Ni-Au Coated Cu Bonding Wire for Corrosion-Resistant Bonding
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Solution Overview
Problem
Conventional Cu bonding wires face issues with galvanic corrosion and poor bond reliability in high-temperature environments, particularly in on-vehicle devices, where Ni-coated Cu wires exhibit inadequate bondability and capillary clogging, while bare Cu wires fail to achieve fine-pitch bonding and sufficient bond reliability.
Innovation Solution
A Cu-based bonding wire with a coating layer containing Ni as the main component on the core material side and Au/Ni on the surface, with a specific thickness and concentration ratio, and optionally including Pd, B, P, Mg, Se, Te, As, Sb, Ga, Ge, or In, to enhance bond reliability and prevent capillary clogging.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Pd-coating layer is applied to Cu bonding wire to prevent oxidation, then oxidation resistance is improved, but galvanic corrosion occurs in high-temperature environments causing poor bond reliability
Solution Approach 1:
The patent applies a multi-layer composite coating structure consisting of a Ni base layer and an Au outer layer. The Ni layer provides oxidation resistance and serves as a diffusion barrier, while the Au layer prevents galvanic corrosion by being more noble than Cu. This composite structure resolves the contradiction by combining materials with complementary properties to achieve both oxidation resistance and galvanic corrosion prevention in high-temperature environments.
Solution Approach 2:
The Ni coating layer acts as an intermediary between the Cu core and the external environment. It provides a protective barrier that prevents direct contact between Cu and oxidizing agents, while also serving as a suitable intermediate layer for ultrasonic bonding. The Ni layer mediates the interaction between the Cu wire and the bonding process, enabling reliable bonding without causing galvanic corrosion.
2Manufacturing precision
If Ni-coating is applied to Cu bonding wire to improve FAB shape, then compression-bonding shape is improved, but bondability of the 2nd bonded part deteriorates due to capillary clogging
Solution Approach 1:
The patent optimizes the Ni layer thickness to a specific range (5-20 nm) to resolve the contradiction. This precise parameter control allows the Ni layer to provide sufficient surface quality for good FAB shape formation while remaining thin enough to prevent capillary clogging during the bonding process. By carefully adjusting the thickness parameter, both manufacturing precision and ease of operation are achieved.
3Object-affected harmful factors
If bare Cu wire is used to avoid galvanic corrosion, then galvanic corrosion is prevented, but FAB shape and compression-bonding quality deteriorate
Solution Approach 1:
The patent uses a Cu core with a Ni-Au composite coating rather than bare Cu wire. The Ni layer provides a suitable surface for ball formation and compression bonding, improving FAB shape quality, while the Au outer layer prevents galvanic corrosion. This composite structure allows the wire to have both good bonding characteristics and corrosion resistance.
Solution Approach 2:
The patent applies different materials at different locations of the wire surface. The Ni layer is applied as a base coating to improve surface quality for bonding, while the Au layer is applied as a thin outer coating (0.1-5 nm) specifically to prevent galvanic corrosion. This local quality differentiation allows each layer to perform its specific function optimally.
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 wire achieves a favorable FAB shape, improved bondability of the 2nd bonded part, and enhanced bond reliability of the 1st bonded part in high-temperature environments, while preventing capillary clogging and maintaining productivity in semiconductor device manufacturing.
Implementation Method 1
the conventional Cu bonding wires with the Pd-coating layers cause a galvanic corrosion in a high-temperature environment
Implementation Method 2
Cu has the drawback of being more susceptible to oxidation than Au. As a method of preventing the surface oxidation of the Cu bonding wire
Implementation Method 3
a tip end of wire is heated and melted by arc heat input to form a free air ball (FAB: Free Air Ball; hereinafter also simply referred to as 'ball' or 'FAB') through surface tension
Implementation Method 4
a tip end of wire is heated and melted by arc heat input to form a free air ball (FAB: Free Air Ball; hereinafter also simply referred to as 'ball' or 'FAB') through surface tension
Implementation Method 5
the wire part is compression-bonded (hereinafter referred to as 'wedge-bonded') onto the external electrode by applying ultrasonic waves and load to the wire part
Data Source
AI summary
The bonding wire for semiconductor devices includes a core material of Cu or Cu alloy and a coating layer containing conductive metal other than Cu formed on a surface of the core material. The coating layer has a region containing Ni as a main component on a core material side, and has a region containing Au and Ni on a wire surface side, in a thickness direction of the coating layer, a thickness of the coating layer is 10 nm or more and 130 nm or less, a ratio of a concentration CAu (mass %) of Au to a concentration CNi (mass %) of Ni relative to the entire wire is 0.02<CAu/CNi≤0.7, and a concentration of Au at the surface of the wire is 10 atomic % or more and 90 atomic % or less.