Ceramic-Copper Joining Layer Hardness for Thermal Cycle Reliability
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Solution Overview
Problem
Conventional ceramic metal circuit boards face difficulties in enhancing thermal cycle test (TCT) characteristics as the operation guaranteed temperature of semiconductor elements increases, primarily due to the hardness of the joining layer, which fails to adequately mitigate stress between the ceramic substrate and copper plate, especially under high-temperature environments.
Innovation Solution
A ceramic-copper joined body with a joining layer having a nanoindentation hardness between 1.0 GPa and 2.5 GPa, utilizing a brazing material with a controlled Ag-Cu-Ti composition, including Ag-Ti compounds and optionally In, Sn, and C, to achieve a soft yet durable joining layer that reduces thermal resistance and enhances durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional Ag-Cu-based brazing material with Ag:Cu = 7:3 mass ratio is used, then the joining layer has high hardness, but it fails to sufficiently mitigate the stress generated between ceramic substrate and copper plate under high-temperature conditions
Solution Approach 1:
The invention changes the compositional parameters of the brazing material by introducing Ag-Ti intermetallic compounds and controlling the Ag/Cu mass ratio to be 2.0 or less. This parameter change transforms the joining layer from a hard conventional structure to a softer structure with enhanced stress mitigation capability while maintaining adequate strength through the specific intermetallic compound formation.
2Temperature
If the operation guaranteed temperature of semiconductor elements is increased to 175°C or more, then the performance of semiconductor elements is improved, but the TCT characteristics of ceramic metal circuit boards become insufficient
Solution Approach 1:
The invention creates a composite joining layer structure containing Ag-Ti intermetallic compounds combined with Ag-Cu eutectic. This composite material approach enables the joining layer to withstand higher operating temperatures (175°C or more) while maintaining excellent TCT characteristics through the synergistic effects of the different phases present in the composite structure.
3Stability of the object's composition
If the Ag-Cu eutectic composition is used with Ag:Cu = 7:3 mass ratio, then the crystal structure is relatively hard, but the joining layer hardness becomes too high to adequately mitigate thermal stress
Solution Approach 1:
The invention applies local quality by creating specific regions of Ag-Ti intermetallic compounds within the joining layer while maintaining Ag-Cu eutectic in other areas. This localized differentiation allows certain regions to provide structural stability while other regions provide stress mitigation, resolving the contradiction between crystal structure stability and thermal stress handling.
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 effectively improves the durability and reliability of the ceramic-copper joined body under high-temperature conditions, allowing for excellent TCT characteristics even at temperatures up to 175°C, thereby ensuring the stability and performance of semiconductor circuit boards.
Implementation Method 1
a copper member joined to the ceramic member with a joining layer therebetween
Implementation Method 2
reduces thermal resistance
Data Source
Figure 1~2
Figure 3~4
AI summary
This bonding body is provided with a ceramic member and a copper member bonded to the ceramic member via a bonding layer. The nano-indentation hardness HIT of the bonding layer is 1.0-2.5 GPa inclusive.