Create SMT stencils with a SLA printer

Up until now, I have used a solder paste syringe to apply solder paste to the pads of my PCBs. While I have considered buying SMT stencils in the past, I didn't find it worth the cost for the amount of times I would use them. However, recently I got my hands on a SLA printer and watched tutorials online about making PCBs with it. This led me to wonder if I could use an SLA printer to create SMT stencils from resin.

Materials:

• SLA printer
• Water washable resin (e.g. Elegoo Water Washable resin)

Solder mask to model

For my pcb design I use easyEDA. In easyEDA you can export the solder mask to dxf. After exporting import the dxf into fusion 360. Then extrude your design by the desired thickness. I choose 0.12 mm.

Printing the stencil

To print the stencil, import the model into your preferred slicing software and adjust the settings. It is crucial to fine-tune the exposure time to achieve the desired results. Too much exposure will make finer details appear solid and clogged, while too little exposure will result in poor adherence to the print surface. Keep in mind that, due to the stencil's thinness, you may need to adjust the bottom exposure time.

After printing, it is recommended that you clean the stencil under running hot water. You do not need to be gentle when cleaning, especially with the smaller details. Other wise they endup clogged

My Attempts

On the right: 40 seconds exposure. As you can see most of the holes are solid and the squares are more rounded.

On the left: 25 seconds exposure. Most of the finer details are visible, but still clogged.

My final attempt was a succes with an exposure of just 5 seconds.

Not bad

Final thoughts

I think the 0.12 mm is a little bit too thick, because after melting the solder without components on it, it made a lot of smaller pads like the micro usb ones ono big blob.

Also, the flexible nature of such a thin piece of partially cured resin doesn't help either. The paste spreads out under the stencil and also sticks too much to the stencil. Maybe curing it between 2 peices of acrylic or something else would help.