GROUP PROJECTS : ELECTRONICS PRODUCTION

PCB Production process

GROUP TASK

Characterize your PCB production processes for your machine

The cnc

Micro CNC 3020

Specifications

  • Name: Micro CNC 3020
  • Spindle: 500w, maximum speed 12,000 rpm
  • tracks:20mm linear bars
  • motion: 16mm ball screw
  • Stepper motors: nema 57
  • Max travel: x-axis 200mm, y-axis 300mm, z-axis 85mm
  • Workbench size: 310mm*440mm
  • Dimensions: 560mm * 530mm * 600mm
  • software: Mach3
  • repeatability: 0.03mm
  • weight: 34.5kg

    • Caracterisation

    Milling

    For the milling process we will use the following software:

    • Fab Modules
    • Mach3

    Fab Modules

    We start by downloading a hi-res pattern at the electronics production site.

    image downloaded from electronics production site at MIT image downloaded from electronics production site at MIT

    At Fab Modules

  • click on input format
    •
  • click on the image (.png)
    •
  • chose your image
    •
  • now select output format
    •
  • now select G-codes (.nc)
    •
  • now select PCB traces (1/64)
    •
  • Before calculating confirm cut depth and tool diameter (in our lab the defaults are fine
  • press calculate
  • review the path calculated by fabmodules
    •
  • save the files to the desired path in your computer
    •
  • To outline I followed the same steps as before exept I chose to "PCB outline (1/32)" instead of traces;
  • Check the tool diameter and the stock thickness;
  • Save the gcode file to the same location with a diffeent name for the file.
    •

    FABRICATION

    Here are the two gcodes

  • iterior traces
  • exterior traces

    • The preliminar results milling

    After milling the test patterns we notice that the results were very bad

    After a close inspection of the cnc spindle we came to the conclusion that the cnc had its spindle's shaft bent and due to that the cuts were not smoth. In the following photo you can see the instrument used to measure the variation.

    We disassembled the spindle and took it to a machinist. After a few days we returned with the spindle but the problem continued. So our solution was to hammer side of the shaft with the highest variation with a metal mallet

    Success we fixed the spindle's Shaft and no more variation as seen on these recording:

    Doing it over

    Now with the shaft fixed and a new bit we made the folowing test.

    Main setings:

  • iterior traces (code)
    1. cut speed (mm/s): 10
    2. cut depth (mm): 0.035mm
    3. tool diameter (mm): 0.23
    4. path error (pixels): 0.7
  • exterior traces (code)
    1. cut speed (mm/s): 10
    2. cut depth (mm): 1.7
    3. tool diameter (mm): 1.5
    4. path error (pixels): 0.7

    The final result

    We milled again the template and the traces are better defined. I am not totally happy with the results as I used the only mill bit suitable for the job at the lab. And thats still not so good. This mill bit is not straigth it is angled with 30 degrees. So if the piece is not totally flat some parts will be getting a bigger with than the other.

    Conclusion

    On a examination of the cutted template we can assume our settings are ideal for the current mill bit. Its crucial to have a flat bed. Also the lab is aquiring new mill bits that should improve the results even more.

    Selected settings:

  • iterior traces (code)
    1. cut speed (mm/s): 10
    2. cut depth (mm): 0.035mm
    3. tool diameter (mm): 0.23
    4. path error (pixels): 0.7
  • exterior traces (code)
    1. cut speed (mm/s): 10
    2. cut depth (mm): 1.7
    3. tool diameter (mm): 1.5
    4. path error (pixels): 0.7