PCB Tech - Introduce the precautions of the FPC copy board process

1. Stacking of pads:

1. The stacking of pads means the stacking of holes. During the drilling process, the drill bit will be broken due to repeated drilling in one place, causing damage to the hole.

2. In the FPC multilayer board, two holes are stacked. One hole should be an isolation disk and the other hole should be a connection disk. Otherwise, the film will appear as an isolation disk after drawing, which will be scrapped.

2. Unreasonable character placement:

1. The SMD soldering pad of the character cover pad brings great inconvenience to the soldering of the components and the on-off test of the printed circuit board.

2. The character design is too small, which makes the screen printing difficult, and the character design is too large, which makes it difficult to distinguish between the characters.

3. The spacing of the area grid is too small:

The edges between the same lines that make up a large area of grid lines are too small (less than 0.3mm). In the FPC printed board manufacturing process, after the image transfer process is completed, a lot of broken films are easily attached to the board, resulting in breakage. String.

Fourth, draw pads with filling blocks:

When designing FPC circuits, drawing pads with filler blocks can go through DRC introspection, but processing is not possible, because such pads cannot directly generate solder mask data. When solder resist is applied, the filler block area will be blocked. The flux is concealed, which makes the device soldering difficult.

5. Setting of single-sided pad aperture:

1. Ordinary single-sided pads do not need to be drilled. If they need to be drilled, they should be marked, and the hole diameter should be designed to be zero. If the value is designed, perhaps when drilling data occurs, this position will show the coordinates of the hole, and the problem will appear.

2. If a single-sided pad needs to be drilled, it should be marked out.

Sixth, the abuse of the graphics layer:

1. Useless connections are made on some graphic layers, that is, a four-layer board is designed with more than five layers of circuits, which will cause misinterpretation.

2. Save trouble during design. Take 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 the light drawing data is not selected, the board layer is missing, If the connection is broken, it may be short-circuited due to the selection of the marking line of the Board layer. Therefore, the design of the graphic layer should be intact and clear.

3. Violation of conventional design, such as the FPC component surface is designed on the Bottom layer and the welding surface is designed on the Top, causing unnecessary trouble.

Seven, the electrical ground layer is also a connection and a flower pad:

Because of the power supply designed as a flower pad method, the ground layer and the image on the actual printed board are opposite, and all the connections are isolated lines. The designer should be very clear about this. When drawing several sets of power or ground isolation lines, pay attention to not leaving gaps, short-circuiting the two sets of power supplies, and blocking the area where the connection is formed.