Silicon Nitride Substrate In-Plane Orientation for Thermal Conductivity
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Solution Overview
Problem
Conventional silicon nitride substrates face challenges in achieving balanced thermal conductivity and fracture toughness, leading to issues with thermal resistance and reliability in semiconductor modules due to the degree of in-plane orientation, which affects the bonding of metal circuit plates and heat sinks with ceramics, causing stress and potential cracking.
Innovation Solution
A silicon nitride substrate with a specific degree of in-plane orientation (0.4-0.8) is developed, incorporating β type silicon nitride particles and doped elements like lutetium and gadolinium, which enhances fracture toughness along the thickness direction and thermal conductivity, while maintaining sufficient in-plane toughness, using a manufacturing method involving sintering at 1700-2000°C in a nitrogen atmosphere.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If copper is used for metal circuit plate and heat sink due to high thermal conductivity, then thermal conductivity is improved, but thermal expansion coefficient difference with ceramics generates heat stress causing cracking and reduced reliability
Solution Approach 1:
The invention changes the material parameters by selecting copper alloy plates with specific thermal expansion coefficients (10-20×10^-6/K) that match the ceramic substrate, and controls the thickness ratio between circuit plate and heat sink to be 1:0.5-2:0.5-4, optimizing thermal and mechanical performance simultaneously
Solution Approach 2:
The invention applies different thickness ratios for circuit plates and heat sinks locally, with the circuit plate being thinner (0.05-0.5mm) than the heat sink (0.1-2mm), to balance thermal management and stress distribution in different regions of the assembly
2Loss of energy
If silicon nitride substrate has high degree of in-plane orientation to improve thermal conductivity along thickness direction, then thermal conductivity is improved, but fracture toughness along thickness direction deteriorates
Solution Approach 1:
The invention optimizes the degree of in-plane orientation parameter fa to a specific range of 0.2-0.6, balancing thermal conductivity and fracture toughness. This controlled orientation ensures sufficient heat dissipation while maintaining mechanical strength to resist cracking from thermal stress
Solution Approach 2:
The invention uses β-type silicon nitride particles (30-70 mass%) as sintering aids that are consumed during the sintering process to form a microstructure with optimal orientation and porosity, recovering the desired balance between thermal and mechanical properties
3Quantity of substance
If metal plate thickness is increased to 0.3-0.5mm to carry high current, then current carrying capacity is improved, but thermal stress and cracking risk increase due to larger thermal mass
Solution Approach 1:
The invention reduces circuit plate thickness to 0.05-0.5mm and heat sink thickness to 0.1-2mm, optimizing the balance between current carrying capacity and thermal stress resistance. The thinner design reduces thermal mass and stress while maintaining electrical functionality
Solution Approach 2:
The invention uses copper alloy plates with specific compositions (Cu-5-15wt%Sn, Cu-5-15wt%Ni, or Cu-5-15wt%Zn) that provide both adequate electrical conductivity for high current and improved mechanical properties to reduce cracking risk
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 substrate achieves high thermal conductivity (>90 W/m·K) and fracture toughness (>6.0 MPa·m1/2) along the thickness direction, reducing thermal resistance and improving reliability in semiconductor modules by inhibiting crack progression and facilitating heat dissipation.
Implementation Method 1
sintering at 1700-2000°C in a nitrogen atmosphere
Implementation Method 2
thermal conductivity (>90 W/m·K) along the thickness direction
Implementation Method 3
degree of in-plane orientation fa, which is a ratio of orientation along in-plane direction
Implementation Method 4
doped elements comprising at least one element selected from rare earth (RE) elements, wherein Lu is doped with 0.14-1.30 mol % of Lu2O3, 1.70-10 mol % of MgO, and 0.39-1.5 mol % of oxide of doped elements
Implementation Method 5
thermal conductivity along the thickness direction is 90 W/m·K or more
Implementation Method 6
fracture toughness along the thickness direction is 6.0 MPa·m1/2 or more
Data Source
AI summary
In the silicon nitride substrate concerning an embodiment of the invention, degree of in-plane orientation fa of β type silicon nitride is 0.4-0.8. Here, degree of in-plane orientation fa can be determined by the rate of the diffracted X-ray intensity in each lattice plane orientation in β type silicon nitride. As a result of research by the inventors, it turned out that both high fracture toughness and high thermal conductivity are acquired, when degree of in-plane orientation fa was 0.4-0.8. Along the thickness direction, both the fracture toughness of 6.0 MPa·m1/2 or higher and the thermal conductivity of 90 W/m·K or higher can be attained.