After importing the design data, the PCB design engineer will start the PCB layout design. The quality of layout often determines the success or failure of veneer. What are the layout problems we encountered in those years? Have you laid out the layout and found that there is no room for punching holes? The extra filter capacitor is placed around BGA, and it crosses when dividing the power supply. So painful?
It’s always hard to connect, there will always be cross, and the layout has to be adjusted again.
First, rapid modularization
Modular PCB layout is a common method for high-speed PCB layout. According to the schematic diagram, the small functional modules are laid out before the overall layout in the board.
The determined modules can be given priority, such as DDR, power module, etc., or the modules on other boards can be reused.
Try to make the module into a regular shape, such as a square or a rectangle (which is beneficial to layout, later adjustment, and even the adjustment of revision design).
Consider the module as a whole and sort out its input and output.
Have an overall grasp of the module size, and make full use of the space between modules.
Distinguish between primary and secondary, and consider in advance the places that need special treatment.
Second, the zoning layout
Third, the overall pre-layout
Point: We need to have an overall grasp of veneer and find a direction.
The overall layout of PCB can be designed without the limitation of board and frame size, and DRC can be ignored. After the modules are finished, you should have a general understanding of each module. In the process of pre-layout adjustment, you should know which one belongs to the power supply, which one is DDR and which one is interface without looking at the schematic diagram.
Fourth, modular layout
1. power supply
Whether the power supply is stable and reliable is one of the key factors for successful product design.
Firstly, the power flow direction of the whole board should be clarified, and the power input socket should usually be set in the corner of the board.
Next, the pre-layout of each switching power supply conversion module is carried out.
Need to sort out:
Input, output, ground, sampling or feedback.
Pre-distribution of switching power supply
According to datasheet recommendation or schematic diagram,
Then compress the space according to the specific situation.
Fanout plans the wiring channel in advance
BGA filter capacitor placement:
Place them from inside to outside.
Swing the cross channel first, and then swing other PLL power supplies.
Large capacitors are evenly placed around or on the power supply channel.
The extra capacitor is placed around the BGA.
Fifth, layout optimization
After clarifying the direction, we began to optimize and adjust.
On the veneer with plenty of space, we often make the modules well, and usually put them in the frame. However, when making high-density boards, it is found that there is not enough space for the finished modules, and there are always conflicts in some places, so it has to be readjusted, which sometimes repeats a lot of useless work. When optimizing the module, we must first evaluate whether it can fit into the predetermined area.
Principle of optimizing module layout: estimate the space and allocate it reasonably!