Flexible Spacer Structure for CTE-Stressed Semiconductor Assemblies
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Solution Overview
Problem
Semiconductor devices experience cracking and fracturing due to thermomechanical stress caused by coefficient of thermal expansion (CTE) mismatches between the semiconductor die and the substrate, leading to unreliable solder joints and conductive trace failures, especially in applications involving temperature or power cycling.
Innovation Solution
Implementing a flexible spacer with a flexible main body and embedded support structures between the semiconductor die and the substrate to absorb and distribute thermomechanical stress, reducing CTE mismatch effects and providing structural support during assembly processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a rigid structure is used to provide structural support, then mechanical strength is improved, but thermomechanical stress cracking increases due to CTE mismatch
Solution Approach 1:
The patent applies a flexible spacer comprising a flexible main body between the semiconductor die and substrate. This flexible structure can deform to accommodate thermomechanical stress caused by CTE mismatch, preventing cracking while maintaining structural support. The flexible main body acts as a compliant layer that absorbs expansion/contraction forces during temperature cycling.
Solution Approach 2:
The flexible spacer is formed as a composite structure with a flexible main body and embedded support structures. The flexible main body provides compliance to handle CTE mismatch, while the embedded support structures (such as stiffening ribs or reinforcement elements) provide necessary mechanical strength and structural support. This composite approach resolves the contradiction between flexibility and strength.
2Device complexity
If the semiconductor die is directly mounted on the substrate, then device complexity is reduced, but cracking and fracturing occur due to CTE mismatch
Solution Approach 1:
The flexible spacer serves as an intermediary element between the semiconductor die and substrate. It mediates the thermomechanical stress caused by CTE mismatch, preventing direct stress transmission to the conductive traces and solder joints. The flexible main body deforms to accommodate dimensional changes, protecting the electrical connections from cracking.
3Reliability
If a flexible spacer with embedded support structures is implemented, then solder joint reliability is improved, but device complexity increases
Solution Approach 1:
The flexible spacer merges multiple functions into a single component: the flexible main body provides stress absorption and compliance, while the embedded support structures provide mechanical reinforcement. This integration achieves both reliability improvement and structural support without requiring separate components for each 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 flexible spacer enhances the reliability and robustness of semiconductor devices by improving solder joint reliability and reducing stress on conductive traces, particularly in harsh conditions like automotive applications.
Implementation Method 1
a flexible spacer positioned between the semiconductor die and the package substrate that reduces both board level solder joint deformation and stress on the conductive traces of the substrate caused by CTE mismatches
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.