Printed using black PLA on my Wanhao Duplicator I3+ MK2. Black and white PLA usually have warping issues above what's tolerated for mounting electronic circuits. This time I used thermal paste on the extruder's heatsink and a new thermal barrier tube (90% cheaper in bulk) for better flow on the first layer, calibrated Z on a pre-heated bed, used a mix of glue and 70% alcohol as adhesion, minimized temperature difference between nozzle and bed, designed the whole model for minimum warping, and added a large brim just in case. You cannot slide a thin sheet of paper under the sides of the finished print, so the warping is below 100 micrometers. The models can easily be modified to support more circuit dimensions than just 4x6cm and 5x7cm. Just move the vertices to change size without affecting the aspect ratios of details. Because there may be different screw holes on different circuit boards and it's hard to find the right screws, I made it tight enough to snap in place based on dimensions alone. This may require your printer to be calibrated with a long test model. The 0.4mm erosion (0.2mm radius in each direction) around the board for standard 0.4mm filament nozzles becomes a tight fit that can withstand a few kilograms of pressure without falling off. You can also glue or solder it in place using the edge, but then it's permanent.