the complete PCB, other layers are required. They are usually named by their functionality and position.

 

5. What are the components of a PCB?
Some common PCB components include:
Battery: provides the voltage to the circuit.
Resistors: control the electric current as it passes through them. They’re colour coded to determine their value.
LEDs: light emitting diode. Lights up when current flows through it, and will only allow current to flow in one direction.
Transistor: amplifies charge.
Capacitators: these are components which can harbour electrical charge.
Inductor: stores charge and stops and change in current.
Diode: allows current to pass in one direction only, blocking the other.
Switches: can either allow current or block depending if they are closed or open.

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