Homebrew PCBs

Donald,
In the Gerber code D1 is "expose on", D2 is "expose off" and D3 is "flash".  For the Gcode one could convert these to M codes like spindle on/off.  Another way is to convert D1/D1 to S codes "spindle speed"  Then in the laser diode electronics one could modulate the power ie.  S0 = off  S100 = full power  S50 = 50% power etc. Its just some code for the file conversion program.

I am not sure how much trouble the mill's X and Y acceleration ramp will be to the exposure profile.  Would like not to have to compensate the power during movement ramp up. I think in Mach3 one would treat it like a plasma cutter and use CV mode.

Craig

--- In Homebrew_PCBs@yahoogroups.com, Donald H Locker <dhlocker@...> wrote:
>
> Hi, Craig.
> 
> The vector plotting reminds me of pen plotters - pen-down would be laser-on; pen-up would be laser-off.  I don't think that's part of the G-code or Gerber instruction set, though.
> 
> The round spot may take some non-spherical optics.  Think astigmatism.
> 
> As for the rest - very cool.
> Donald
> 
> ----- Original Message -----
> From: "designer_craig" <cs6061@...>
> To: "Homebrew PCBs" <Homebrew_PCBs@yahoogroups.com>
> Sent: Friday, November 13, 2009 2:21:00 PM GMT -05:00 US/Canada Eastern
> Subject: [Homebrew_PCBs] Re: Making PCB using these new 405nm LASER Diodes
> 
> I had the same idea last spring and purchased a 405nm laser diode with holder/lense and some Riston film off ebay.  I added a heat sink to the holder and have driven it up to 110ma.  At that power level it will burn through paper, so I have no doubts that it should harden the photo resist. I did some initial crude calculations based on the Riston data and estimated diode power that led me to believe it would be possible to write a .001" dia spot at 80"/sec.
> 
> My initial plan is not to raster scan the board but to vector draw the pattern using my Bridgeport mill that is currently being converted to CNC. I will need to write some code to convert the Gerber photo plot file to a G-Code file to drive the mill.  These files are very similar, the Gerber format being an offshoot of the G-code format. Since I plann on using a fixed spot size, wide traces will need multiple passes as will donuts etc. This all has to be coded in the conversion program.  
> 
> Currently I am working on the mill's CNC conversion and have not done any testing on the direct exposure part of the project. It will be a couple of months before the mill is ready for PCB testing.
> 
> Issues to be resolved:
> 1.Is the exposure of photo resist linear ie. is high power UV for a short time the same as low power UV for a longer time.
> 
> 2.Code to make multiple passes for trace and shape widths from the point gerber data.
> 
> 3.How to get a .001" dia round spot.  The laser diode output is not round. How to measure the spot dia.
> 
> 4.How long will it take to expose a 3'x5" board?
> 
> Craig
>