G'day! I'm going to show you how I made my very first solder stencil. This is a stencil I made to suit this prototype that I'm working on, and this is a simple board. You could hand solder this, but I just couldn't resist getting into the weeds and learning something new, so I'll show you how I went from the PCB design files to this laser cut polyamide stencil. Let's do it!

Okay, so starting off with a PCB that we want to prototype, I'm working in Keycap at the moment (for anyone interested). We're going to generate the artwork that's going to make its way onto our stencil. To do that, we can go to the plot dialog. You'd usually use this to generate Gerbers to send to your PCB manufacturer, but instead of plotting Gerbers for our stencil, we're going to plot an SVG - just a graphics file that we could send to a printer. After all, most laser cutters are basically printers if you think about it. So, I'll just select the SVG format and I don't need any of the other layers, so I'll deselect everything and just go with the front paste layer - that's the front solder paste. As for these other options, I think these are okay, so I'll just hit the plot button there.

Now, if I open my project directory inside the output directory Gerbers, I've plotted my paste layer. Great! We've got a graphics file and we could just send that to the printer - that would work, we would get a stencil out of it. But there's just a little adjustment that we need to make to it, and I'll show you why.

If I zoom in on one of the components here, this is one of the LEDs. You can see the red layer is the top copper layer, we have the four pads here. Now, if I turn off all the layers and show just the front copper and the front paste, if I toggle the front copper on and off, you can see that the paste layer matches exactly the outline of the top copper layer. In fact, maybe I can change the color of the paste layer to make it a bit more obvious - so you can see that the paste layer is exactly the same shape as the top copper layer, and that's not what we want. We want the paste layer to be slightly larger than the top copper layer, so that when we place the stencil on the board and we apply pressure to it, the paste is forced into the gaps between the pads, and that's what's going to give us a good solder joint.

I'm going to use Adobe Illustrator to shrink the size of the apertures in the solder stencil. To do this, I'll open my PCB directory and open the SVG file that we created before. I'll center it on the canvas and then ungroup the object into its constituent parts by going to Object > Ungroup or by pressing Ctrl + Shift + G.

Now I have just the single rectangles which are the apertures in the silk screen. I want to shrink them all by some amount, so I'll select all of the objects and navigate to Object > Transform > Transform Each. This will transform each individual aperture around its center rather than transforming the whole group which might change the location of the apertures.

On a normal PCB with solder mask, this purple paste layer matches the pad exactly. However, since I'm prototyping on a bare copper clad board with no solder mask, I need to shrink the pads in the artwork to prevent unintended solder bridges.

Very easily, we can just enter a new scale. I'm just going to select 80 for both the horizontal and vertical scales and if I toggle this preview option, you should see the effect of what's going to happen. All of those apertures are just going to shrink about their center and that's going to give us just a little more clearance to avoid solder bridges and also gives us a bit of tolerance for manual alignment of the stencil on the PCB.

Great, got a file that's ready for lazy cutting, but I've never laser cut capton on film before, so I had to characterize the material on our laser cutter. We're using a Trotec Speedy 400 with 60 Watt laser and these are the results of my experiment. On the left is the power percentage and on the right is the speed percentage. So I started off with 60/50 and that gave this kind of discoloring printing effect. You could theoretically use this setting to print onto capton, that's pretty cool. I tried way overshot the mark with 150, that left quite a bit of scorching actually around the edge. I've cleaned that off since, but after going through and going up and down a little bit, I landed on a setting I was happy with, which was 85.50. So that's 85 percent power, 50 speed on a 60 Watt laser.

That's everything I had to do to prepare the file. After that, all I did was send that to the laser cutter and cut out the stencil. So overall, making the laser cut solder paste stencil was really straightforward. It's just quite a small step in the process of making this prototype. You could easily knock that over in a few minutes even just while the PCB is being milled.

I did use that stencil to assemble this PCB. If you're wondering why things are looking not super level, I was designing as if this was going to be made by a PCB manufacturer. So actually underneath all of these LEDs is a small via and...

By having to put a small piece of wire through each one of the vias and solder it on, I've created a bump that's lifted the LEDs in place. The stencil performed really nicely after making just one board and it appears to have not been worn or damaged in any way. I wouldn't be surprised if you could do a small once-off run of 10 or 20 boards before wearing one of these out or damaging it.

Let's talk more about those power and speed settings. That setting was just something that I arrived at after a little bit of experimentation. The power was about 85 and the speed was about 50. There's my solution, but there could easily be some envelope of solutions that may produce even better results. Maybe some kind of lower power and slower speed would be appropriate. I don't anticipate it, but maybe going full speed with a higher power might create a good cut.

If you've got any tips for laser cutting this material or any experience with that, I'd love to hear from you. Just leave it in the comments below.

And there you have it: a rapid prototype PCB solder stencil. I hope you learned something along the way. I know I did. Thanks for watching!