Solder Layer Encapsulation for Thermomechanical Stress Mitigation
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Solution Overview
Problem
Power electronics devices face increased thermomechanical stresses due to rising operating temperatures, which existing bonding materials and cooling structures struggle to mitigate effectively, particularly in high-power applications like hybrid and electric vehicles.
Innovation Solution
A bonding assembly is created with a low-melting solder layer sandwiched between high-melting intermetallic compound layers, which melts and forms a liquid at elevated temperatures to reduce stress, and a coating encapsulates the solder layer to maintain it in a liquid state, providing stress mitigation between substrates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solder layer with low melting temperature is used to mitigate thermomechanical stresses, then stress mitigation and flexibility are improved, but the solder layer may leak or escape at elevated temperatures
Solution Approach 1:
A coating layer is introduced as an intermediary between the solder layer and the external environment. This coating layer has a melting temperature higher than the operating temperature, preventing the solder layer from leaking while allowing it to remain in liquid form for stress mitigation. The coating acts as a containment barrier that mediates between the need for solder fluidity and the need to prevent leakage.
Solution Approach 2:
The melting temperature parameter of the containment structure is changed by applying a coating layer with specifically higher melting temperature than the solder layer. This parameter change allows the system to maintain solder layer fluidity at operating temperatures while preventing leakage, as the coating remains solid and structurally intact at temperatures where the solder is liquid.
2Reliability
If the solder layer is allowed to melt at elevated temperatures for stress relief, then thermomechanical stress mitigation is improved, but the bonding strength may be compromised
Solution Approach 1:
The bonding structure is segmented into distinct functional layers: a solder layer for stress mitigation and a coating layer for structural support. The solder layer melts to provide flexibility and stress relief, while the coating layer remains solid to maintain bonding strength. This segmentation allows each layer to perform its specific function without compromising the other.
Solution Approach 2:
The bonding assembly uses a composite structure combining a low-melting-point solder layer with a high-melting-point coating layer. This composite material approach allows the system to exhibit both the stress-mitigating properties of the liquid solder and the structural integrity of the solid coating, achieving a combination of properties that neither material could provide alone.
3Temperature
If cooling structures are increased in size to handle higher operating temperatures, then thermal management is improved, but device complexity and size increase
Solution Approach 1:
The solder layer provides self-service stress mitigation by automatically melting at elevated temperatures to relieve thermomechanical stresses. This passive, temperature-dependent response eliminates the need for active cooling systems or complex thermal management mechanisms, allowing the device to self-regulate stress without additional components.
Solution Approach 2:
The system exploits the phase transition of the solder layer from solid to liquid at elevated temperatures to mitigate thermomechanical stresses. This phase change provides automatic stress relief without requiring external cooling structures, simplifying the thermal management approach while maintaining device integrity under thermal stress.
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 assembly effectively mitigates thermomechanical stresses at high temperatures, enhancing the life expectancy of power electronics devices by allowing flexibility and reducing the risk of cracking, while maintaining the solder layer within the assembly.
Implementation Method 1
The solder layer melts into a liquid form when the assembly operates at a temperature above the low melting temperature of the solder layer
Implementation Method 2
a coating is disposed over at least the pair of bonding layers and the solder layer such that the coating encapsulates the solder layer between the pair of bonding layers
Implementation Method 3
a first intermetallic compound layer bonded to the bonding surface of the metal substrate and a second intermetallic compound layer bonded to the bonding surface of the semiconductor device
Data Source
AI summary
An assembly that includes a first substrate, a second substrate, and a pair of bonding layers disposed between and bonded to the first and second substrates. The assembly further includes a solder layer disposed between the pair of bonding layers such that the solder layer is isolated from contacting the first substrate and the second substrate. The solder layer has a low melting temperature relative to a high melting temperature of the bonding layers. A coating is disposed over at least the pair of bonding layers and the solder layer such that the coating encapsulates the solder layer between the pair of bonding layers. The solder layer melts into a liquid form when the assembly operates at a temperature above the low melting temperature of the solder layer and the coating maintains the liquid form of the solder layer between the pair of bonding layers.