PCB News - Talking about the PCB board design process

In the PCB design, in fact, before the formal wiring, it has to go through a very long step. The following is the main design process:

System specifications
First, we must first plan out the various system specifications of the electronic equipment. Including system functions, cost constraints, size, operating conditions, and so on.
System function block diagram
Next, a functional block diagram of the system must be produced. The relationship between the squares must also be marked.
Divide the system into several PCBs
If the system is divided into several PCBs, not only the size can be reduced, but also the system has the ability to upgrade and exchange parts. The system function block diagram provides the basis for our division. For example, a computer can be divided into a motherboard, a graphics card, a sound card, a floppy disk drive, a power supply, and so on.
Decide on the packaging method and the size of each PCB
When the technology and the number of circuits used in each PCB are determined, the next step is to determine the size of the board. If the design is too large, then the packaging technology must be changed or re-divided. When choosing a technology, the quality and speed of the circuit diagram should also be taken into consideration.
Draw a schematic diagram of all PCB circuits
The outline drawing should show the details of the interconnection between the parts. All PCBs in the system must be traced. Nowadays, CAD (Computer Aided Design) methods are mostly used.
Simulation operation of preliminary design
In order to ensure that the designed circuit diagram can work normally, this must be simulated once with computer software. This type of software can read design drawings and display the operation of the circuit in many ways. This is much more efficient than actually making a sample PCB and then manually measuring it.
Place the part on the PCB
The way the parts are placed is determined based on how they are connected. They must be connected to the path in the most efficient way. The so-called efficient wiring is that the shorter the wire and the fewer the number of layers through (this also reduces the number of vias), the better, but we will mention this issue again when we are actually wiring. The following is how the bus is routed on the PCB. In order for each part to have perfect wiring, the placement position is very important.
Test wiring possibilities and correct operation at high speed
Part of the current computer software can check whether the positions of the various parts can be connected correctly, or check whether it can operate correctly under high-speed operation. This step is called arranging parts, but we will not study them too deeply. If there is a problem with the circuit design, you can rearrange the position of the parts before exporting the circuit on the spot.
Export circuit on PCB
The connections in the overview map will now be made on the spot as wiring. This step is usually fully automatic, but in general, some parts need to be changed manually. Below is the wire template of the 2-layer board. The red and blue lines respectively represent the part layer and solder layer of the PCB. The white text and squares represent the markings on the screen printing surface. The red dots and circles represent drill holes and pilot holes. On the far right, we can see that there are gold fingers on the soldering surface of the PCB. The final composition of this PCB is usually called an artwork.
Each design must comply with a set of regulations, such as the minimum reserved gap between the lines, the minimum line width, and other similar practical restrictions. These regulations vary according to factors such as the speed of the circuit, the strength of the transmitted signal, the sensitivity of the circuit to power consumption and noise, and the quality of materials and manufacturing equipment. If the current intensity increases, the thickness of the wire must also increase. In order to reduce the cost of PCB, while reducing the number of layers, we must also pay attention to whether these regulations are still in compliance. If a structure with more than 2 layers is required, then the power layer and ground layer are usually used to prevent the transmission signal on the signal layer from being affected, and it can be used as a protective cover for the signal layer.
Circuit test after wire
In order to confirm that the circuit can function normally after the wire, it must pass the final test. This test can also check for incorrect connections, and all connections follow the outline.
Create production file
Because there are many CAD tools for PCB design, manufacturers must have files that meet the standards before they can manufacture boards. There are several standard specifications, but the most commonly used is Gerber files specifications. A set of Gerber files includes the plan view of each signal, power and ground layer, the plan view of the solder mask layer and the screen printing surface, and designated files such as drilling and picking and placing.
Electromagnetic compatibility
Electronic devices that are not designed according to EMC (Electromagnetic Compatibility) specifications are likely to emit electromagnetic energy and interfere with nearby electrical appliances. EMC imposes maximum limits on electromagnetic interference (EMI), electromagnetic field (EMF) and radio frequency interference (RFI). This requirement can ensure the normal operation of the appliance and other nearby appliances. EMC has strict limits on the energy scattered or conducted to another device for one device, and the susceptibility of external EMF, EMI, RFI, etc. should be reduced when designing. In other words, the purpose of this regulation is to prevent electromagnetic energy from entering or emitting from the device. This is actually a difficult problem to solve. Generally, power and ground layers are used, or the PCB is placed in a metal box to solve these problems. The power and ground layers can prevent the signal layer from being disturbed, and the effect of the metal box is similar. We will not go too far into these issues.
The maximum speed of the circuit depends on how to comply with EMC regulations. Internal EMI, such as current loss between conductors, will increase as the frequency increases. If the current gap between the two is too large, then the distance between the two must be lengthened. This also tells us how to avoid high voltage and minimize the current consumption of the circuit. The delay rate of the wiring is also very important, so the shorter the length, the better. Therefore, a small PCB board with good wiring is more suitable for high-speed operation than a large PCB.

The above is an introduction to the PCB board design process. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.