Multilayer Bonding Wire Grain Structure for Lean Failure
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Solution Overview
Problem
Conventional bonding wires face challenges in reducing leaning failure and spring failure, particularly in fine pitch bonding and stacked chip bonding, where the wire length and loop height variations lead to issues like leaning of the upright portion of the ball and spring failure, which are difficult to address with existing materials and designs.
Innovation Solution
A multilayer-structured bonding wire is developed with controlled crystal grain textures in the skin layer and core material, where the average size ratio of crystal grains in the skin layer to the core material is optimized to improve leaning failure and spring failure, and the skin layer is composed of materials like Pd, Pt, or Ag, while the core material is made of Cu or Au with specific alloy additions, along with an intermediate metal layer and diffusion layer to enhance adhesion and mechanical properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a copper-based bonding wire is used to reduce material cost and improve electrical conductivity, then cost and conductivity are improved, but bonding strength is lowered due to oxidation and wire surface corrosion occurs
Solution Approach 1:
The patent employs a composite wire structure with a copper core material and a skin layer containing a corrosion-resistant metal (such as Pd, Pt, Ru, or Ag). This composite structure allows the copper core to provide excellent electrical conductivity and cost-effectiveness, while the skin layer protects against oxidation and corrosion, thereby maintaining bonding strength and reliability in harsh environments.
2Strength
If alloying elements are added to gold to enhance strength and bonding properties, then mechanical properties are improved, but bondability degradation and increased electrical resistance occur
Solution Approach 1:
The patent applies local quality by concentrating alloying elements (such as Pd, Pt, Ru, or Ag) in the skin layer rather than uniformly distributing them throughout the wire. This allows the core material to maintain its excellent electrical conductivity and bondability, while the skin layer provides the necessary mechanical strength and corrosion resistance, thus avoiding the trade-offs associated with bulk alloying.
3Length of moving object
If wire length and loop height are increased to achieve certain bonding configurations, then bonding reach is improved, but leaning failure and spring failure increase
Solution Approach 1:
The patent optimizes the crystal grain structure parameters of both the core material and skin layer, controlling the average crystal grain size ratio to be 0.5 or less. This parameter optimization enhances the wire's mechanical properties, including elasticity and resistance to deformation, thereby reducing leaning failure and spring failure even when the wire length and loop height are increased for complex bonding configurations.
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 multilayer wire effectively reduces leaning failure and spring failure, stabilizes loop linearity, and enhances bonding performance, making it suitable for advanced semiconductor mounting technologies such as fine pitch, three-dimensional mounting, and stacked chip bonding.
Implementation Method 1
a multilayer-structured bonding wire in which a skin layer and a core material have different crystal grain textures
Implementation Method 2
The tip of a bonding wire is heated and melted by arc heat input, thereby forming a ball by surface tension
Implementation Method 3
The tip of a bonding wire is heated and melted by arc heat input, thereby forming a ball by surface tension
Implementation Method 4
thermocompression bonding with the aid of ultrasound
Implementation Method 5
the ball portion thus formed is compressively bonded onto an electrode
Data Source
Figure 1
Figure 2(a)~2(c)
AI summary
An object of the present invention is to provide a high-performance bonding wire that is suitable for semiconductor mounting technology, such as stacked chip bonding, thinning, and fine pitch mounting, where wire lean (leaning) at an upright position of a ball and spring failure can be suppressed and loop linearity and loop height stability are excellent. This bonding wire for a semiconductor device includes a core material made of a conductive metal, and a skin layer formed on the core material and containing a metal different from the core material as a main component; wherein a relationship between an average size (a) of crystal grains in the skin layer on a wire surface along a wire circumferential direction and an average size (b) of crystal grains in the core material on a normal cross section, the normal cross section being a cross section normal to a wire axis, satisfies an inequality of a/b ≤ 0.7.