This is useful tip for anyone making or using surface mount components on PCBs.
It relies on access to a laser cutter, so if you don’t have one, look away now…..
I cut a plastic stencil on the laser, align it with the PCB pads and then squeegee a thin layer of solder paste through the holes.
Peeling away the stencil will leave a perfect pattern of pads with the correct amount of solder on each one.
I have just successfully used this process on components with a 0.025″ pitch (0.65mm) – that’s VERY small,
The prototype in the pictures has been made by my good friends at Spirit Circuits in the UK, and is a full plated through, double sided board. with immersion silver coating.
ALL PCB design programs these days will let you produce solder masks for surface mount boards. We take the solder mask output from the program, and direct it to plain, simple HPGL “plotter” files.
Here, I’m using Number One Systems “Easy-PC”, which may look very familiar to anyone using Design Spark’s free offering.
Turn OFF all the other layers, turn ON the mask layer, change the output device to “plotter” and plot to file. I mirrored the mask, but I am not sure its important. Technically, the holes benefit the process if they are smaller on the TOP of the stencil than the BOTTOM. This ensures a clean peel at the later stages
Import the artwork on the laser cutter. I originally expected to CUT the stencil. THIS DOES NOT WORK.
The secret is to ETCH MULTIPLE times, to get very clean edges.
All I used for the stencil was OHP transparency. I suspect even paper might work, but the VOLUME of solder in the joint depends on the thickness you employ, and transparency is thicker and paper – and gives good results.
Read More: Soldering stencils for DIY circuit boards.