Semiconductor Package Rigid UBM Stack for ELK Dielectric Stress
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Solution Overview
Problem
Flip-chip semiconductor packages with extra-low-k (ELK) dielectric layers are susceptible to cracking due to stress, affecting the reliability and quality of the finished product, as increased I/O pin counts and high-performance demands put strain on these layers.
Innovation Solution
The semiconductor package incorporates a conductive pillar bump structure with an under bump metallurgy (UBM) stack and a conductive plug, where the UBM stack has a thicker second metal pad with a larger diameter than the conductive plug, providing improved mechanical strength to reduce stress on the ELK dielectric layers. The UBM stack is formed using photolithography and electroplating processes, with a nickel buffer layer and a solder cap, enhancing the structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the I/O pin count is increased to achieve multi-functionality and high-performance ICs, then the functionality and connection density are improved, but the stress on ELK dielectric layers increases causing cracking and reduced reliability
Solution Approach 1:
The patent applies local quality by creating a UBM stack with non-uniform metal layer thicknesses, where the first metal layer has a first thickness and the second metal layer has a second thickness greater than the first thickness. This localized thickening of the second metal layer directly addresses the stress concentration issue at the bump-die interface, providing enhanced mechanical support precisely where needed to prevent ELK dielectric cracking while maintaining the high I/O pin count configuration.
2Productivity
If the I/O pin count is increased to achieve multi-functionality and high-performance ICs, then the connection density is improved, but the mechanical stress on the die structure increases
Solution Approach 1:
The patent employs composite materials by constructing the UBM stack with multiple metal layers of different thicknesses and properties. The first metal layer provides baseline conductivity and adhesion, while the second metal layer with greater thickness provides enhanced mechanical strength and stress distribution. This composite structure allows the die to maintain high connection density while withstanding the increased mechanical stress from multiple bumps.
3Ease of manufacture
If a conventional UBM structure with uniform thickness is used, then the manufacturing process is simple, but the stress distribution is inadequate leading to ELK dielectric cracking
Solution Approach 1:
The patent applies parameter changes by modifying the thickness parameter of the metal layers in the UBM stack. Specifically, the second metal layer is formed with a second thickness that is greater than the first thickness of the first metal layer. This parameter variation optimizes the stress distribution across the bump structure, preventing ELK dielectric cracking while maintaining compatibility with standard photolithography and electroplating manufacturing 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 configuration reduces the stress on the ELK dielectric layers, minimizing the likelihood of cracking and thereby enhancing the reliability and quality of the semiconductor package by distributing mechanical forces more effectively.
Implementation Method 1
The UBM stack is formed using photolithography and electroplating processes, with a nickel buffer layer and a solder cap
Data Source
Figure 1
Figure 2A~2B
Figure 3A~3B
AI summary
The invention provides a semiconductor package. The semiconductor package includes a semiconductor die and a conductive pillar bump structure and a conductive plug. The semiconductor die has a die pad thereon. The conductive pillar bump structure is positioned overlying the die pad. The conductive pillar bump structure includes an under bump metallurgy (UBM) stack having a first diameter and a conductive plug on the UBM stack. The conductive plug has a second diameter that is different than the first diameter.