Printed Circuit Board Mk2

[Keith Colson]

I had a second go at making a printed circuit board on the laser this week. I had some translucent green lacquer specially mixed in a spray can for the job. Here are a couple of pictures. Its really awesome being able to kick out a professional board overnight for a customer. Loving this laser! Hating Corel though haha. I need some training or something.

Seeing as the process is quite in depth I have written a blog post (http://www.edns.co.nz/index.php/blog/laser-cut-printed-circuit-board-pcb/) covering the whole process.

Bottom Side
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Top Side
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Cheers
Keith

[Mike Null]

Keith

You're welcome to post your blog in our blog section if you like.

[Aaron Koehl]

Love this!!

[Keith Colson]

Here is the complete unit assembled and tested. If I could get the laser to solder it next, that would be fun.
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And installed in the laser cut case. Oversize black Abs for the sides which adds some drop/shock resistance, and some feet.
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I really hate drilling and tapping the acrylic. I should do some recessed nuts next time, or even better a clip together case.

Cheers
Keith

[Balsanu Gabi]

Hi Keith,

I am very interested in this approach. I will pass the drilling and cutting (with laser) steps since I have a CNC router, but I do have some questions:
- what PCB package do you use?
- I try to replicate the Corel step, but I failed big time. Can you shed some light on this? A step by step little tut will be great.
- what kind of paint do you use for mask?

Many thanks in advance for taking time to post this technique.
Gabi

[Keith Colson]

Hi Gabi, did you follow the link to the blog? It details a lot of it. Yes, Corel is always challenging for me too.

A cnc will not be as flexible on the drilling as you will need to do bit changes and drilling say a 0.3mm hole can get tricky too. If you do it I would be interested to hear how it went.

Cheers
Keith

[Balsanu Gabi]

Hi Keith,

Yes, I read that few times and the questions are still there.
- pcb package
- in Corel did you group the traces and after that you the outline board rectangle behind?
- paint?

Regarding holes I was thinking to make a single dimension hole. I dont know if that's ok. I will try and report back.

Thank you
Gabi

[Ian Johnson]

I do a similar process, and I use Eagle. Here are my steps-

Show top (or bottom), pads, vias, dimension layers.
Print-> Save as PDF with the all black option, and mirror if it is the bottom layer.
I do this once for Top, once for Bottom (mirrored).
In the command line, type Run Drill-Aid.ulp. This will create layer #116 with just the holes. I change the setting for the layer so it shows them solid rather than cross hatched.
Save a PDF of just this new holes layer along with Dimension.
I also create PDFs of just the pads for both front and back.

In Corel, import the PDF for top, and hit spacebar so it positions it automatically.
Select the imported image and ungroup it.
Select the board outline and change the stroke color (pen icon) to a color such as blue. I use lasercut which lets me assign different settings to different colored lines, so the color isn't important, only that it is different.
Copy the outline and paste it to a new layer. I use this later to cut out the board.
Back on the imported layer, select everything other than the board outline and Transform/Invert.
Draw a rectangle that covers the area of the board.
Double-click the paint can and set the fill to black.
Send the black rectangle to the back of the layer. All the inverted stuff will now show as white on top of that black rectangle.
Select everything and convert to bitmap, setting to Black and White and 2400dpi.

Raster the bitmap into the paint (matte finish black spraypaint). The copper will be coated with residue from the burned away paint, which can be cleaned away with a q-tip and some alcohol. Be gentle because you can clean off thin traces.

After etching, I convert the holes to bitmap (without inverting) and raster the board enough to create starter holes that will position the drill bit on my press. When doing double sided boards you have to do holes after etching, and I find doing it with the laser damages the copper. After the etching holes and drilling, I might spray paint the board again, and then raster the pads file (again, no need to invert). This creates a solder mask, with only the pads exposed.

Every layer I send to the laser contains the board outline, except for Top and Bottom since those already contain it within the bitmap. For something like holes or pads, I change the board outline to another color and keep it vector while changing everything else to bitmap. With my Chinese laser, I can set the board outline to not be output so it will only do the raster. However it still takes that outline into account when positioning the job. As long as the outline is in every file sent to the laser, everything will line up. At the end, I send the outline only layer to the laser and cut out the board.

[Keith Colson]

Hi Ian

I pretty much do the same thing as you, here are the only things I do differently.

When I raster the copper I do it twice. The second run cleans the copper really nicely so it can drop straight into the etch tank with no cleaning at all. I do use a soft paint brush on the board during the etch to remove the oxide layer.

I export the cutting layer as a dxf with the holes undersized to compensate for the kerf. I find the laser drills the board with very little effort.

Cheers
Keith

[Ian Johnson]

I had been doing multiple passes, but it seemed like it was thinning out the pads and traces more, which were already a bit thin from the kerf. I've been accumulating a bit of a library of larger pad versions of things, but it's a pain to go in and edit every device I use. Most of what I DIY is meant to go to fab, so there is a bit of struggle between taking into account the laser's limitations while prototyping, while wanting the prototype to be as close to a final design as possible.

[Keith Colson]

Hi Ian

Good point, the only thing I customise is the through hole pads. I add one undersize circle line on a different layer. Other than that the rest of the design is stock, so it's not much effort for me. If you are are doing fine pitch then I can see the pads could come out a bit thin. For 50 mil pitch I run the stock pads, for smaller than that it is probably too hard to go down the laser path. I only do this process when I need a board tomorrow.

As for the 2nd pass thinning out the artwork, You may not have your laser in tip top condition. I have spent a lot of time getting my focus right and also tuning out the mechanical backlash in the belt system.

[Balsanu Gabi]

Thank both of you. It is pretty clear now.

Gabi