Shape Memory Alloy Substrate for Thermal Stress Reduction
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Solution Overview
Problem
Conventional die attachment methods in integrated circuits face challenges due to thermal expansion issues caused by differences in the coefficient of thermal expansion between the die and the substrate, leading to thermal stress and inefficient heat transfer.
Innovation Solution
Embedding shape memory alloys like nitinol into the substrate, particularly along the perimeter and corners of the die, to create a composite bus bar with a mesh-like pattern, which balances thermal expansion and enhances conductive properties, using additive manufacturing techniques such as cold spray and ultrasonic consolidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional die attachment methods are used, then the die can be mounted to the substrate, but thermal stress occurs due to mismatched thermal expansion coefficients
Solution Approach 1:
The patent modifies the thermal expansion parameters of the substrate by embedding shape memory alloy particles, transforming the substrate's thermal expansion coefficient to match that of the die, thereby eliminating thermal stress during temperature cycling
Solution Approach 2:
The patent creates a composite substrate structure by combining conventional substrate material with shape memory alloy particles, achieving a composite material with tailored thermal expansion properties that match the die material
2Strength
If eutectic bonding is used for high-powered applications, then strong attachment is achieved, but thermal expansion issues persist and cost increases
Solution Approach 1:
The patent changes the thermal expansion parameter of the substrate through shape memory alloy embedding, enabling strong die attachment without the need for expensive eutectic bonding processes while eliminating thermal expansion mismatches
3Ease of manufacture
If direct gluing is used for low-cost applications, then cost is reduced, but thermal stress and inefficient heat transfer occur
Solution Approach 1:
The patent employs a composite substrate with shape memory alloy particles that improves heat transfer efficiency while maintaining the cost-effectiveness of direct gluing methods, eliminating thermal stress without requiring expensive bonding processes
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 approach reduces thermal stress and promotes efficient heat transfer by matching the thermal expansion coefficients of the die and substrate, resulting in a bus bar with a net zero coefficient of thermal expansion, improving the reliability and manufacturability of the assembly.
Implementation Method 1
Embedding shape memory alloys like nitinol into the substrate, particularly along the perimeter and corners of the die
Implementation Method 2
balances thermal expansion and enhances conductive properties, using additive manufacturing techniques
Implementation Method 3
enhances conductive properties, resulting in a bus bar with a net zero coefficient of thermal expansion, improving the reliability
Data Source
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AI summary
An integrated circuit assembly element formed via an additive manufacturing technique, such as mixing a conductive material with a memory metal (110) to form a portion of a substrate (105) in desired locations, such as along the footprint of die (135), are discussed herein. In operation (e.g. in response to thermal cycling of the assembly) the memory metal (110) contracts while the conductive material expands. The result is an element having reduced thermal expansion, which can be net zero coefficient of thermal expansion and/or be catered to the coefficient of thermal expansion of a desired material, such as the silicon die (135).