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PCB Layout Notes Cheat Sheet (DRAFT) by

Standard values and "Rules of Thumb" for PCB design

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Grids

Visible Grid
100 thou
typical for throug­h-hole work
Snap Grid
50/25/10 thou
typically used for track layout

Tracks

Signal
25 thou
Ground
50 thou
"neck down"
10-15 thou
 
neck down to pass between component pads
keep track widths as large as possible to
   minimize resist­ance, induct­ance, etc.
See track width chart to the right for track width recomm­end­ations based on current flow, for a 10 deg C temper­ature rise within the track.

Spacing

10 thou
typical amount
8 thou
achievable with homemade PCBs
See minimum spacing chart to right for track spacing based on voltages.

Pads

Throug­h ho­le,­ ­lea­ded­ ­com­ponents
(resis­tors, capaci­tors, etc.)
Round
70 thou
Dual In-Line
(eg. IC's)
Oval
60 thou , 90-100 thou
SMT packages
Rectan­gular for most
Oval for SO packages
 
pin 1 is in a rectan­gular shape
keep track widths as large as possible to minimize resist­ance, induct­ance, etc.

Vias

Round
0.5mm-­0.7mm

Holes (eg. throug­h-hole compon­ents)

Round
1mm (39 thou)

NOTES

Board Dimensions
Measured in mm
Copper Weight­/Th­ickness Guilde­lines
General Purpose: 1oz copper
High Current: 2oz - 4oz copper
Design and Layout (eg. grids, pads, tracks, spacing)
use thou
Mechanical and Manufa­cturing (eg. hole sizes, board dimens­ions)
use mm
 

Minimum Track Width for 10 deg C rise

Current
Amps
Width 1oz
thou
Width 2oz
thou
milliOhms
per inch
1
10
5
52
2
30
15
17.2
3
50
25
10.3
4
80
40
6.4
5
110
55
4.7
6
150
75
3.4
7
180
90
2.9
8
220
110
2.3
9
260
130
2.0
10
300
150
1.7

Minimum Spacing (based on voltage)

Voltage
(DC/Peak AC)
Internal
mm / thou
External
mm / thou
0-15V
0.05mm/2 thou
0.1mm/4 thou
16-30V
0.05mm/2 thou
0.1mm/4 thou
31-50V
0.1mm/4 thou
0.6mm/23.6 thou
51-100V
0.1mm/4 thou
0.6mm/23.6 thou
101-150V
0.2mm/8 thou
0.6mm/23.6 thou
151-170V
0.2mm/8 thou
1.25mm/49 thou
171-250V
0.2mm/8 thou
1.25mm/49 thou
251-300V
0.2mm/8 thou
1.25mm/49 thou
301-500V
0.25mm­/98.5 thou
2.5mm/98.5 thou

Best Practices

Best Practices
Track Size: Keep track size as large as you can get away with, necking down as needed when things get crowded.
 
Track Size: Design track size for a 10deg C temp rise within the tracks (see table, pg.7, in PCB design tutorial article by Dave Jones)
 
Profes­sional Manufa­cture: When having your board profes­sio­nally manufa­ctured, consult their design guides to see what their minimum track size/s­pacing is.
 
Pad/hole ratio: the ratio of pad size to hole diameter. Rule of thumb is to aim for the pad to be 1.8 times larger than the diameter of the hole (allows for alignment tolerances between drill and artwork).
PCB design tutorial article by Dave Jones
http://alternatezone.com/electronics/files/PCBDesignTutorialRevA.pdf