Angstrom-Thick Copper Oxide Layer for Bonding Reliability
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Solution Overview
Problem
Copper bonding wires face challenges due to surface oxidation, which affects their fatigue behavior and bonding performance, and existing solutions like coatings are not entirely effective in preventing oxidation and ensuring robust bonding.
Innovation Solution
A copper wire with a 0.5 to < 6 nm thin circumferential surface layer of copper oxide, either pure or alloyed with silver and palladium, is developed using a process involving wire drawing, annealing, and quenching, which results in a wire with a wide wire bonding process window suitable for industrial applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used for bonding applications, then electric and thermal conductivity is improved, but susceptibility to oxidation increases
Solution Approach 1:
The patent converts the harmful effect of oxidation into a beneficial feature by controlling the formation of a thin copper oxide layer (0.5 to <6 nm) on the wire surface. This controlled oxide layer, achieved through specific annealing conditions (580-750°C for 0.2-0.4 seconds in 90-96 vol.-% inert gas : 4-10 vol.-% hydrogen), actually improves bonding performance while maintaining oxidation resistance. The oxide layer serves as a bonding-friendly surface without compromising the wire's electrical and thermal conductivity.
Solution Approach 2:
The patent applies parameter changes by precisely controlling the annealing process parameters (temperature: 580-750°C, time: 0.2-0.4 seconds, atmosphere composition: 90-96 vol.-% inert gas : 4-10 vol.-% hydrogen) to achieve the optimal oxide layer thickness. This parameter optimization allows the copper wire to have just enough surface oxidation for good bonding while preventing excessive oxidation that would harm conductivity and reliability.
2Object-affected harmful factors
If conventional coatings (noble metal, glass, or polymer) are applied to prevent oxidation, then oxidation resistance is improved, but bonding performance and process robustness deteriorate
Solution Approach 1:
The patent extracts and eliminates the need for conventional oxidation-resistant coatings (noble metal, glass, or polymer coatings) by directly controlling the surface oxide layer formation on the copper wire itself. This removal of external coating layers simplifies the wire structure and ensures optimal bonding performance without the drawbacks of additional coating materials that can interfere with bonding processes.
Solution Approach 2:
The copper wire performs its own oxidation protection function by forming a self-controlled thin oxide layer (0.5 to <6 nm) through the annealing process. This self-formed layer provides sufficient oxidation resistance while maintaining bonding compatibility, eliminating the need for external protective coatings and allowing the wire to serve both structural and protective functions simultaneously.
3Ease of manufacture
If uncoated copper wire with typical oxide layer (6-20 nm) is used, then manufacturing simplicity is maintained, but bonding performance is insufficient
Solution Approach 1:
The patent applies parameter changes by optimizing the annealing process (temperature: 580-750°C, time: 0.2-0.4 seconds, atmosphere: 90-96 vol.-% inert gas : 4-10 vol.-% hydrogen) to reduce the oxide layer thickness from the conventional 6-20 nm range to a optimized 0.5 to <6 nm range. This parameter optimization maintains manufacturing simplicity while dramatically improving bonding performance through the thinner, more controlled oxide layer.
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 copper wire exhibits a wide wire bonding process window, ensuring robust bonding performance and resistance to oxidation, with a thin copper oxide layer allowing for effective bonding across various diameters and types, enhancing the reliability of wire bonding processes.
Implementation Method 1
copper wires are susceptible to oxidation of the wire
Implementation Method 2
annealing, and quenching
Implementation Method 3
quenching
Data Source
AI summary
A copper wire having a diameter of 10 to 80 μm, wherein the copper wire bulk material is ≥ 99.99 wt.-% pure copper or a copper alloy consisting of 10 to 1000 wt.-ppm of silver and/or of 0.1 to 3 wt.-% of palladium with copper as the remainder to make up 100 wt.- %, characterized in that the copper wire has a 0.5 to < 6 nm thin circumferential surface layer of copper oxide.