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This section describes the information that a professional PCB fabrication house needs to know about your design in order to produce circuit boards from your design.

Design Guidelines

The PCB fabrication house will ask for the board design parameters when you contact them about fabricating your circuit boards:

• Minimum width of the traces you have used.
• Size of your smallest via
• Minimum spacing between the traces you have used.
• Minimum spacing between the pads you have used.
• Minimum spacing between traces and vias.
• Minimum spacing between traces and pads.
• Minimum spacing between vias.
• Minimum spacing between vias and pads.

The best thing to do is to send them the design files. The PCB fabrication house can extract all the information from the design files and also check them for any errors.

Minimum trace width

Circuit board fabrication houses routinely build boards with trace widths of 4 mils or 0.004". The smaller the trace width, the lower the yield the fabrication house achieves and the more costly your boards will be.

Via size

Try to use a single via for your entire design. Via size is defined as a pad size and a drill size. For example, a pad size of 30 mils and a drill size of 18 mils is commonly referred to as an 18C30 via. Circuit board fabrication houses routinely build boards with via size of 30 mil pad and 18 mil drill. Vias can be much smaller with techniques such as laser drilling but you will pay more for them.

Minimum trace spacing

Circuit board houses can handle boards with all spacing 4 mils or less. As with trace width, the smaller the spacing, the lower the yield the fabrication house achieves and the more costly your boards will be.

All other minimum spacing

Professional circuit board houses can handle boards with all spacing 4 mil or less.

Some General Principles to make your life easier

• For easy-to-read silkscreen on a professionally fabricated circuit board, make the text height 100 mils and the stroke width 10 mils. If you have a circuit board with lots of surface mount components or closely spaced components, make the silkscreen size 80 mils with a stroke width of 8 mils. Anything smaller will just be illegible.
• Make your circuit board look more professional by keeping all the text height and stroke widths the same. Try not to have 100 mil characters in one section and 200 mil characters in another.
• Make all pads for components as large as possible. For increased manufacturability and solderability, the pad size minus the hole radius should be at least 20 mils. This 20 mil ring is referred to as annular ring. Professional circuit board houses can produce boards with as little as 3 mils of annular ring. But the smaller the annular ring, the higher the cost.
• The circuit board fabrication houses normally have standard and high density processing. The latter is more expensive.

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