Composite Flexible Spacer for Thermomechanical Stress in Die Assembly
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Solution Overview
Problem
Semiconductor packages experience cracking and stress due to coefficient of thermal expansion (CTE) mismatches between the semiconductor die and the substrate, leading to inoperability under thermomechanical stress, especially in cyclic heating and cooling conditions.
Innovation Solution
Implementing a flexible spacer with a flexible main body and embedded support structure between the semiconductor die and the substrate, which absorbs and mitigates thermomechanical stress, reducing stress on solder joints and conductive traces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid structure is used to support the semiconductor die, then structural strength is improved, but stress from CTE mismatch causes cracking and inoperability under thermomechanical stress
Solution Approach 1:
The patent employs a flexible spacer comprising a flexible main body with embedded support structures instead of a completely rigid structure. The flexible main body can deform to accommodate CTE differences between the semiconductor die and substrate during thermal cycling, while the embedded support structures provide necessary mechanical support. This combination resolves the contradiction by allowing the structure to be both strong and flexible.
Solution Approach 2:
The flexible spacer is constructed as a composite structure with a flexible main body and embedded support structures having different mechanical properties. The support structures have higher stiffness than the flexible main body, creating a composite material system that balances flexibility and structural strength. This composite approach allows the spacer to absorb thermomechanical stress while maintaining structural integrity.
2Reliability
If the flexible spacer has high flexibility to absorb stress, then reliability under thermal cycling is improved, but structural support during assembly may be insufficient
Solution Approach 1:
The flexible main body of the spacer provides the necessary flexibility to absorb thermomechanical stress during thermal cycling, improving reliability under temperature variations. The flexible material allows the spacer to deform without cracking, accommodating CTE mismatches between components.
Solution Approach 2:
The embedded support structures within the flexible main body provide enhanced structural strength during assembly operations. These support structures have higher stiffness than the flexible main body, creating a composite system where the flexible portion absorbs stress while the rigid portions provide mechanical support during handling and assembly.
3Strength
If a thick spacer is used to provide structural support, then mechanical strength is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
Instead of increasing the overall thickness of the spacer to achieve mechanical strength, the patent embeds support structures within a relatively thin flexible main body. This composite approach provides the necessary structural support without requiring a thick spacer, thereby reducing device complexity and manufacturing difficulty while maintaining mechanical strength.
4Strength
If the embedded support structures have high stiffness to provide structural support, then mechanical strength is improved, but the spacer becomes less flexible in absorbing thermomechanical stress
Solution Approach 1:
The embedded support structures have higher stiffness than the flexible main body, creating a composite material system with graded mechanical properties. The flexible main body provides stress absorption capability while the stiffer support structures provide mechanical strength. The combination allows the spacer to maintain both flexibility for stress absorption and structural strength for mechanical support.
Solution Approach 2:
The support structures are strategically embedded within the flexible main body at specific locations where structural support is most needed. This local reinforcement approach allows the spacer to have high stiffness where required while maintaining overall flexibility in other regions, optimizing both mechanical strength and stress absorption capability.
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 flexible spacer enhances the reliability and robustness of semiconductor devices by reducing stress and improving solder joint reliability, particularly in harsh conditions like automotive applications.
Implementation Method 1
The flexible main body is configured to provide a buffer that absorbs the stress caused by these deformations
Implementation Method 2
The support structure has a higher stiffness than the flexible main body and is configured to provide structural reinforcement to the flexible spacer
Implementation Method 3
cyclic heating and cooling of the semiconductor package can induce significant thermomechanical stress
Implementation Method 4
The flexible spacer reduces cracking and fracturing by compressing, stretching, or bending in response to thermomechanical stress
Data Source
AI summary
A semiconductor device assembly includes a semiconductor die, a substrate, and a spacer directly coupled to the substrate. The spacer includes a flexible main body and a support structure embedded in the flexible main body, wherein the support structure has a higher stiffness than the flexible main body. The spacer carries the semiconductor die. The flexible main body of the spacer mitigates the effects of thermomechanical stress, for example caused by a mismatch between the coefficient of thermal expansion of the semiconductor die and the substrate. The embedded support structure provides strength needed to support the semiconductor die during assembly.