PCB design issues: PCB board prototype manufacturing plant
The following is a summary of the common undesirable phenomena in PCB design.
1.1 The PCB design lacks the process edge or the process edge design is unreasonable, resulting in the device not being able to be mounted.
1.2 The PC design lacks a positioning hole, the positioning hole position is incorrect, and the device cannot be accurately and firmly positioned.
1.3 The Mark point is missing, and the Mark point design is not standardized, which makes the machine identification difficult.
1.4 The screw holes are metallized and the pad design is unreasonable.
The screw holes are used to fix the PCB board with screws. In order to prevent plugging after wave soldering, the inner wall of the screw hole is not allowed to be covered with copper foil. The screw hole pad on the crest surface needs to be designed as "m" or plum (if the carrier is used during wave soldering, it may not exist). The above questions).
1.5 PCB pad size design error.
Common pad size problems include pad size error, excessive or too small pad pitch, asymmetrical pads, and unreasonable pad design. Solder joints, shifts, tombstones, etc. are prone to soldering. phenomenon.
1.6 There are vias on the pads or the pads are too close to the vias.
When soldering, the solder melts and flows to the bottom surface of the PCB, resulting in less tin defects in the solder joints.
1.7 The test point is too small and the test point is placed under the component or too close to the component.
1.8 Silk screen or solder mask on the pad, test point, the bit number or polarity mark is missing, the bit number is reversed, the character is too large or too small.
1.9 The distance between PCB components is not standardized and the maintainability is poor.
Sufficient distance must be ensured between the chip parts. Generally, the distance between the reflow soldered chip parts is required to be at least 0.5 mm, and the distance between the wave soldering chip parts is 0.8 mm, between the tall device and the rear patch. The distance should be bigger. SMD parts are not allowed within 3mm around BGA and other devices.
1.10 IC pad PCB design is not standardized.
The QFP pad shape and the distance between the pads are inconsistent, the interconnection between the pads is short-circuited, and the shape of the BGA pad is irregular.
1.11 PCB design is unreasonable.
Component interference after PCB assembly, V-Cut increase leads to deformation, and yin and yang panels cause poor soldering of heavy components.
1.12 ICs and connectors using wave soldering processes lack lead pads, resulting in short circuits after soldering.
1.13 The arrangement of components does not meet the corresponding process requirements.
When using the reflow soldering process, the layout of the components should be consistent with the direction in which the PCB enters the reflow oven. When using the wave soldering process, the wave soldering shadow effect should be considered. The main reasons for the poor PCB design are as follows: (1) PCB designers are not familiar with SMT process, equipment and manufacturable PCB design; (2) enterprises lack corresponding design specifications; (3) product design There is no process personnel involved in the process, lack of DFM review; (4) management and institutional issues.
In order to effectively solve this problem, it is necessary to carry out PCB optimization design.
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