Semiconductor Package Buffer Structure for UBM Edge Crack Mitigation
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Solution Overview
Problem
The challenge in semiconductor packaging is the stress-induced cracking at the edges of under-bump metallizations due to mismatched coefficients of thermal expansion between interposer and semiconductor devices, which affects device reliability.
Innovation Solution
A redistribution structure with buffer features, such as a buffer layer or buffer rings, is introduced to mitigate stress by using materials with controlled Young's modulus and coefficient of thermal expansion, enhancing the bonding strength and reducing the risk of cracks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a redistribution structure is formed to connect interposer to semiconductor device, then electrical connection is established, but stress-induced cracking occurs at under-bump metallization edges due to thermal expansion mismatch
Solution Approach 1:
A buffer layer is introduced as an intermediary component between the interposer and the under-bump metallization. This buffer layer has a coefficient of thermal expansion that is intermediate between the interposer and the under-bump metallization, thereby reducing the thermal expansion mismatch stress. The buffer layer absorbs and distributes the stress, preventing crack formation at the under-bump metallization edges while maintaining electrical connection integrity.
Solution Approach 2:
The invention changes the physical parameters of the buffer layer, specifically its coefficient of thermal expansion and Young's modulus, to optimize stress distribution. By selecting a buffer layer material with appropriate thermal expansion properties (intermediate between interposer and under-bump metallization) and controlled Young's modulus (0.1-10 GPa), the stress concentration at critical interfaces is reduced, preventing cracking while maintaining structural integrity.
2Strength
If buffer features are added to mitigate stress, then bonding strength is enhanced, but device complexity increases
Solution Approach 1:
The buffer feature is segmented into discrete regions positioned at specific locations around the under-bump metallization, particularly at the edges where stress concentration occurs. This segmented approach provides targeted stress mitigation and bonding enhancement only where needed, rather than requiring a complete buffer layer across the entire structure, thereby reducing overall device complexity while maintaining bonding strength.
Solution Approach 2:
The buffer features are applied locally at critical stress concentration points around the under-bump metallization edges rather than uniformly across the entire structure. This local application provides enhanced bonding strength and stress mitigation precisely where required, while minimizing the addition of structural complexity and material usage in non-critical areas.
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 buffer features effectively buffer stress, improving device reliability by reducing the risk of cracking and enhancing the bonding strength at the interface, thereby ensuring stable electrical connections.
Implementation Method 1
forming a buffer layer on the upper dielectric layer and on an under-bump metallization of the redistribution structure... The buffer features effectively buffer stress
Implementation Method 2
forming dangling bonds on an upper dielectric layer of the redistribution structure by treating the upper dielectric layer
Data Source
AI summary
Semiconductor device packages and methods of forming the same are discussed. In an embodiment, a device includes: a redistribution structure comprising an upper dielectric layer and an under-bump metallization; a buffer feature on the under-bump metallization and the upper dielectric layer, the buffer feature covering an edge of the under-bump metallization, the buffer feature bonded to the upper dielectric layer; a reflowable connector extending through the buffer feature, the reflowable connector coupled to the under-bump metallization; an interposer coupled to the reflowable connector; and an encapsulant around the interposer and the reflowable connector, the encapsulant different from the buffer feature.