Power Module Substrate Brazing with Aligned Crystalline Grain Structure
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Solution Overview
Problem
Conventional power module substrates experience insufficient joint strength and reliability due to fracture propagation at the interface between metal and ceramic substrates, especially under thermal cycles, which is exacerbated by the rigidity of heat radiation plates and high shear forces.
Innovation Solution
A method involving a ceramics substrate and pure aluminum metal plates with an Al-Si brazing filler metal, where the brazing filler is fused and solidified to create a crystalline grain structure aligned with the metal plates, preventing fracture propagation by absorbing distortion and stress concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the roughness surface of the ceramics substrate is reduced to improve joint strength, then the surface smoothness is improved, but the joint strength remains insufficient and peeling occurs at the interface
Solution Approach 1:
The invention applies different surface treatments to different regions of the ceramics substrate. The first surface (joining surface with metal plate) is maintained with roughness Ra≤0.5μm for good joint strength, while the second surface (joining surface with heat radiation plate) undergoes honing treatment to achieve Ra≤0.2μm. This local differentiation of surface quality resolves the contradiction by optimizing each surface for its specific function.
Solution Approach 2:
The invention changes the surface roughness parameter differently for the two surfaces of the ceramics substrate. By controlling the roughness of the first surface to be Ra≤0.5μm and the second surface to be Ra≤0.2μm through selective honing treatment, the patent optimizes both joint strength and thermal contact, resolving the contradiction between surface smoothness and joint strength.
2Temperature
If the power module substrate is rigidly fixed by the heat radiation plate to improve heat dissipation, then the thermal performance is improved, but a large shear force is generated at the joint interface during thermal cycles causing fracture propagation
Solution Approach 1:
The invention applies different surface treatments to different regions of the ceramics substrate. The first surface (joining surface with metal plate) is maintained with roughness Ra≤0.5μm for good joint strength, while the second surface (joining surface with heat radiation plate) undergoes honing treatment to achieve Ra≤0.2μm. This local differentiation of surface quality resolves the contradiction by optimizing each surface for its specific function.
Solution Approach 2:
The honing treatment on the second surface creates a smoother surface that can better distribute and cushion the shear forces generated during thermal cycles. This preparatory surface treatment absorbs and distributes the thermal stress before it reaches the joint interface, preventing fracture propagation while maintaining rigid fixation for heat dissipation.
3Manufacturing precision
If conventional surface treatments like honing or polishing are applied to reduce roughness, then the surface smoothness is improved, but peeling still occurs at the interface in peeling tests
Solution Approach 1:
The invention applies different surface treatments to different regions of the ceramics substrate. The first surface (joining surface with metal plate) is maintained with roughness Ra≤0.5μm for good joint strength, while the second surface (joining surface with heat radiation plate) undergoes honing treatment to achieve Ra≤0.2μm. This local differentiation of surface quality resolves the contradiction by optimizing each surface for its specific function.
Solution Approach 2:
The invention creates a composite structure by joining the ceramics substrate with both a metal plate and a heat radiation plate through optimized surface treatments. The combination of different materials (ceramics, metal, and heat radiation plate) with differentiated surface qualities creates a multi-layer composite structure that prevents peeling by distributing stresses across different interfaces.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method enhances joint strength and reliability by minimizing fracture propagation at the interface, even under severe thermal cycles, through the controlled crystalline orientation and distribution of the melting point-lowering element Si, ensuring the power module substrate's durability.
Implementation Method 1
forming a fused aluminum layer (26, 27) at an interface between the ceramics substrate (11) and the metal plate (22, 23) by fusing the brazing filler metal (24, 25) which is caused by heating
Implementation Method 2
solidifying the fused aluminum layer (26, 27) by cooling, wherein the method is characterized in that in the step of solidifying the fused aluminum layer (26, 27), a crystal adjacent to the interface between the ceramics substrate (11) and the metal plate (22, 23) is grown so as to be arranged in [001] direction
Implementation Method 3
a brazing filler metal (24, 25) being interposed therebetween, forming a fused aluminum layer (26, 27) at an interface between the ceramics substrate (11) and the metal plate (22, 23) by fusing the brazing filler metal (24, 25)
Data Source
Figure 1
Figure 2
Figure 3A~3C
AI summary
A method for manufacturing a power module substrate (10), includes: preparing a ceramics substrate (11) and a metal plate (22, 23) made of pure aluminum; a fusion step in which the ceramics substrate (11) and the metal plate (22, 23) are stacked in layers with a brazing filler metal (24, 25) interposed therebetween, and a fused aluminum layer (26, 27) is formed at an interface between the ceramics substrate (11) and the metal plate (22, 23) by fusing the brazing filler metal (24, 25) which is caused by heating; and a solidifying step in which the fused aluminum layer (26, 27) is solidified by cooling, and a crystal is grown so as to be arranged in a crystal orientation of the metal plate (22, 23) when the fused aluminum layer (26, 27) is solidified.