Circuit is the infrastructure of the electrical world. However, perhaps last time the most people saw a traditional circuit connected by wires or cables was on their physics class. Why is that? The answer is PCB.
1. What is PCB?
PCB stands for printed circuit board. It’s the board etched from one or more layer of copper laminated onto and/or between sheet layers of a non-conductive substrate. Other components in a circuit such as resistor and capacitor are generally soldered onto the PCB.
That is, the PCB replaces the role of wires or cables in the circuit, and as a result, those mess and space consuming wires or cables are no longer needed.
PCBs can be single-sided, double-sided or multi-layer. The single-sided PCB has only one copper layer, while the double-sided one has two copper layers on the both sides of the same substrate layer.
Multi-layer means the PCB has outer and inner layers of copper, alternating with the layers of substrate. Multi-layer PCBs allow for much higher component density, because circuit traces on the inner layers save the surface space between components.
2. Manufacturing process of PCB
Main principle of the PCB manufacturing technology is etching, which means you need to design and set down the circuit pattern in advance, and then etch the pattern onto board.
As the multi-layer PCB is the most complicated one, let’s take it as an example to introduce the manufacturing process of PCB.
2.1 Circuit pattern design
To start manufacturing, we have to generate fabrication data using CAD (computer aided design). The data should include copper patterns, drill files, inspection and others.
In subsequent the pattern data is read into the CAM (computer aided manufacturing) system and then replicated on a protective mask.
2.2 Substrate board preparation
The raw substrate board often comes in a large piece. We have to cut it into designed size, and clean the surface of board in order to get the circuit pattern of good quality.
2.3 Copper patterning
- Place the protective mask on the substrate board.
- Expose the board to UV (ultraviolet) light.
- Develop the circuit pattern by removing the unexposed part of protective mask using chemical solution.
- Etching the copper through chemical reaction. The copper covered by the protective mask will remind to form the circuit.
- Remove the protective mask and clean the board. Carry out AOI (automated optical inspection) to check the quality of the circuit.
2.4 Layup and lamination press
Layup several patterned board with prepreg. Place copper foil on each side of the multi-layer board. Vacuum lamination press the board through machine.
2.5 CNC (computerized numerical control) drilling and electroplating copper
Drill the hole according to the design. Plate copper on the hole to connect every layer of the board.
2.6 Copper patterning
Repeat the copper patterning on the two side of multi-layer board.
2.7 Electroplating on copper pattern
We electroplate more copper to thicken the circuit pattern and the copper on the hole.
2.8 Solder mask application
To protect the circuit in the following soldering step, we need a protective cover, or called solder mask, making only the solder pad exposed. To form a solder mask, we apply LPI (liquid photoimageble) film on both side of board.
2.9 Surface treatment
Process HASL (hot air solder leveling) or ENIG (electroless nickel immersion gold) to help ensuring the soldering quality of solder pad and to prevent oxidation.
2.10 Legend printing
Print legend on both side of board if needed.
2.11 Final test and packaging
Do a sequence of test and then pack the board.
That’s all for this post. If you want to know more about PCB or you have any question considering PCB, just contact us!