A simple FDM-printable custom pasting jig.

solderpastejig.scad

pcb = [90.0, 40.0, 1.65];
gap = 0.2;

base = [180, 180, 0.2];

/* WTFPL yada yada

The idea is to bring the surface around the PCB to the same height as the
top surface of the PCB so that the stencil on top lies nice and flat.

Below the PCB there is a single layer of plastic, usually 0.2 mm

The larger holes are meant to aid removing the PCB after pasting.

Corners are cut out so that even if you didn't round your
PCB corners (which you should by the way) the board will still fit.

See Elen using this here: https://chaos.social/@ln/106352244269789569
*/

module corners(dim, center=true) {
    coords = [[0,0], [0, dim.y], [dim.x, 0], dim];
    for (vector=coords)
        translate(vector - (center?([dim[0], dim[1]]/2):0))
            children();
}

module jig() {
    difference() {
        union() {
            translate([0, 0, (base.z+pcb.z)/2])
                cube(base + [0,0, pcb.z], center=true);
        }
        union() {
            translate([0, 0, base.z+pcb.z/2+0.01])
                cube(pcb+[1,1,0]*gap, center=true);
            
            for(i=[0:1])
                translate([(i*2-1)*pcb.x/4,0,-1])
                    cylinder(d=min([pcb.x,pcb.y])/2, h=pcb.z+base.z+2);
            
            for(i=[0:1])
                translate([0,(2*i-1)*pcb.y/2,-1])
                    cylinder(d=min([pcb.x,pcb.y])/2, h=pcb.z+base.z+2);
            
            translate([0,0,-1])
                corners(pcb, center=true)
                    cylinder(d=min([pcb.x,pcb.y])/4,h=pcb.z+base.z+2);
                
        }
    }
}

jig();

$fn = 64;