system: pushbutton two-layer pcb mill

update: final

update: clank build

update: casette build

Desktop-scale PCB maker that completes a 2-layer board in under an hour.

state of the world / why

• PCBs from China are cheap and fast (JLC, PCBWay)
  • Still too slow for iterating effectively
• PCBs from the US are expensive and slow, but required sometimes for export control
• DIY options have major drawbacks
  • Approaches
    • Mill
    • Lasercut
    • Chemical etch
    • Print conductive ink
  • < 1 day turnaround, but at the cost of babysitting and obtuse tooling
  • Low quality
    • Process variability
    • Resolution limits
  • Process limitations:
    • 2-layer is difficult, > 2 infeasible
    • Masking is difficult
    • Silks are difficult

The product I want can take a KiCad project and produce a consistent board (with mask, no assembly) within the hour without supervision.

requirements

• At least 200um trace width
• 2 layers
• (Nice-to-have) selectively applies solder mask
• (Nice-to-have) conductive vias
• If milling
  • Mesh bed leveling
  • Automatic tool changer

design draft

Currently planning on using most recent revision of Clank (stretch variant) as the platform.

Additional features:

• Vacuum holddown

• Toolchanger

  • Isolation: V-bit
  • Cutout: endmill

• Stock loading and manipulation (ER arm)

anticipated flow

• Upload KiCad board file to website hosted by rpi attached to clank

  • Export gerbers
  • Run mods or pcb2gcode as CAM -> GCode
  • Auto-tabs (require at least 2)

• GCode translation / edits as required -- working with Jake

  • Trying MAXL
  • Fallback: GRBL or similar on a COTS controller + motor driver board

• Stock handling

  • Goals:

    • Load sheets from stack of stock, index to consistent position
    • Flip stock for second side of board, reindex stock outline to same position

  • Want to use ER mycobot arm with suction cups (vacuum)

    • Probably need to reserve some real-estate on the stock for clean pickup points

  • Open-loop stock indexing: pins, push into corner

  • Indexing side 2

    • Cutouts for X-Y probing?
    • Could do CV, but not really a fan. Maybe the right thing to do here though.
    • Maybe just measure width of stock, compute where board should be, fix x zero

  • Outfeed to stack by machine

• Vacuum holddown

  • Just a plate with hole pattern and a plenum underneath. Use a shop vac with a relay.
  • Selected because it seems most straightforward way to automatically control holddown

• Autoleveling

  • Probe with Clank's load cell

• Machining sequence

  • V-bit isolation (front)
  • Flip
  • V-bit isolation (back)
  • Cutout

• Tool changing

  • Use "fork" design suggested by Jake
  • Interpose a holdable U slot shape in the Kleat interface stackup
  • Several forks mounted to the bed
  • Lower the U of the tool onto the fork, release the Kleat, pull back
  • Inverse for pickup

Solder mask

Not in first rev of the machine. If the two-sided milling works, will add.

Concept:

• squeegee liquid mask through screen for consistent application amount
• cure with UV light mounted to machine or on tool head
• selectively mill off with springloaded v-bit

Sequencing: after isolation on each layer.

Vias

Not in first rev of the machine. If the two-sided milling works, will add.

Concept:

• rivets
• anvil / die at a fixed location mounted to bed
• cobot picks up and holds stock, referencing gerbers or pcb file (** cobot probably insufficient for precision)
• custom end effector with a rivet magazine and punch

Sequencing: after both sides isolated, before cutout.