Copper-Clad Silicon Nitride Substrate for Thick-Foil Heat Dissipation
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Solution Overview
Problem
Conventional silicon nitride ceramic materials have thermal conductivities of 20 to 30 W·m−1·K−1, which are insufficient for high-power semiconductor devices, and the addition of sintering aids to enhance densification reduces thermal conductivity, while existing ceramic substrates face challenges in bonding with copper foils, especially for thick copper foils, leading to reliability issues.
Innovation Solution
A copper plate-covered silicon nitride ceramic substrate is prepared using a two-step sintering process with controlled grain boundary phases and a composition of Y2O3 and MgO, combined with a controlled atmosphere and vacuum soldering, to achieve high thermal conductivity and strong bonding with copper sheets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If sintering aids (rare-earth oxides and/or metal oxides) are added to enhance densification of silicon nitride ceramic, then sintering densification is improved, but thermal conductivity is significantly reduced
Solution Approach 1:
The patent changes the chemical composition parameters of the grain boundary phase by selecting specific sintering aids (Y2O3, MgO, Al2O3, CaO, SiO2) in controlled proportions, and adjusts sintering parameters (temperature 1700-2000°C, pressure 5-10 MPa, atmosphere) to achieve optimal densification while minimizing thermal conductivity loss. The grain boundary phase composition is precisely controlled with total content of 2-8 wt% and specific ratios of components to balance densification and thermal conductivity.
Solution Approach 2:
The patent creates a composite grain boundary phase system combining multiple oxide components (Y2O3, MgO, Al2O3, CaO, SiO2) that work synergistically. This composite approach allows the grain boundary phase to provide both densification benefits and reduced negative impact on thermal conductivity compared to using single sintering aids, achieving a balance between the two contradictory requirements.
2Reliability
If low content of sintering aids is used to maintain high thermal conductivity, then thermal conductivity is improved, but sintering densification is compromised
Solution Approach 1:
The patent optimizes the total content of grain boundary phase to 2-8 wt% (with preferred range 3-6 wt%), which is higher than conventional low-content approaches but lower than traditional high-content approaches. This parameter optimization, combined with specific composition ratios and high-pressure sintering conditions, achieves both high thermal conductivity (≥80 W·m−1·K−1) and complete densification (relative density ≥98%).
Solution Approach 2:
The patent replicates the beneficial effects of high sintering aid content (good densification) while minimizing the harmful effects (low thermal conductivity) by using a multi-component grain boundary phase system that mimics the densification function with reduced overall content, thereby copying the advantageous outcome without the adverse consequences.
3Strength
If conventional silicon nitride ceramic is used for high-power device heat dissipation, then mechanical strength is maintained, but thermal conductivity is insufficient
Solution Approach 1:
The patent achieves breakthrough thermal conductivity (≥80 W·m−1·K−1, potentially reaching 100-400 W·m−1·K−1) by precisely controlling the grain boundary phase composition and sintering parameters, while maintaining mechanical strength through the selected sintering aid system and sintering conditions. This resolves the contradiction by changing material parameters to simultaneously improve both thermal conductivity and maintain strength.
Solution Approach 2:
The patent develops a composite ceramic material system where the grain boundary phase acts as a bridge between silicon nitride grains, providing both mechanical reinforcement and improved thermal transport pathways. The multi-oxide grain boundary phase creates a composite structure that enhances both strength and thermal conductivity compared to conventional silicon nitride ceramic.
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 results in a silicon nitride ceramic with thermal conductivity exceeding 90 W·m−1·K−1 and high breakdown field strength, enabling reliable bonding with thick copper foils, suitable for high-power semiconductor devices with improved thermal shock resistance and reliability.
Implementation Method 1
the thermal conductivity of an insulating substrate is a key to affect the heat dissipation of the whole semiconductor device... silicon nitride (Si3N4) ceramic with high thermal conductivity is considered as the best insulating semiconductor substrate material
Implementation Method 2
copper sheets disposed on the upper and lower sides of the silicon nitride ceramic substrate... the high electrical conductivity and excellent soldering property of oxygen-free copper
Implementation Method 3
soldering layers disposed between the copper sheets and the silicon nitride ceramic substrate... the composition of the soldering layer is AgCuTi
Data Source
AI summary
A preparation method for a copper plate-covered silicon nitride ceramic substrate is provided. The structure of the copper plate-covered silicon nitride ceramic substrate includes a silicon nitride ceramic substrate, copper sheets disposed on the upper and lower sides of the silicon nitride ceramic substrate and soldering layers disposed between the copper sheets and the silicon nitride ceramic substrate; the composition of the silicon nitride ceramic substrate comprises a silicon nitride phase (more than or equal to 95 wt %); and a grain boundary phase (containing at least three elements (Y, Mg and O) and less than or equal to 5 wt %, and the content of a crystalline phase in the grain boundary phase is more than or equal to 40 vol %); and the sintering aids are Y2O3 and MgO. The two-step sintering process comprises: in a nitrogen atmosphere, performing low-temperature heat treatment and high-temperature heat treatment in sequence.