Redistribution Structure UBM Geometry for Stress-Resistant IC Packaging
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Solution Overview
Problem
The semiconductor industry faces challenges in creating smaller and more reliable packaging techniques for semiconductor dies, particularly in buffering mechanical stresses and ensuring high integration density, as existing methods struggle to maintain reliability and prevent cracking and delamination in redistribution structures.
Innovation Solution
The development of under-bump metallurgies (UBMs) with specific height-to-width ratios and thick dielectric layers to buffer mechanical stresses, allowing for increased reliability and reduced risk of solder bridging, while also optimizing the size and shape of UBMs to enhance signal routing and mechanical stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If existing packaging techniques are used, then integration density can be improved, but mechanical reliability deteriorates due to stress-induced cracking and delamination
Solution Approach 1:
The patent applies beforehand cushioning by introducing a compliant layer between the redistribution structure and the substrate. This layer is specifically designed to absorb and buffer mechanical stresses before they can propagate through the redistribution structure and cause cracking or delamination. The compliant layer acts as a stress cushion that protects the brittle redistribution structure from stress-induced failure while allowing the package to achieve high integration density through advanced packaging techniques.
2Length of moving object
If redistribution structures are made thinner to reduce size, then device footprint is reduced, but mechanical strength deteriorates leading to increased stress cracking
Solution Approach 1:
The patent applies the intermediary principle by inserting a compliant layer between the thin redistribution structure and the substrate. This intermediary layer serves multiple functions: it provides mechanical support to the thin redistribution structure, buffers stress transmission, and prevents direct stress concentration at the interface. This allows the redistribution structure to be made thinner for reduced device footprint while maintaining adequate mechanical strength through the supportive action of the compliant layer.
3Strength
If UBMs are enlarged to improve solder joint reliability, then connection strength increases, but risk of solder bridging increases
Solution Approach 1:
The patent applies parameter changes by modifying the geometry and material properties of the UBM structure. Specifically, the compliant layer beneath the UBM allows for optimization of UBM dimensions - enabling larger UBM area for improved solder joint reliability while the compliant layer's stress-buffering capability prevents stress concentration that would lead to solder bridging. The parameter changes in the underlying compliant layer create a more favorable stress distribution environment that decouples the trade-off between UBM size and solder bridging risk.
Data Source
AI summary
In an embodiment, a device includes: an integrated circuit die; an encapsulant at least partially encapsulating the integrated circuit die; a conductive via extending through the encapsulant; a redistribution structure on the encapsulant, the redistribution structure including: a metallization pattern electrically coupled to the conductive via and the integrated circuit die; a dielectric layer on the metallization pattern, the dielectric layer having a first thickness of 10 μm to 30 μm; and a first under-bump metallurgy (UBM) having a first via portion extending through the dielectric layer and a first bump portion on the dielectric layer, the first UBM being physically and electrically coupled to the metallization pattern, the first via portion having a first width, a ratio of the first thickness to the first width being from 1.33 to 1.66.