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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 make a lot of PCBs using surface mount technique, reflowing is safer and easier way instead of hand soldering. But, to do that you will need to print paste on the pads. Then, we introduce our method to prepare solder stencils in-house. This method is a low cost technique you can do yourself.

How to make PCB solder stencils

requirements

1. A cutting plotter (We use Craft-ROBO or Silhouette CAMEO. both costs less than USD300.)
2. Polypropylene synthetic paper (​polypropylene synthetic paper is available here!)
3. Scotch tape

Software

1. Eagle CAD
2. ROBO Master or Silhouette Studio (Bundled software of the cutting plotters.)

directions

• Create stencil data

1. Download "cream-dxf.ulp", and put the file into the ulp folder of EagleCAD. This Eagle ULP script exports the Eagle cream layers to DXF for a cutting plotter. ​cream-dxf.ulp is available here!
   

2. Open your EAGLE .brd file.
3. Click "ULP", choose "cream-dxf.ulp", and click "Open".

4. Click "Run".

5. You can find "xxx-bcream.dxf" and "xxx-tcream.dxf" in the folder of the .brd file.

• Cut!

1. 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
2. Set the cutting option

   Speed: 1
   Thickness: 33
   Adjust your blade to the following setting: 5
   

3. Set polypropylene synthetic paper
   • Please use a shabby cutting mat. New cutting mat is too sticky for polypropylene synthetic paper.

4. Remove the cutting part using Scotch tape.

5. 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.

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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;

1. low accuracy
2. requires expensive machines (e.g., laser cutter) and/or poisonous materials (e.g., the polyimide film)
3. 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.

Laser cutter

We visited one of FabLab in Japan, and used a laser cutter to try cutting PET-film and polyimide film.

• PET-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.

Cutting plotter

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).

• PET-film

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. 現在のところそれぞれ上記のような理由で、ポリプロピレン合成紙を使用しています。​ポリプロピレン合成紙はこちらからご購入いただけます。

cream-dxfの工夫点

実は、ここがポイントなんです。

1. 閉じた矩形を描く
   クラフトロボの仕様により、パスの終点と次のパスの始点が近い場合につながってしまう。
2. 矩形を2回描く
   クラフトロボのカッターの刃の特性上、1回だと始点終点がうまく閉じず、切り抜けない場合がある。
3. 開口部をデータよりも小さくする
   データ通りの大きさで切ると、隣の足とつながることがある。