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Common problems in designing circuit board
Add time:2020/11/6 10:20:22 From: Hits:3417

General circuit board is based on the circuit schematic diagram to design, so as to achieve the required functions. Printed circuit board needs to consider the layout and connection of each part, and pay more attention to the optimization of components. Optimize wire and hole, electromagnetic protection, heat dissipation and other factors. Generally, a good circuit design diagram is from saving production cost to achieve good circuit performance and heat dissipation performance. Therefore, we should pay special attention to the following points:

1、 Draw pad with filler block

The pad drawn with filler block can pass the DRC inspection when designing the circuit, but it is not suitable for processing. Therefore, the solder mask data cannot be generated directly. When the solder mask is applied, the area of the filler block will be covered by the ink solder resist, resulting in the difficulty of component welding and assembly.

2、 Character shuffling

1. It is inconvenient for the on-off test of PCB and the welding of components.

2. The character design is too small, resulting in screen printing difficulties, too often make characters overlap each other, difficult to distinguish.

3、 The distance between large area copper foil and outer frame is too close

The distance between the large area copper foil and the outer frame should be at least 0.2mm. If the copper foil is milled to the copper foil during milling, it is easy to cause the copper foil warping and the solder resist falling off.

4、 The spacing of large area grids is too small

The edge between the same lines of large area grid lines is too small (less than 0.3 mm). In the process of PCB manufacturing, many film fragments are easy to be attached to the board after the development of graphic transfer process, resulting in wire breakage.

5、 Pad overlap (drill overlap)

1. The overlap of pad (except for the pad attached on the surface) means the overlap of holes. In the drilling process, drill bit will be broken due to multiple drilling at one place, resulting in hole damage.

2. Two holes overlap in a multilayer board. For example, one hole is an isolation plate, and the other is a connection pad (solder pad). In this way, the negative is shown as an isolation plate, resulting in scrapping.

6、 Abuse of PCB graphic layer

1. Some useless wires have been made on some graphic layers, but more than five layers of circuits have been designed for the original four layer boards, which causes misunderstanding.

2. Taking Protel software as an example, the board layer is used to draw the lines of each layer, and the board layer is used to draw the marking line. In this way, when photo drawing data, because the board layer is not selected, the connection line is missed and the circuit is short circuit, so the graphic layer is complete and clear during the design.

3. It violates the conventional design, such as the component surface is designed in the bottom layer, and the welding surface is designed at the top, causing inconvenience.

7、 SMD pad too short

This is for on-off test. For too dense surface mount devices, the distance between the two legs is quite small, and the pad is also very thin. To install the test pin, the upper and lower (left and right) staggered position must be used. If the pad design is too short, although the device installation is not affected, the test pin will not be disconnected.

8、 Uneven graphic design

In the process of graphic electroplating, the coating is not uniform and the plate area is large, which will cause the plate warping. Affect the quality.

9、 Setting of single side pad aperture

1. Generally, single-sided pad is not drilled. If the drilling needs to be marked, the hole diameter should be designed as zero. If the numerical value is designed, the coordinates of the hole will appear at this position when the drilling data is generated, which will cause problems.

2. Single side pad such as drilling shall be specially marked.

10、 The electric layer is both a flower pad and a connecting line

Because of the power supply designed in the way of flower pad, the stratum is opposite to the image on the actual printed circuit board, and all the connecting lines are isolation wires. The designer should be very clear about this. By the way, when drawing the isolation lines of several groups of power supply or several kinds of land, care should be taken not to leave a gap to short circuit the two sets of power supply, or to block the area of the connection (so that a group of power supplies are separated).

11、 The design of outline frame is not clear

Some customers have designed contour lines in the keepoutlayer, board layer and top over layer, and these contour lines do not coincide, which makes it difficult for the PCB manufacturer to determine which contour line to take.

12、 The definition of processing level is not clear

1. The single panel is designed in the top layer. If it is not specified, the board may be made with devices and not easy to weld.

2. For example, the top, mid1, mid2 and bottom four layers are used in the design of a four layer board, but the processing is not placed in this order, which requires explanation.

8、 There are too many fillers in the design or the fillers are filled with very fine lines

1. The photo data is lost and the photo data is incomplete.

2. Because filling blocks are drawn one by one in photo data processing, the amount of photo data generated is quite large, which increases the difficulty of data processing.

13、 Abnormal element hole too short

The length / width of the special-shaped hole should be more than 2:1 and the width should be more than 1.0 mm. Otherwise, the drilling machine is easy to break when processing the special-shaped hole, resulting in processing difficulties and increasing costs