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Technical Article

PCB Layout: Essential PCB Design Rules

Time:2017-05-02 15:11:29 Click:

In order to reduce the chances of manufacturing errors and to lower the cost of you Printed Circuit Boards, following PCB design guidelines are set for best practice. Printed Circuit Boards that work on relatively higher power have an entirely different set of design guidelines when it comes to issues such as power isolation, track widths, track spacing and density, etc. Requirements of various PCB manufacturers differ; it is therefore important that you have read the rules provided by them before your design submission. Similar is the case with file formats and naming conventions which vary with different PCB manufacturers. 

Printed Circuit Board Layout Guideline 
1. Your board frame should be created on a grid of 0.05 inches with the lower left corner starting at the reference 0.0. 
2. Different shapes such as polygons can only be used in specific cases. Normally rectangular board frame is utilized. 
3. A 0.05 inch grid is to be utilized for sticking parts. This rule has to be strictly followed unless it’s absolutely necessary to be broken. 
4. LEDs used on the PCB should be marked for identification. (For example: Status, Lock, D1, D2, Fault) 
5. Connectors should be marked as well, such as Vin, Input Port, Vout, etc. 
6. Pins on the board are to be labeled, such as, RX, Power, +5V, -5V, etc. 
7. Labels for switched should be used, such as, Test, USB, Off, On, etc. 
8. You should try to avoid Vias going through silkscreen when labels are being added. 
9. It is advised to place components in groups. For example capacitors and resistors around an IC in the schematics should be placed near to the IC on the PCB during layout. 
10. 15mil is the minimum size for drill. 
11. 7mil should be set as the minimum size for the annular ring. 
12. Minimum trace size should be kept 7mil. 10mil is the recommended size for the traces but 7mil or 8mil can be accepted. 
13. Power lines have to be kept comparatively thicker. For max 100mA, use 12mil; for max 500mA you can use 16mil and so on. 
14. Distance between space and traces should be 7mil. 
15. 90o bends are not recommended. Instead straight lines with two 45o bends are preferred. 
16. If possible, ground pour can be used on first and last layers. 
17. Pours can get shorted to traces; an isolation of 10mil is to be used on ground pours to avoid this from happening. 

Printed Circuit Board Schematic Rules 
18. For Ground connections, a symbol “GND” is to be used. 
19. Power sources should be labelled accordingly, e-g: Vdd, Vc, 3.3V, 15V, etc. 
20. Colour notes can be used to make smaller section of a larger complicated circuit. E-g: Power Section, Current Sense, etc. 

21. A reference designator {{reference}} is required for footprints. You should ensure all parts have this and then save your library. Pin one marker is to be set for parts that require this. 
22. Silkscreen labels that show dimensions or wired aspects of a part are required by all footprints. 
23. Pads or exposed metal parts shouldn’t have silkscreen over them. Silkscreen will flake off from a footprint in these cases. 
24. A red cross in the center will mark the top layer. 
25. Outline layers of a package are to be exactly equal to their real size. 
26. All pins are to be indicated by the top courtyard layer. 
27. Soldermask should be added alone with a footprint 
28. Labels of new parts or footprints should be easily visually inspected or read.

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