Pd-Coated Cu Bonding Wire for High-Humidity Ball Bond Reliability
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Solution Overview
Problem
Conventional Cu bonding wires with Pd coating layers fail to meet the stringent bonding reliability requirements in high-temperature and high-humidity environments, particularly for on-vehicle devices, as they exhibit reduced longevity and reliability in accelerated tests.
Innovation Solution
A Cu alloy bonding wire with a Pd coating layer containing 0.031 to 1.2% In by mass and a Pd coating thickness of 0.015 to 0.150 µm, which enhances bonding reliability by forming a Pd-concentrated layer that reduces diffusion and corrosion at the bonding interface, improving oxidation resistance and longevity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a Pd coating layer is applied to Cu bonding wire to prevent oxidation, then oxidation resistance is improved, but bonding longevity in high-temperature high-humidity environment deteriorates
Solution Approach 1:
The patent changes the chemical composition parameters of the Cu alloy core material by adding specific elements (In: 0.03-1.2 mass%, Ga: 0.03-1.2 mass%, Ge: 0.03-1.2 mass%) to modify the bonding characteristics and improve longevity in HAST environments while maintaining oxidation resistance through the Pd coating
Solution Approach 2:
The patent creates a composite structure with a Cu alloy core material containing specific elements (In, Ga, Ge) combined with a Pd coating layer, where the core material provides mechanical strength and the coating provides oxidation resistance, achieving both improved bonding longevity and maintained oxidation protection
2Quantity of substance
If high-purity Cu is used for bonding wire to reduce cost compared to Au, then material cost is reduced, but bonding reliability deteriorates
Solution Approach 1:
The patent uses a composite structure with Cu alloy core material (containing In, Ga, and Ge elements) and a Pd coating layer, maintaining the cost advantage of Cu while improving bonding reliability through the alloying elements and protective coating that prevent oxidation and enhance bonding performance
Solution Approach 2:
The patent modifies the chemical composition of the Cu core material by adding specific alloying elements (In: 0.03-1.2 mass%, Ga: 0.03-1.2 mass%, Ge: 0.03-1.2 mass%) to enhance bonding reliability and oxidation resistance while maintaining the cost-effectiveness of Cu-based material
3Object-affected harmful factors
If Pd coating thickness is increased to improve oxidation protection, then oxidation resistance is improved, but wedge bondability deteriorates
Solution Approach 1:
The patent optimizes the Pd coating thickness parameter to a specific range (0.015-0.150 μm) that provides sufficient oxidation protection while maintaining adequate wedge bondability, balancing the competing requirements through precise parameter control
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 significantly increases the bonding longevity and reliability of the ball bonded part in high-temperature and high-humidity conditions, meeting the requirements for on-vehicle devices by reducing the formation of corrosive compounds and improving adhesiveness, while maintaining suitable wedge bondability and shape integrity.
Implementation Method 1
heating and melting a tip of wire by arc heat input to form a ball (FAB: free air ball) through surface tension
Implementation Method 2
heating and melting a tip of wire by arc heat input to form a ball (FAB: free air ball) through surface tension
Implementation Method 3
forming a Pd-concentrated layer that reduces diffusion and corrosion at the bonding interface
Implementation Method 4
a thermal compressive bonding technique with the aid of ultrasound
Implementation Method 5
a thermal compressive bonding technique with the aid of ultrasound
Data Source
AI summary
There is provided a Cu bonding wire having a Pd coating layer on a surface thereof, that improves bonding reliability of a ball bonded part in a high-temperature and high-humidity environment and is suitable for on-vehicle devices. The bonding wire for a semiconductor device includes a Cu alloy core material and a Pd coating layer formed on a surface of the Cu alloy core material, and the bonding wire contains In of 0.011 to 1.2% by mass and has the Pd coating layer of a thickness of 0.015 to 0.150 µm. With this configuration, it is able to increase the bonding longevity of a ball bonded part in a high-temperature and high-humidity environment, and thus to improve the bonding reliability. When the Cu alloy core material contains one or more elements of Pt, Pd, Rh and Ni in an amount, for each element, of 0.05 to 1.2% by mass, it is able to increase the reliability of a ball bonded part in a high-temperature environment of 175°C or more. When an Au skin layer is further formed on a surface of the Pd coating layer, wedge bondability improves.