Microscopy and material analysis
I can’t smear anything this time, only microscopically. What we see here as a kind of “streak” is the pad, which has already been exposed to various influences during production, assembly and packaging. However, this is not a bad thing, as it will melt under pressure and heat anyway and adapt beautifully to the surface.
The risk of outgassing or bleeding of a simple silicone base is of secondary importance here. The polymer used in the PCM (phase change material) is quite constant and durable. The particle sizes of the largest particles are around 2 to 4 µm, but there are many nanoparticles with a grain size of well under 1 µm. This is good and gives us hope.
Now let’s take a closer look at what’s actually in it and what’s not. The paste contains a lot of fillers, mainly very fine aluminum oxide. The zinc oxide content is significantly lower, but still completely sufficient. The ZnO is primarily used as a gap filler between the somewhat larger (and harder) Al2O3 grains. The pad therefore benefits from its viscosity and you have to take these circumstances into account when applying it, because the thin pad breaks or tears very quickly. But it is certainly feasible.
Test equipment for material tests, accuracy and test preparation
My Keyence VHX 7000 and EA-300 are responsible for material testing and measuring the pastes and pads, enabling both exact measurements and fairly precise mass determinations of the chemical elements. But how does it actually work? The laser-induced breakdown spectroscopy (LIBS) I used for the article is a type of atomic emission spectroscopy in which a pulsed laser is directed at a sample in order to vaporize a small part of it and thus generate a plasma.
The emitted radiation from this plasma is then analyzed to determine the elemental composition of the sample. LIBS has many advantages over other analytical techniques. Since only a tiny amount of the sample is needed for analysis, the damage to the sample is minimal. The real damage is caused in today’s article by my rather coarse cutting and separating tools. This still quite new laser technique generally requires no special preparation of the samples for material analysis. Even solids, liquids and gases can be analyzed directly.
LIBS can detect multiple elements simultaneously in a sample and can be used for a variety of samples, including biological, metallic, mineral and other materials. And you get true real-time analysis, which saves a tremendous amount of time. As LIBS generally requires no consumables or hazardous reagents, it is also a relatively safe technique that does not require a vacuum as with SEM EDX. As with any analytical technique, there are of course certain limitations and challenges with LIBS, but in many of my applications, especially where speed, versatility and minimally invasive sampling are an advantage, it offers significant benefits.
I would first like to point out that the results of the percentages in the overviews and tables have been intentionally rounded to full percentages (wt%, i.e. weight percent), as it happens often enough that production variations can occur even within what is presumably the same material. Analyses in the parts per thousand range are nice, but not very useful today when it comes to reliable evaluation and not trace elements. However, every day in the laboratory starts with the same procedure, because when I start, I work through a checklist that I have drawn up. This takes up to 30 minutes each time, although I have to wait for the laser to warm up and the room to reach the right temperature anyway.
- Mechanical calibration of the X/Y table and the camera alignment (e.g. for stitching)
- White balance of the camera for all lighting fixtures used
- Check alignment of LIBS optics and standard lens, calibrate alignment of laser to own optics (x300)
- Test standard samples of the materials to be measured and correct the curve if necessary (see image above)
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