Intro: DIY Solder Paste Stencil
Most people learn throughhole soldering before taking the leap to go into SMT (surface mount technology) soldering. When I was first advised to try my hand at SMT soldering, my immediate thought was, whoa, that's way too small! I'll get solder paste everywhere!
But with a steady hand and some perseverance, I learned how to SMT solder, one pad at a time. And of course, the same engineers that suggested I learn how to SMT solder also suggested I look into solder paste stencils. I haven't until now!
Our hackerspace, the Rabbit Hole was generously provided a Silhouette Portrait which is capable of cutting different types of materials and I thought, what non-artsy idea can I come up with that I need in my daily electronics life? Ah-hah! Solder Paste Stencil! So this instructable is a proof-of-concept demonstration of how to get a relatively reliable solder paste stencil created with your Silhouette Portrait!
- Silhouette Portrait machine
- Silhouette backing sheet (with one side that's sticky)
- Material you'd like to make your stencil out of. I proofed of concept-ed with Silhouette branded vellum
- Solder paste
- SVG file from the PCB you're trying to make a stencil for
- Inkscape (open source/freely available vector graphic program)
Step 1: Export Your SVG File
We use KiCad for our PCB designs, but if you use any other PCB design program, this should be easily done. First, you'll want to export an SVG file for the paste layers of your PCB. In our case, only one side of the PCB required exporting.
Step 2: Open Your File in Inkscape
If you don't have another graphics program that is capable of working with SVG files, be sure to get Inkscape. It's an open-source and free vector-based graphics editor.
Open up your SVG file from KiCad in Inkscape. Other tutorials mention resizing the file by 125%, so that's what I did. This requires selecting all (ctrl-A), going to Object, Transform, Scale, then applying a 125% increase in size.
- I actually don't know that this resizing was necessary because of what Silhouette does to the file, but opening it in Inkscape also allows you to save the file as a PNG, which is what the Silhouette Studio Basic program can use.
Save the file as a PNG.
Step 3: Open the PNG File in Silhouette Studio and Resize
Open the PNG file in Silhouette's program. When you select it, you may notice that the size of the overall paste pads is significantly smaller than what your actual board pads are. At least, I noticed it was about 1/2 the size of what it needed to be.
I measured the rough dimensions of what my board's length and width was and expanded the graphic until it was roughly 0.5"x0.5". This is of course the main detraction from using this method to create a reliable stencil, but again, I was trying to go for proof-of-concept.
Step 4: Create the Boxes That Will Be Cut
Using the box feature in Silhouette Studio, highlight the areas you want the Silhouette to cut from your material. This coincides to the copper pads that solder will eventually go on.
Step 5: Prepare Your Materials + Silhouette for Cutting
The settings on the Silhouette that I used for cutting the vellum were blade size 7, speed 1, and pressure 33. The Silhouette comes with a grid plastic sheet with one side which is sticky. This allows you to place your material on it and prevents unwanted movement as the blade cuts in.
Take one sheet of the vellum and attach it to the grid plastic sheet.
You'll then want to center this sheet between the rollers on the Silhouette Portrait and press the top button. This will automatically feed the plastic sheet to its starting spot. Be wary not to use the second button. I tried this and it ended up cutting ON the plastic sheet instead of my material - I think it didn't feed it through enough.
Go back to the Silhouette Studio program and "Send to Silhouette" via the top right icon. Press Start, and watch/listen the Silhouette cutter do its thing!
Step 6: Peel and Clean
When the cutting has completed, the Silhouette will reverse its rollers towards you. Finish unloading it by pressing the middle button. This will completely release the grid plastic sheet back to you.
Since the SMT pads are so small, when you peel up the vellum, you may notice there are some straggling squares hanging on. Carefully get rid of these with tweezers or brush them away with your finger. With any luck, some of them will also stick to the sticking backing.
Nice thing about vellum is that it's strong enough that it won't tear easily, even when you're cleaning the little hanging bits off.
Step 7: Compare to Your Board!
This is where you get to see how it compares to your board, to see whether it will actually work as a stencil for you!
And this looked nearly perfect!
Step 8: Use It As an Actual Stencil!
To test this, I placed it down, put a line of solder paste on one side, and essentially squeegee'd it towards the other side. I had to add a few more spots of solder paste to get enough, but if you look at the end result, it turned out to be a workable solution that saved me from having to individually solder 16 points!
The components on this board were mostly 0805s and the smallest was a SOT-23.
What I would change:
- Given that I now know it works, I would probably change the material from vellum to something like a transparency, just so that it's slightly more rigid. But the steps would be no different than how I demonstrated!
- I would also try to find a more reliable scaling method so that when I imported the image into Silhouette Studio, I would not have to resize it by eye.