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Surface mount components often intimidate people. For me, making the jump from breadboards and perforated PCB to creating schematics in Altium and using a PCB mill was huge. I no longer had to spend an entire day soldering jumper wires around a perf board, crossing wire after wire, only to find out that something wasn’t working. All that was very frustrating.
When I was hired at SparkFun, I made the switch from Altium to Eagle, and instead of milling my PCBs, I had easy access to BatchPCB.
Recently, however, I started designing a PCB that has lots of LEDs, lots of rotary encoders, and lots of outputs to relays. Trying to pack this board with through-hole components like resistors and transistors was challenging and resulted in having to increase the board size larger than I would have liked. The increased area of the board also drove the cost of the board up, very high. If only there was a way to make the board smaller, but still get the functionality that I needed. But of course! Use surface mount components. Surface Mount Devices (SMD) are very small and take up less space! I had never considered using surface mount components before, but since I had the resources available to do so, the time had come to learn.
There was still one problem though, how to solder the SMD components. I didn't want to have to solder each component on by hand. That would be very tedious and time consuming. I needed to be able to apply solder paste quickly and easily. I needed a stencil. At SparkFun, we use metal stencils. They are strong and last for thousands of builds. They're expensive though. Not very practical for building one or two boards. Especially if they are prototypes and their design could change.
We had heard rumor of people creating their own stencils using vinyl sheeting and a plotting cutter. But what was the secret? How did they do it? Well in no time at all, I had my answer.
In this tutorial we are going to talk about making solder paste stencils out of board files in Eagle.
For this tutorial, I will be using the following software:
Note: Adobe Illustrator is not required. Craft Robo Pro has made a plug-in for Illustrator that makes it easy to orient your files to be cut. If you wanted something free, Inkscape would do the trick. Be warned though, it will take some practice to get your files to cut out in the orientation and location you want without using the plugin.
For convenience, I am going to use the Arduino Pro eagle files found on the SparkFun website. If you have never used Eagle, there is a great series of tutorials right here that will get you going! I am going to skip over all of that and get right to the goods though. I have submitted my files to BatchPCB and, in the blink of an eye, have a plain Arduino Pro board. You don’t have you use BatchPCB. You can get your board made however you would like.
Now we want to prepare a file to be cut out. Open up the .brd file from your project. If you use SparkFun hotkeys, F8 and F11 will get you our ‘standard’ layers view. Don’t worry about it if you don’t have the hot keys. We don’t need to see these layers for long anyways.
Click on the images for a closer view
Next, go to the Display button (also under View -> Display/hide layers.) Turn off every layer except for tCream. You should see something like the picture below. These are the pads that the paste will go on.
This is good, but we don't want the cross hatching fill. If we leave it there, the cutter will cut along all of those lines. To remove them, select the tCream layer and hit the Change button. Click the Fillstyle option and change it to solid. Go ahead and hit Ok.
If everything worked correctly, you should see the tCream layer with no fill inside the boxes!
At this point you will need a .pdf printer. There are several free ones out there. You can use any one that you would like. I choose Bullzip for no particular reason. Head over to their website, and get a copy installed on your computer. Once it is installed, open your board file back up. Go to File -> Print and choose Bullzip PDF Printer. Be sure that the ‘Scale Factor’ is 1. Otherwise your stencil will not fit on your board correctly.
Hit OK and wait for the next window to appear.
Make sure the format is PDF and hit Save. Also, be sure to pay attention to where you are saving it!
After it finishes, you should have a .pdf that looks like this:
This is our Graphtec 15" CE5000-40 Craft Robo Pro Vinyl Cutter. Basically, it is a knife with a brain. It essentially works like an inkjet printer: a combination of very precise X and Y movements allow it to cut very complicated shapes.
Here you can see the tiny cutting blade.
No, we aren’t going to alert the newspapers and magazines. I’m talking about your stencil material. Here at SparkFun, we have a jumbo roll of vinyl. Since this material requires a sticky backer, we need to cut a section of vinyl that will fit in the machine. The sticky backer holds the vinyl in place while it is being cut.
We need a piece that will fit on the sticky backer, like so:
At this point we could just print it to the cutting plotter. Notice how the tCream layer came out in the center of the page though? That will create a lot of wasted material. Since we are all about being scrappy, let's edit the file a bit. You can also adjust the alignment in the printing options, but I like to know exactly how my file is placed before I cut it out. This will also be useful if you want more than one copy or different stencils cut out at the same time.
I’m going to use Illustrator because as I mentioned before, it has a nice plug-in that makes it easy to use. CorelDraw also has a plug-in for this cutter but I wasn't having much luck getting it to work. If you don’t have Illustrator, Inkscape will work just fine. Best of all: it’s free! Be warned though, I have found it to be difficult to know exactly where the file will be cut out on the vinyl in relation to where is it on your screen without the plug-in. However, with a little practice it shouldn't be a problem.
Open up the .pdf in the program of your choice. I have found that it helps to set your page size to the match the size of the vinyl you will be cutting on. I like to be able to see exactly how everything is going to cut out. Be sure to add a border around the tCream pads. That way you wont have to cut it out by hand at the finish. Arrange the .pdf so that it is in the corner of your page.
At this point, if you aren't using Illustrator or CorelDraw, you will have to venture into the unknown by yourself. It takes a few tries to figure out how the stencil will be cut out in relation to your screen layout.
If you are using Illustrator or CorelDraw, now is the time to use the plugin!
At this point we can send the job to the plotter if want. There are, however, several adjustments that you can make on the machine including speed, force, and quality. Each one of these will change the quality of your stencil. You want the force to be great enough to cut through the vinyl but not hard enough to cut into the sticky backing. Cutting at a faster speed will get your stencil out sooner, but cut too fast and you will start to tear the corners of your rectangles. There is a sweet spot that gives you good speed and good quality!
On this tab, we can change several variables - most importantly being the media size. Set it to match the size of the vinyl on the sticky backer.
On another tab we can set the most important variables of all: Speed, Force, and Quality. You will need to experiment with your cutter to see what works best. Every material has its own setting.
Once the material has been loaded, we hit Send and the machine cuts it out!
You'll notice that the vinyl is very choppy around the Atmel IC pins. The pins are so small and so close together that the machine rips the vinyl. Don't worry about it though, we'll get to that later.
If you are using Inkscape for this part, use the control panel on the cutter to set the speed, force, and quality before you send the job over.
Now that the stencil has been cut out we can use it to apply solder paste to our board. It’s pretty straight forward: just line up the stencil, hold it firmly down with one hand, and drag the putty knife away from that hand with your other hand. Pressing hard will give you a nice thin layer of solder paste on your pads! If you look closely, the pins on the ATMEL have paste bridging between them. That is okay, we will take care of that later! If you need a Solder Paste Stenciling refresher, check out Nate's tutorial!
We’re almost there! Place components in their correct place using tweezers. Don’t forget to pay attention to any components that have a polarity and, of course, the Atmel IC! The solder paste will hold the components in place, just be gentle! Here I have two of all the required components to make a 5v Arduino Pro.
Once all the components are in place we are ready to heat up the boards and solder everything down. Check out this Reflow Tutorial if you need more info!
Remember earlier how we saw that the stencil area around the Atmel IC had ripped? It is quite possible that some of the pins on the chip have bridged because of that. No Problem. Use some solder wick to remove the jumpers leaving you with a finished PCB! Look over here for a SMD tutorial.
At last the jumpers have been removed. I used a magnifying glass to look very closely and check for any other problems before I powered it up.
At long last, we are ready to test it. I jogged over to Theo, our expert QC and Diagnostics guy, and had him put the Arduino bootloader on it. After a moment of suspense, the board lit up and was running the blink sketch! Success!
So there you have it, making your own stencils and using them too. For a single person, buying this cutter might be out of the question. For a group of people, like a hacker space, this would be a great investment! Now all you need to do is learn how to etch your own copper plated boards and you'll be all set to start your own production line!
I hope you found this tutorial helpful! Please feel free to post any questions or comments below and I will try and answer! Or if you just want to yell, you can do that here, too.
Here are links to other tool related SparkFun Tutorials.
Other useful links.