The following is a summary of the common bad phenomena in PCB design, and we will study and discuss with you.
1. PCB lack of process side or unreasonable process side design, resulting in the equipment can not be mounted. As shown in Figure 1.1.
2. PCB lack of positioning holes, positioning hole position is not correct, the equipment can not be accurate and firm positioning. As shown in Figure 1.2.
3. The screw hole is metallized and the pad design is unreasonable.
Screw hole is used to fix PCB with screw. In order to prevent hole plugging after wave crest welding, copper foil is not allowed to cover the inner wall of screw hole, and the screw hole pad on wave crest surface needs to be designed as “meter” shape or plum blossom shape (if the carrier is used during wave crest welding, the above problems may not exist). As shown in figures 1.4A and 1.4b.
4. PCB pad size design error.
The common problems of pad size are wrong pad size, too large or too small pad spacing, asymmetric pad, unreasonable design of compatible pad, etc., which are prone to false welding, displacement, Monument and other adverse phenomena. As shown in figures 1.5A, 1.5b and 1.5C.
5. There is a via on the pad or the pad is too close to the via.
When soldering, the solder melts and flows to the bottom of PCB, resulting in less solder defects. As shown in figures 1.6A and 1.6B.
6. The lack of mark points and the nonstandard design of mark points make it difficult to identify the machine. As shown in figures 1.3A, 1.3b and 1.3c.
7. The test point is too small, the test point is placed under the component or too close to the component. As shown in Figure 1.7.
8. The screen printing or solder resist is on the pad and test point, the tag number or polarity mark is missing, the tag number is reversed, and the character is too large or too small. As shown in figures 1.8A, 1.8b and 1.8c.
9. The distance between components is not standardized, and the maintainability is poor.
There must be enough distance between the patches. Generally, the minimum distance between the reflow soldering patches is 0.5mm, the minimum distance between the wave soldering patches is 0.8mm, and the distance between the high component and the rear patches should be larger. There is no chip within 3mm around BGA and other devices. As shown in Figure 1.9.
10. IC pad design is not standard.
QFP pad shape and the distance between pads are inconsistent, the design of interconnection short circuit between pads, the irregular shape of BGA pad and so on. As shown in figures 1.10a and 1.10b.