Multilayer Composite Bonding for Power Electronics Thermal Stress
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Solution Overview
Problem
Traditional bonding techniques for semiconductor devices to metal substrates in power electronics fail to adequately compensate for thermal cooling stresses caused by coefficient of thermal expansion mismatch, leading to delamination issues at high operating temperatures.
Innovation Solution
A multilayer composite bonding material with thermal stress compensation layers, featuring a core layer with a specific stiffness sandwiched between outer layers of different stiffness, where the core layer has a melting point above the sintering temperature and the bonding layers have a melting point below, providing a graded stiffness to mitigate thermal contraction mismatch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional bonding layers are used for TLP bonding, then the bonding process can be completed at sintering temperatures between 280°C and 350°C, but large thermal cooling stresses due to CTE mismatch cause delamination between the semiconductor device and metal substrate
Solution Approach 1:
The bonding layer is segmented into a multilayer composite structure consisting of a core layer and outer layers. The core layer has a first stiffness and the outer layers have a second stiffness different from the first, creating a graded stiffness structure that compensates for thermal cooling stresses and prevents delamination while maintaining bonding reliability at sintering temperatures between 280°C and 350°C
Solution Approach 2:
A multilayer composite bonding material is used instead of a traditional single-layer bonding material. The composite structure includes a core layer with a first stiffness sandwiched between outer layers with a second stiffness, creating a graded stiffness profile that mitigates thermal stress while providing reliable bonding at the required sintering temperature range
2Reliability
If bonding layers with melting point below sintering temperature are used, then TLP bonding can occur through melting and solidification, but the bonding layers must be replaced by thermal stress compensation layers with melting point above sintering temperature for stress compensation
Solution Approach 1:
The bonding material is segmented into functionally distinct layers: bonding layers with melting point below sintering temperature that enable TLP bonding through melting and solidification, and thermal stress compensation layers with melting point above sintering temperature that prevent delamination. This segmentation allows each layer to perform its specific function optimally
Solution Approach 2:
Different regions of the bonding material structure are assigned different properties: the bonding layers have low melting point for TLP bonding functionality, while the thermal stress compensation layers have high melting point and graded stiffness for stress management. Each layer's local properties are optimized for its specific function
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 multilayer composite bonding material effectively compensates for thermally-induced stresses, preventing delamination and ensuring secure bonding of semiconductor devices to metal substrates even at high temperatures, thus enhancing the reliability and durability of power electronics assemblies.
Implementation Method 1
The bonding layer at least partially melts and isothermally solidifies to form a TLP bond between the semiconductor device and metal substrate at TLP bonding temperatures
Implementation Method 2
The bonding layer at least partially melts and isothermally solidifies to form a TLP bond
Implementation Method 3
The semiconductor devices and metal substrates have different coefficients of thermal expansion (CTE) and large thermally-induced stresses (e.g., cooling stresses) may be generated between a semiconductor device and metal substrate upon cooling from a TLP sintering temperature
Implementation Method 4
a core layer with a first stiffness sandwiched between a pair of outer layers with a second stiffness that is different than the first stiffness such that a graded stiffness extends across a thickness of the thermal stress compensation layers
Data Source
AI summary
A multilayer composite bonding material for transient liquid phase bonding a semiconductor device to a metal substrate includes thermal stress compensation layers sandwiched between a pair of bonding layers. The thermal stress compensation layers may include a core layer with a first stiffness sandwiched between a pair of outer layers with a second stiffness that is different than the first stiffness such that a graded stiffness extends across a thickness of the thermal stress compensation layers. The thermal stress compensation layers have a melting point above a sintering temperature and the bonding layers have a melting point below the sintering temperature. The graded stiffness across the thickness of the thermal stress compensation layers compensates for thermal contraction mismatch between the semiconductor device and the metal substrate during cooling from the sintering temperature to ambient temperature.