The benefit of X-ray is they go through everything (so you can see metal). The problem is they go through everything, so you have little signal. For metal/bump

The benefit of X-ray is they go through everything (so you can see metal). The problem is they go through everything, so you have little signal. For metal/bump voids, hard to inspect any other way The harder problem for X-ray inspection is that 1) resolution is difficult to scale economically (possible, but hard). And 2) if any version of wafer or die direct bond dominates (I tend to believe it will), then x-ray won't be good enough anyway, so hard to spend the investment on this.