PCB Tech - Summary of common mistakes in PCB design

Summary of common mistakes in PCB design
1. Random placement of characters

1. The SMD soldering pad of the character cover pad brings inconvenience to the continuity test of the printed board and the soldering of the components.

2. The character design is too small, resulting in difficulties in screen printing, and too large will cause the characters to overlap each other and be difficult to distinguish.

Second, the abuse of the graphics layer

1. Some useless connections were made on some graphics layers. The original four-layer board was designed with more than five layers of wiring, 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 lines. In this way, when performing light drawing data, because the Board layer is not selected, it is omitted. The connection is broken, or it may be short-circuited due to the selection of the marking line of the Board layer, so the integrity and clarity of the graphics layer is maintained during design.

3. Violation of conventional design, such as component surface design in Bottom layer and welding surface design in Top, causing inconvenience.

Third, the overlap of the 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 disk and the other hole is a connection pad (flower pad). In this way, the film will appear as an isolation disk after drawing, resulting in scrap.

Fourth, the setting of the single-sided pad aperture

1. Single-sided pads are generally not drilled. If the drilling needs to be marked, the hole diameter should be designed to be zero. If the numerical value is designed, then when the drilling data is generated, the coordinates of the hole appear at this position, and there is a problem.

2. Single-sided pads should be specially marked if they are drilled.

Five, use filler blocks to draw pads

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

Sixth, the electrical ground layer is also 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. The designer should be very clear about this. By the way, when drawing several sets of power supplies or ground isolation lines, you should be careful not to leave gaps, short-circuit the two sets of power supplies, and block the connection area (to separate a set of power supplies).

Seven, 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 manufactured 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 PCB 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 one by one with lines when processing the light drawing data, the amount of light drawing data generated is quite large, which increases the difficulty of data processing.

Nine, the surface mount device pad 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 does 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 lines are too small (less than 0.3mm). During the manufacturing process of the printed board, after the image transfer process is completed, it is easy to produce a lot of broken films attached to the board, causing the line to break.

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 of the copper foil, it is easy to cause the copper foil to warp and the solder resist falling off caused by it.

12. The 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 drilling when processing the special-shaped hole, which will cause processing difficulties and increase the cost.

13. Uneven graphic design

When pattern plating is performed, the plating layer is uneven, which affects the quality.

14. The design of the outline frame is not clear

Some customers have designed contour lines for Keep layer, Board layer, Top over layer, etc. and these contour lines do not overlap, which makes it difficult for PCB manufacturers to determine which contour line shall prevail.