Common Problems in PCB Circuit Design
1. Overlap of pads
1) The overlap of the pads (except the surface mount pads) means the overlap of the holes. During the drilling process, the drill bit will be broken due to multiple drilling in one place, resulting in damage to the holes.
2) Two holes in the multilayer board overlap. For example, one hole is an isolation plate, and the other hole is a connection plate (flower pad), so that the film will appear as an isolation plate after drawing, which will cause scrap.
2. Misuse of the 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, which caused misunderstandings.
2) Save trouble during design. Take the Protel software as an example to draw the lines on each layer with the Board layer, and use the Board layer to mark the line. In this way, when the light drawing data is performed, the Board layer is not selected, and the board layer is not selected. If the connection is disconnected, the circuit will be broken, or it will be short-circuited due to the selection of the marking line of the Board layer, so the integrity and clarity of the graphics layer should be kept in the design.
3) Violation of conventional design, such as component surface design on the Bottom layer and welding surface design on the Top, causing inconvenience.
3. Random placement of characters
1) The character cover pad SMD soldering piece brings inconvenience to the continuity test of the printed board and the soldering of the components.
2) If the character design is too small, it will be difficult for screen printing. If it is too large, the characters will overlap each other and be difficult to distinguish.
4. Setting of single-sided pad aperture
1) Generally, single-sided pads are not drilled. If the drilling needs to be marked, the hole diameter should be designed to be zero. If the value is designed, then when the drilling data is generated, the coordinates of the hole will appear at this position, and there will be a problem.
2) Single-sided pads such as drilling should be specially marked.
5. Draw pads with filler blocks
Drawing pads with filler blocks can pass the DRC inspection when designing the circuit, but it is not good for processing. Therefore, the solder mask data cannot be directly generated by the similar pads. When the solder resist is applied, the area of the filler block will be covered by the solder resist, resulting in It is difficult to solder the device.
6. The electrical ground layer is also a flower pad and a connection
Because the power supply is designed as a pattern pad, the ground layer is opposite to the image on the actual printed board. All the connections are isolated lines. The designer should be very clear about this. By the way, you should be careful when drawing isolation lines for several sets of power supplies or grounds, not to leave gaps, short-circuit the two sets of power supplies, and block the connection area (to separate a set of power supplies).
7. The processing level is not clearly defined
1) The single-sided board is designed on the TOP layer. If the front and back are not specified, the board may not be easy to be soldered with components installed.
2) For example, a four-layer board is designed with four layers of TOP mid1 and mid2 bottom, but it is not placed in this order during processing, which requires explanation.
8. There are too many filler blocks in the design or the filler blocks are filled with very thin lines
1) The gerber data is lost, and the gerber data is incomplete.
2) Because the filling block is drawn with lines one by one when processing the light drawing data, the amount of light drawing data generated is quite large, which increases the difficulty of data processing.
9. The pad of the surface mount device is too short
This is for continuity testing. For surface mount devices that are too dense, the spacing between the two pins is quite small, and the pads are also quite thin. To install the test pins, they must be staggered up and down (left and right), such as pads. The design is too short, although it will not affect the device installation, but it will make the test pin staggered.
10. The spacing of large-area grids is too small
The edges between the same lines that make up the large-area grid are too small (less than 0.3mm). In the printed board manufacturing process, the image transfer process is likely to cause a lot of broken films to adhere to the board after the image is developed, causing wire breakage.
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 or more, because when milling the shape, if it is milled onto the copper foil, it will easily cause the copper foil to warp and cause the solder resist to fall off.
12. The design of the outline frame is not clear
Some customers have designed contour lines in Keep layer, Board layer, Top over layer, etc. and these contour lines do not overlap, which makes it difficult for PCB manufacturers to judge which contour line shall prevail.
13. Uneven graphic design
In the process of pattern plating, the plating layer is not uniform, which affects the quality.
14. When the copper area is too large, grid lines should be used to avoid blistering during SMT
Main items to be checked after the design is completed:
The following inspections include all aspects related to the design cycle, and some additional items should be added for special applications.
1) Has the circuit been analyzed? Is the circuit divided into basic units to smooth the signal?
2) Does the circuit allow short or isolated key leads?
3) Where must be shielded, are they effectively shielded?
4) Have you made full use of the basic grid graphics?
5) Is the size of the printed board the best size?
6) Do you use the selected wire width and spacing as much as possible?
7) Is the preferred land size and hole size used?
8) Are the photographic plates and sketches appropriate?
9) Is the use of jumper wires the least? Do jumper wires pass through components and accessories?
10) Are the letters visible after assembly? Are their size and model correct?
11) In order to prevent blistering, is there a window on the large area of copper foil?
12) Are there tool positioning holes?