Typical hobby / prototype rules
| Rule | Cheap fab | Standard | High-tech |
|---|---|---|---|
| Min trace width | 6 mil (0.15 mm) | 5 mil | 3 mil |
| Min trace clearance | 6 mil | 5 mil | 3 mil |
| Min annular ring | 6 mil | 5 mil | 3 mil |
| Min drill hole | 0.3 mm | 0.2 mm | 0.1 mm laser |
| Min via diameter | 0.6 mm | 0.5 mm | 0.3 mm |
| Copper weight | 1 oz | 1 oz | 2+ oz |
| Board thickness | 1.6 mm | 1.6 mm | 0.4–3.2 mm |
| Minimum finished hole | 0.3 mm | 0.2 mm | 0.1 mm |
IPC classes
| Class 1 | General electronics — consumer, no-mission-critical |
|---|---|
| Class 2 | Dedicated-service / industrial — long service life, uninterrupted operation expected |
| Class 3 | High-reliability — medical, aerospace, life support |
Current vs trace width (1 oz copper, 10 °C rise)
| Current | External layer | Internal layer |
|---|---|---|
| 1 A | 10 mil | 30 mil |
| 2 A | 25 mil | 70 mil |
| 5 A | 90 mil | 250 mil |
| 10 A | 225 mil | 650 mil |
Rules of thumb
- Keep high-speed digital traces as short as possible with continuous ground reference under them.
- 45° or rounded corners (no 90° bends) on high-speed signals reduce reflections.
- Decoupling caps close to the IC pin — short trace to GND plane.
- Differential pairs: length-match within ~5% of rise time; keep the pair spacing constant.
- Avoid split ground planes under signals that cross the split.
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