2.6 Feature - Offset Adjustment

By far the most powerful feature of inspectAR 2.6.0 is the Overlay Adjustment feature. You can now adjust your overlays down to 0.2mm and well below to make sure that things line up perfectly.

News & Updates
 Min read
June 16, 2022

By far the most powerful feature of inspectAR 2.6.0 is the Overlay Adjustment feature. You can now adjust your overlays down to 0.2mm and well below to make sure that things line up perfectly.

To date, a major weakness of inspectAR has been that if you calibrate a project but then see one component line up correctly, you have to go back out and make another calibration. Except this time A component on a different area of the board does not line up correctly, maybe you only discover this after you have started work, and now you need to flip the board over again to re-calibrate. We've always noticed great accuracy from our AR technology, from the very beginning overlays consistently appear in the same area and are related to each other by the same distance defined by the design data. However, getting the overlays to be precise, that is line up perfectly on the board beneath the camera, is much larger challenge for many different reasons. It can depend on the camera you’re using, your lighting, and manufacturing tolerances within the PCB. The Overlay Adjustment window gives you the ability to overcome small perturbances which you might notice in your overlays by physically adjusting their alignment until you see them match 1:1.  

Here is an example of a really good inspectAR calibration. Looking at the board outline alone it is impossible to tell if any misalignments will be present when we start activating overlays. Displaying all pads and vias is a quick way to tell how well things are lining up. In this case, you can notice a few little blemishes which I have circled in pink.

The LimeSDR fresh out of calibration, the only thing visible is the outline you just calibrated.
The LimeSDR with the top copper overlay activated, and fills + traces filtered out. You can see pretty good alignment throughout most of the board. This is due to a successful calibration and good lighting conditions.
Some small misalignments in the calibration might not even be noticeable until you look at that area of the board to do some work.

Now let’s use the offset adjustment to fix one of these misalignments and get the overlays lined up 1:1. Let’s try the 24-pin WFQFN chip circled at the bottom of the board. Open up the offset adjustment icon from the toolbar, and click enable to activate it. You’ll notice a small indicator appear at the top right of your camera feed, more on why this is important later. Zoom into the overlay, if you notice that you lose tracking (tracking indicator is at the top left of your screen) or that you don’t have enough resolution to see the component clearly, try using some stretch zoom. Once you are zoomed in try and use the x and y arrows only to make the alignment of a single part perfect. Here’s a quick diagram showing you everything I just talked about along with a before and after of the adjustment.

Here is an image indicating the buttons mentioned above.
Now that your alignment is perfect, look what you can do with inspectAR

Looking at the broader image again, it is clear now that while we have lined up IC25 pretty nicely, some other components are now in worse alignment than when we started. A good example is an area of passives in the upper-centre of the design. While we just lined up overlays perfectly in one area, there is still some skew and rotation in our overlay plane, meaning not everything on the board is lined up perfectly. To get the entire board at 100% alignment first adjust the rotation on your overlays until you believe it is perfect, then adjust the height. Our AR technology tends to put the overlays slightly above surface of the board and on top of the mean raised surface that it meets. On this board that is just slightly on top of the USB connector (if you turn the board our tracking will change the height to make it look normal, it is impossible for you to observe this small height). Decrease the Z height of the overlays until you see general alignment.  

Lowering the board height has the same effect as shrinking the board. When you lower it, you’re actually ‘centering’ your overlay plane which is not perfectly flat and skewed in one axis. In the next step we’ll fix up the board outline to make things look good again.

Then look at your board outline, by now it will have shrunk slightly from the edges of the board due to our Z adjustment. Now, increase the stretch, making slight adjustments to the x position, y position, and rotation of the board as you go until things line up perfectly.  

This is the best alignment overall for this board, where there are some very small offsets on certain components there are no ‘pin off by one’ errors anywhere on the board.

This algorithm will not produce perfect alignment for every board, but even if it does not it should at least improve the alignment and you can always make a local adjustment when you move to a new area of the board and begin working on a new fine-pitch component at the pin-level.  

We’re hoping to write a lot more about specific use cases for this new feature – stay tuned!

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