X-Ray Computed-Tomography System
X-ray computed tomography (XCT), electron energy-loss spectroscopy (EELS), and electron probe microanalysis (EPMA) each extract a different, hard-to-reach kind of information — XCT builds a full internal 3D structure non-destructively, EELS reads chemical bonding state from energy lost by transmitted electrons, and EPMA maps elemental composition quantitatively with higher precision than standard EDS provides.
XCT's defining advantage is seeing a package's or structure's full internal 3D geometry without physically cutting it apart first — every other technique here, and most elsewhere in this analytical toolkit, is inherently destructive or surface-limited. A package cross-section for SEM or TEM inspection only reveals the structure along one chosen plane, and cutting that cross-section destroys the sample for any further use; XCT reconstructs a full non-destructive 3D volume from many X-ray projections, letting an engineer inspect internal structure — solder joint voids, wire bond positions, internal cracks — from any angle afterward, and still have an intact sample if further non-destructive analysis is needed.
EPMA's precision advantage over standard EDS comes from a slower, more deliberate measurement approach that trades speed for quantitative accuracy. EDS, used broadly as a quick elemental-ID add-on to SEM, collects a full X-ray spectrum rapidly but with comparatively coarse quantitative accuracy; EPMA uses more precisely calibrated detectors and longer counting times specifically tuned for quantitative composition measurement, delivering elemental percentages accurate enough for applications — like confirming the exact stoichiometry of a compound film — where EDS's faster but rougher numbers aren't good enough.
XCT, EELS, and EPMA each answer a question none of the fab's more routine imaging and elemental-ID tools can answer well on their own, and reaching for one of them signals that a failure-analysis or materials question has moved past standard SEM/EDS characterization into territory needing a non-destructive internal view, a bonding-state answer, or quantitative composition precision specifically.