I'm playing with mine, using a 38.1mm looking at SMD's around the 0402. I'm unimpressed so far, difficult to see what I'm looking at.
I have the got the lens the right way, flat side closest to the sensor?
What one can see when looking at small SMD components is usually the solder joints, as they are metal they reflect the surrounding temperatures.
While yes this is difficult to see, if it has the same temperature as the surrounding PCB, from what I know, it's likely not an issue with the component.
If you look at the last image of the Exxbx vs UTi690A comparison, you'll see that the same is true for that high resolution thermal imagers, you only see the solder joints of the 0402 components.
(Marked a few of them on the image below).
It may take a while to learn; If there is a short circuit component that is generating heat then you should be able to see the heat signature between the solder joints, even with the UTi690A.
Dont get me wrong, the UTi690A is in no way optimized for thermal imaging of PCB.
If using it daily for PCB work then you may want a higher resolution sensor for sure, but for occasional use at least I find it good enough, but that may also be that I've used thermal imagers for a few years now?
If running a buisiness or doing these types of work daily then there are specialized thermal imager developed for PCB work as Fraser mentioned, those will outperform the UTi690A for PCB work in every way, but you're also paying a lot more for it, and they are not a standalone unit that you can use everywhere.
For the low budget range the UTi690A is to my knowledge the thermal imager with the highest resolution, most in this price range are 32x32 pixel sensors, and a very few at 80x60 pixels.
For lens orientation, flat side against the sensor did seem to work best for my images when I tried.
Perhaps you can upload a few images with information about the working distance you used?