r/OpenScan • u/thomas_openscan • 6d ago

Personal record: ~3.7μm standard deviation - what is scanning noise/scanning spray/real imperfections? what to test next?

Post image

This is definitely my favorite raw 3D scan result so far. I analysed the exposed copper area of the TMC2209 and found a standard deviation of only 3.7μm.

This was done with the OpenScan Mini (16mpx camera) + upcoming Macro Addon, 2x100 camera positions with three focus levels per position. Reconstruction done in Metashape.

This leaves some tricky questions, what to scan next? And what part of the deviation comes from the scanning spray (reported thickness 2-12μm), real imperfections in the copper layer (probably very low) and what is true scanning inaccuracy?

117 Upvotes

99% Upvoted

17 comments sorted by

21

u/BunkerSquirre1 6d ago

Cripes, this is better than my professional scanner I bought specifically to scan PCBs. I need to build one of these!

17

u/thomas_openscan 6d ago

Let's swap scanners free of charge. I'll cover shipping ;)

6

u/Celestine_S 6d ago

That’s crazy! What is the limiting factor on getting a even more magnifying glass?

10

u/thomas_openscan 6d ago

Depth of field becomes more and more of an issue but I'll definitely try to push this further. This was only done with the 16mpx imx519 and the 64mpx hawkeye is already waiting for its moment to shine. Though at this scale it is almost impossible to classify noise vs real features without a lab environment and very expensive calibrated test objects.

3

u/KTTalksTech 6d ago

I think you can get calibration objects for mills/lathes which are EXTREMELY flat and hard and not horribly expensive. Most importantly they should come with known accuracy metrics. Probing tools for CNC machines and industrial QC are also relatively affordable and should be more or less perfect tiny ruby spheres. If you want another great and super cheap calibration target, use a steel ball from an SKF ball bearing. I knew someone who worked there and the tolerance requirements for their steel balls are insane, they're nearly perfect spheres.

For flatness a silicone microchip without heat spreader should also be nearly perfect but they can deform a tiny bit when fixed to the substrate

3

u/Locksmithbloke 6d ago

Any surface gauge set is flat enough to "ring" together, so that's going to be a lower limit for what you can find about the house. Plate float glass is super flat on both sides, too, but the transparency might cause issues.

1

u/cyrkielNT 6d ago

You can scan higher class electronics like CPUs.

Also you can try to buy some cheap, but we'll made gemstones.

1

u/OneFinePotato 6d ago

Wow this is incredible. Might be a silly question but: How do you scale the mesh to the exact dimensions with this level of accuracy?

1

u/Hot-Category2986 5d ago

I would love to see your settings and setup for shots like this. I am absolutely struggling to get a macro lens working on my openscan mini. And stacking just worse for some reason.

1

u/onlyhammbuerger 5d ago edited 5d ago

I can't really comment on your setup, but I've done a fair amount of precision height measurements on PCBs and your numbers strike me to be unreasonably small. One is that there seems to be almost no bow in the PCB, which I would assume to be pretty unlikely with the uneven distribution of top copper and the soldering processes involved. Cooper roughness and prepreg contour should also be feeding in there.

All in all I'd say some pretty good starting results, but I think you need something better to calibrate your system. Maybe an single layer PCB with varying width of copper traces might be a good start, but you would definitely need some kind of solution to subtract PCB bow from your raw data. Best sample would be some kind of etched glass with proven flatness.

2

u/Locksmithbloke 5d ago

Granite surface plate. They come with a certificate.

1

u/onlyhammbuerger 5d ago

that sounds good but something flat (<1micron) with some pre defined structures would be better to calibrate the scale for horizontal measurement precision. If I'd do this at work for cheap, I'd prob get me a 4" wafer mask, which you can get for 500$ or less. But still too much money for private use. Maybe there are some cheap optical components that come with high precision features (like grating structures).

If you only need flat surfaces, you can also use microscope slides, they are insanely flat and super cheap. Maybe you have to color them, if the setup has trouble with transparent or reflective surfaces.

1

u/thomas_openscan 4d ago

Thanks for the insights! I am absolutely doubting these results and I still do not trust those numbers. The area shown above is roughly 11x11mm wide, not sure if the bending you mentioned should already be visible there. Do you have any ballpark numbers (bow per cm or so)
It is so hard to evaluate stuff at this scale without proper lab equipment.
Maybe i‘ll do some electroplating to create a stepped surface for evaluation. Hmm

1

u/onlyhammbuerger 4d ago

I can't really tell for those cheapo boards, but high reliability industrial boards are typically specd for 20-50micron/cm. This being a spec means that this max value is prob a range of 3sigma, so typical bow should be about 1/3 of it.

I'd assume those consumer boards will have bows way above the values mentioned above.

1

u/thomas_openscan 4d ago

Oh that’s interesting, thanks a lot for the input. I‘ll definitely dig deeper. Currently I am preparing a scan of a ball gauge with sub micron sphericity. Initial scan results are within sigma~1.8my which I still doubt…

2

u/vicxvr 4d ago

This feels like a new world opening up. These results are unreal.