Sn-Au Bonded Structure for Kirkendall Void Suppression
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Solution Overview
Problem
The formation of Kirkendall voids is a challenge in bonded structures due to the diffusion of metal elements forming intermetallic compounds with Sn, particularly when Au is used, leading to brittleness and structural instability.
Innovation Solution
A bonded structure is designed with a specific layer configuration where the second metal layer containing Sn is limited to 50% or less of the total thickness and volume of the combined layers, including a first metal layer forming an intermetallic compound with Sn and an intermetallic compound layer, with the intermetallic compound layer extending to the terminal of the wiring substrate, reducing the concentration gradient and diffusion driving force.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If an intermetallic compound is dispersed at a ratio of 5 to 50% as an area fraction of a bonded cross-section to overcome brittleness, then brittleness of the Sn-Au-based intermetallic compound is reduced, but a Kirkendall void is generated at a location where the element forming an intermetallic compound with Sn existed due to diffusion
Solution Approach 1:
The patent applies local quality by creating a non-uniform distribution of Sn and Au layers with specific thickness ratios. The second metal layer (Sn) is controlled to be 50% or less of the total thickness, creating localized regions with different compositions that suppress diffusion while maintaining mechanical properties. This localized control of layer thickness prevents Kirkendall void formation at critical interfaces.
Solution Approach 2:
The patent changes the critical parameter of layer thickness ratio, specifically controlling the second metal layer thickness to be 50% or less of the total thickness of all metal layers. This parameter change fundamentally alters the diffusion dynamics, reducing the concentration gradient that drives Kirkendall void formation while still allowing sufficient intermetallic compound formation to reduce brittleness.
2Strength
If Sn is used in the bonding structure, then bonding is achieved via solder bonding or diffusion bonding, but a metal element tends to be easily diffused in an alloy containing Sn due to low melting point
Solution Approach 1:
The patent changes the thickness parameter of the Sn-containing second metal layer to be 50% or less of the total metal layer thickness. This parameter change reduces the driving force for diffusion while maintaining adequate bonding strength, effectively decoupling the bonding function from excessive diffusion.
Solution Approach 2:
The patent creates a composite metal layer structure with at least two different metal layers (including Sn and another metal forming an intermetallic compound). This composite structure leverages the complementary properties of different metals to achieve bonding while suppressing unwanted diffusion through the controlled thickness ratio.
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 effectively suppresses Kirkendall void formation, maintaining structural integrity and reliability by minimizing diffusion and reaction extent of metal elements, even when Au is used.
Implementation Method 1
bonding is performed by solder bonding or diffusion bonding
Implementation Method 2
an intermetallic compound of Au and Sn tends to be formed at a bonding interface by eutectic reaction
Implementation Method 3
since Sn has a low melting point, a metal element tends to be easily diffused in an alloy containing Sn
Data Source
AI summary
A bonded structure is a bonded structure in which an electronic component and a wiring substrate are bonded to each other, the bonded structure including, in order from the electronic component side: a first metal layer containing a metal forming an intermetallic compound with Sn; an intermetallic compound layer composed of an intermetallic compound containing Sn; and a second metal layer containing Sn, in which a thickness of the second metal layer is 50% or less of a total thickness of the first metal layer, the intermetallic compound layer, and the second metal layer.