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Make solder stencil in-house
In this page, we introduce our method to prepare solder stencils in-house using a low-cost cutting plotter and polypropylene synthetic paper.
If you want to assemble 3 or more PCBs using surface mount parts, reflow soldering is safer and easier way instead of hand soldering. However, reflow soldering requires solder stencils to print solder paste on the PCB pads. Generally, solder stencils are made of stainless steel foil and somewhat expensive.
We introduce our method to prepare solder stencils in-house. This method is a low cost technique you can do yourself. It is useful for trial and small quantity manufacturing.
How to make PCB solder stencils
Hardware and Materials
- A cutting plotter (We use Craft-ROBO or Silhouette CAMEO. Both costs less than USD 300.)
- Polypropylene synthetic paper (polypropylene synthetic paper is available here!)
- Scotch tape
- EAGLE CAD
- ROBO Master or Silhouette Studio (Bundled software of the cutting plotters.)
Prepare the cutting data
- Download "cream-dxf.ulp", and put the file into the ulp folder of EAGLE CAD.
This Eagle ULP script exports the Eagle cream layers to DXF for a cutting plotter. cream-dxf.ulp is available here!
- Open your EAGLE .brd file.
- Click "ULP", choose "cream-dxf.ulp", and click "Open".
- Click "Run".
- You can find "xxx-bcream.dxf" and "xxx-tcream.dxf" in the folder of the .brd file.
- Import DXF into ROBO Master or Silhouette Studio
If you use Silhouette Studio, please set the import options before importing data
- If you use Windows -> File>Option>Import Options and set Document Position "As-is", and File>Open
- If you use Mac OSX -> Silhouette Studio > Preferences... > Import Options and set Document Position "As-is" and File>Open
- Set the cutting option
Speed: 1 Thickness: 33 Adjust your blade to the following setting: 5
- Set polypropylene synthetic paper
Please use a shabby cutting mat. New and clean cutting mat is too sticky for polypropylene synthetic paper.
- Remove the cut frakes using Scotch tape.
- Remove the stencil from the cutting mat
When you remove the stencil from the cutting mat, you should bend the cutting mat, not pull the stencil. Polypropylene synthetic paper gets longer when you pull it forcibly.
The trial and error; finding the best machine and material for stencil
A lot of people try to prepare stencils in-house, e.g., http://www.ladyada.net/library/smt/laserstencils.html, and http://www.instructables.com/id/Create-Solder-Paste-Stencils-with-Cricut/. However, these methods still have some problems as followings;
- low accuracy
- requires expensive machines (e.g., laser cutter) and/or poisonous materials (e.g., the polyimide film)
- requires time and troubles to setup stencil data and/or the machine
To solve these problems, we made trial-and-errors using 4 methods and 6 materials.
We visited one of FabLab in Japan, and used a laser cutter to try cutting PET-film and polyimide film.
The cutting edge swells up, and the heat of laser may fill the holes again.
- Polyimide film
Polyimide film emits poisonous gas under high-temperature. The cutting edge is not straight.
The laser cutter is expensive but cannot be used for fine pitch PCB design.
CNC milling machine
We used a CNC milling machine to try cutting a phosphor bronze plate.
- Phosphor bronze plate
The cutting edge wells up.
The hole size and the diameter of the corner depend on the endmill diameter. The larger endmill is proper for high-speed manufacturing and slow degradation of endmills, but it is not proper for fine pitch PCB design. The small size endmill easily degrades and it is expensive.
We tried cutting 4 kinds of materials, PET-film, vinyl chloride sheet, laminate film, and polypropylene synthetic paper using a cutting plotter named Craft-ROBO (made by Japanese company GRAPHTEC).
The rigidity of the PET-film makes it easy to be broken, and the neighboring pads easily get together. It cannot be used for fine pitch PCB design. And our Craft-ROBO could not cut out if thicker than 100um (micro-meter).
- Vinyl chloride
It stretches easily, i.e., the accuracy is low. It is weak against alcohol.
- Laminate film
Laminate film is the double-layered film of PET-film and vinyl chloride, generally used for laminate pouches. It is difficult to cut completely because the vinyl chloride layer is soft, but the accuracy is not so low. However, it tends to tear easily.
- Polypropylene synthetic paper
Polypropylene synthetic paper is paper like sheet made of polypropylene fiber. It is easy to cut completely, of course it is a paper, i.e., the accuracy is high enough. It is just paper, but it is difficult to tear by hands, i.e., it is tough enough for stencil use. It has good resistance to alcohol and water.
Based on the results, we chose the cutting plotter and polypropylene synthetic paper. Polypropylene synthetic paper is available here!