Hacking A Digital Microscope Camera For Fun And Automated PCB Inspection

A desire for automated PCB inspection has led [charliex] down some deep rabbit holes. He’s written his own inspection software, he’s mounted his PCB vise on a stepper-controlled table, and now he’s hacked his digital microscope camera to allow remote and automated control.

Eakins cameras have become a relatively popular, relatively inexpensive choice for electronics hobbyists to inspect their small-scale work. The cameras have a USB port for a mouse and overlay a GUI on the HDMI output for controlling the camera’s various settings and capturing images to the SD card. Using the mouse-based GUI can feel clunky, though, so users have already endeavored to streamline the process to fit better in their workflow. [charliex] decided to take streamlining a few steps further.

One issue in microscope photography is that microscopes have an extremely tight focus plane. So, even at the minuscule scales of an SMD circuit board, the components are simply too tall. Only a sub-millimeter-thick layer can be in focus at a time. If you take just a single image, much of what you want to see will be lost in the blurry distance. Focus stacking solves this problem by taking multiple pictures with the focus set at different depths then combining their focused bits into a single sharp image.

This takes care of the focus issue, but even the most streamlined and intuitive manual controls become tedious given the multitude of pictures required. So [charliex] searched for a way to remotely control his camera, automating focus stacking and possibly even full PCB scans.

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As anyone who has ever assembled a run of PCBs will tell you, quality inspection of solder joints can be a difficult process. Even under a microscope their appearances can be deceptive, and one silver blob can be perfect while its neighbour conceals a problem. The electronics industry have developed inspection tools to help, including optical inspection devices. It’s one of these that [Sina Roughani] has built, in the form of a hemispherical 3D printed dome with concentric rings of coloured LEDs mounted within it.

The principle behind this tool is as unexpected and simple as it is clever; by having different colours of light from different elevations of the dome it ensures that each different angle of the solder joint surface reflects a different colour. Thus a colour photograph shot from directly above the board allows visual inspection of the quality of the solder joints by the rainbow of colours that appears around their edges. This process can even be automated with OpenCV or similar, hence the process is referred to as Automated Optical Inspection, or AOI.

The technique is demonstrated with some pictures of a Raspberry Pi Pico, on which it shows really well the rainbow-edged solder joints and the red colour reflected from flat pads. What at first might seem like a novelty lighting effect becomes a very useful inspection tool.

PCB inspection is a subject we’ve covered before, though perhaps we don’t all have access to X-rays.

PCB Holder For Limited Depth-of-Field Microscopes

As time marches on, so does the need to have the right tools to deal with the ever increasing popularity of SMD components. Ok. Maybe “popularity” isn’t the best word choice, as there are plenty of people out there that prefer through-hole components for ease of prototyping. But, whether you like it or not, you’ll eventually need to deal with SMDs.

One of the problems with smaller packages is that with such small pins, their solder joints are difficult to inspect with the naked eye. A lighted magnifying lamp will only let you see so much. You can switch to a jeweler’s loupe for a quite a bit more magnification if you like – but nothing beats a microscope on your workbench. Unfortunately, unless you’re willing to spend the price of a used car on a microscope, the limited depth-of-field (DOF) can be a concern. It’s often handy to hold the PCB and move it around at different angles to get a good view of the solder pad fillets. But then you’re fighting the a very small DOF, and the steadiness of your hands.

[Tom Keddie] came up with this super simple hack – it’s nothing more then an angled PCB holder. It allows you to view your PCB at 30 or 60 degrees. Sometimes it’s the simple things in life that make your work that much more enjoyable. You can find the source files on github. And have a gander at our overview article if you’re thinking of getting your feet wet with SMDs.


[via Dangerous Prototypes]