By what percentage may the width of lands be reduced for Class 2 and 3 assemblies?

The width of lands for Class 2 and Class 3 assemblies can be reduced by 20% as per the J-STD-001 requirements. This specification allows for a moderate adjustment in the land dimensions to accommodate manufacturing processes while still ensuring the integrity and functionality of solder joints.

Reducing the width of the lands helps in optimizing space on the printed circuit board (PCB) without compromising the soldering quality required for such classes of assemblies. Class 2 assemblies operate under less stringent reliability requirements compared to Class 3, which is designed for high-reliability applications. Nonetheless, both class types have defined allowances for land reduction to ensure adequate performance and manufacturability.

The other options suggest wider reductions, which would not align with the recognized industry standards for maintaining needed manufacturability and reliability.