How to Read an EDS Spectrum for Ceramic Submount Incoming Inspection | FerraLink

EDS is the fastest way to confirm you received the correct ceramic material. Two peaks tell you everything you need for ALN and SiC submount receiving inspection.

What EDS measures

Energy-dispersive X-ray spectroscopy detects characteristic X-rays emitted when an electron beam excites atoms in a sample. Each element produces peaks at specific energy levels (keV). For ceramic submount incoming inspection, EDS answers one question: did we receive the material we ordered?

EDS does not measure thermal conductivity, crystal structure, or metallization thickness — those require separate tests. But as a first-pass composition check on every incoming lot, it takes minutes and catches material mix-ups before they reach your die attach line.

ALN: look for Al and N peaks

A qualified polycrystalline ALN submount shows two dominant peaks: nitrogen (N) at ~0.4 keV and aluminum (Al) at ~1.5 keV. The spectrum below is from a FerraLink ALN lot at receiving inspection.

EDS spectrum of ALN submount showing aluminum peak at 1.5 keV and nitrogen peak at 0.4 keV — FerraLink ALN submount EDS spectrum. Dominant Al (~1.5 keV) and N (~0.4 keV) peaks confirm stoichiometric aluminum nitride.

Acceptance criteria: Al and N are the only significant peaks. Trace oxygen (O at ~0.5 keV) from surface adsorption is normal. Reject if Si, C, or heavy metal peaks appear above trace levels — these indicate wrong material or contamination.

SiC: look for Si and C peaks

Single-crystal SiC submounts show silicon (Si) at ~1.7 keV and carbon (C) at ~0.3 keV. The Si peak is typically the tallest in the spectrum.

EDS spectrum of SiC submount showing silicon peak at 1.7 keV and carbon peak at 0.3 keV — FerraLink single-crystal SiC submount EDS spectrum. Si (~1.7 keV) and C (~0.3 keV) peaks confirm stoichiometric silicon carbide.

Acceptance criteria: Si and C only. Reject if Al or N peaks appear — you may have received ALN instead of SiC, a common mix-up given similar part geometries.

Pair EDS with SEM for full material verification

EDS confirms composition. SEM confirms microstructure — and the two together distinguish single-crystal SiC from polycrystalline ALN even when part numbers look similar.

SiC (single crystal)

SEM micrograph of single-crystal silicon carbide submount at 2000× magnification — smooth crystalline facets without grain boundaries — Single-crystal SiC, 2000×. Smooth crystalline facets — no polycrystalline grain structure.

FerraLink SiC submounts use single-crystal silicon carbide. Without grain-boundary phonon scattering, thermal conductivity reaches 350–400 W/m·K — the highest of any practical ceramic substrate available to packaging engineers.

ALN (polycrystalline)

SEM micrograph of polycrystalline aluminum nitride submount at 2000× magnification — grain boundaries visible at fracture surface — Polycrystalline ALN fracture surface, 2000×. Individual grains and grain boundaries are clearly visible.

ALN submounts are polycrystalline ceramics. Phonons scatter at grain boundaries, which limits bulk thermal conductivity to 170–210 W/m·K — still 6–8× better than alumina, with excellent CTE match to InP and GaAs laser diodes.

Incoming inspection checklist

Step	Method	Pass criteria
1. Visual	Microscope, 10–50×	No chips, cracks, or contamination on bonding surface
2. Composition	EDS	ALN: Al + N peaks. SiC: Si + C peaks. No foreign elements
3. Microstructure	SEM (spot check)	SiC: single-crystal facets. ALN: polycrystalline grains
4. Dimensions	Calipers / optical	Length, width, thickness per drawing tolerance
5. Metallization	XRF or cross-section	Stack thickness per spec (Ti/Pt/Au or Au/Sn)
6. Documentation	Review C of C	Lot number, material grade, thermal conductivity test method

For a full supplier qualification workflow, see our ceramic substrate supplier qualification guide.

Frequently asked questions

What peaks confirm ALN on an EDS spectrum?expand_more

Aluminum (~1.5 keV) and nitrogen (~0.4 keV) as the dominant peaks. Trace oxygen from surface adsorption is normal.

What peaks confirm SiC on an EDS spectrum?expand_more

Silicon (~1.7 keV) and carbon (~0.3 keV). The Si peak is typically the tallest in the spectrum.