3D Print A Stenciling Frame For Your PCB

For many a hacker, stenciling a board for the first time is a game-changing experience – the solder joints you get, sure do give your PCB the aura of a mass-manufactured device. Now, you might not get a perfect print – and neither did [Atul R]. Not to worry, because if you have a 3D printer handy, he’s showing you how to design a 3D-printed frame using Blender and TinkerCAD, making your solder paste print well even if you’re trying to rest a giant stencil on top of a tiny board.

[Atul]’s situation was non-characteristic – the project is a 2mm thick PCB designed to plug right into a USB port, so the usual trick of using some scrap PCBs wouldn’t work, and using a 3D-printed frame turned out to be key. To get it done, he exported a .wrl from KiCad, processed it in Blender, and then designed a frame with help of TinkerCAD. These techniques, no doubt, will translate into your CAD of choice – especially if you go with .step export instead of .wrl.

This kind of frame design will get you far, especially for boards where the more common techniques fail – say, if you need to assemble a double-sided board and one side is already populated. Don’t have a stencil? You could surely make a 3D printed stencil, too, both for KiCad boards and for random Gerber files. Oh, and don’t forget this 3D-printable stencil alignment jig, while you’re at it – looks like it ought to save you quite a bit of trouble.

PCB sitting inside a 3D printed holder job, with holes to apply vacuum

Solder Paste Stencilling That Doesn’t Suck

Working with solder paste stencils can be a real faff, they rarely sit flat and move around when you so much as breath on them. [Unexpected Maker] airs his frustrations, and comes up with a simple solution, he simply makes a 3D-printed jig to align the PCB panel and applies his shop vacuum cleaner and hey presto!

If you’re ever been tempted to switch from frameless to framed solder stencils, then you’ll notice they can be rather awkward to work with. The usual online vendors have plenty of listings for stencil frame holders, but they do all seem to us, exactly the same, and more suited to stencilling T-shirts, than working with tiny PCB footprints.

The problem with unframed stencils is one of clamping and registration to the PCB, which framed stencils fix, when used with a jig that can dial in the rotation and translation errors.

But problem with those is, unless you have a perfectly flat support region all round the PCB, the weight of the frame tends to make the stencil bow up over the PCB, causing parts of it to lift away from the solder lands. This results in paste not being pushed into the places you want it, and instead it sticks to the stencil apertures and comes away when you lift it up. Most irritating.

You can try offset it by taping spare PCBs of the same thickness all around, but this is not always terribly successful in this scribe’s extensive experience doing this job by hand. [Unexpected Maker] solves this bowing issue by making a 3D printed jig that bolts to the stencil holder, takes a custom top plate with holes in, which in turns allows a vacuum to be applied from below. This sucks the PCB down to the jig, keeping it flat (in case it is also warped) and also pulls the stencil plate directly down to the PCB, making it also lie perfectly flat.

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PCB Stencils For $200

stencil

There’s some really cool stuff to find if you wander around a Michaels craft shop or Hobby Lobby long enough. Recently, [Ben] picked up a craft cutter – a small vinyl cutter-like device meant for scrapbooking and other crafty endevours. He’s using this machine to create solder paste stencils that are better than any laser cut stencil he’s used before.

Like a build we’ve seen before, [Ben] is using a desktop-sized vinyl cutter, the Sihouette Portrait,  with 4 mil Mylar. After converting the relevent layers of a Gerber file into .SVG files, [Ben] loaded up Robocut to cut very, very small holes in his solder stencil. The results are great; much better than a laser would cut Mylar, and good enough to apply paste to a few hundred boards at least.

While [Ben] is using his stencils to apply solder paste, we’re wondering if a similar process could be used to apply a UV-curing solder mask to home-fabbed boards. That would allow for some very professional-looking boards to be produced with a turnaround time of just a few hours.