pcb circuit design

PCB circuit board is a substrate used to support and connect electronic components. It is made of insulating material and covered with copper foil on the surface and/or inside. Through the wires and electrical connections of copper foil, the PCB circuit board can realize functions such as signal transmission, power supply, and ground connection. So do you know how PCB circuits are designed?

General steps for designing PCB circuits:

1. Determine requirements: Clarify the functions, performance requirements and special needs of the circuit. Understand the input and output signals, voltage, current and other parameters required by the circuit.
2. Draw the schematic diagram: Use electronic design automation (EDA) tools, such as Eagle, Altium Designer, etc., to draw the schematic diagram of the circuit. A schematic diagram shows the connections between components in a circuit.
3. Select components: According to the functional requirements of the circuit, select appropriate components from various available components. Taking into account the dimensions, parameters, characteristics and availability of components.
4. Layout design: Place selected components in appropriate locations on the PCB to meet space constraints and circuit routing requirements. Consider factors such as signal integrity, heat dissipation, and electromagnetic interference.
5. Connection and wiring: Carry out wiring layout on the PCB according to the schematic diagram. Follow good routing rules, such as minimizing signal line lengths, reducing cross-coupling, etc. Ensure the stability and reliability of signal transmission.
6. Ground wire planning: Design appropriate ground wires to provide good grounding and return. Reduce ground return path resistance and noise.
7. Improve auxiliary circuits: add filters, protection circuits, clock circuits and other auxiliary circuits according to actual needs. Ensure circuit stability and reliability.
8. Power management: Consider the stability and efficiency of the power supply and design appropriate power distribution and filtering circuits.
9. Conduct simulation and verification: Use EDA tools to simulate the PCB layout to ensure the performance and reliability of the circuit. Make necessary modifications and improvements as needed.
10. Prepare production files: Generate Gerber files or manufacturing files in other formats required for production. These files contain the layer information and details of the PCB.
11. Manufacturing and Assembly: Submit PCB files to PCB manufacturer for production. After completion, the components are welded and assembled.
12. Testing and Verification: The manufactured PCB is fully tested and verified to ensure the circuit works as expected.

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General steps for designing PCB circuits:

1. Determine requirements: Clarify the functions, performance requirements and special needs of the circuit. Understand the input and output signals, voltage, current and other parameters required by the circuit.
2. Draw the schematic diagram: Use electronic design automation (EDA) tools, such as Eagle, Altium Designer, etc., to draw the schematic diagram of the circuit. A schematic diagram shows the connections between components in a circuit.
3. Select components: According to the functional requirements of the circuit, select appropriate components from various available components. Taking into account the dimensions, parameters, characteristics and availability of components.
4. Layout design: Place selected components in appropriate locations on the PCB to meet space constraints and circuit routing requirements. Consider factors such as signal integrity, heat dissipation, and electromagnetic interference.
5. Connection and wiring: Carry out wiring layout on the PCB according to the schematic diagram. Follow good routing rules, such as minimizing signal line lengths, reducing cross-coupling, etc. Ensure the stability and reliability of signal transmission.
6. Ground wire planning: Design appropriate ground wires to provide good grounding and return. Reduce ground return path resistance and noise.
7. Improve auxiliary circuits: add filters, protection circuits, clock circuits and other auxiliary circuits according to actual needs. Ensure circuit stability and reliability.
8. Power management: Consider the stability and efficiency of the power supply and design appropriate power distribution and filtering circuits.
9. Conduct simulation and verification: Use EDA tools to simulate the PCB layout to ensure the performance and reliability of the circuit. Make necessary modifications and improvements as needed.
10. Prepare production files: Generate Gerber files or manufacturing files in other formats required for production. These files contain the layer information and details of the PCB.
11. Manufacturing and Assembly: Submit PCB files to PCB manufacturer for production. After completion, the components are welded and assembled.
12. Testing and Verification: The manufactured PCB is fully tested and verified to ensure the circuit works as expected.

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Common problems in PCB circuit design

PCB circuit designers need to implement the required functions in PCB circuit design based on the circuit schematic diagram. PCB circuit design is a very complex and highly technical task. Usually beginners in PCB circuit design will encounter many problems. (This article lists “Common Problems in PCB Circuit Design”). I also hope that PCB circuit designers can It requires continuous learning and experience accumulation to continuously improve circuit design time after time to achieve excellent circuit performance and heat dissipation performance, which can effectively save production costs.

1. Overlap of pads

(1). The overlap of soldering pads (except for surface-mounted soldering pads) means the overlap of holes. During the drilling process, the drill bit will be broken due to drilling multiple holes in one place, resulting in damage to the holes.
(2). Two holes in a multilayer board overlap. For example, one hole is an isolation plate and the other hole is a connection pad (flower pad). This will appear as an isolation plate after drawing the negative, resulting in scrapping.

2. Abuse of graphics layer

(1). Some useless connections were made on some graphics layers. It was originally a four-layer board but more than five layers of circuits were designed, causing misunderstanding.
(2). It saves trouble when designing. Taking the Protel software as an example, use the Board layer to draw the lines that exist in each layer, and use the Board layer to draw the label lines. In this way, when performing light drawing data, because the Board layer is not selected, the lines will be missed. The circuit may be broken due to the connection, or the circuit may be short-circuited due to selecting the label line of the Board layer. Therefore, the graphics layer should be kept intact and clear during design.

Violate the conventional design, such as the component surface is designed on the Bottom layer and the welding surface is designed on the Top, causing inconvenience.

3.Indiscriminate placement of characters

(1). The character cover pad SMD solder piece brings inconvenience to the continuity test of the printed board and the welding of components.
(2). If the characters are designed too small, it will be difficult to screen print. If they are too large, the characters will overlap each other and be difficult to distinguish.

4. Setting the single-sided pad aperture

(1). Single-sided pads are generally not drilled. If drilling needs to be marked, the hole diameter should be designed to be zero. If the value is designed, when the drilling data is generated, the coordinates of the hole will appear at this position, and problems will occur.
(2). If the single-sided pad is drilled, special markings should be made.

5. Use filler blocks to draw pads

Drawing pads with filler blocks can pass DRC inspection when designing circuits, but it is not possible for processing. Therefore, such pads cannot directly generate solder mask data. When solder resist is applied, the filler block area will be covered by solder resist, resulting in Device soldering is difficult.

6. The electrical ground layer is both a flower pad and a connection.

Because the power supply is designed as a flower pad, the ground layer is opposite to the image on the actual printed board, and all connections are isolated lines. The designer should be very aware of this. By the way, when drawing isolation lines for several sets of power supplies or grounds, you should be careful not to leave gaps to short-circuit the two sets of power supplies, nor to block the connected area (so that one set of power supplies is separated).

7. The processing level is not clearly defined

(1). The single-board design is on the TOP layer. If you do it in the forward and reverse directions without instructions, the manufactured board may be difficult to weld with components installed on it.
(2). For example, a four-layer board is designed with four layers of TOP mid1, mid2 and bottom, but they are not placed in this order during processing. This requires explanation.

8. There are too many filling blocks in the design or the filling blocks are filled with extremely thin lines.

(1). The light painting data is lost and the light painting data is incomplete.
(2). Because the filling blocks are drawn one by one during light drawing data processing, the amount of light drawing data generated is quite large, which increases the difficulty of data processing.

9. The surface mount device pad is too short

This is for continuity testing. For surface-mounted devices that are too dense, the distance between the two pins is quite small, and the pads are also quite thin. When installing the test pins, they must be staggered up and down (left and right), such as the pads. If the design is too short, although it does not affect the installation of the device, it will make the test pins misaligned.

10. The spacing of large-area grids is too small

The edges between the same lines that make up a large-area grid are too small (less than 0.3mm). In the printing board manufacturing process, after the image transfer process is completed, a lot of film fragments are likely to adhere to the board, causing breakage.

11. The distance between the large area of copper foil and the outer frame is too close

The distance between large-area copper foil and the outer frame should be at least 0.2mm, because milling onto the copper foil during contour milling can easily cause the copper foil to warp and the solder resist to fall off.

12. Unclear appearance and frame design

Some customers have designed outline lines for Keep layer, Board layer, Top over layer, etc., and these outline lines do not overlap, making it difficult for PCB manufacturers to determine which outline line should be used.

13. Uneven graphic design

When performing pattern plating, the plating layer is uneven and affects the quality.

14. When the copper laying area is too large, use grid lines to avoid blistering during SMT.

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