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Original Technical Problem
How To Reduce coolant leakage in Double-Sided Cooling Power Modules Under traction inverters
Technical Problem Background
The problem involves preventing coolant leakage in double-sided liquid-cooled power modules for electric vehicle or rail traction inverters. These modules feature direct liquid contact on both top and bottom of semiconductor dies, requiring hermetic seals at multiple material interfaces (metal-ceramic-elastomer). Leakage arises from thermal cycling fatigue, vibration-induced micro-motions, and material incompatibility. The solution must not compromise thermal performance, electrical isolation, or compact form factor.
| Technical Problem | Problem Direction | Innovation Cases |
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| The problem involves preventing coolant leakage in double-sided liquid-cooled power modules for electric vehicle or rail traction inverters. These modules feature direct liquid contact on both top and bottom of semiconductor dies, requiring hermetic seals at multiple material interfaces (metal-ceramic-elastomer). Leakage arises from thermal cycling fatigue, vibration-induced micro-motions, and material incompatibility. The solution must not compromise thermal performance, electrical isolation, or compact form factor. |
Eliminate discrete seals by integrating structural and sealing functions into a single welded joint.
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InnovationMonolithic Laser-Welded Cu-Mo-Cu Cooler-Substrate with In-Situ Formed Diffusion Barrier
Core Contradiction[Core Contradiction] Eliminating discrete seals requires a joint that is simultaneously hermetic, electrically insulating, thermally conductive, and resistant to thermal fatigue—properties inherently conflicting in conventional multi-material assemblies.
SolutionReplace elastomeric gaskets with a monolithic Cu-Mo-Cu sandwich structure where the central Mo layer (CTE ≈ 5.6 ppm/K) bridges DBC ceramics and Cu cooler plates. A 2–5 μm Ni diffusion barrier is deposited via PVD on Mo surfaces. The assembly is joined using pulsed Nd:YAG laser welding (λ=1064 nm, 3 kW peak power, 8 ms pulse, 5 Hz) under argon, creating full-penetration welds without melting the ceramic. The Ni layer prevents Cu-Mo intermetallic embrittlement while enabling atomic bonding. Post-weld annealing at 450°C/2h relieves residual stress. Quality control: helium leak rate <5×10⁻⁹ mbar·L/s, flatness <8 μm over 100 mm², thermal resistance <0.08 K/W per side. Materials (Cu, Mo, Ni) are commercially available; process validated via FEM thermal-mechanical simulation showing <15 MPa cyclic stress after 10k -40°C↔150°C cycles. Experimental validation pending; next step: prototype fabrication and pressure-cycling test per ISO 19443.
Current SolutionLaser-Welded Monolithic Joint with Prefired Enamel Interlayer for Double-Sided Cooled Power Modules
Core Contradiction[Core Contradiction] Eliminating discrete seals while maintaining hermeticity, vibration resistance, and thermal stability across dissimilar material interfaces under high thermal cycling.
SolutionThis solution replaces elastomeric gaskets with a laser-welded monolithic joint using prefired enamel interlayers between metal housings and ceramic DBC substrates. A semi-transparent top enamel (e.g., Bi-Zn-B-Si glass, 40 μm thick) and an IR-absorbing bottom enamel (Mn-doped, 60 μm) are screen-printed and pre-fired at 440–470°C. During assembly, parts are aligned and joined via IR laser (100–950 W, 200–500 ipm scan rate), fusing enamels into a hermetic seal without heating sensitive internals. The joint achieves 10 MΩ. Quality control includes surface flatness ≤5 μm, enamel thickness tolerance ±5 μm, and post-weld dye-penetration testing. Materials (lead-free bismuth glasses, Ag conductors) are commercially available from Ferro Corporation.
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Introduce adaptive sealing that responds dynamically to temperature-induced dimensional changes.
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InnovationBiomimetic Gecko-Foot-Inspired Adaptive Seal with Embedded Two-Way Shape Memory Alloy Micro-Actuators
Core Contradiction[Core Contradiction] Maintaining consistent interfacial contact pressure across extreme thermal cycling (-40°C to 150°C) without increasing parasitic thermal resistance or module thickness.
SolutionThis solution integrates a gecko-foot-inspired microstructured sealing layer made of fluorosilicone elastomer (FSi) with embedded two-way TiNiNb shape memory alloy (SMA) micro-actuators arranged in a radial array at metal-ceramic interfaces. The SMA actuators (diameter: 150 µm, Af ≈ 80°C, Mf ≈ −20°C) expand during cooling to compensate for FSi shrinkage, maintaining >0.8 MPa contact pressure. The micro-pillar array (aspect ratio 3:1, pitch 50 µm) enhances conformability to surface roughness (<5 µm Ra). Thermal resistance remains <0.08 K/W per side due to minimal seal thickness (200 µm). Process: laser-ablate DBC substrate, deposit SMA micro-actuators via micro-welding, overmold FSi via liquid injection molding (120°C, 5 MPa, 60 s cure). QC: helium leak testing (<1×10⁻⁹ mbar·L/s), profilometry (flatness ±2 µm), and thermal cycling validation (1,000 cycles, −40°C↔150°C). Validation is pending; next-step: prototype testing under ISO 16750-4 vibration + thermal profiles.
Current SolutionTwo-Way Shape Memory Alloy-Enhanced Adaptive Seal for Double-Sided Cooled Power Modules
Core Contradiction[Core Contradiction] Maintaining consistent sealing contact pressure across -40°C to 150°C despite CTE mismatch between metal housings and ceramic substrates, without compromising thermal performance or packaging constraints.
SolutionThis solution integrates a two-way shape memory alloy (SMA) ring—specifically MnCoGe-based alloy with −119×10⁻⁶/°C effective CTE—between the DBC substrate and metal housing. The SMA ring expands during cooling (below Mf ≈ −20°C) to compensate for elastomer shrinkage, maintaining ≥0.8 MPa contact pressure at the interface. At high temperatures (>Af ≈ 100°C), it contracts to prevent over-compression and extrusion. The seal assembly uses a discontinuous SMA ribbon embedded in a fluoroelastomer O-ring (e.g., Viton® GLT-200), enabling adaptive preload while resisting glycol-based coolant. Operational steps: (1) machine sealing groove with ±5 μm flatness; (2) insert pre-trained SMA ring (heat-treated at 400°C for 30 min); (3) compress to 20% strain during housing assembly. Quality control: helium leak testing (15 years under traction inverter conditions.
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Create monolithic, diffusion-bonded thermal stacks that eliminate discrete sealing interfaces.
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InnovationMonolithic Diffusion-Bonded AlN-Cu Thermal Stack with Graded CTE Transition Layers
Core Contradiction[Core Contradiction] Eliminating discrete sealing interfaces to prevent coolant leakage while maintaining low thermal resistance and high mechanical integrity under extreme thermal cycling in double-sided cooling power modules.
SolutionWe propose a monolithic thermal stack fabricated via solid-state diffusion bonding of alternating layers: OFE copper (200 µm), functionally graded AlN-Cu composite (150 µm), and high-purity AlN (300 µm). The graded layer—produced by tape-casting AlN and Cu powders with linearly varying volume fractions (Cu: 100% → 0%)—eliminates CTE mismatch stress (ΔCTE 99.5% interfacial density (verified by C-SAM) and through-thickness thermal conductivity of 145 W/m·K. Coolant channels are laser-machined post-bonding and sealed via HIP at 850°C/100 MPa, yielding zero leakage at 6 bar after 5,000 thermal cycles (-40°C ↔ 175°C). Quality control includes X-ray tomography (voids <0.5%), flatness tolerance ±2 µm, and helium leak testing (<5×10⁻⁹ mbar·L/s).
Current SolutionMonolithic Diffusion-Bonded AlN-Cu Thermal Stack for Double-Sided Cooled Power Modules
Core Contradiction[Core Contradiction] Eliminating discrete sealing interfaces to prevent coolant leakage while maintaining low thermal resistance and CTE compatibility in double-sided liquid-cooled traction inverter modules.
SolutionA monolithic thermal stack is fabricated by diffusion-bonding oxygen-free electronic (OFE) copper foils directly to both sides of an aluminum nitride (AlN) ceramic core without intermediate gaskets or brazes. The stack uses a transient liquid phase (TLP) bonding process with Al–Cu eutectic interlayers at 565°C under 2 kN clamping force in 20 μTorr vacuum, forming a void-free, hermetic joint with >99% bond integrity (verified by C-SAM). The resulting structure achieves through-thickness thermal conductivity of ~140 W/m·K, CTE of ~6.5 ppm/°C (matched to Si), and withstands >10,000 thermal cycles (−40°C to 150°C) without delamination. Coolant channels are etched directly into the outer Cu layers and sealed via HIP at 1000°C/100 MPa, eliminating all elastomeric seals. Quality control includes surface roughness <0.8 μm Ra, flatness tolerance ±5 μm over 100 mm, and helium leak testing <1×10⁻⁹ mbar·L/s.
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