Ni-Alloyed Pd-Coated Cu Bonding Wire for Stable Ball Bonding
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Solution Overview
Problem
Conventional Cu bonding wires with Pd coating layers fail to meet the bonding reliability and ball formability requirements for on-vehicle devices, especially under high-temperature and high-humidity conditions, due to issues like surface oxidation, voids, and poor sphericity, which are exacerbated by the low thermal conductivity of Pd and the formation of corrodible compounds.
Innovation Solution
A Cu alloy bonding wire with a Pd coating layer and a Ni concentration of 0.1 to 1.2 wt.% and a thickness of 0.015 to 0.150 µm, along with an optional Au skin layer, is used to concentrate Pd or Ni at the bonding interface, reducing the growth rate of corrodible compounds and improving thermal conductivity, thus enhancing bonding reliability and ball formability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a Pd coating layer is applied to Cu bonding wire to prevent surface oxidation, then oxidation resistance is improved, but thermal conductivity decreases and ball formability deteriorates
Solution Approach 1:
The patent optimizes the thickness parameter of the Pd coating layer to a specific range (50-200 nm) to balance oxidation protection with thermal conductivity requirements. By precisely controlling this dimensional parameter, the solution achieves sufficient corrosion resistance while minimizing the negative impact on heat transfer during ball bonding.
Solution Approach 2:
The patent creates a composite structure consisting of a Cu core material with a Pd coating layer. This composite design combines the high thermal conductivity and electrical conductivity of Cu with the excellent oxidation resistance of Pd, achieving a synergistic effect that satisfies multiple contradictory requirements simultaneously.
2Reliability
If a Pd coating layer is applied to Cu bonding wire, then oxidation resistance is improved, but ball formability and sphericity deteriorate due to surface irregularities
Solution Approach 1:
The patent identifies and optimizes multiple parameters including Pd coating thickness (50-200 nm), Cu core purity (99.99%), and processing conditions to achieve smooth ball formation. By precisely controlling these parameters, the solution eliminates surface irregularities while maintaining oxidation protection.
Solution Approach 2:
The patent applies the Pd coating with controlled local thickness and distribution to ensure uniform coverage without creating surface irregularities. The localized optimization of coating quality allows the ball surface to remain smooth and spherical while still providing oxidation resistance at the bonding interface.
3Productivity
If wire diameter is reduced to increase mounting density, then mounting capacity is improved, but bonding strength decreases due to reduced bonding area
Solution Approach 1:
The patent optimizes the bonding interface composition and thickness parameters to maximize bonding strength per unit area. By controlling the Pd layer thickness and Cu core properties, the solution achieves superior interfacial adhesion that compensates for the reduced total bonding area in thinner wires.
Solution Approach 2:
The composite Cu-Pd structure enhances bonding strength through the synergistic combination of Cu's ductility and Pd's oxidation resistance. This material composition allows thinner wires to maintain adequate bonding strength by improving the quality and reliability of the bonding interface.
4Manufacturing precision
If Ni concentration is increased to improve ball formability, then sphericity is improved, but wire composition complexity increases
Solution Approach 1:
The patent optimizes the Ni concentration parameter within a specific range (0.1-1.2 wt.%) to achieve improved ball formability without excessive alloying. This precise parameter control enhances spherical shape formation while keeping the composition relatively simple and manufacturable.
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 proposed bonding wire configuration significantly improves bonding reliability and ball formability, reducing surface irregularities and maintaining bonding strength over extended high-temperature and high-humidity tests, while also enhancing wedge bondability and loop formability for on-vehicle applications.
Implementation Method 1
heating and melting a tip of wire by arc heat input to form a ball through surface tension
Implementation Method 2
heating and melting a tip of wire by arc heat input to form a ball through surface tension
Implementation Method 3
thermal compressive bonding technique with the aid of ultrasound
Implementation Method 4
thermal compressive bonding technique with the aid of ultrasound
Data Source
AI summary
There is provided a bonding wire that improves bonding reliability of a ball bonded part and ball formability and is suitable for on-vehicle devices. The bonding wire for a semiconductor includes a Cu alloy core material, and a Pd coating layer formed on a surface of the Cu alloy core material, and is characterized in that the Cu alloy core material contains Ni, a concentration of Ni is 0.1 to 1.2 wt.% relative to the entire wire, and a thickness of the Pd coating layer is 0.015 to 0.150 µm.