Semiconductor Bonding Wire with Crystalline Skin Layer
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Solution Overview
Problem
Conventional semiconductor-device bonding wires face issues with surface flaws and scrapes, leading to instability in loop shape, reduced strength, and increased failure rates, particularly in fine pitch and three-dimensional packaging applications, where the formation of petal-like deformations and misalignments are common, limiting their practical use.
Innovation Solution
A multilayer bonding wire structure is developed with a core member of an electrically-conductive metal and a skin layer composed of a face-centered cubic metal, where greater than or equal to 50% of crystalline orientations in the wire lengthwise direction are optimized to suppress surface flaws and scrapes, enhance mechanical strength, and improve bonding properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a monolayer bonding wire structure is used, then the manufacturing process is simple, but surface flaws and scrapes occur leading to unstable loop shapes and reduced reliability
Solution Approach 1:
The patent applies a multilayer composite structure consisting of a core member (copper or copper alloy) and a skin layer (different metal composition). This composite structure combines the high conductivity of copper with the surface properties of other metals, suppressing oxide film formation and reducing surface flaws while maintaining manufacturing feasibility through controlled deposition processes.
Solution Approach 2:
The patent implements different material compositions at different locations within the wire structure. The core member provides bulk mechanical strength and conductivity, while the skin layer provides oxide resistance and surface quality. This local differentiation of material properties resolves the contradiction between manufacturing simplicity and bonding reliability.
2Strength
If alloy elements are added to improve strength and bonding property, then mechanical strength increases, but electrical resistance increases and bonding property deteriorates
Solution Approach 1:
The patent uses a composite structure where the core member can be copper or copper alloy providing strength, while the skin layer is composed of metals with excellent bonding properties and low oxide formation. This composite approach allows the wire to achieve both high strength from the alloyed core and good bonding property from the pure metal skin layer, resolving the trade-off between strength and bonding quality.
Solution Approach 2:
The patent differentiates material composition between the core and surface regions. The core member contains alloy elements for strength enhancement, while the skin layer maintains a composition optimized for bonding and oxide resistance. This spatial separation of functional requirements allows simultaneous optimization of strength and bonding property without mutual interference.
3Loss of substance
If copper bonding wires are used to reduce material cost, then cost decreases, but bonding strength reduces due to oxidization and corrosion
Solution Approach 1:
The patent creates a composite wire structure with a copper-based core member providing cost effectiveness and electrical conductivity, covered by a skin layer of metals resistant to oxidization and corrosion. This composite structure protects the copper core from environmental degradation while maintaining the cost advantages of copper, thereby resolving the contradiction between material cost and bonding strength reliability.
Solution Approach 2:
The skin layer acts as an intermediary protective barrier between the copper core member and the external environment. This intermediate layer prevents direct contact between oxygen/moisture and the copper surface, eliminating oxidization and corrosion issues while allowing the copper core to maintain its cost and conductivity advantages.
4Quantity of substance
If fine pitch technique is introduced to increase density, then packaging density improves, but loop controllability and bonding property become more difficult to maintain
Solution Approach 1:
The patent employs a multilayer composite structure where the skin layer provides a smooth, oxide-free surface that reduces friction and improves loop formation consistency. This enhanced surface quality enables better loop controllability in fine pitch applications where precise positioning is critical, while the core member maintains mechanical strength for reliable bonding despite increased packaging density.
Solution Approach 2:
The patent optimizes the surface properties of the bonding wire through the skin layer composition and structure, providing localized improvement in surface quality that directly impacts loop formation and bonding precision. This local optimization of surface characteristics enables fine pitch technique to achieve high density packaging while maintaining the manufacturing precision required for loop controllability.
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 optimized multilayer structure effectively reduces surface flaws and scrapes, stabilizes loop shapes, and enhances bonding wire performance, enabling reliable fine pitch and three-dimensional packaging by improving surface strength, workability, and bonding reliability.
Implementation Method 1
greater than or equal to 50% of crystalline orientations in the wire lengthwise direction at a crystal face of a surface of the skin layer is <100>
Implementation Method 2
a bonding wire in which copper is covered with a noble metal or a corrosion-resistant metal, such as gold, silver, platinum, palladium, nickel, cobalt, chrome, titanium, and the like
Implementation Method 3
A thermal compressive bonding technique with the aid of ultrasound is generally applied to bond bonding wires
Implementation Method 4
A leading end of a bonding wire is heated and melted by arc heat inputting
Data Source
Figure 1
AI summary
It is an object of the present invention to provide a highly-functional bonding wire which has good wire-surface nature, loop linearity, stability of loop heights, and stability of a wire bonding shape, and which can cope with semiconductor packaging technologies, such as thinning, achievement of a fine pitch, achievement of a long span, and three-dimensional packaging. A semiconductor-device bonding wire comprises a core member formed of an electrically-conductive metal, and a skin layer mainly composed of a face-centered cubic metal different from the core member and formed thereon. The percentage of<100> orientations in crystalline orientations in the lengthwise direction in the surface of the skin layer is greater than or equal to 50%.