A planned life will make people feel at ease; naturally, a planned PCB design is more convincing, and layout engineers can also avoid detours
The number of layers of the PCB board is generally not determined in advance, and the engineer will give a plan based on the overall board situation. The total number of layers is composed of the number of signal layers plus the number of power ground layers.
First look at the main points of the number of layers planning
1. Planning of the number of signal layers;
2. Planning of power supply and number of stratums.
Signal layer planning method
To plan the number of signal layers, it is mainly to calculate the wiring channels of each main part.
1. Evaluate the main IC part's outlet channel first. For example, for design projects with BGA devices, consider the depth of the BGA and the PIN spacing of the BGA, and plan the number of wire layers. Generally, the pad spacing of 1.0mm and the spacing of 1.0mm or more are generally Two wires can pass between vias, and only one wire can pass between ordinary BGA vias with a pad pitch of 0.8mm and below. For example, if there is a connector, the depth of the connector needs to be considered, and the number of wires passing between its 2 pins needs to be considered to evaluate the number of wire layers.
2. Evaluate the high-speed signal wiring channels on the board. In general PCB design, there are strict requirements for high-speed signal line width and line spacing, and there are many restrictions. Cross-segmentation, STUB line length, line spacing, etc. should be considered, and the high speed should be calculated. The number of channels required for the signal area and the number of wiring layers required.
3. Evaluate the routing channels in the bottleneck area. After the basic layout is handled, the narrower bottleneck area needs to be paid attention to. Comprehensive consideration of differential lines, sensitive signal lines, special signal topologies, etc., to specifically calculate how many lines can go out of the bottleneck area, and how many layers can pass all the required lines through this area.
Planning of power supply and number of layers
The number of power layers is mainly determined by the number of power types, distribution, current-carrying capacity, performance indicators of the single board, and the cost of the single board. The evaluation of the number of power plane layers generally considers that power supplies are not interlaced, and important signals of adjacent layers are not divided across.
When setting the number of ground layers, you need to pay attention to the following points: the second layer corresponding to the main device surface should have a relatively complete ground plane; important signals such as high-speed, high-frequency, and clock should refer to the ground plane; the main power supply and the ground plane are tightly coupled , Reduce the power plane impedance and so on.
Considering the above two points comprehensively, there will be basically no line failure. Some people say that PCB design is like a process of building a high-rise building. The wiring layer plan is the design drawing. After the plan is completed, the wiring will be natural. It can be a matter of course.
A life without a plan is called a puzzle, a life with a plan is called a blueprint; a life without a goal is called a wandering, and a life with a goal is called sailing!
Shenzhen Kate Technology Co., Ltd. , https://www.katevape.com