Al-Coated Copper Bond Wire for Oxidation Resistance
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Solution Overview
Problem
Copper bonding wires face challenges such as limited flexibility, susceptibility to oxidation, and high costs, while aluminum wires have issues with bondability and corrosion resistance, necessitating an improvement in wire technology for reliable and durable electrical connections in power electronics.
Innovation Solution
A copper core wire with an aluminum coating, where the coating layer occupies 10-60% of the cross-sectional area, forming an intermetallic phase during heat treatment, enhancing electrical and thermal conductivity, corrosion resistance, and bondability, and allowing for standard wedge-bonding processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used for bonding, then electrical and thermal conductivity is improved, but susceptibility to oxidation and bondability deteriorate
Solution Approach 1:
The patent applies composite material structure by combining copper core with aluminum coating layer. The copper core provides excellent electrical and thermal conductivity, while the aluminum coating layer protects against oxidation. This composite structure resolves the contradiction by integrating materials with complementary properties - the inner copper maintains conductivity while the outer aluminum prevents oxidation.
Solution Approach 2:
The aluminum coating layer creates a protective environment around the copper core, effectively isolating it from oxidizing conditions. The aluminum oxide layer that forms on the aluminum coating provides an additional protective barrier, creating an inert-like environment that prevents oxidation of the copper, thus resolving the oxidation susceptibility issue while maintaining copper's conductivity benefits.
2Ease of manufacture
If aluminum wire is used for bonding, then cost and oxidation resistance are improved, but bondability and corrosion resistance deteriorate
Solution Approach 1:
The patent applies local quality principle by providing different functional properties at different locations of the wire. The aluminum coating layer at the outer surface provides oxidation resistance and cost benefits, while the copper core at the inner location provides excellent bondability and corrosion resistance. This spatial differentiation of material properties allows the wire to exhibit both aluminum's cost advantages and copper's bonding advantages.
3Reliability
If copper wire is used, then electrical conductivity is improved, but flexibility and bending capability deteriorate
Solution Approach 1:
The aluminum coating layer acts as a flexible shell around the copper core. Aluminum has inherently better ductility and flexibility compared to copper, allowing the coated wire to bend more easily while the copper core maintains excellent electrical conductivity. The flexible aluminum shell accommodates bending stresses that would otherwise be problematic for pure copper wires.
4Object-affected harmful factors
If aluminum coating thickness is increased, then oxidation resistance is improved, but electrical conductivity deteriorates
Solution Approach 1:
The patent applies parameter changes principle by optimizing the aluminum coating thickness to a specific range (1-10 μm). This controlled parameter selection ensures sufficient oxidation protection while maintaining adequate electrical conductivity. The thickness parameter is precisely controlled to balance the competing requirements - thick enough to provide oxidation resistance but thin enough to allow the copper core's conductivity to dominate the overall wire performance.
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 solution provides wires with improved reliability, extended lifetime, and reduced corrosion, enabling higher current flow with reduced internal bridging and simplified manufacturing, maintaining compatibility with conventional device dimensions and production lines.
Implementation Method 1
forming an intermetallic phase during heat treatment
Implementation Method 2
during heat treatment
Implementation Method 3
improved resistance to corrosion and/or oxidation
Implementation Method 4
enhancing electrical and thermal conductivity
Implementation Method 5
enhancing electrical and thermal conductivity
Data Source
Figure 1~2
Figure 3~4
Figure 5~7
AI summary
The invention relates to a wire, preferably a bonding wire for bonding in microelectronics, comprising a copper core (2) with a surface and coating layer (3), which coating layer (3) is superimposed over the surface of the core (2), wherein the coating layer comprises aluminium (3), wherein in any cross-sectional view of the wire the area share of the coating layer is in the range of from 20 to 50 %, based on the total area of the cross-section of the wire, and wherein the aspect ratio between the longest path and the shortest path through the wire in any cross-sectional view is in the range of from larger than 0.8 to 1.0, and wherein the wire has a diameter in the range of from 100 µm to 600 µm. The invention further relates to a process for making a wire, to a wire obtainable by said process, to an electric device comprising at least two elements and at least aforementioned wire, to a propelled device comprising said electric device and to a process of connecting two elements through aforementioned wire by wedge bonding.