Electronic Design - Manual for avoiding process defects in PCB design

1. Overlap of pads

The following two points should be paid attention to the pads in PCB design

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 the film, resulting in scrap.

Second, the random placement of characters

There are two points for attention to character position control in PCB design:

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.

Three, single-sided pad aperture setting

There are two points for attention to the setting of single-sided pad aperture in PCB design:

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.

Fourth, the abuse of the graphics layer

There are three points for attention to the use of the graphics layer in PCB design:

1. Some useless connections were made on some graphics layers. The original four-layer board was designed with more than five layers of circuits, 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 the Bottom layer and soldering surface design on the Top, causing inconvenience.

Five, use filler blocks to draw pads

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

6. The electrical ground layer is both 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 actually printed board. All connections are isolated lines. The designer should be very clear. 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).

Seven, the processing level is not clearly defined

There are two points for attention to the definition of processing level in PCB design:

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

The following two points should be paid attention to in the design of the filler block in the PCB design:

1. The Gerber data is lost, and the Gerber data is incomplete.

2. Because the filling blocks are 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, it will make the test pin staggered.

10. The spacing of the large-area grid is too small. The edge between the large-area grid lines and the same line is too small (less than 0.3mm). During the manufacturing process of the printed board, the image conversion process is likely to produce a lot of fragments after the image is developed. The film adheres to the board, causing disconnection.

11. The distance between the large area of copper foil and the outer frame is too close

The distance between the large area of copper foil and the outer frame should be at least 0.2mm because when milling the shape, if it is milled to the copper foil, it is easy to cause the copper foil to warp and the solder to resist falling off caused by it.

12. The length and width of the special-shaped hole are too short. The length and 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 pattern design will cause uneven plating during pattern electroplating, which will affect quality.

14. The design of the outline frame is not clear

Some customers have designed contour lines in the 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.