PCB News - Analysis of common errors in PCB board design

1. The design of PCB pad size is wrong.

Common pad size problems include incorrect pad size, too large or too small pad spacing, asymmetric pads, unreasonable compatible pad design, etc., and defects such as false soldering, displacement, and tombstones are prone to occur during soldering. Phenomenon.

2. There are vias on the pad or the distance between the pad and the via is too close.

During soldering, the solder melts and flows to the bottom surface of the PCB board, resulting in fewer solder joints.

3. The IC pad design is not standardized.

The QFP pad shape and the distance between the pads are inconsistent, the interconnection short circuit design between the pads, and the BGA pad shape is irregular.

4. The distance between the components is not standardized, and the maintainability is poor.

Sufficient distance must be ensured between the patch parts. Generally, the minimum distance between the reflow soldering patch parts is 0.5mm, and the minimum distance between the wave soldering patch parts is 0.8mm. The distance between the tall device and the following patch The distance should be greater. SMD parts are not allowed within 3mm around BGA and other devices.

5. The screw hole is metalized and the pad design is unreasonable.

The screw holes are used to fix the PCB board with screws. In order to prevent the hole from being blocked after wave soldering, copper foil is not allowed on the inner wall of the screw hole, and the screw hole pad on the wave surface needs to be designed in a "m" shape or a plum blossom shape (if a carrier is used during wave soldering, it may not exist The above question).

6. The test point is too small, the test point is placed under the component or too close to the component.

7. The silk screen or solder mask is on the pads and test points, the bit number or polarity mark is missing, the bit number is reversed, and the characters are too large or too small, etc.

8. The PCB lacks the process side or the process side design is unreasonable, causing the equipment to fail to mount.

9. The PCB lacks positioning holes and the position of the positioning holes is incorrect. The equipment cannot be positioned accurately and firmly.

10. The lack of Mark points and the non-standard design of Mark points make machine identification difficult.

11. The PCB board design is unreasonable.

After PCB splicing, component interference, V-Cut increase leads to deformation, and yin-yang splicing leads to poor soldering of heavier components, etc.

12. ICs and Connectors using wave soldering process lack solder conductive pads, resulting in short circuits after soldering.

13. The arrangement of the components does not meet the corresponding process requirements.

When using the reflow soldering process, the arrangement direction of the components should be consistent with the direction that the PCB enters the reflow oven. When using the wave soldering process, the shadow effect of the wave soldering should be considered.

The main reasons for poor PCB design are as follows:

(1) Because designers are not familiar with SMT process, equipment and manufacturability design;

(2) There is no technical personnel involved in the product design process and lack of DFM review;

(3) Management and system issues.

(4) The enterprise lacks corresponding design specifications;

In order to effectively solve this problem, it is very necessary to optimize the design of PCB.

The above is an introduction to the analysis of common errors in PCB board design. Ipcb is also provided to PCB manufacturers and PCB manufacturing technology.