PCB Tech - Fourteen common process defects in PCB design

1. The overlap of PCB 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 multi-layer 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, resulting in scrap

Second, the abuse of the graphics layer

1. Some useless connections were made on some graphics layers. It was originally a four-layer board but with more than five layers of circuits 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 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 PCB component surface design on Bottom layer and soldering surface design on Top, causing inconvenience.

Third, the 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, which makes screen printing difficult, and too large will make the characters overlap and make it difficult to distinguish.

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 such as drilling should be specially marked.

5. Drawing 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 filler block The area will be covered by solder resist, making it difficult to solder the device.

6. The electrical ground layer is also a flower pad and a connection) Because it is designed as a power supply of the flower pad method, the ground layer is opposite to the image on the actual printed board, and all the connections are isolated lines. This is the designer It should be very clear. 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 board may not be easy to be soldered with components installed.

For example, a four-layer board is designed with four layers of TOP mid1 and mid2bottom, 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 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, PCB surface mount device pad is too short This is for the continuity test. For a surface mount device that is too dense, the distance between the two pins is quite small, and the pad is also quite thin. Install test pins. The position must be staggered up and down (left and right). For example, if the PCB pad design is too short, although it will not affect the device installation, it will cause the test pins to be staggered.

10. The spacing of the large-area grid is too small. The edge between the same line of the large-area grid is too small (less than 0.3mm). In the PCB printed board manufacturing process, the image transfer process is likely to produce a lot after the image is displayed. Broken film attached to the board, causing disconnection.

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 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 determine which contour line shall prevail.

13. Uneven graphic design. Uneven plating is caused when pattern plating is performed, which affects quality

14. 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 costs.