Controller

BluRay Laser PCB exposer

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Design criteria:

160 x 100mm exposure area (Eurocard). Able to render at least down to 0.25mm (10 mil, 250um) track/track separation. Easy workflow.

Vector vs. raster plotting:

Vector plotting requires parsing of a vector format to control the drive mechanism, most PCB-design packages are able to output the design in Gerber and/or HPGL-formats.

Raster plotting is similar to inkjet printing, the laser is fired for the individual pixels.

I decided to use raster plotting since this is relatively simple to implement.

By using the belt calculator available at buildlog.net I found that 17 teeth pulleys and 8 microsteps would result in a resolution of 1195.297 steps per inch, which is pretty close to 1200 dpi (21.250 um/step). Near enough for hobby use, resolution may be adjusted when generating the bitmap file to match the actual resolution if a perfect match is required.

Photosentive PCBs:

I had some blank PCBs lying around so I wanted to try Dupont Riston dry-film photoresist. This has optimal sensitivity in the 350-380nm range, and may be exposed by 405nm as there is some sensitivity up to 450nm. Lines and spaces achievable: In optimized production environment: 75um/3mil In lab environment: 50um/2mil

The (teoretical) resolution of the design is thus somewhat better than the resolution of the film.

Workflow for KiCad EDA:

Plot the design to PDF in 1:1 format. Print resulting files via PDFCreator to PNG-format files, I use 4bpp in order to avoid artefacts in the bitmap.

Firmware:

Firmware is provided for MSP430G2553 LaunchPad or MSP430F5310 on a custom PCB. The MSP430F5310 is slightly faster and has more RAM, useful for buffering. It also supports adjusting the laser power via the desktop application.

Firmware may be compiled in the cloud, there is no need to install a local IDE.

Hackaday project:

PCB Exposer

Improvements:

A closed design with an interlocked door to block reflections from the laser. The published version is an open design, ALWAYS use protective eyewear when operating the exposer!

Laser cut acrylic bed? My prototype has an aluminium bed that requires access to a mill to fabricate.

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BOM:

3 SC6UU 25x30x18 polymer bearing in aluminium housing 2 LM6UU 5x10x14 polymer bearing (or Oilite sintered bronze bearings) 4 6mm ground shafts, 300mm 2 3mm ground shafts or similar, 25mm for the belt idlers 1 3D printed laser carrier, FreeCAD design provided 1 diode housing 13x16x15,5 1 lens 405nm 8mm focal length? 1 405nm laser diode, 100mW 2 Nema 17 stepper motors, max 34mm long 2 17T pulleys 2 idlers to match the pulleys GT2 6mm belt, approx. 1m 6mm acrylic for laser cut case, dxf-files provided 4mm acrylic for laser cut case, dxf-files provided 1 MSP430G2553 LaunchPad or custom controller PCB (design included). Please refer to schematics for BOM for the latter. 1 laser driver PCB (design included). Please refer to schematics for BOM.