Requirements for PCB Wiring Design
Generally, basic PCB design process follows seven steps: pre-preparation- structural design- layout- optimization and silkscreen- net check, DRC check, and structural check- board fabrication. In this article, requirements for PCB wiring design will be outlined.
In general, the signal wire width is 0.3mm (12mil), the power wire width is 0.77mm (30mil) or 1.27mm (50mil). 0.33mm (13mil) spacing is at least between two lines or between the line and the pad, but in practice, if condition is allowed, the distance shall be increased. When wiring density is high, you can consider (but not recommend) using two lines between IC feet; the wire width is 0.254mm (10mil), and wire spacing is no less than 0.254mm (10mil). Under special circumstances, when pins are denser and their width is narrower, it is better to reduce the wire width and wire spacing to some extent.
The basic requirement for pad and via is listed as follows: the diameter of the pad is 0.6 mm bigger than via’s; for example, general pin-type resistors, capacitors and integrated circuits, etc., use 1.6mm (63mil) pad and 0.8mm (32mil) via, while sockets, pins and 1N4007 diodes, etc., use 1.8mm (71mil) pad and 1.0mm (39mil) via. In practice, components’ size should be used based on the actual condition. If allowed, pad size can be added to some extent, designed components installed aperture should be about 0.2 ~ 0.4mm larger than the actual pin size.
The general size is 1.27mm / 0.7mm (50mil / 28mil); when the wiring density is high, the via size can be appropriately reduced, but not too small, 1.0mm/0.6mm (40mil/24mil) is recommended.
Spacing requirements for pad, wire, via
pad and via: ≥0.3mm(12mil); pad and pad: ≥0.3mm(12mil); pad and wire: ≥0.3mm(12mil); wire and wire: ≥0.3mm(12mil)
When the density is high: pad and via: ≥0.254mm(10mil); pad and pad: ≥0.254mm(10mil); pad and wire: ≥0.254mm(10mil); wire and wire: ≥0.254mm(10mil)