Make Your Own PCB Solder Mask with a Desktop CNC

In this how-to, we show you how to apply and mill a solder mask using our precise Bantam Tools Desktop PCB Milling Machine. A solder mask is used to protect circuit boards from oxidation and to help prevent solder bridges from forming between your traces. Solder masks aren’t always necessary when you’re quickly prototyping circuit boards on your Bantam Tools Desktop PCB Milling Machine, but if you’re planning to make a PCB that will last, they’re essential.

 
 

TOOLS

MATERIALS

FILES

For this how-to we’re going to be using an ATtiny breakout board we designed in EAGLE. Feel free to use your own files as you follow along or download our project files to follow along.

STEP 1: CREATE AN SVG FILE

First you’ll need to create an SVG file for the tStop layer of your PCB. The tStop indicates where a solder mask should not be applied. You’ll use this SVG later in Step 4 to mill away the excess solder mask and expose your copper pads. Download the eagle-2-svg-1.4.1.ulp file from the EAGLE website. 

 
 

Open up your board design in EAGLE. In the top left corner, click Layer Settings. In the pop-up window, click Hide Layers, select the tStop layer, and then click Okay. Now the tStop layer is isolated and should be the only one visible.

 
 

Using the command line, execute the ULP with the Run command, followed by the ULP file location.

 
 

Follow the prompts, and you’ll have SVG in seconds! Save the SVG for later. We’ll use it in Step 4. 

STEP 2: MILL PCB TRACES

For this step, you’ll use the EAGLE (.brd) file for your PCB. Mount the PCB alignment bracket onto the Desktop PCB Milling Machine’s spoilboard, load your tooling, and drop your PCB design file into the Bantam Tools Desktop Milling Machine Software. While setting up your file, make sure that only Traces is selected.

 
 

Mill your PCB.

Note: For this milling operation, we used a 1/32” flat end mill and a 0.005” PCB engraving bit. The tools you use may vary depending on your board design. 

STEP 3: APPLY AND CURE YOUR SOLDER MASK

After you’ve milled the traces, remove the PCB from the spoilboard and place it on a flat surface. This part can get a little messy, so you’ll want to wear gloves. Place a small amount of UV solder resin on the PCB. Cover the resin with a plastic sheet and gently spread it with a straight edge (e.g., a scraper, credit card, butter knife). To ensure the resin is spread as evenly as possible, place a piece of polycarbonate or glass on top of the plastic sheet and press down. 

Once you’ve spread out the resin, with the plastic sheet still on, use the UV light to cure the solder mask. The exposure time will vary depending on how thickly you applied the resin, the size of the UV light you’re using, and the size of your circuit board. If you’re successful, you’ll be able to easily peel off the plastic sheet. Roughly 15-30 seconds of continuous exposure worked in our tests, but you may need to experiment and adjust depending on the UV light you’re using.

STEP 4: MILL AWAY THE SOLDER MASK

Now it’s time to use the SVG file you made in Step 1. Using the alignment bracket as your guide, place the PCB back onto the spoilboard. Probe the material thickness using the built-in probing routine in the Bantam Tools software. Because board thickness can vary, you’ll want to use a spring-loaded tip that will adjust to the small surface height differences. We used this floating engraving tool along with our 0.005” PCB engraving bit for this operation. 

Note: The floating engraving tool we used requires a ¼” collet. 

Next, load the SVG file into the Bantam Tools software and align it with the board design (as shown below). Set the engraving depth for the SVG at 0.003”, and set the Plan placement at +0.003” on the Z-axis. This will tell the mill to cut at the top of the copper and barely touch it—as long as everything is as even as possible.

When you’re all set up, hit Start Milling.

 
 

STEP 5: MILL THE HOLES AND OUTLINE

With the pads clear of solder, finish up the board by milling the holes and outline. Remember to select Holes and Outline and deselect Traces when you’re setting up your EAGLE file in the Bantam Tools software.

 
 

And just like that you’ve successfully milled a custom PCB board and applied a solder mask right on your desktop. Time to solder!

 
 

Is there a topic you’d like us to cover in our next how-to video? Email resources@bantamtools.com or reach out to us on our social media channels. Be sure to follow us on Instagram, Facebook, and Twitter for the latest how-tos, CNC projects, and updates!

How-To'sDevin CooperSolder Masks, PCB