2.3 Zoning and Navigation – Solder Mask and Silkscreen

A PCB requires zoning laws and signage to function. The visual characteristics of a board — the green color and the white text — are functional layers applied to facilitate assembly and prevent electrical accidents.

Solder Mask: The Insulation

The "Green Oil" covering the board is a photo-imageable epoxy polymer.

• Function: It acts as an electrical insulator, preventing solder from bridging between two adjacent copper traces and causing a short circuit.
• Application: It is sprayed over the entire board and then exposed to UV light through a film pattern. Unexposed areas are washed away, leaving openings (soldermask dams) only where components need to be soldered.
• Color Coding: While green is standard (offering the best visual contrast for inspection), masks can be black, blue, or white. Black masks absorb heat and are harder to inspect; white masks reflect light and are used for LED boards.

Silkscreen: The Map

The white text printed on the board is the "Legend."

• Reference Designators: Labels like "R102" or "C5" identify specific components, mapping the physical object to the schematic diagram.
• Polarity Marks: Critical indicators (dots, lines) showing the orientation of chips and diodes. A missing polarity mark is a leading cause of assembly error, as a robot may place a symmetric component backwards without a visual guide.

Final Checklist