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7. Activity of Day 7

PCB Milling & Cutting

PCB milling is a subtractive fabrication process hat carves circuits from a copper-clad board.

Designing with milling in mind ensures a smooth transition from the digital PCB design to a functional physical board.

Milling-friendly designs are typically single-sided to simplify fabrication and reduce errors.

The Essence of PCB Milling

PCB milling allows designers to:

  • Precisely remove copper from a copper-clad board to define circuit traces (subtractive process).
  • Rapidly prototype and test PCB designs in-house.
  • Fabricate boards independently without relying on external manufacturers, reducing time and cost.

Understanding Traces, Clearance, Pads & Vias

  1. Trace Width
    Determines current-carrying capacity and machinability. Wider traces are stronger and easier to mill.

  2. Clearance
    Maintains isolation between traces and copper areas to prevent short circuits.

  3. Pads
    Are large enough to support reliable soldering and maintain mechanical stability.

  4. Vias
    Are difficult to mill on single-sided boards and are often replaced with wire jumpers in prototypes.

Phyical fabrication process

Phyical fabrication involves three main stages:

  • Trace Isolation– The milling tool removes copper around traces, creating the circuit paths.
  • Hole Drilling – Holes are drilled for component leads and mounting points.
  • Board Profiling – The PCB outline is cut to separate the board from the raw material.

Implementation

Recap from Day 3

This activity builds on Day 3, where a single-sided PCB is designed in KiCad:

  • ATtiny45 microcontroller
  • LED controlled using a push button
  • 6-pin ISP header for programming

The schematic, component placement, and routed tracks are verified and prepared for fabrication.
This same design file is used for the PCB milling process.

== "Step 1: Preparation"

  • The milling tool is mounted onto the machine.
  • Carbide Motion software is downloaded and installed.
  • The copper-clad board is secured on the cutter bed using double-sided tape.
  • In the project folder (in our case :Microcontroller_PCB_Design), the Gerber folder containing Gerber files is located.
  • The cutter is connected to Carbide Motion.
  • Gerber files are imported into Carbide Motion, which combines them into a single milling job.
  • Tool position, and cutting depth are carefully configured in Carbide motion.

== "Step 2: Milling the Traces"

  • The machine origin is set correctly.
  • Once all configurations are verified, the machine engraves the copper traces according to the PCB design.

Milling Traces

== "Step 3: Cutting the Board Outline"

  • The milling bit is changed to the tool used for board profiling.
  • Tool position and depth are re-adjusted.
  • The machine cuts the PCB outline from the copper-clad board.

Cutting Outline

== "Result"

  • The final PCB is successfully fabricated.
  • The board is ready for cleaning and component soldering.

Final PCB