Copper Trace Design – PCB DFM Part 7

7.1 Trace Width, Spacing and Routing Requirements

[65] The width and spacing of copper traces vary according to the thickness of the copper material and which
layer the trace is located. Recommended trace widths and spacing for inner and outer layers of various copper
thicknesses is shown in table 8.

Table 8: Recommended trace widths and spacing.
Recommended trace widths and spacing
[66] For outer layers, the distance between the trace and copper pads should satisfy the requirements shown in
figure 43.

solder mask opening

Figure 43: Recommended spacing between trace and pads.

[67] The distance between outer layer traces, inner layer power/ground planes and ground bus traces to the
board edge should be greater than 20mil.

[68] There should not be any traces going through the metal shell of components (e.g. heatsink). The region of
components’ metal shell should have a 1.5mm clearance area around it.

components’ metal shell

Figure 44: Clearance area of components with metal cases.

[69] Distance from the trace to non-plated through holes is summarised in table 9.
Table 9: Distance from the trace to the edge of NPTHs.

Distance from the trace to the edge of NPTHs

7.2 Solder Pad to Trace Connections

[70]  Asymmetry should be avoided in the trace and connected solder pads.


Figure 45: Symmetric and asymmetric traces

[71] Traces should start from the center of solder pads

symmetric trace

Figure 46: Starting position of the trace to the pad.

Figure 46: Starting position of the trace to the pad.

Starting position of the trace to the pad

[72] When the width of the trace is wider than the pad, the trace should not overlap the pad. The trace width
should be reduced at the point of contact as shown in figure 48. When adjacent pins of fine pitch components
need to be connected, the trace should not run directly between the pads. Instead, it should run outside of the
row and connect as shown in figure 49.

trace width reduced

Figure 48: Connecting the trace and pad when the trace width is larger.

Connecting the trace and pad

Figure 49: Connecting adjacent pads of fine pitch components

[73] The below designs are recommended for ensuring a strong connection between a trace and hole.

connection between a trace and hole

Figure 50: Connections between the trace and holes

7.3 Copper Pour Design Requirements

[74] When the traces on the same layer are unevenly distributed, or the copper distribution in different layers is
asymmetric, including a hatched style copper pour grid into the design is recommended

[75] If there is a large section of the board without copper, copper pour can be used to even out the copper

[76] Recommended copper grid size is about 25mil x 25mil.

copper grid size

Figure 51: Copper grid design.

More Chapters:
1. Brief Introduction
2. Seeed Fusion PCB Specification
3. Panelization and Bridge Design
4. Component Layout Considerations
5. PCB Hole design
6. Solder Mask Design
8. Silkscreen Design
9. PCB Lamination Structure
10. PCB Dimensions Specification
11. Fiducial Mark Design
12. Surface Treatment
13. Files for Manufacture Requirements
14. Appendix 

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June 2017