This is a fixture I made to help me assemble Quantum altimeters from Eggtimer Rocketry using paste solder and solder mask stencils from OSH.  The design will allow you to stencil the solder onto both sides of the board.  In the photo you can see how I set up the fixture for use, with the top and bottom stencils hinged with masking tape on each side of the opening.  Once you get the stencils in register with the board, you can do a number of boards in succession with minimal fiddling around.

There are two parts in the fixture - an insert which is specialized to the Quantum's mounting hole pattern that holds the board via its mounting holes, and a table into which the insert is glued with Plasti-Zap super glue (or screwed on as I did to make the insert removable).  The design is such that it would be easy to make a different table with several copies of the insert to use when installing the through-hole parts, or to adapt the table for different altimeter inserts.  The bottom of the insert needs to be open because the Quantum comes with a pre-installed baro sensor chip that would interfere with a solid bottom.

You can get solder stencils made by downloading the Gerber cream files from the eggtimerrocketry.com site here http://eggtimerrocketry.com/eggtimer-quantum-support/eggtimer_quantum_a18_creams/ and uploading those with your order to oshstencils.com.  I strongly recommend using the OSH editor to open up the area around the baro sensor - remove the “+” shaped area separating the 4 pads - rather than cutting the stencil after you receive it.  With the Kapton stencils there is risk of mangling your stencil, and the stainless steel stencils are very hard to cut.

The CAD design is in OnShape here: https://cad.onshape.com/documents/6f7fae1a447b5be11ea38076/w/32077afb5e40d6d37e446c7b/e/3bb59603642e6ec1f1c56992

In addition to the solder fixture parts, the CAD also includes a drill pattern for drilling your avionics sled to mount the Quantum in your rocket.

Material: PETG

Nozzle: 0.4

Layer Height: 0.25 to 0.3

Infill: 100% (doesn't matter much, it's almost all perimeters)