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Technical Article

Common Mistakes In PCB Layout

Time:2020-10-30 17:45:47 Click:





1. Random Placement Of Silkscreen

> The SMD soldering pads of the silkscreen cover pad brings inconvenience to the on-off test of board and the soldering of the components.


> If the silkscreen layout is too small, causing difficulties in screen printing; While too large will cause the silkscreen to overlap each other and be difficult to distinguish.


2. The Abuse Of The Graphics Layer

> Some useless connections were made on some graphics layers. The original four-layer board was designed with more than five layers, which caused misunderstanding.


> It saves trouble when designing. 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 performed, the Board layer is not selected, and the board layer 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.


> Violation of conventional layout, such as the component surface layout in the Bottom layer but the soldering surface layout in the Top, causing inconvenience.





3. The Overlap Of Pads

> The overlap of pads (except the surface mount pads) means the overlap of holes. During the drilling process, the drill bit will be broken due to multiple drilling in one place, resulting in damage to the holes.


> Two holes in the multilayer board overlap. For example, one hole is an isolation disk and the other hole is a connection pads. In this way, the film is drawn as an isolation disk, resulting in scrap.


4. Setting Of Single-Sided Pads Aperture

> Single-sided pads are generally not drilled. If the drilled holes need 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.

> Single-sided pads should be specially marked if they are drilled.


5. Layout Pads With Filler Blocks

Drawing pads with filler blocks can pass the DRC inspection during PCB layout, but it is not good for assembly. Therefore, similar pads cannot directly generate solder mask data. When solder resist is applied, the filler block area will be covered by solder resist, and which is difficult to solder the device.







6. The Electrical Ground Layer: A Connection Pads & Connection Area

Since the power supply is designed as a connection pad, the ground layer is opposite to the image on the actual printed board. All the connections are isolated lines. The layout engineer should be very clear about this. By the way, you should be careful when routing the 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 one set of power supplies).


7. Not Clearly Defined Assembly Level

> The single-sided board is designed on the TOP layer. If the front and back are not specified, the manufactured board may not be easy to be soldered with components installed.


> For instance, a four-layer board is designed with four layers of TOP mid1 and mid2 bottom, but it is not placed in this order during assembly, which requires extra introduction.


8. Too Many Filler Blocks In PCB Layout Or Too Thin Lines Fill with The Filler Blocks
> The ight drawing data is lost, and the ight drawing data is incomplete.

> Due to 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.






9.Too Short SMD Pads

This is for continuity testing. For surface mount components 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 will not affect the device installation, but it will make the test pin staggered.


10. Small Spacing Of Large-Area Grids

The edges between the same lines that make up the large-area grid are too small (less than 0.3mm). During the manufacturing process of the printed board (PCB), the image transfer process will easily produce a lot of broken films attached to the board after the image is developed, causing the line to break.


11. Close Distance Between The large Area Copper Foil & The Outer Frame

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. Short Special-Shaped holes

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.


13. Uneven Graphic Layout

When pattern plating is performed, the plating layer is not uniform and affects the quality.


14. Unclear Outline Frame

Some customers have designed contour lines for 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.



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Next:PCBA - SMT Assembly Process Introduction

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