The recommended solder mask expansion depends on the number of layers in your PCB.
Generally, solder mask expansion is the amount by which the solder mask opening is larger than the copper pad it exposes. This ensures reliable soldering and prevents the mask from overlapping the pad, which can cause issues during assembly.
Here's a breakdown of suggested solder mask expansion values:
- For 2-layer boards: Use a solder mask expansion of 2 mil (0.0508 mm).
- For 4-layer boards: Use a solder mask expansion of 1.5 mil (0.0381 mm).
Alternatively, you can use a 2 mil (0.0508 mm) expansion for both 2 and 4 layer boards. However, if you choose to use a 2 mil expansion on a 4-layer board, it's recommended to adjust the isolation of copper pours and ground planes to 6 mil (0.1524 mm) or larger. This ensures sufficient clearance and prevents shorts.
The specific value may vary slightly depending on your manufacturer's capabilities and design requirements, but the above values represent a good starting point. Always consult with your PCB manufacturer for their recommended specifications.
