Issue link: https://iconnect007.uberflip.com/i/1545206
JUNE 2026 I SMT007 MAGAZINE 71 lighting gate oxide failure as a major challenge. 8 That does not mean SiC is unsuitable, but that ma- terial quality, screening, drive conditions, thermal control, and package design must be tighter than many engineers have been accustomed to in older silicon systems. If those issues are not addressed, the failures are straightforward. A device that switches faster than the package or layout can support may generate overshoot, higher local heating, insulation stress, and premature aging. A gate oxide that drifts or weakens may alter switching response long before hard failure occurs. A device that survives lab qualification but carries latent defects may still fail early in vehicle service. These risks directly affect inverter durability, charging performance, warranty cost, and driver confidence. 1,2,6 Substrates Carry More Than Heat In EV power modules, the substrate is not just a heat spreader. It must provide electrical insula- tion, move heat away from the die, support copper circuitry, and tolerate repeated thermal cycling. Direct-bonded copper (DBC) on alumina, alumi- num nitride, or silicon nitride remains widely used. Aluminum nitride offers much higher thermal conductivity than alumina, which makes it attrac- tive for high-power designs, but it is mechanically less forgiving. Published work and industry technical reviews note that AlN-based DBC can face greater thermo-mechanical reliability limits during cycling, while alumina is tougher but ther- mally weaker. 9,10 That tradeoff matters in EV duty cycles because traction inverters and power converters see re- peated temperature swings during acceleration, regenerative braking, fast charging, and ambient weather changes. Cracking, copper-ceramic de- lamination, and solder or sinter fatigue can follow when thermal expansion mismatches are not prop- erly handled. 7,11 The material choice becomes a balance among heat removal, insulation, mechani- cal durability, cost, and manufacturability. Silicon nitride is often discussed as an attractive middle path because it offers strong fracture toughness with good thermal performance, though usually at higher cost and with process complexity. 8 What has gone wrong historically in power mod- ules is well documented. Bond wires have often been identified as one of the weakest elements in module lifetime, and substrate-related fatigue is a known wear-out path under power cycling. 9,12 That history is one reason newer module designs are steadily moving toward stronger substrate systems and bond-wire-light or bond-wire-free topologies. Interconnects Still Decide Lifetime Interconnect materials and structures remain central to EV reliability. Traditional aluminum wire bonds are proven and widely used, but they are also vulnerable to heel cracking, lift-off, and fatigue during thermal and power cycling. Survey litera- ture on power module reliability identifies bond wires as a common failure location and ties those failures to thermo-mechanical stress at the bond interface. 9,10 Additional studies show that bond quality and process parameters strongly influence degradation rate under cycling. 13 This is why alternatives such as copper clips, ribbon bonds, and sintered die attach are gaining ground. Silver sintering is attractive because it offers high thermal conductivity and high-tem- perature stability compared with many conven- tional solders. At the same time, it is not a cure-all. Sintered joints still depend on surface condition, pressure, porosity control, and process consisten- cy. Poorly controlled sintering can leave voids or weak regions that undermine the expected lifetime benefit. Why does this matter? Because interconnect degradation often shows up first as rising electri- cal resistance and temperatures. That can turn a manageable packaging issue into a module-level failure. In an EV inverter or onboard charger, this may lead to power derating, thermal shutdown, or permanent damage to neighboring devices. The link between materials choice, process discipline, and field reliability is direct. Thermal Materials Can Set the Failure Clock Thermal management is one of the clearest examples of materials dictating system life. Even when semiconductor devices are highly capable, the actual junction temperature depends on the interfaces between die, substrate, baseplate, cold plate, and coolant loop. Thermal interface materi- als (TIMs) are often the weak link because their