Layered Bonding Material for CTE-Matched Pb-Free Power Modules
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Solution Overview
Problem
Existing semiconductor devices face strain and crack issues due to coefficient of thermal expansion (CTE) differences between the semiconductor device and the substrate under high-temperature conditions, leading to reduced product life, and existing lead-free solder solutions do not meet environmental regulations.
Innovation Solution
A layered bonding material comprising a base material with a specific coefficient of linear expansion (5.5 to 15.5 ppm/K) and lead-free solder sections with controlled thickness (0.05 to 1.0 mm) is used, where the base material is made of Cu-W or Cu-Mo-based materials, and the solder is selected from specific Sn-based alloys, with a Young's modulus of 45 GPa or higher and tensile strength of 100 MPa or lower, to relax strains under high-temperature environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If lead-free solder is used to conform to environmental regulations, then environmental compliance is improved, but strain relaxation capability deteriorates due to higher CTE mismatch
Solution Approach 1:
The bonding material uses a composite structure consisting of a Pb-free solder layer (Sn-Ag-Cu alloy) combined with a Cu-W or Cu-Mo base material. This composite configuration allows the Pb-free solder to provide environmental compliance while the Cu-W or Cu-Mo base material compensates for CTE mismatch and provides strain relaxation capability through its intermediate thermal expansion properties between the semiconductor device and substrate.
2Stability of the object's composition
If solder layer thickness is increased to improve strain relaxation, then stress buffer capacity is improved, but bonding section height increases leading to structural complexity
Solution Approach 1:
The patent specifies precise parameter ranges for the solder layer thickness (0.05 to 1.0 mm) and base material thickness (0.1 to 2.0 mm). By optimizing these parameters, the bonding material achieves adequate stress buffer capacity within the solder layer while controlling the overall bonding section height. The Cu-W or Cu-Mo base material further contributes to strain relaxation without requiring excessive thickness.
3Use of energy by moving object
If Cu content in base material is increased to improve thermal conductivity, then heat dissipation is improved, but CTE mismatch increases leading to higher strain
Solution Approach 1:
The bonding material structure assigns different functional qualities to different layers: the Pb-free solder layer (Sn-Ag-Cu alloy) provides environmental compliance and basic bonding, while the Cu-W or Cu-Mo base material provides intermediate CTE matching and strain relaxation. The Cu-W or Cu-Mo base material itself contains specific alloying elements that balance thermal conductivity with CTE control, achieving local optimization of both heat dissipation and dimensional stability.
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 relaxes strains in the bonding section, enhancing the reliability and extending the product life by balancing CTE differences and preventing cracking, while adhering to environmental regulations.
Implementation Method 1
a strain due to a difference between CTEs (Coefficients of Thermal Expansion) of a semiconductor device and a substrate occurs in a bonding section
Implementation Method 2
a strain that occurs in a bonding section due to a CTE difference can be relaxed by using a material having a coefficient of thermal expansion within a predetermined range
Data Source
Figure 1~2
Figure 3A
Figure 3B
AI summary
A layered bonding material 10 includes a base material 11, a first solder section 12a stacked on a first surface of the base material 11, and a second solder section 12b stacked on a second surface of the base material 11. A coefficient of linear expansion of the base material 11 is 5.5 to 15.5 ppm/K, the first solder section 12a and the second solder section 12b are made of lead-free solder, and both of a thickness of the first solder section 12a and a thickness of the second solder section 12b are 0.05 to 1.0 mm.