Noble-Metal Coated Copper Bonding Wire for Room-Temperature Wedge Bonding
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Solution Overview
Problem
Conventional bonding wires for semiconductor devices face issues with corrosion and bond reliability in environments with ionic impurities and moisture, especially when subjected to resin sealing and high-temperature conditions, and existing copper wires struggle with bondability and reliability in wedge bonding at room temperature.
Innovation Solution
A bonding wire composed of a copper core material with a noble metal coating, where the concentration of copper at the surface ranges from 30 to 80 at %, and the noble metal coating contains palladium and optionally gold, with a specific concentration profile determined by Auger electron spectroscopy, enhancing bondability and reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a copper wire with noble metal coating is used for wedge bonding at room temperature, then bondability is improved, but bond reliability deteriorates due to corrosion in environments with ionic impurities and moisture
Solution Approach 1:
The patent applies local quality by creating a non-uniform copper concentration distribution within the wire structure. The surface region has a different copper concentration (30-80 at %) compared to the core, with the surface having lower copper content to reduce corrosion susceptibility while the core maintains higher copper content for electrical conductivity and bonding performance. This spatial variation in material composition resolves the contradiction between bondability and corrosion resistance.
Solution Approach 2:
The patent employs composite materials by combining copper core material with a noble metal coating layer. This composite structure integrates the advantages of both materials: the copper core provides excellent electrical conductivity and bondability for wedge bonding, while the noble metal coating layer provides corrosion resistance in environments with ionic impurities and moisture, thereby resolving the reliability issue.
2Temperature
If aluminum wire is used for bonding, then room temperature bonding is achieved, but bond reliability deteriorates due to corrosion and recrystallization in high-temperature and moisture environments
Solution Approach 1:
The patent replaces the conventional aluminum wire with a composite copper-noble metal wire structure. The copper core material maintains room temperature bonding capability similar to aluminum, while the noble metal coating provides superior corrosion resistance in high-temperature and moisture environments, eliminating the recrystallization and corrosion issues associated with aluminum wires.
Solution Approach 2:
The patent changes the material composition parameters by transitioning from pure aluminum to a copper-noble metal composite system. This parameter change fundamentally alters the wire's chemical stability and thermal properties, enabling it to maintain bond reliability in high-temperature and moisture-prone environments while preserving room temperature bonding capability.
3Reliability
If Pd-coated Cu wire is used for ball bonding, then oxidation resistance is improved, but wedge bonding at room temperature becomes difficult
Solution Approach 1:
The patent applies local quality by creating a spatially varying copper concentration profile within the wire. The surface region has reduced copper content (30-80 at %) to enhance oxidation resistance, while the core maintains high copper content for bonding performance. This localized compositional variation enables the wire to achieve both oxidation resistance and wedge bonding capability at room temperature.
Solution Approach 2:
The patent modifies the concentration parameter of copper within the wire structure, establishing a gradient from the core to the surface. This parameter change creates regions with different properties: the core provides bonding performance while the surface provides oxidation resistance, resolving the contradiction between wedge bonding ease and oxidation resistance.
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 bonding wire achieves favorable bondability and excellent bond reliability at room temperature, even under resin sealing and high-temperature conditions, reducing corrosion and thermal stress, and maintaining connection integrity.
Implementation Method 1
a corrosion of the Al wire remarkably proceeds, and a bond reliability is difficult to maintain... a noble metal coating formed on a surface of the Cu core material
Implementation Method 2
the Al wire is easily recrystallized and has a large coefficient of thermal expansion due to its physical property, so that the Al wire is difficult to be applied to a high-temperature use... a thermal stress is caused in respective members due to heating and cooling
Implementation Method 3
a core material of Cu or Cu alloy... electrodes formed on a semiconductor element are connected with electrodes on a lead frame or a substrate using a bonding wire
Data Source
AI summary
There is provided a bonding wire for semiconductor devices that exhibits a favorable bondability even when being applied to wedge bonding at the room temperature, and also achieves an excellent bond reliability. The bonding wire includes a core material of Cu or Cu alloy (hereinafter referred to as a “Cu core material”), and a coating containing a noble metal formed on a surface of the Cu core material. A concentration of Cu at a surface of the wire is 30 to 80 at %.