PCB mechanical fit testing

One of my latest designs needed more mechanical fit checks that usual, it was to work with specific hardware and I wanted to check the case design with the PCB and battery and so on all fitted before ordering the PCB. So I 3D printed the PCB.

This is not really a new idea, but first I have done it. We actually did recently for some FireBrick work - 3D printing the case, but also 3D printing the PCB. This was FDM, which was fine for checking the mechanics.

But the result in resin is stunning beyond belief. I actually ended up going through the KiCAD models and updating some of the 3D model STEP files even to be even more accurate. Some points of mention.

• The USB-C socket has the inner part, but you can plug in a USB-C cable properly and not break anything. This allows the exact fit of cable in socket and confirming is it not fouling anything in the case design.
• The battery connector even has the pins - that is crazy. And again, the plug of a real battery could plug in and not even break the pins! This was great to confirm exactly the right connector and polarity and confirm battery lead length fits as expected and is reachable from where the battery will be located.
• The ribbon connector has the gap for the ribbon from an e-paper, and allows me to verify the length fits and again is something one can reach in the case to install.
• The sticky out bits fit in the case design which has slots for them (button, USB, WiFi antenna, and lugs).

I am amazed at the precision. But actually there was one area that was technically too accurate!

KiCAD output the board, and will even output the solder pads, and output the components. But in real life the components would be in solder paste. The actual output had maybe tens of microns gap between component leads and the PCB itself. This meant a print slice layer had nothing.

The result was most components were fine, amazingly, even though all of the SMD had this gap. The contact area after the gap was enough, even on even 0201 resistors. But the leads of SOT parts were curved to a point as they are in reality. In reality solder would wick up those legs.

The result was interesting. The components printed perfectly but very loosely connected to the PCB!

I ended up with a lot of missed components when taken out of the printer (and had to clean the release film) and even more missing after a wash.

What I need (and have a feature request in) is KiCAD to have a solder paste export to fix the component legs to the pads as they would be in real life.

For now I export PCB and components separately and load in to FreeCAD and move one 50um down. The result is a solid print with stuck down components!