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PCB Layout Tips
At Black Stick we would like to help engineers get started in schematic and PCB layout.
If you would like to help this resource to grow please send your content to tips@blackstick.co.uk and we will add it into this page.
Learn about:
Via Size
As a general rule for standard via's the pad should have a 0.15mm(6 thou) annular ring I.e. finished hole size of 0.3mm(12 thou), pad size of 0.6mm(24 thou). This provides a tolerance for drill wander / breakout.
Silkscreen rules
Silkscreen should be kept between 0.10 mm(4 thou) and 0.20 mm(8 thou) away from anything conductive, not covered by solder mask. The minimum line thickness should be 1mm(40 thou) and the minimum letter height should be 0.15 mm(6 thou).
Routing
Right Angle Tracks
Avoid right angle tracks where possible as they can cause issues with signal integrity. Also, on finer tracks they can cause the trace to be broken due to acid traps and erosion over time (see acid traps).
T - Junctions
It is advisable to avoid T junctions as they lead to impaired signal integrity. They can also cause acid traps on each side, which gives a higher chance of causing an open circuit.
Tracks from the board edge
The general rule for placing tracks from the board edge is three times the minimum track spacing I.e. track spacing 0.254mm(10 thou) then track to board edge should be at least 0.762mm(30 thou). But the bigger the distance the better.
Antenna
Antenna are small tracks that don't join to another net causing and picking up noise.
Loops
It is best to avoid loops where possible as they can cause a large amount of noise, which in turn can affect the signal integrity of many tracks on your board. Also they cause inductance which can also lead to increased noise.
Acute Angles
Acute angles during the routing of a PCB can cause acid traps. This is where the etching solution gets trapped in the small corners and over time can etch away the track which can lead to an open circuit.
Track Spacings
The minimum track spacing is dependant on the voltage the tracks are carrying, this can be worked out in our C4 calculator . Generally if spacing goes below 0.127mm(5 thou), manufactring costs can increase.
