Laser cut printed circuit board PCB

Here is a simple printed circuit board I needed really quickly so I made it on my Universal laser cutter. I am really pleased with it and so is my customer. If you read on, I will tell you the details about the process I have come up with. Note that the holes were drilled with the laser! The soldermask was done on laser engraver too.

Laser_Cut_PCB_Bottom.jpg

Laser_Cut_PCB_Top.jpg

I used my PCB software to design the PCB. I exported several layers as listed.

  • Top layer - this was printed to a PDF using cutePDF. It just had the "top overlay" designators etc
  • Cut Layer - this layer was exported as a 0 line width DXF. It was exported as a 0 line width DXF. It had all the holes and the outline of the board. I put all the cutting on their own layer.  I made all the "cut circles" (holes)  0.2mm undersize in the PCB library.
  • Copper Layer - this was printed as a PDF using "mirror, show holes". This was basically an image of the copper e.g. bottom layer and multilayer was printed
  • Solder mask Layer - I exported just the top layer so I would get the multilayer pads only. I guess I will need a better solution here for SMT or multi-layer. I will work that out later.

ALL LAYERS have a 2.8mm alignment circle at the top of the board. I imported all files above into CorelDraw and used the 2.8mm alignment circle to stack all the layers on top of each other. In CorelDraw I used the object manager put them into Top Layer, Nest Layer, Copper Layer, Mask Layer. Make sure all PDF layers are black and white.

Top Layer

The top layer has 3 colours. Red is the vector layer which is cut, blue is a raster layer which is engraved, green is the alignment layer which is also cut (just the two circles at the top).

I ran this all as one batch on the laser. I was cutting FR3 board. Note: the copper will not get cut through but will look dimpled on the bottom of the PCB. When complete you can snap the board out being careful not to tear the copper off the board. Don't breathe the burnt fiberglass, I do this all under the lasers extraction system.

top_layer.PNG

Nest Layer

I remove the laser cutting bed. Now I stick some 6mm acrylic down to the engraving bed with 4 small pieces of double sided tape. I simply re run the top layer with all colours turned off except for the green layer which is just two alignment circles of 2.8mm.When done I have two holes. Now I run a 3mm drill through those holes by hand. Then I place some 3mm steel dowel pins in the holes. While I have the 3mm drill bit in hand I run it through the PCB alignment holes too.

Note: Once you have your dowel pins in place avoid turning the laser off or adjusting the bed as things can move about 50 to 150um on my machine. Your best bet is to cut the nest with the laser already focused for the PCB engrave.

Bottom Layer Prep

The circuit board can now be given a good clean. A good scrub with a Scotch-Brite pad followed by a wipe down with some isopropyl works great. Now I spray paint the board with some cheap black spray paint, for contrast and etch resist. It's naughty but I dry the paint in the laser with the extraction turned on. I also leave the air assist on so no paint vapours wander up into my lens etc.

Bottom Layer

I find CorelDraw very difficult to deal with at this point (and every day lol) but here is what seems to work for me. Select your bottom layer and click effects->transform->invert. At this point it looks like Corel stuffed it all up but wait! Now place a black rectangle the size of the board behind this mess and it all looks ok again! Now you can place the board on the dowel pins and burn that paint off. Two passes of 100% speed x 50% power seems to work well for me.

  bot_layer.PNG

The reason I filled in all the extra copper was to make etching faster and use less chemicals, consider this. Etch the board in ferric chloride or ammonia persulfate etc. Once etched, wash it off with water and rap it on the work table. All the carbon soot will fall out, and your holes will be clear if you got everything right. Its pretty cool to have a drilled board at this stage.

Solder Mask or Solder Resist

Get your nicely etched board and paint it with solder mask. I paint both sides. I got some paint specially made up at the paint shop. I got them to mix a pure green 10% with a clear lacquer 90% for a nice green tint. This gave me that classic circuit board look. Once it is dry, stick it on the dowel pins again. Now you can laser off the paint to reveal the copper pads. Solder mask!

mask_layer.PNG

You're finished! She looks shiny and new!

 Laser_Cut_PCB_Bottom.jpg

Afterthoughts

Could I make a double sided PCB? yes but plated through hole might be hard at home but I have some copper pins made for this. They are like super small thumb tacks so I should give that a crack.

How fine can you make the track and space? If the laser is in tip top shape with a 2.0 focus I can get 0.18mm (7mil) track and space.With a better lens that might be halved.

One bonus, most PCB fabricators can't cut square holes, the laser can!

Assembled

It soldered up nicely and all the parts fit very well.

100_7471.jpg

 

Laser cut and engraved enclosure.

To finish it off I quickly designed up a case in Acrylic and ABS, the ABS is over-sized to give drop/shock protection. The ABS also has feet cut out on the bottom.\

100_7478.jpg

 

If you try it please let me know! Good luck

Keith Colson

 

 

Posted by

Share: