Power Module Substrate Unit Warp Reduction via Purity-Graded Aluminum Layers
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Solution Overview
Problem
Conventional power-module substrate units with heat sinks face issues of warp generation due to linear expansion differences between the insulator substrate and heat sink, leading to bonding reliability problems and increased thermal resistance, especially under temperature fluctuations during mounting and usage.
Innovation Solution
A power-module substrate unit design featuring a ceramic substrate with a circuit layer and a metal layer, where the metal layer is bonded to an aluminum plate with 99.99% purity and the heat sink is made from an aluminum plate with 99.90% purity or lower, utilizing a stacked structure to balance internal stresses and prevent warp by arranging high-rigidity components symmetrically around the ceramic substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a heat sink is bonded to a ceramic substrate with an aluminum plate circuit layer, then heat radiation performance is improved, but warp is generated due to linear expansion difference between the insulator substrate and heat sink
Solution Approach 1:
The patent changes the material parameters by using high-purity aluminum (99.99% or higher) for the circuit layer instead of conventional aluminum alloys, and controls the thickness ratio between the circuit layer and heat sink to be 0.5:1 or greater. This parameter optimization reduces the linear expansion difference and balances thermal stress, thereby reducing warp while maintaining heat radiation performance.
Solution Approach 2:
The patent creates a composite structure consisting of high-purity aluminum circuit layer, ceramic substrate, and aluminum heat sink. The high-purity aluminum provides different mechanical and thermal properties compared to conventional aluminum alloys, creating a composite material system that balances thermal conductivity with dimensional stability during thermal cycling.
2Reliability
If the warp is generated in the mounting process, then bonding reliability is deteriorated since solder bonding part position may be shifted or distortion and cracks may be generated
Solution Approach 1:
By changing the material purity parameter to 99.99% or higher aluminum and optimizing the thickness ratio (circuit layer thickness/heat sink thickness ≥ 0.5), the patent reduces thermal stress and linear expansion differences, thereby minimizing warp during the mounting process and protecting solder bonding integrity.
3Temperature
If the warp is generated in the usage environment, then thermal conductive grease may flow out by pump-out phenomenon, so adhesion of heat sink and cooler is deteriorated and thermal resistance is increased
Solution Approach 1:
The patent optimizes material parameters (99.99% purity aluminum) and dimensional parameters (thickness ratio ≥ 0.5) to reduce thermal stress and linear expansion differences. This minimizes warp during usage, preventing thermal conductive grease pump-out and maintaining low thermal resistance and strong adhesion between heat sink and cooler.
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
This design effectively reduces warp and enhances bonding reliability by balancing internal stresses and preventing thermal stress-induced deformation, maintaining long-term reliability under temperature variations during semiconductor element mounting and usage.
Implementation Method 1
a warp is generated by temperature fluctuation after bonding the heat sink, in a heating process of mounting semiconductor elements or in a usage environment
Implementation Method 2
bonding an aluminum plate on a ceramic substrate such as aluminum nitride and bonding an aluminum based heat sink on one surface of the ceramic substrate with an intervening aluminum plate
Data Source
Figure 1(a)~1(c)
Figure 2
Figure 3(a)~3(b)
AI summary
A power-module substrate unit having at least one power-module substrate including one ceramic substrate, a circuit layer formed on one surface of the ceramic substrate, and a metal layer formed on another surface of the ceramic substrate, and a heat sink on which the metal layer of the power-module substrate is bonded, in which the metal layer is made of an aluminum plate having purity of 99.99 mass% or higher; the heat sink is made of an aluminum plate having purity of 99.90 mass% or lower; and the circuit layer has a stacking structure of a first layer made of an aluminum plate having the purity of 99.99 mass% or higher and being bonded to the ceramic substrate and a second layer made of the aluminum plate having the purity lower than 99.90 mass% and being bonded on a surface of the first layer.