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FEBRUARY 2026 I SMT007 MAGAZINE 29 tors, dimensionally stable, and capable of surviving where plastics couldn't. Thick-film technology emerged to build conductive and resistive layers directly on ceramic substrates. Engineers screen-printed metallic and dielectric pastes—often silver, palladium, or gold—and fired them in furnaces to form durable, adherent traces. The result was a rugged, compact circuit that could endure thermal cycling and mechanical stress. Thick- film hybrids became the standard for military, aero- space, and medical electronics, providing unmatched reliability in demanding conditions. Even today, thick-film remains a vital technology. It is flexible, proven, and highly customizable for complex circuit topologies and sensor integration. The Drive for Power: Enter DBC and Active Metal Brazed (AMB) Substrates By the 1980s, power electronics were advancing rapidly. Engineers needed substrates that could move large amounts of current and heat, something thick- film struggled to manage. That led to the next evolutionary leap: direct bond copper (DBC) and active metal brazed (AMB) substrates. DBC technology bonds a thick copper layer (typi- cally 200–400 µm) directly to a ceramic substrate, usually aluminum oxide or aluminum nitride. The process uses a high-temperature oxidation and bond- ing reaction to fuse copper and ceramic at the atomic level, with no adhesives or intermediates. The result was outstanding thermal conductivity and mechanical strength, making DBC ideal for high- power devices like IGBTs, MOSFETs, and SiC modules. AMB followed soon after, using active-metal braz- ing alloys (like titanium-based solders) to achieve simi- lar copper-to-ceramic bonds at slightly lower process temperatures, allowing use with beryllia and alumi- num nitride for even higher performance. With DBC and AMB, engineers could finally achieve low thermal resistance and high current capacity in compact, durable packages, perfect for the rising tide of power electronics in industrial drives, automotive inverters, and renewable energy systems. The Material Revolution: Aluminum Nitride, Silicon Nitride, and Beyond Ceramic packaging isn't standing still; it's evolving at the same pace as semiconductors. While process innovation was key, material science kept driving the next wave of change. Alumi- num nitride (AlN) entered mainstream production in the 1990s, offering thermal conductivity up to 180 W/m·K, nearly eight times higher than alumina, and with excellent dielectric strength. Then came silicon nitride (Si₃N₄), a material with slightly lower conductivity but dramatically better mechanical toughness and thermal shock resis- tance. Silicon nitride's ability to survive vibration and cycling made it ideal for EV traction inverters, aero- space converters, and rail power modules, where reliability literally determines safety. These new materials allowed engineers to push junc- tion temperatures higher, reduce cooling requirements, and increase power density, thus fundamentally chang- ing what was possible in electronic packaging. Why the Evolution Matters: Design Realities in Today's Systems The shift from thick-film to DBC isn't about replacing old technology, but rather about matching the right tool to the job. Thick-film remains unmatched for mixed-signal circuits, hybrid modules, and sensor assemblies that require fine geometry and multilayer capability. It's cost-effective, flexible, and ideal for moderate- power applications. DBC and AMB, on the other hand, dominate where heat flux, current load, and structural reliabil- ity are mission-critical. Design engineers must now balance multiple vari- ables: • Thermal conductivity vs. mechanical strength (AlN vs. Si₃N₄) • Cost vs. performance (alumina vs. AlN) • Metallization type vs. process compatibility (thick-film vs. direct copper bonding) • CTE matching between substrate, copper, and attached devices This goes beyond materials science to system engineering. A substrate that saves 5°C in junction temperature can extend device life by years and allow downsizing of the heat sink, saving weight and cost across the system. P OW E R I N G T H E F U T U R E