PCB Fiber Laser Etch with ComMarker B4 and Lightburn

Initial revision April 6^th 2023.

Property of Paul Ruby of PaulRubyAmplifiers.com

Contents

PCB Prep for Single Sided Board. 1

Express PCB Plus. 1

Hole Size. 1

Express PCB Example. 1

Processing in Lightburn. 1

Image Import 1

Creating Vector Outline Layers. 1

Getting Perfect Focus. 1

Time To Etch. 1

Lightburn Settings. 1

Results. 1

DISCLAIMER. 1

PCB Prep for Single Sided Board

Express PCB Plus

Free PCB creation software: ExpressPCB+ https://www.expresspcb.com/expresspcb-plus-pcb-layout-software/

Hole Size

Assuming you will hand-drill, only a small dimple is needed on pads for bit alignment.

If made too small, however, there isn’t enough room for gas to escape and the pad can bubble.

This image shows an example of 0.01” hole, which is too small.

The shiny part is where the pad has lifted into a cone shape. With 0.02” holes, this does not happen.

I’m going to try 0.015” holes next and show how to do this here.

Express PCB Example

Here’s an example PCB created with ExpressPCB Plus.

I show this mainly for hole size setting.

Select everything in the PCB and then change the hole size to desired value.

This shows 0.015” which is what I’m going to etch next.

I’ve hand-filled as much of the space between lines using rectangles and polygons.

ExpressPCB can fill the spaces by drawing a rectangle on the bottom copper and setting it to “pour.”

Adjust the pour clearance as desired.

I’ve tried this but the result is copper that is not connected to any nodes.

It’s all free-standing copper islands.

I’ve not figured out how to make a pour that explicitly connects to the ground node.

Here’s what the above would look like with a pour fill added, which may result in a better etch.

With the PCB created and ready, print it to PDF for etching:

Once you have a PDF, the bottom copper page must be cropped while leaving a bit of blank outline.

I use GIMP to import the PDF and crop but you can use any tool you like.

When editing the PDF, use a very high resolution, at least 1000DPI, for very crisp edges.

This will be important once in Lightburn.

I also use GIMP to add some bit of text into the copper.

This is strongly suggested so that you can be sure the image is not mirrored once in Lightburn.

Here's the PNG image after GIMP processing.

Note the required bit of blank border and a bit of text for visual orientation for later in lightburn.

Also note this is mirrored horizontally when printing to PDF from ExpressPCB because it is the bottom copper.

Correct orientation is obviously very important.

Processing in Lightburn

Image Import

Create a new Lightburn file and drag in the image to layer 00.

This image layer will not be used directly for etching.

Set the layer properties to NOT output but leave it showing.

Creating Vector Outline Layers

The reason for using a very high resolution prior to importing is to ensure the tracing of the image is very accurate.

I used 2000DPI for my image.

Select the image, right click and choose “Trace Image.”

This brings up a new window with options for tracing the image into a vector file.

Set Threshold to 0 to trace outside the entire copper area.

Click “Show Points” to see the created nodes of the trace.

Zoom in with the mouse wheel to look closely at the results.

At 2000DPI, the image is very crisp and easy to trace.

Feel free to adjust the settings to see how things change.

Click OK when you like the result.

Once you click OK, you will have vectors for layer 00.

ComMarker B4 settings are shown here:

500mm/s; 100% power; 20khz pulses; Offset Fill; Dot-width adjustment of 0.03mm; line spacing of 47um.

The intent is to move fast and hot. Going slow causes damage.

Going fast and doing multiple passes yields better results and it’s easy to creep up on being finished.

I would go faster but have found the lines start to wiggle beyond 500mm/s.

UPDATE: After running more boards, I suggest using a line spacing of 30um to get tight overlap of lines.

39um spacing is still leaving a bit of copper between lines.

This image is an offset fill with 39um line spacing on 1.5mm text.

This layer will do the etching using a contour fill around and between all the copper to be left intact.

Here’s a close-up view of the preview to show how this layer will cut.

In order to ensure the copper is well cleared when etching, I also make a second trace layer.

With the tracing selected, hit ctrl-D to duplicate it.

Then click a new layer for it.

This layer will have the same settings with one exception: line spacing 1.3 times the other layer to create interleaving cuts.

In this case, 47um*1.3=61um.

UPDATE: I now use 30um for the first layer and 39um for this 2^nd layer for tight overlap of etching.

Now the preview shows both layers and cut lines that don’t quite overlap, except for the first cut right at the copper edge.

Getting Perfect Focus

Perfect focus for etching is critical.

My B4 has a slight focus variation around the full size of the table.

It’s large enough to make it impossible to etch a very large PCB without a bit of shimming.

Small boards can be done bolted down.

I use the acrylic alignment bars as clamps to bolt the PCB down tight to the table.

This is very important. A half mm out of focus will not etch efficiently.

In order to test the focus, make one more layer to etch the outline of the board.

The tracings we made above already have a cut line around the outside.

Select the tracing and ungroup it with ctrl-u.

Then select only the outermost cut line and duplicate it using ctrl-d and put it on a new layer.

This will be used to test the focus.

At this point, only this layer is selected to be shown and output to the laser.

Run this once to make sure you have a very bright etch on the board around the entirety of the outline.

Only about 10 passes will fully cut through, so you don’t have many chances to do this test.

Don’t use a continuous run. Just once, then small tweak if needed, and repeat.

Time To Etch

Lightburn Settings

When ready to etch, only the two offset fill layers should be output.

Your PCB must be bolted down flat to the table and perfectly in focus.

The two layers are each configured for 1 pass.

So, two cutting passes will be done, one by each layer, for each run of the full job.

Click the Frame button to get to the job dialog box.

From here you can choose the number of repeat passes.

When in perfect focus, I’ve found about 8 total cuts, which is 4 repeats of the job, is enough.

If focus is not perfect or you have some variation in focus across the PCB, you may need a few more passes.

Perfect focus is critical.

Results

After 5 passes of the job and then buffed with steel wool.

The results are very good but do show some signs of burning the phenolic board in some spots.

This is especially true for larger etched spots. Doing a pour-fill to eliminate such areas may result in a better etch.

Small text is very clear. The ruler in this picture is mm. This suggests doing a pour fill with tight clearance would work very well. Next time. 😊

UPDATE: Doing a Pour fill improves the results and drastically reduces run time due to less etching. Well worth doing.

DISCLAIMER

Last updated April 06, 2023

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