PCB Stencil Jig for applying solder paste (parametric, works with double-sided boards)

This jig will hold your PCB and solder paste stencil aligned while you apply the paste. There's space under the PCB for components on the back side, and you can easily remove the PCB while leaving the stencil clamped in place, so you can paste a batch of PCBs quickly.

How to use

1. Adjust the side plates so the PCB fits snugly between them, resting on the ledges.
2. With the PCB in place, slide the stencil under the rear clamp plate, align it with the PCB, and clamp it down.
3. Apply solder paste with a credit card, spreading it evenly.
4. Lift up the stencil by the front edge until it's clear of the PCB
5. Use the ejection tongue to slide the PCB forward until you can grab it (don't smear the paste!)

Features

• Works with double-sided boards
• Keeps the stencil in place while changing boards - the next board is aligned automatically.
• Parametric with OpenSCAD so you can adjust it (e.g. bigger, thinner PCB)

Dimensions

(These can all be changed in OpenSCAD. If you're not confident, leave a comment and I'll try to make an adjusted model)

• Max stencil width: 120mm
• Max PCB dimensions: 100mm x 100mm
• PCB thickness: 1.6mm
• Ledge width (supports sides of PCB): 1mm
• Space under PCB: 15mm
• Foot height (to clear bottom twiddlers): 10mm
• Threaded insert size: M3, 5.7mm length x 4mm hole diameter
• M3 Set Screw length: 15mm

Tips

• When clamping the side plates in place, make sure the PCB is hard up against the rear edge. This will ensure it's square to the side plates.
• Once the side plates are clamped, check the PCB can't wiggle - but it should be loose enough to to slide back and forth on the side plate ledges.
• It may be useful to slightly splay out the front edges only of the side plates to let the PCB slide out easier.
• After inserting a PCB, look through the stencil holes to check the stencil and pads are aligned
• If the stencil clamp plate is left clamped in place over a stencil, the plastic may creep and it may get slightly bowed over time, reducing its clamping effectiveness. In this case, just flip it over and the bowing will then actually help!
• For small PCBs, it may be useful to clamp the ejection tongue in place, keeping the PCB further forward, so it's more central in the jig.

How to print

You will need the following non-printed parts (I'm looking at doing an updated fully-printable version but haven't got there yet). The varying quantities depend on how overkill you want to go on the clamping :)

• 10-15x threaded heat-set inserts, 5.7mm length x 4mm hole diameter
• 6-11x M3x16mm Hex Head Set Screws (bolts with the traditional hexagonal head) for the twiddlers
• 4x rubber feet, 10mm high (or design & print your own with TPU)
• 4x M3x10mm machine screws for use with the feet

Amazon links for reference, but you may be able to find these cheaper locally.

For rigidity, I recommend PETG, and using 6 walls, and a top/bottom thickness of 1.6mm. (I used 3DTomorrow BioPro but I think it's only available in the UK)

You will need to print one each of these stl files:

• Base
• Left side plate
• Right side plate
• Clamp plate
• Ejection tongue (optional)

And you will need to print 6-10 “twiddlers” (thumbscrews) depending on how overkill you want to go with the clamping.

How to assemble

1. Insert heat-set inserts from underneath into the corner holes for the feet, and screw the feet on.
2. Insert heat-set inserts into the two side plates, again from underneath, making sure they're pressed in past the underneath surface of the plastic.
3. Decide if you want to use two or four bolts to hold the stencil clamp plate down, and insert heat-set inserts into the corresponding holes in the rear top surface of the base, again taking care that the inserts are pushed down below the surface.
4. They're probably overkill, but if you want to use the additional clamping holes at the back of the base, insert heat-set inserts there too (using these will stop the stencil from being positioned further back though). Also for the centre hole, if you want to clamp the ejection tongue down to position PCBs further forwards.
5. Insert the hex-head bolts into the “twiddlers”, and use them to secure the two side plates from underneath, and the stencil clamp plate from above.

Future improvements

(all of these could be remixes, if anyone has interest. The OpenSCAD source file is included)

• Versions for different thicknesses of PCB. Maybe a universal version is feasible with different ledge depths.
• Make 3d-printed feet in TPU
• Try to get rid of the non-printed parts. I'm not sure printed screw threads will be strong enough though. The threads & holes would definitely need to be bigger.
• Make the side plates symmetrical so they're not left/right handed.
• Make a bigger version for larger stencils / PCBs, if there's demand for it.