PCB exposer using BluRay laser diode for exposing photosensitized PCBs (etch- and soldermask)
Schematics for the custom controller.
Adobe Portable Document Format - 66.49 kB - 01/29/2019 at 08:44
Schematic for the diode driver. A resistor has been added to limit max base current in the driver transistor - to avoid frying the opamp if powered up when no diode is connected.
Adobe Portable Document Format - 32.96 kB - 01/29/2019 at 08:44
A few pictures of the completed exposer:
and I am happy with the results. I decided to try 0.2mm (8 mil) traces with a presensitized PCB for the latest and this is how it worked out:
The PCB size is 60x70mm, the IC pads are for a TSSOP-16 with 0.65mm pitch (and my drill bit is worn out...). It is just a "quick-and-dirty" prototype I am going to use for design verification. I will redo the design as a two layer board and send it off to a board house if I later decide to make a small run.
Project files uploaded to my GitHub account. These are for prototype #2 referred to below.
A new prototype has been made:
This is a lot stiffer than the first, this setup has the custom controller connected to the LaunchPad version of the diode driver. The PCB on the table is the driver that will be used finally, connected to the controller via a flat cable.
Calibration is vital for good results, I started with coarse adjustment of laser focus. A wax based shopping receipt (the ones used in thermal printers) can be used, the laser light will blacken these when in focus.
Next step is backlash compensation, the original machine has 9 pixels of compensation so I started with that. Remember one pixel is about 20 micrometers at 1200 dpi:
13 pixels, the best one but the 0.1mm line is a bit wider in the horizontal direction than vertical, I suspect focus needs adjustment.
15 pixels. Perhaps I need to test for 12 as well - but focus first:
A quarter turn of the lens in the direction I suspected I needed to go.
A quarter turn more, I think I'll stop here - beeing able to print at 0.1mm (or less) resolution (4mil) is good enough?
For me this means the project is a viable solution to making PCBs for down to 0.5mm pitch components, maybe even less. Presensitized boards is a must when aiming for less than 0.25mm (10mil) trace widths, dust will surely be a problem when using film.
Finally, a shot of a corner of the MCU on the controller board - made with the original exposer (0.5mm pitch):
Custom board for MSP430F5310 has been made, and the firmware is running on a breakout board I have. The mechanincal design has been reviewed and only need a last QC before I laser cut new parts. After this is done I will publish the design. I guess dxf-files are okay for the acrylic parts - originals are in Vectric VCarve format and can be exported in a few other formats if anyone wants to replicate the machine.
Custom controller, can support Z-axis motor for focusing - stepper driver will have to be added to the "print head" board for that.
"Print head" driver board for the laser diode, the FDC connector can be replaced with a 4-pin pin-header for use with a MSP430G2553 LaunchPad - but then software controlled power adjustment is not possible.
Both PCBs are single sided and can thus easily be made with the exposer itself.
Laser driver and a motor driver PCB (BoosterPack) for the MSP430 LaunchPad has been completed. Initial print had a lot of backlash:
Picture taken with half the microstepping needed (Y-axis) for correct resolution, done to reveal individual horizontal lines - they are ~20um high and ~40um apart. Beeing able to discern them means the laser is properly focused.
After tuning the backlash parameter and some mechanical tweaks:
Next, the boring part, write proper documentation...
I finally managed to print a prototype laser carrier, or "print head", I am using a small brass host to house the laser diode. I will mount the driver PCB on top of the carrier (the picture below is a bottom view), total weight will be around 50g so perhaps it will be possible to increase the rendering speed a bit compared to my original design.
I wonder if the plastic (ABS) will hold up to the load, perhaps some reinforecment is needed for the belt grip (or whatever it is called). We'll see...
Driver PCB design is ready after some minor tweaks so a making a prototype is due next.
A short update: the project is not dead but a bit down on my todo list which hopefully is getting shorter by the day.
I am currently making a mini CNC mill that I am going to use for drilling and milling PCBs++, it can bee seen as a companion to the exposer. It is my intention to add an ATC to that (it is the aluminium structure in the table), I am lazy and do not want to change bits myself. The mill will run my ARM port of grbl which by now is quite a bit changed from the original, amongst the numerous changes are canned cycle support, a new state machine - and I am working on spindle sync for my newly aquired mini lathe.
I may start a new project here for that later, especially if I get the ATC to work.
A prototype for the exposer is fairly complete in the mechanical department, I have to finish the laser carrier design (only needs dimensional verification) and 3D-print it - then it will be time for the electronics and firmware changes. It is my intention to make two version of the electronics, one for TIs MSP430G2553 launcpad and one for a custom board with MSP430FF5310 as the MCU.
I have been thinking for a while and recently started to make some drawings for a new mechanical design. To keep the cost down I will try a laser-cut assembly from acrylic and some 3D-printed parts. I will also try to use a belt for the slower moving Y-axis (one microstep per pixel row) but I am unsure if this is unwise as stepper motors are somewhat unprecise when moving one microstep at a time. Since there is a potentially dangerous laser involved I will also add a lid to the enclosure, with interlock, to ensure that it cannot be operated when open.
My original design is based on a GT2-belt and a 17T pulley for X-axis movement, this results in a near 1200 DPI resolultion when switching the laser in a 1:1 relationship between pixels and motor-steps (@ 8x microstepping). For now I will keep this as it simplifies coding and a humble MSP430G2553 (USD 1) microcontroller is up to the task of driving it.
I will soon add a new project to my GitHub account for this project, this far I have made an Inkscape drawing of the acrylic parts, and a FreeCAD drawing of the laser head assembly (to be 3D-printed). These are very much work in progress and can NOT be used for production. For the electronics I am working on a new laser diode driver PCB, this can be used with a MSP430G2 Launchpad or a custom controller board.