I have experience with DIY CNC stages and a pretty good background in electronics, including a fairly comprehensive working knowledge of constant current drivers, but I don't know much about lasers at all. I am primarily interested in Lasers with respect to prototyping PCBs with a casual interest in more industrial venues for cutting sheet materials (from plastics to metals). I don't have any delusions about DIYing a CNC Laser cutter with metal cutting capabilities, but I am interested in exploring the DIY viability of two approaches to PCB prototyping.
The first PCB prototyping method I am interested in is ablating a "painted" photo-resist from a copper clad board. There are is a myriad of info on the net involving Laser Ablation of various consumer paints sprayed onto copper clad board, but most of the information involves fairly high-powered commercial CO2 Lasers; a recurrent problem seems to be selecting a low enough power setting on commercial laser engravers to minimize inadvertent ablation, while still maintaining the beam.....seemingly suggesting it may be possible to achieve the task with a low to medium powered Laser Diode....but there is a tremendous gulf between the "lowest power setting" on a 50W-200W commercial CO2 laser and the readily available 5mW to 3W Laser Diodes.... And Sooooo much I don't know about Laser Diodes....
I am familiar with the concept of "pulsing" conventional LEDs to achieve very high peak power bursts while maintaining the "average power" specifications of the device...and have read that "pulsing" is a technique employed in some situations involving Lasers....but I am not confident I could work much below the 10uS time domain, and I have read pulsing references about pulsing in the nano and pico second time domains...I just don't think those are in my wheelhouse....Sooo, is it possible to achieve paint ablation with a <<5W diode laser? If so, what would be a good starting place? Is pulsing an "option" or mandatory? If mandatory, what are some guidelines regarding frequency and duty cycle? Do Laser diodes behave similarly to conventional diodes wrt (With Respect To) drive requirements such that I could prototype//debug the driver circuitry using a comparatively cheap conventional LED and expect a Laser Diode to act similarly (assuming Vf, If and Power Rating characteristics were similar)?
And as if the above is not enough for a first post, lol, the second Laser//PCB prototyping application I am interested in exploring is Laser based UV Exposure of CEM PCBs. I have not found any information on the net about attempts to use this approach, but the concept seems plausible to me. In a typical PCB production environment copper clad PCB material is coated with a UV photo-resist and then exposed to a UV light source to produce either a positive or negative image on the copper. The unexposed coating is then removed and the PCB etched. For the DITer this process involves printing either a positive or a negative on a clear acetate sheet; then laying the sheet over the CEM coated PCB and exposing it to a UV light source...developing and etching are the same as a production environment, but for "one offs" and "prototypes" this process is more than a little time consuming. My thought is to use a UV Laser Diode and essentially "print" the image directly via an X-Y stage onto the CEM PCB.
I already have the capability of "milling" PCBs using my CNC router, but there are some caveats to direct milling PCBs that can make it a less than ideal method. For instance when possible I use >30mil trace spacing and attempt to keep traces >20mil, but this is obviously not possible with SOIC or smaller packages....which requires the use of a "v-bit" which necessitates a tool change and requires manually defining the tool-paths....
Well, if you as a reader have made it this far, thank you! I don't mind searching and reading, but a bit of guidance toward what I should be searching for would be a great kindness.
Thanks,
Fish
The first PCB prototyping method I am interested in is ablating a "painted" photo-resist from a copper clad board. There are is a myriad of info on the net involving Laser Ablation of various consumer paints sprayed onto copper clad board, but most of the information involves fairly high-powered commercial CO2 Lasers; a recurrent problem seems to be selecting a low enough power setting on commercial laser engravers to minimize inadvertent ablation, while still maintaining the beam.....seemingly suggesting it may be possible to achieve the task with a low to medium powered Laser Diode....but there is a tremendous gulf between the "lowest power setting" on a 50W-200W commercial CO2 laser and the readily available 5mW to 3W Laser Diodes.... And Sooooo much I don't know about Laser Diodes....
I am familiar with the concept of "pulsing" conventional LEDs to achieve very high peak power bursts while maintaining the "average power" specifications of the device...and have read that "pulsing" is a technique employed in some situations involving Lasers....but I am not confident I could work much below the 10uS time domain, and I have read pulsing references about pulsing in the nano and pico second time domains...I just don't think those are in my wheelhouse....Sooo, is it possible to achieve paint ablation with a <<5W diode laser? If so, what would be a good starting place? Is pulsing an "option" or mandatory? If mandatory, what are some guidelines regarding frequency and duty cycle? Do Laser diodes behave similarly to conventional diodes wrt (With Respect To) drive requirements such that I could prototype//debug the driver circuitry using a comparatively cheap conventional LED and expect a Laser Diode to act similarly (assuming Vf, If and Power Rating characteristics were similar)?
And as if the above is not enough for a first post, lol, the second Laser//PCB prototyping application I am interested in exploring is Laser based UV Exposure of CEM PCBs. I have not found any information on the net about attempts to use this approach, but the concept seems plausible to me. In a typical PCB production environment copper clad PCB material is coated with a UV photo-resist and then exposed to a UV light source to produce either a positive or negative image on the copper. The unexposed coating is then removed and the PCB etched. For the DITer this process involves printing either a positive or a negative on a clear acetate sheet; then laying the sheet over the CEM coated PCB and exposing it to a UV light source...developing and etching are the same as a production environment, but for "one offs" and "prototypes" this process is more than a little time consuming. My thought is to use a UV Laser Diode and essentially "print" the image directly via an X-Y stage onto the CEM PCB.
I already have the capability of "milling" PCBs using my CNC router, but there are some caveats to direct milling PCBs that can make it a less than ideal method. For instance when possible I use >30mil trace spacing and attempt to keep traces >20mil, but this is obviously not possible with SOIC or smaller packages....which requires the use of a "v-bit" which necessitates a tool change and requires manually defining the tool-paths....
Well, if you as a reader have made it this far, thank you! I don't mind searching and reading, but a bit of guidance toward what I should be searching for would be a great kindness.
Thanks,
Fish
