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Week 8 > Electronic Production

Characterization of Design Rules for In-House PCB Production (Roland SRM-20) 1. Machine Used

I used the Roland SRM-20 desktop CNC milling machine for PCB fabrication using FR1 copper-clad boards and V-bit / flat end mills.

  1. Tooling Used 1/64” (0.4 mm) end mill → PCB traces 1/32” (0.8 mm) end mill → outline cutting

  2. Characterized Design Rules

A. Minimum Trace Width Reliable minimum trace width: 0.4 mm (16 mil) Safer recommended width: 0.5 mm – 0.6 mm Anything smaller risks breaking during milling or not being milled properly

B. Minimum Clearance (Isolation Gap) Minimum spacing between traces: 0.4 mm Recommended clearance: 0.5 mm – 0.6 mm This ensures the milling bit can fully isolate copper without shorts

C. Minimum Drill / Hole Size

Practical minimum hole size: 0.8 mm – 1.0 mm Smaller holes are unreliable with SRM-20 milling Through-hole components must match drill capability

D. Tool Diameter Constraints Main engraving bit: ~0.4 mm effective cutting width This limits: pad density routing density via size (if used)

E. Copper Removal Strategy Two-pass milling is recommended: Rough pass (clear isolation) Second pass (clean edges if needed) Improves reliability of fine traces

F. Board Flatness Sensitivity FR1 board must be perfectly leveled Even small height variation causes: broken traces (too shallow cut) short circuits (too deep cut)

G. Milling Speed & Feed (Observed)

Spindle speed: fixed (~7000–10000 RPM depending on setup) Feed rate: moderate (too fast causes broken bits) Depth per pass: ~0.1 mm recommended for PCB isolation

  1. Observed Limitations of SRM-20

Board leveling is critical for success

  1. Design Adjustments Made Based on These Rules

To ensure successful fabrication, I:

Increased all trace widths to ≥0.5 mm Increased clearance between components Simplified routing where necessary Verified design using KiCad DRC before milling