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Several common problems in PCB design

Article source:Zhengjiaxiang Technology / Author:Zhengjiaxiang Technology / Publication time:2021-10-29

PCB design is based on the circuit schematic diagram to realize the functions required by the circuit designer. Printed circuit board design mainly refers to layout design, which needs to consider the layout of external connections.

Optimized layout of internal electronic components. Optimized layout of metal wiring and through holes. Electromagnetic protection. Heat dissipation and other factors. Excellent layout design can save production costs,

To achieve good circuit performance and heat dissipation performance, we should pay attention to the following problems in the PCB design process:

 

    1、 Overlap of pads

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

2. Two holes in the multilayer board overlap. For example, one hole position is the isolation disk and the other hole position is the connecting disk (flower pad). In this way, the negative is shown as the isolation disk after drawing, resulting in scrapping.


   2、 Abuse of graphics layer

1. Some useless connections were made on some graphic layers. Originally, it was a four-layer board, but more than five layers of circuits were designed, causing misunderstanding.

2. The drawing is easy to design. Take Protel software as an example, draw the lines on each layer with the board layer and draw the marking lines with the board layer. In this way, when the photo drawing data is carried out, because the board layer is not selected, the connection will be missed and the circuit will be broken, or the marking line of the board layer will be short circuited. Therefore, the integrity and clarity of the graphic layer will be maintained in the design.

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


   3、 Random placement of characters

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

2. The character design is too small, resulting in the difficulty of screen printing. It is too large to make the characters overlap and difficult to distinguish.


    4、 Setting of single side pad aperture

1. Generally, single-sided pad is not drilled. If the drilling needs to be marked, its hole diameter shall be designed as zero. If a numerical value is designed, the coordinates of the hole will appear at this position when generating borehole data.

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


    5、 Drawing pads with filler blocks

Drawing a pad with a filler block can pass the DRC inspection when designing the circuit, but not for processing. Therefore, this kind of pad can not directly generate solder resist data. When applying solder resist, the filler block area will be covered by solder resist, resulting in difficulty in device welding.

 

    6、 The electroformation is both a flower pad and a wire

Because the power supply designed as flower pad mode, the stratum is opposite to the image on the actual printed board, and all wires are isolated wires, which should be very clear to the designer.

By the way, be careful when drawing the isolation lines of several groups of power supplies or several kinds of land. There shall be no gap to short circuit the two groups of power supplies, and the area of the connection shall not be blocked (one group of power supplies shall be separated).


   7、 Unclear definition of processing level

1. The single panel is designed on the top layer. If it is not specified, the positive and negative operation may be carried out, and the fabricated board may be installed with devices and difficult to weld.

2. For example, top, mid1, mid2 and bottom are used in the design of a four layer board, but they are 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 photo data is lost, and the photo data is incomplete.

2. Because the 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.


    9、 Surface mount device pad too short

This is for on-off test. For too dense surface mount devices, the spacing between the two pins is quite small and the pad is quite thin. The test pins must be installed in staggered positions up and down (left and right),

If the pad design is too short, the device installation will not be affected, but the test pin will not be staggered.


    10、 The spacing of large grids is too small

The edges between the same lines of large-area grid lines are too small (less than 0.3mm). In the manufacturing process of printed board, many broken films are easy to be attached to the board after the image is developed, resulting in wire breakage.


 11、 Large area copper foil is too close to the outer frame

The distance between a large area of copper foil and the outer frame shall be at least 0.2mm, because it is easy to cause copper foil warping and solder resist falling off when milling the shape.


    12、 Unclear outline frame design

Some customers have designed contour lines in keepoutlayer, board layer and top over layer, and these contour lines do not coincide, making it difficult for PCB manufacturers to judge which contour line shall prevail.

 

    13、 Uneven graphic design

During pattern electroplating, the coating is uneven and affects the quality.

    

    14、 The hole of special-shaped element is too short

The length / width of the special-shaped hole shall be ≥ 2:1 and the width shall be > 1.0mm. Otherwise, the drilling machine is very easy to break the drill when processing the special-shaped hole, resulting in processing difficulties and increasing the cost.

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