The complete guide for PCB stencils?

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Earlier this year, I was informed of an amazing idea by the author of these two blogs: a complete guide for PCBASIC stencils. A lot of thought and testing went into the goal, and I think that the outcome is great.

Part 1 describes the process of making your own stencils, and part 2 goes over the design process and the test phase.

The theory

When I was little, I had a box filled with colored pencils. During homework time, I’d sit at the Kitchener it to the final product: the PCB that you will use as the interface between you and your board.

Designing PCB stencils and getting to this point was a major task for me. The list of things that I did in order to make this happen is quite long, and so I thought I would put it in a set of blog posts so that it can be properly documented.

As I started planning, I had in mind the following things:

  • Make a stencil maker tool with a touch screen control to print and configure a stencil design that was consistent with the same view-model and flow
  • Experiment with lots of different shapes to save both time and money
  • Get familiar with PCB layouts and see how you can mix them up to keep your design clear and consistent
  • Find and learn a lot about material properties
  • Improve a PCB layout editor I have that was missing some major features
  • Use for a long time the free version of Thingverse to publish a PCB design and a few files needed for the project
  • Build, test and publish my first generation boards with the supplied files
  • Spend a week in Europe to have a longer vacation and some fun
  • Make several prototypes and iterate the project on a fairly high level

Idea gathering

I usually start the brainstorming part in the previous step. This part of the process is when you break the design down into small independent units, and make something small enough so that you can make it without a pattern.

There are a few constraints that you have to consider in this process.

First, the board must be small enough to print on standard 300 dpi text printers. This means the stencil needs to be a few centimeters wide.

Second, the Stencil printing must be big enough to be usable by hand, but not so big that it would require too much time and effort to print.

Even though I knew this going in, it took me several iterations to get it right. I’m glad that I had lots of practice with part number masks and the supplies, and also that I am experienced in PCB layouts.

The second constraint I had to deal with was making sure that I had enough time to complete this project during a vacation in Europe. I did not want to work on it at home, especially when I have other projects that take up a lot of my time.

Before I headed for Europe, I wrote a list of things to accomplish and tested the time limits:

Sketches

Sketches are very important to this process. A sketch is something that you can quickly create and test.

Print: More or Less in the Browser

Printing a PCB is a complicated process that requires a lot of information to be translated into patterns. If you want to print on high-resolution monitors, you have to cut through layers of paper, be careful about the adhesive and also mark the top layer.

You need to use many different fonts, but there are also restrictions with the sizes, aspect ratios, and color:

These constraints may be all you need to define for a PCB pattern, but it is always good to have some abstraction. That’s why I always recommend you to use stencils as I describe in part 1.

If you want to print a PCB that will meet the constraints of your design, you should design your own stencils.

Testing

I remember when I had to cut a test pattern and test the adhesive: it took me several hours just to get to this point.

Now, with PCBs, it should be pretty easy. You just need to print them. But how can you test them without a pattern? That’s where the 3D-printing part comes in.

Printing a PCB with patterns and samples

The 3D-printing part of the project is really simple. The second advantage of using 3D printers is that they let you produce your 3D printing in two dimensions, so you can print out a model or shapes in the same direction you want to print the PCB.

For example, you can print out the following:

A series of tiny PCBs. They are going to be the first samples I publish in the project.

The default options that most 3D printers offer are great for PCBs, but if you want to add some interesting features or rules to your prototypes, you will have to edit the STL files.

Take a look at this sample:

I added all kinds of transparency:

Now, I will be able to add glass to the mold. This is a benefit that the usual 3D printers cannot provide.

I found this pattern on Thingiverse, printed it, and decided to use it as my test material for a few days.

Stencils

I used cutout stencils for my test samples.

One of the advantages of this is that I can make patterns to fit a specific stencil without having to cut a big blank board to fit it. The most important thing is that the size of your PCB stencils can be printed without errors.

There are many ways to use stencils:

You can cut the stencils with scissors. The most popular size of a stencil is for a 50×50 cm board. You can order them for different sizes, but be careful about the fit.

Another option is to print them on your 3D printer. But this is very costly, and the files are not a professional quality, so it is better to take advantage of the advantages of a 3D printer.

Or you can cut a stencil yourself. The most important thing here is to make sure that you can clean the board with a toothbrush. The second thing to make sure about is that you have enough room on the stencil.

Final Thoughts

Finally, you can use a 3D printer to cut stencils for you. The easiest option is to print a template on your 3D printer. But it is also a great way to learn more about the technology of 3D printers.

 

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