I recently had to do some surface mount solder inspection. The chip – one of these tiny little 0.65mm pitch SSOP-28 packages – apparently stopped working. Was there a problem with the soldering? I didn’t know. But I did some rough handling of the PCB. So how to check? I thought: Ruben, get yourself an USB microscope.
But which one? There are many different types in the market. But most reviews don’t show you actual performance of the microscope (like measuring the area the image consumes). But to start up front: If you are looking for a review. You could try it here:
EEVBlog #566 Cheap USB Microscope Reviews
mikrocontroller.net USB-Mikroskope – was taugt das Zeug?
Unfortunately all the information shown there wasn’t exactly what I was looking for. So finally – after some consideration – I bought an Andonstar microscope. There where at least a few positive remarks about this one. And so it’s a good starting point for my own testing. Just a reminder: This is not a review. It’s just a collection of stuff I was missing in a proper review. So here we go…
First look it seems to be really solid. It’s all metal. It has a solid screw-in-post which I really like. Just by turning the post you can slide the microscope up and down. This is really nice and helps a lot if you want to bring your sample into focus. But there is a downside to this as well.
Tolerances of at least my microscope stand are way to high. If you start turning the post the microscope head swings at least two millimeters side wards. And if you use the microscopes high magnification the whole picture starts to jump. That is really annoying as you can see in the image to the right. I took these two images at the same distance of about one centimeter above the sample. And I didn’t move the sample at all. I just tipped the microscope head. So if you start moving the microscope head up and down it starts tilting to one or the other side. I actually don’t know if that’s a common fault with these stands or if my microscope is especially bad. If you know, leave a note in the comments and I might add it here.
Another thing not shown here is the fixation of the microscope in the stands head. There is a screw to fix it at any position. But there is not a possibility to align it in an prechosen way. So you can turn it around as much as you want even allowing you to seeing your sample upside down. And because right is not always right and left not where you expect it this is annoying. But on the other hand it adds so much flexibility, too. So it might actually be a feature.
The Zoom Factor
As you can see from the picture there is a decent zoom on this microscope. To get a real figure I took several photos from minimum and maximum height. The ruler on these pictures has a metric scale. The minimum zoom is something around 72mm x 55mm at around 120mm distance. The maximum zoom is around 2.5mm x 2.0mm at around 7mm distance. That is around 1/28th of the image size of the other picture. I was really impressed by that size.
The Depth of Field
The Depth of Field is not super-great but you get used to it. As you can see in the left image the ferrite bead in the back is totally blurred. It’s even worse in the right image. The image is taking from close distance therefore there is not much to expect. So it’s best to have all your components on one level.
The microscope has it’s own lights. Eight surface mount LED’s near the lens are used to lighten things up. But as you can see from the image below it’s not always a good thing. When using these LED’s there are highlights and shades and therefore an really uneven illuminated view area. For example I also added the same image (see the scratches) using a different light source. The image is much more evenly light up.
Another issue we haven’t yet talked about is the chromatic aberration. Yes, it is visible and it’s strong. Cause it’s a tiny little microscope there is the problem that colors are not even distributed. See the image for details. There you can see the bottom of the stand. Left side is without correction, right side is color corrected.
Well, not really much in here. There are different video modes this microscope can use.
- 1600 x 1200 with a framerate of 5fps
- 1280 x 960 with a framerate of 9fps
- 800 x 600 with a framerate of 20fps
- 640 x 480 with a framerate of 30fps
If you want to use this microscope for soldering stick to the 800×600 or 640×480 resolutions. Otherwise the lag between images seems at least IMHO to high.
So what can we do to make even more use of this microscope? I found at least these things really helpful…
If you want to use this microscope in Linux you are free to do so. It uses a more or less common webcam interface. At least mplayer works right of the bash. You can try this:
mplayer -cache 32 -vf screenshot -zoom -tv noaudio:width=1600:height=1200:fps=5:device=/dev/video0 -vo gl tv://
Or use my two little programs here: GitHub
When you start using your microscope you realize pretty soon that this shiny metal surface where you place your sample looks good but is absolute hopeless if you want to know how large the visible area is right now or if you just want to know in what angle your camera is facing the surface. Well there is a quick fix. Just print this cross-hair and go on (files on GitHub). The little crosses are 5 millimeter apart. Large rectangles show the maximum size of the viable area. The tiny little rectangles show the minimum size. The little dot next to the tiny rectangle indicates the direction of the stand. The Circle has a diameter of 50mm.
The Illumination Improved
I already talked about illumination issues. But how to solve them? Get yourself one of these round shaped led lights. They are often used in car illumination and therefore often called “Angel Eyes”, round lights of different diameters. Mine has an outer diameter of 60 millimeters. Which is pretty good. Now you just need something to hold it in place. I’m sure you will figure something out.
The Color Improved
Well we already have seen there are some color issues with most of the images I can create. How to solve? Just apply a color filter to all the relevant images. Here are the steps:
- Create the Image you are interested in
- Remove the sample from your view area and position a white sheet of paper there
- Create an image from this assumed white sheet of paper
- Do some gimp filter magic: The thing that worked best for me was the “Grain extract” layers filter at an opacity of 80%. Just apply this filter to the image of the white sheet and you should be fine.
Well, enough of the talking. Let’s see some pictures.
Raspberry Pi 3:
Do you see these little solder balls on the FTDI-board? Whoever soldered here that is not how it’s done. But the solder ball underneath the SSOP-28-package is visible as well. So I’m impressed by this microscope.
Ancient 200Byte EPROM:
10W RGB LED:
As it is clearly visible the different colors of course have different semiconductors. Up right is blue, down left green, down right red. In between the lines should be the p-n-junction.
Random stuff (Brush, Amoled display, burned resistor):
I hope I could present you a more detailed view of the Andonstar microscope. Decide for yourself if it’s a useful tool. As for me it gave me some awesome insights into many different aspects of my surrounding environment but it didn’t help me finding the issue with my SSOP-28. So that problem is still to be fixed ;).
Even if most pictures look like they are 800×600, the original file is 1600×1200 real resolution. I just “webified” the pictures.