TiN Bonding Layer for Copper-Ceramic Substrate Thermal Stress
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Solution Overview
Problem
Conventional power semiconductor modules face reliability issues due to thermal stress-induced cracks in ceramic substrates caused by thermal expansion differences between copper and ceramic materials, especially when thick copper plates are used, and the presence of silver (Ag) in the bonding layer affects thermal cycle reliability.
Innovation Solution
A bonded substrate is developed with a TiN bonding layer between a nitride ceramic substrate and a copper plate, where Ag is distributed in the copper plate, and an Ag-rich phase is present at the interface, enhancing thermal cycle reliability and heat-dissipation properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a thick copper plate is used to satisfy heat-dissipating property and scale reduction, then heat-dissipating property is improved, but thermal expansion difference between copper and ceramic substrate increases causing cracks in the ceramic substrate
Solution Approach 1:
A bonding layer comprising a Cu-rich phase and a Ti-rich phase is introduced between the copper plate and the nitride ceramic substrate. This intermediary layer acts as a buffer to reduce thermal stress generated by thermal expansion differences, preventing cracks in the ceramic substrate while maintaining effective heat dissipation through the thick copper plate structure.
Solution Approach 2:
The bonding layer is designed as a composite structure with distinct Cu-rich and Ti-rich phases. The Cu-rich phase ensures good thermal conductivity and bonding to the copper plate, while the Ti-rich phase provides strong bonding to the nitride ceramic substrate and reduces thermal stress. This composite approach allows the system to simultaneously achieve thick copper plate heat dissipation and thermal cycle reliability.
2Strength
If a bonding layer is formed using a brazing material containing Ag, then bonding between copper plate and ceramic substrate is achieved, but the mode of presence of Ag in the vicinity of the interface affects thermal cycle reliability
Solution Approach 1:
The bonding layer is designed with spatially varying composition and structure, comprising a Cu-rich phase and a Ti-rich phase distributed in specific patterns. This local quality variation ensures that Ag is present in controlled amounts and configurations that promote strong bonding while preventing harmful effects on thermal cycle reliability. The Cu-rich phase provides good bonding to copper, while the Ti-rich phase provides strong bonding to the ceramic substrate.
3Device complexity
If direct bonding of thin copper plate to ceramic substrate is used, then simple structure is achieved, but heat-dissipating property is insufficient
Solution Approach 1:
The bonding layer is segmented into distinct Cu-rich and Ti-rich phases rather than being a homogeneous material. This segmentation allows each phase to perform its specific function: the Cu-rich phase provides thermal conductivity and bonding to the copper plate, while the Ti-rich phase provides bonding to the ceramic substrate and stress reduction. This segmented structure achieves superior heat dissipation compared to thin direct bonding while maintaining reasonable structural complexity.
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 solution significantly improves the thermal cycle reliability and heat-dissipation properties of power semiconductor modules by reducing thermal stress and preventing electric insulation breakdown, while maintaining high reliability against thermal cycles and electric insulation breakdown.
Implementation Method 1
a heat stress generated at the bonding end of the copper plate and the ceramic substrate increases due to the thermal expansion difference between copper and ceramics
Implementation Method 2
a silicon nitride substrate and a copper plate are bonded by the diffusion bonding method
Implementation Method 3
the mode of presence of Ag in a vicinity of the interface between the copper plate and the bonding layer exerts an influence on the reliability to the thermal cycle
Implementation Method 4
a bonding layer consisting of TiN intervenes between the nitride ceramic substrate and the copper plate
Data Source
Figure 1~2
Figure 3~4
Figure 5
AI summary
Provided is a bonded substrate mainly for mounting a power semiconductor in which the reliability to a thermal cycle has been enhanced as compared with a conventional one. In a bonded substrate in which a copper plate is bonded to one or both main surface(s) of a nitride ceramic substrate, a bonding layer consisting of TiN intervenes between the nitride ceramic substrate and the copper plate and is adjacent at least to the copper plate, and an Ag distribution region in which Ag atoms are distributed is set to be present in the copper plate. Preferably, an Ag-rich phase is set to be present discretely at an interface between the bonding layer and the copper plate.