What Is a SiC Submount?

A definition of the single-crystal silicon carbide submount: why 350–400 W/m·K matters for pulsed lidar, laser bars, and GaN RF, and when polycrystalline AlN is still the better CTE match.

What a SiC submount does

A SiC submount is the silicon carbide piece under a laser diode, laser bar, or GaN device. FerraLink uses single-crystal SiC. With no grain boundaries in the heat path, phonons travel farther, and the part conducts 350–400 W/m·K.

Thermal spreading. About twice polycrystalline AlN, and roughly 13–15 times standard alumina. That margin is what pulsed lidar and multi-watt bars use when peak current is high.
Mechanical platform. CTE is 3.7–4.3 ppm/°C, which pairs with GaN and with high-power III-V dies that have already outgrown AlN’s heat limit.
Electrical routing. Ti/Pt/Au or AuSn metallization gives a die-attach pad and wire-bond pads on an electrically insulating crystal.

When SiC is the right submount

Application	Why SiC	When AlN is enough
Pulsed lidar	Peak current needs fast spreading	Low-duty, modest peak power
Laser bar	Power density above the AlN margin	Single-emitter CW telecom
GaN RF	CTE 3.7–4.3 ppm/°C and high CW heat	Small-signal or low dissipation

For a telecom DFB where expansion match matters more than peak conductivity, start with what an AlN submount is. The shared definition of the part itself is what a laser diode submount is.

Catalog sizes

FerraLink SiC samples start at $50 and ship in 2–4 weeks. FL-SiC-035455-001 is 3.5 × 4.55 × 0.30 mm. Smaller squares run from FL-SiC-005 through FL-SiC-020. A 10-piece box is $500 and includes material documentation.

Specs and the sample form are on the SiC submount page. If SiC is still short of the thermal budget, the next material note is CVD diamond, when SiC is not enough.

The part that depends on your die

The rules above hold for most edge-emitter modules. What changes from program to program is geometry, duty cycle, and how hard you are pushing junction temperature — those inputs decide material, thickness, and whether catalog samples are enough.

Footprint, thickness, and solder pad art for your specific die.
Reliability vs your duty cycle and cycling profile.
A short internal-review memo your team can sign off before prototyping.

Go deeper — Pick material

These guides answer adjacent questions teams ask while choosing a submount. Each ends the same way: what you can decide in general, then what needs your die and power.

More topics coming — thermal path, attach yield, qualification, and packaging context.

Frequently asked questions

What is a SiC submount?

A single-crystal silicon carbide ceramic between a high-power chip and the package. It spreads heat at 350–400 W/m·K and provides metallized pads for die attach and wire bonding.

How is a SiC submount different from an AlN submount?

SiC is single crystal and conducts about twice as much heat (350–400 vs 170–210 W/m·K). AlN is the closer CTE match for InP and GaAs telecom lasers. SiC is the usual step up for pulsed lidar, laser bars, and GaN RF.

What does a SiC submount sample cost?

FerraLink catalog SiC pieces start at $50. A 10-piece box is $500 and ships in 2–4 weeks with material documentation.

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