Sintered Silver Bonding Layer for Power Module Thermal Stress
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Solution Overview
Problem
The power module substrate with a heat sink experiences increased thermal resistance and potential breaking of the insulating substrate due to thermal cycles, as solder materials used for bonding are damaged by internal stress from differences in linear expansion coefficients between the substrate and heat sink.
Innovation Solution
A power module substrate with a heat sink featuring a bonding layer composed of a sintered body of silver particles with a relative density between 60% and 90% and a thickness of 10 μm to 500 μm, which alleviates internal stress and maintains high thermal conductivity by using a metal layer of aluminum or copper alloys and a silver or gold plating layer for enhanced bonding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If solder material is used for bonding the power module substrate and heat sink, then initial thermal conductivity is achieved, but thermal resistance increases and bonding reliability deteriorates over long-term thermal cycles due to internal stress damage
Solution Approach 1:
The patent changes the material parameters of the bonding layer from traditional solder materials to a composite material consisting of sintered silver particles (60-90% relative density) combined with a porous body. This parameter change enables the bonding layer to maintain both low thermal resistance and high reliability under long-term thermal cycling conditions by adjusting the density and compositional parameters of the bonding material.
Solution Approach 2:
The patent employs a composite material structure for the bonding layer, combining sintered silver particles with a porous body. This composite approach allows the bonding layer to simultaneously achieve good thermal conductivity through the silver particles and stress absorption capabilities through the porous structure, resolving the contradiction between thermal performance and bonding reliability under thermal stress.
2Loss of energy
If the bonding layer density is increased to improve thermal conductivity, then heat dissipation performance improves, but the bonding layer becomes more susceptible to damage from internal stress during thermal cycles
Solution Approach 1:
The patent optimizes the density parameter of the bonding layer by controlling the relative density of sintered silver particles to be within 60-90%, combined with the porous body structure. This parameter optimization achieves a balance where sufficient thermal conductivity is maintained while the porous structure provides stress absorption capacity, preventing bonding layer damage during thermal cycling.
Solution Approach 2:
The patent incorporates a porous body into the bonding layer structure, which provides void spaces that can absorb and accommodate internal stresses generated during thermal expansion and contraction. This porous structure allows the bonding layer to maintain its integrity under thermal stress while still providing adequate thermal conduction pathways through the silver particle network.
3Strength
If a thick bonding layer is used to accommodate thermal expansion differences, then stress resistance improves, but thermal resistance increases and heat dissipation efficiency decreases
Solution Approach 1:
The porous body structure within the bonding layer provides distributed void spaces that can accommodate thermal expansion differences between the power module substrate and heat sink. This allows the bonding layer to absorb thermal stresses without requiring increased thickness, thereby maintaining efficient heat dissipation while providing adequate stress resistance.
Solution Approach 2:
The composite structure of sintered silver particles and porous body creates a multi-functional bonding layer where the silver particles provide thermal conduction pathways and the porous structure provides stress accommodation. This composite approach enables the bonding layer to achieve both thermal stress resistance and low thermal resistance without requiring increased thickness.
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 configuration effectively suppresses the increase in thermal resistance and prevents breaking in the insulating substrate over long-term thermal cycles, ensuring reliable heat dissipation and structural integrity.
Implementation Method 1
the bonding layer has a high melting point and is not easily melted. In addition, since the sintered body of silver particles forming the bonding layer is a porous body having a relative density in a range of 60% or more and 90% or less and has a thickness in a range of 10 μm or more and 500 μm or less, internal stress caused by a difference in linear expansion coefficient between the power module substrate and the heat sink during loading of a thermal cycle is alleviated
Implementation Method 2
internal stress caused by a difference in linear expansion coefficient between the power module substrate and the heat sink during loading of a thermal cycle is alleviated
Implementation Method 3
internal stress caused by a difference in linear expansion coefficient between the power module substrate and the heat sink during loading of a thermal cycle is alleviated
Data Source
AI summary
The invention provides a power module substrate with a heat sink, which includes a power module substrate provided with an insulating substrate, a circuit layer provided on one surface of the insulating substrate and a metal layer provided on the other surface of the insulating substrate. The heat sink is bonded to the power module substrate via a bonding layer (30) to a surface on an opposite side to the insulating substrate of the metal layer. Bonding layer is a sintered body of silver particles, a porous body having a relative density in a range of 60% or more and 90% or less, and having a thickness in a range of 10 μm or more and 500 μm or less.