Microscopy: Tear-off test
If you spread a paste with a spatula on a smooth surface (glass slide) and then pull it off thinly until the layer tears off, you can already conclude two things. You can see how well the inferior paste from 2024 (which is also the sole subject of the following) adheres to a smooth surface such as a GPU die and you can see how it tears off at the resulting edges.
The paste from 2023 looks much more homogeneous and also more spreadable, without tearing and beading. And yes, it’s the same resolution!
You can see these differences even more clearly at a much higher magnification, because the tear-out paste from 2024 is much more sensitive when removed under pressure. Something like this will probably not last quite as long in the PC either.
The paste from 2023 is also more stable and remains much more homogeneous on the surface. It’s not much better, but a little.
Microscopy: Particle sizes
This is where I reach the limits of the resolution of the Keyence VHX-7100, because in the sub-micron range and with nanoparticles I can see that there is still something there, but even at 2000x resolution it is no longer possible to identify or even measure such small particles cleanly. I even go back to 1500x magnification to rule out possible image errors (shadows etc.), which the image stabilization may then sell to me as grain. However, the somewhat coarser grinding degrees of some particles can be easily analyzed and determined. In the paste from 2024, the particles in the matrix soup disappear a little more than in that from 2023 and almost look like fish eggs.
You can see significantly more particles in the paste from 2023, but the mixture is not quite ideal (various clumps). However, this is a manufacturing problem.
Material analysis
I also need to say something up front to help you better understand the quantitative weights determined, as I normally use LIBS to determine the quantitative weights of individual chemical elements and not compounds. The aluminum found is a component of the contained Al2O3and thus binds the listed oxygen together with the zinc in the ZnO and with the polymer of the matrix (silicon). I have deliberately included the hydrogen here, as the small amount can only be located in the siloxanes, but this does not mean that none was present. While in the four microscope images above the paste from 2023 and that from 2024 were taken with slightly different illumination settings for better visibility, the default setting for the LIBS, including white balance, is identical and freshly calibrated. The color difference of the matrix is barely perceptible.
The proportions of the solids are slightly different, but the matrix is no longer completely identical. This is because the paste from 2023 contains slightly more Al2O3 and therefore slightly less ZnO than the better paste from 2024 in the picture above.
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