Semiconductor Module Dual-Solder Design for Thermal Stress Management
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Solution Overview
Problem
Semiconductor modules face issues with solder deterioration and stress-induced damage due to repeated heat generation and cooling, leading to potential cracking and peeling at the solder bonding interface, especially in high-temperature environments.
Innovation Solution
A semiconductor module design featuring a first solder with lower tensile strength for bonding the lead terminal to the semiconductor element and a second solder with higher tensile strength for bonding the element to the metal substrate, with a tensile strength ratio of the first solder to the second solder being less than 1, to absorb and relax thermal stress.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the same solder is used for bonding both the lead terminal and the metal substrate to the semiconductor element, then the manufacturing process is simplified, but the solder bonding interface deteriorates due to repeated thermal stress from heat generation and cooling
Solution Approach 1:
The patent applies different solders with different properties to different locations (lead terminal bonding vs. metal substrate bonding) based on the specific stress conditions at each location. The first solder has lower tensile strength to absorb stress from lead terminal expansion, while the second solder has higher tensile strength to provide stable support from the metal substrate, resolving the contradiction between manufacturing simplicity and bonding durability.
2Stability of the object's composition
If the lead terminal is pressed by sealing resin to prevent movement, then the terminal is securely fixed, but the terminal expands toward the thin semiconductor element during thermal expansion, applying great stress that may cause cracking
Solution Approach 1:
The first solder acts as an intermediary layer between the lead terminal and the semiconductor element. It absorbs the thermal expansion stress of the lead terminal through its lower tensile strength and higher elasticity, preventing direct transmission of stress to the semiconductor element surface electrode, thus resolving the contradiction between terminal stability and prevention of element damage.
3Strength
If high-tensile-strength solder is used for all bonding applications, then the bonding strength is maximized, but the stress from thermal expansion cannot be absorbed, leading to crack propagation at the bonding interface
Solution Approach 1:
The patent changes the tensile strength parameter of the solder material based on the specific application location and stress conditions. The first solder has lower tensile strength (30-80 MPa) to absorb thermal stress, while the second solder has higher tensile strength (>80 MPa) to provide stable support, resolving the contradiction between maximizing bonding strength and resisting thermal stress fatigue.
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
This design enhances the reliability of the semiconductor module by extending power cycle life and preventing damage to the surface electrode, with improved stress absorption and reduced risk of cracking.
Implementation Method 1
a first solder which bonds the lead terminal and the one surface of the semiconductor element together; a second solder which bonds the other surface of the semiconductor element and the metal substrate together, wherein a value obtained by dividing the tensile strength of the first solder by the tensile strength of the second solder is less than 1
Implementation Method 2
when the semiconductor element repeatedly generates heat, a strain is repeatedly induced in the solder and the solder deteriorates. As a result, peeling may occur because of a crack at a solder bonding interface
Data Source
AI summary
A semiconductor module includes a semiconductor element having one and the other surface, a lead terminal connected electrically and thermally to the semiconductor element, a first solder which bonds the lead terminal and the one surface of the semiconductor element together, a circuit layer over which the semiconductor element is disposed and a second solder which bonds the other surface of the semiconductor element and the circuit layer together. The inequality(A/B)<1holds, where A and B are the tensile strength of the first and second solder, respectively. As a result, even if the lead terminal which thermally expands because of heat generated by the semiconductor element expands or contracts toward the semiconductor element, a stress applied by the lead terminal is absorbed and relaxed by the first solder. This prevents damage to the surface electrode of the semiconductor element by suppressing the occurrence of cracks.