Thick Copper Wire Annealing for Bonding Reliability
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Solution Overview
Problem
The manufacturing of thick copper bonding wires faces challenges such as oxidation susceptibility, deformation during bonding, and limited flexibility, which affect the reliability and bondability of the wires, particularly in wedge bonding applications, and there is a need for improved mechanical properties and corrosion resistance.
Innovation Solution
A process involving a copper core with ≥ 98.0% purity, annealed at temperatures between 650°C to 1000°C for specific times to achieve an elastic limit of 40 to 95 N/mm², allowing for optimized mechanical and bonding properties, including enhanced softness and resistance to oxidation, while minimizing mechanical stress during packaging and handling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wire is used for bonding, then electric and thermal conductivity is improved, but susceptibility to oxidation and deformation during bonding increases
Solution Approach 1:
The patent applies parameter changes by controlling the copper purity at ≥98.0% and implementing specific annealing treatments to achieve an elastic limit of 40-95 N/mm². This transforms the mechanical properties of the copper wire, reducing deformation during bonding while maintaining excellent electrical and thermal conductivity. The parameter optimization resolves the contradiction between conductivity and deformation resistance.
Solution Approach 2:
The patent employs inert atmosphere protection during the bonding process to prevent copper oxidation. By creating an oxygen-free or low-oxygen environment, the harmful oxidation effect is eliminated while the copper wire maintains its superior conductivity properties, thus resolving the contradiction between conductivity and oxidation susceptibility.
2Strength
If wire thickness is increased for bonding applications, then bond strength is improved, but flexibility and bendability deteriorate
Solution Approach 1:
The patent resolves this contradiction by changing the material parameters through controlled annealing processes. By treating the thick copper wire with specific annealing conditions, the internal stress is reduced and the crystal structure is optimized, achieving an elastic limit of 40-95 N/mm². This allows the wire to maintain high bond strength while recovering flexibility and bendability required for complex bonding geometries.
3Reliability
If copper wire undergoes welding and larger deformation during bonding, then electrical contact is improved, but damage to bond pad and underlying structures increases
Solution Approach 1:
The patent applies parameter changes by precisely controlling the copper wire's elastic limit to 40-95 N/mm² through annealing treatment. This optimized parameter range allows the wire to undergo necessary deformation for reliable electrical contact while staying within safe limits that prevent damage to the bond pad and underlying semiconductor structures. The parameter optimization enables adequate bonding deformation without causing harmful effects.
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 process results in bonding wires with improved reliability, bondability, and resistance to corrosion, ensuring stable interfaces with printed circuit boards and other electrical elements, with optimized microstructure and mechanical properties that maintain performance throughout the bonding process.
Implementation Method 1
the copper core with ≥ 98.0% purity, annealed at temperatures between 650°C to 1000°C for specific times to achieve an elastic limit of 40 to 95 N/mm²
Implementation Method 2
annealed at temperatures between 650°C to 1000°C for specific times to achieve an elastic limit of 40 to 95 N/mm²
Implementation Method 3
annealed at temperatures between 650°C to 1000°C for specific times to achieve an elastic limit of 40 to 95 N/mm², allowing for optimized mechanical and bonding properties, including enhanced softness
Data Source
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AI summary
A process for the manufacture of a bonding wire comprising a core with a surface, wherein the core comprises ≥ 98.0% copper and has a cross sectional area in the range of 7500 to 600000 μm2 and an elastic limit RP0.2 (yield strength) in the range of 40 to 95 N/mm2, the process comprising the steps of: a) providing a copper core precursor; b) drawing the precursor until a final diameter of the wire core is reached; c) annealing the drawn wire at a minimum annealing temperature in the range of 650 to 1000 °C through its entire cross section for a minimum annealing time in the range of 4 seconds to 2 hours.