At the risk of resurrecting a zombie thread, I thought it may be of interest to see inside a couple of high-capacity microSD cards.
On the left is a 512GB card of indeterminate brand - it may look like a dodgy fake but it genuinely is 512GB. On the right is a SanDisk 1TB microSD - again, genuine.
I took the 'easy' X-Rays first, with the cards flat on the imaging plane, then the much harder transverse view with the cards stood on end or on edge. Due to the way the bond wires are placed, the 512GB card X-Rayed better when stood on its long edge, while the 1TB card was better viewed when standing on its short edge. If you look really carefully at the 1TB transverse view you can just see the gold contacts (at the bottom) as an undulation of about 1 pixel thickness.
Those who know more than me are welcome to correct me, but looking at the side-on view of the 512GB card, it appears to have four layers (dies) stacked on top of each other and wire-bonded at the 'pins' end of the card. The 1TB card, on the other hand, appears to have three separate stacks of dies - two of five and the bottom one of six, I think. It's hard to see clearly on the X-Ray, but do bear in mind that the cards are only about 900µm thick except at the 'bottom', so being able to resolve any detail is good going!
Both of the cards have a much smaller driver die in the bottom right. In the 1TB card it's actually tucked under the overhang of the bottom stack of memory dies!
I think the reason we see the individual dies in the stacks as thin lines separated by voids is that the lines may be the metallisation layer(s) on the dies, which are more opaque to the 35kV X-Rays than bulk silicon. But on the 1TB card the dies have been thinned to such an extent that there's precious little silicon left under the metallisation. Assuming the stack of 16 dies is 800µm high then each die can only be 50µm thick. I think it's amazing that I can (just) resolve details that fine - but not as amazing as the engineering that has gone into making it possible to store a terabyte of data in an overall package of 15 x 11 x 1mm (165 cubic mm, according to Wikipedia). Put is another way, the overall storage density is something like 6GB per cubic millimetre.
Wow.
Please note: I wish to retain the copyright of this image but you can use it under the terms of CC BY-SA, credited to Ultrapurple.