Summary of Common Mistakes in PCB Design

Simply put, a PCB is a thin plate with integrated circuits and other electronic components. It will appear in almost every electronic device, and it is the basis of the entire electronic product, so it is particularly important.

This article summarizes some common design mistakes in PCB design for your reference.

1. Misplacement of characters.

①The SMD pad of the character cover pad brings inconvenience to the on-off test of the printed board and the welding of components.
②If the character design is too small, it will cause difficulty in screen printing. If it is too large, the characters will overlap and it is difficult to distinguish.

2. The abuse of graphics layer.

①Some useless connections were made on some graphics layers. It was originally a four-layer board but more than five layers of lines were designed, which caused misunderstandings.
②Save trouble when designing the diagram. Taking Protel software as an example, use the Board layer to draw the lines that exist in each layer, and use the Board layer to mark the lines. In this way, when performing light drawing data, because the Board layer is not selected, it is missing If the connection is broken, or it will be short-circuited due to the selection of the label line of the Board layer, so the design layer should be kept complete and clear.
③Violation of the conventional design, such as the design of the component surface on the Bottom layer and the design of the soldering surface on the Top layer, causing inconvenience.

3. Overlapping pads

①The overlapping of pads (except surface mount pads) means the overlapping of holes. During the drilling process, the drill bit will be broken due to multiple drilling in one place, resulting in damage to the hole.

②The two holes in the multi-layer board overlap. For example, one hole is an isolation plate, and the other hole is a connection plate (flower pad). After drawing the negative, it will appear as an isolation plate, resulting in scrap.

4. Setting of single-sided pad aperture.

①Single-sided pads are generally not drilled. If the drilled holes need to be marked, the aperture should be designed as zero. If the value is designed, then when the drilling data is generated, the coordinates of the hole appear at this position, and problems arise.
②Single-side pads such as drilling holes should be specially marked.

5. Draw pads with filler blocks.

Drawing pads with filler blocks can pass the DRC inspection during PCB design, but not for processing. Therefore, such pads cannot directly generate solder mask data. When solder resist is applied, the area of the filler block will be covered by solder resist. It makes it difficult to solder the device.

6. The electrical ground is 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 the connections are isolated lines, which the designer should be very clear about. By the way, care should be taken when drawing several groups of power supplies or isolation lines of several grounds, not to leave gaps, short-circuit the two groups of power supplies, or block the area of the connection (separating one group of power supplies).

7. The definition of processing level is not clear.

①The single-sided board is designed on the TOP layer. If there is no instruction to do it front and back, it may be difficult to solder the finished board with devices.
②For example, a four-layer board is designed with TOP mid1, mid2 bottom four layers, but it is not placed in this order during processing, which requires an explanation.

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

①The photoplotting data may be lost, and the photoplotting data is incomplete.
②Since the filling block is drawn one by one in the light drawing data processing, the amount of light drawing data generated is quite large, which increases the difficulty of data processing.

9. Surface mount device pads are too short.

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

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

The edge between the lines forming the large-area grid line is too small (less than 0.3mm). During the manufacturing process of the printed board, many broken films are likely to be attached to the board after the image transfer process is completed, resulting in broken lines.

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

The distance between the large-area copper foil and the outer frame should be at least 0.2mm, because it is easy to cause the copper foil to warp and cause the solder resist to fall off if it is milled on the copper foil when milling the shape.

12. The special-shaped hole is too short.

The length/width of the special-shaped hole should be ≥2:1, and the width should be >1.0mm, otherwise, the drilling machine will easily break the drill when processing the special-shaped hole, which will cause processing difficulties and increase costs.

13. Uneven graphic design.

In the process of graphic electroplating, the plating layer is uneven, which affects the quality.

14. The outline design is not clear.

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

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