What Is The PCB Design Layout Idea

Layout is based on comprehensive consideration of signal quality, EMC, thermal design, DFM, DFT, structure, safety and other requirements, place the device on the board reasonably. In high-speed PCB design, reasonable layout is the first step in PCB design success. Next, I will introduce the ideas and principles of PCB layout.

Layout ideas

In the PCB layout process, the first consideration is the size of the PCB. Secondly, we must consider the devices and areas that have structural positioning requirements, such as whether it is limited in height, limited in width, and punched and slotted areas. Then, according to the circuit signal and power flow direction, pre-layout each circuit module, and finally the layout of all components according to the design principles of each circuit module.

Basic principles of layout

1. Communicate with relevant personnel to meet the special requirements of structure, SI, DFM, DFT, EMC.

2. According to the structural element diagram, place connectors, mounting holes, indicator lights and other devices that need to be positioned, and give these devices non-removable attributes and dimension them.

3. According to the structural element diagram and the special requirements of some devices, set prohibited wiring area and prohibited layout area.

4. Comprehensively consider PCB performance and processing efficiency to select the process flow (priority is single-sided SMT; single-sided SMT + plugin; double-sided SMT; double-sided SMT + plugin), and layout according to different processing characteristics

5. Refer to the results of the pre-layout when arranging, according to the layout principle of 'big first' and 'difficult first'.

6. The layout should meet the following requirements as far as possible: the total wiring is as short as possible, the key signal line is the shortest; the high voltage, high current signal is completely separated from the weak signal of low voltage and small current signal; the analog signal is separated from the digital signal; high frequency signals is separated from low frequency signals; the spacing of high-frequency components should be sufficient. Under the premise of meeting the requirements of simulation and timing analysis, local adjustments are made.

7. As far as possible, the same circuit part adopts a symmetrical modular layout.

8. The recommended grid layout for layout is 50 mil, and for IC device layout, the recommended grid is 25 mil. When the layout density is high, for small surface mount devices, the grid setting is recommended to be no less than 5mil.

Layout principles of special components

1. Shorten the connection length between FM components as much as possible. Components that are susceptible to interference cannot be too close to each other, try to reduce their distribution parameters and electromagnetic interference from each other.

2. For devices and wires that may have a higher potential difference, the distance between them should be increased to prevent accidental short circuits. Devices with strong electricity should be placed in places where the human body is not easily accessible.

3. Components weighing more than 15g should be fixed with brackets and then welded. For large and heavy components with large heat generation, it is not appropriate to install them on the PCB. The heat dissipation should be considered on the casing of the whole machine. The thermal devices should be far away from the heating devices.

4. For the layout of adjustable components such as potentiometers, adjustable inductance coils, variable capacitors, and micro switches, the structural requirements of the whole machine should be considered, such as height limit, hole size, and center coordinates.

5. Reserve the positions occupied by PCB positioning holes and fixed brackets.

Check after layout

In PCB design, reasonable layout is the first step in the success of PCB design. Engineers need to strictly check the following after the layout is completed:

1. Whether PCB size marking and device layout is consistent with the structural drawings, and whether it meets the PCB manufacturing process requirements, such as minimum aperture and minimum line width.

2. Whether the components interfere with each other in two-dimensional and three-dimensional spaces, and whether they will interfere with the structural shell.

3. Whether all components have been placed.

4. Whether the components that need to be frequently plugged or replaced are easy to plug and replace.

5. Is there a proper distance between the thermal device and the heating element?

6. It is convenient to adjust the adjustable device and press the button.

7. Whether the air of location where the radiator is installed is clear.

8. Whether the signal flow is smooth and the interconnection is the shortest.

9. Whether the problem of line interference is considered.

10.Whether the plug and socket are inconsistent with the mechanical design.