Semiconductor Buffer Layer for Thermomechanical Stress Relief
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Solution Overview
Problem
Components with semiconductor chips on metal carriers experience internal thermomechanical stresses due to differing thermal expansion coefficients, leading to potential damage, deformation, and delamination during temperature variations.
Innovation Solution
Incorporating a buffer layer with a ductile material, such as gold or copper, between the semiconductor chip and the metal carrier, which has a lower yield strength than the carrier, to absorb and reduce internal stresses, and a connecting layer like AuSn-based solder for secure fixation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a semiconductor chip is fastened on a metal carrier by means of a connecting layer, then mechanical support and electrical connection are achieved, but internal thermomechanical stresses occur during temperature variations leading to deformation and potential fracture
Solution Approach 1:
A buffer layer made of ductile material (such as gold or copper) is introduced between the semiconductor chip and the metal carrier. This intermediary layer absorbs thermomechanical stresses that arise during temperature variations, preventing stress transmission to the brittle semiconductor chip and connecting layer, thereby resolving the contradiction between mechanical support and stress resistance
Solution Approach 2:
The buffer layer is designed with specific material properties (ductile material with lower yield strength than the carrier) and controlled thickness (1 μm to 10 μm) to optimize its stress-absorbing capability. By changing the material parameters and geometric dimensions, the buffer layer effectively mitigates thermomechanical stresses while maintaining mechanical stability
2Reliability
If a buffer layer with ductile material is added between the semiconductor chip and metal carrier, then thermomechanical stress is reduced, but device complexity increases
Solution Approach 1:
The buffer layer serves multiple functions simultaneously: it acts as a stress-absorbing element, provides an additional thermal conduction path, and serves as a diffusion barrier. This multi-functionality justifies the added layer by delivering multiple benefits from a single structural addition, thereby mitigating the complexity increase
3Reliability
If the buffer layer has lower yield strength than the carrier, then it effectively absorbs internal stresses, but the buffer layer may deform more than the carrier
Solution Approach 1:
The buffer layer is designed with lower yield strength than both the semiconductor chip and the metal carrier, creating a progressive deformation mechanism. During thermal stress events, the buffer layer deforms first (absorbing the stress), while the more critical components (chip and carrier) remain intact. This beforehand cushioning protects the overall structure by sacrificing the buffer layer's shape integrity
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 buffer layer effectively minimizes deformation and fracture risks, ensuring mechanical stability and efficient heat dissipation, while the connecting layer provides reliable soldering, reducing the risk of cracks and maintaining component integrity across varying temperatures.
Implementation Method 1
The buffer layer has a yield strength which is lower than a yield strength of the carrier and/or of the substrate. The buffer layer is configured to be coarse-grained
Implementation Method 2
In particular, the connecting layer is a solder layer, in particular an AuSn-based solder layer and/or a solder layer containing indium
Implementation Method 3
The metal carrier has a thermal expansion coefficient which is at least 1.5 times as great as a thermal expansion coefficient of the substrate of the semiconductor chip or of the entire semiconductor chip
Data Source
AI summary
A component may include a semiconductor chip, a buffer layer, a connecting layer, and a metal carrier. The semiconductor chip may include a substrate and a semiconductor body arranged thereon. The metal carrier may have a thermal expansion coefficient at least 1.5 times as great as a thermal expansion coefficient of the substrate or of the semiconductor chip. The chip may be fastened on the metal carrier by the connecting layer, and the buffer layer may have a yield stress ranging from 10 MPa. The buffer layer may have a thickness ranging from 2 um to 10 um and adjoin the chip. The substrate and the metal carrier may have a higher yield strength than the buffer layer.