Pd-Coated Cu Bonding Wire for Hot-Humid Ball Bond Reliability
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Solution Overview
Problem
Conventional Cu bonding wires with Pd coating layers fail to provide sufficient bonding reliability in high-temperature and high-humidity environments, particularly for on-vehicle devices, as they exhibit reduced longevity and reliability in accelerated temperature and humidity stress tests.
Innovation Solution
A Cu bonding wire with a Pd coating layer and additional elements such as As, Te, Sn, Sb, Bi, and Se, which improves bonding reliability by reducing the diffusion of Cu and Al at the bonding interface and enhancing oxidation resistance, thereby increasing the longevity of the ball bonded part.
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 reliability in high-temperature and high-humidity environment deteriorates
Solution Approach 1:
The patent applies a multi-layer composite coating structure consisting of Pd, Au, and alloy layers on Cu core material. This composite structure combines the oxidation resistance of Pd with the stability of Au and the controlled diffusion properties of alloy layers, resolving the contradiction between oxidation protection and bonding reliability in harsh environments.
Solution Approach 2:
The patent creates different functional layers with specific compositions and thicknesses tailored for different purposes: Pd layer for oxidation resistance, Au layer for stability, and alloy layers for controlled diffusion. Each layer has locally optimized properties to address specific requirements, thereby improving overall bonding reliability while maintaining oxidation resistance.
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 longevity in high-temperature and high-humidity environment deteriorates
Solution Approach 1:
The patent uses Cu core material with multi-layer coating structures to achieve both cost effectiveness and long bonding longevity. The Cu core provides low cost compared to Au, while the Pd, Au, and alloy coating layers work together to ensure bonding longevity exceeds 100 hours in HAST conditions by controlling diffusion and preventing degradation.
Solution Approach 2:
The patent carefully controls the composition, thickness, and structure of coating layers to optimize performance. By adjusting parameters such as Pd layer thickness (0.01-0.5 μm), Au layer thickness (0.01-0.1 μm), and alloy element concentrations, the patent achieves bonding longevity >100 hours while maintaining cost advantage over pure Au wires.
3Quantity of substance
If Cu bonding wire is used to replace Au bonding wire for cost reduction, then material cost is reduced, but bonding reliability in rigorous environment deteriorates
Solution Approach 1:
The patent transforms Cu bonding wire from a low-reliability material into a high-reliability solution by applying Pd, Au, and alloy coating layers. This composite structure maintains the cost advantage of Cu while achieving bonding reliability suitable for on-vehicle devices in rigorous environments through controlled diffusion and enhanced protection.
Solution Approach 2:
The Pd, Au, and alloy coating layers act as intermediary barriers between the Cu core and the external environment. These intermediary layers prevent direct interaction between Cu and corrosive elements, thereby improving bonding reliability while maintaining the cost benefits of Cu material.
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 Cu alloy core material with a Pd coating layer and selected elements significantly enhances bonding reliability and longevity in high-temperature and high-humidity conditions, ensuring reliable performance for on-vehicle devices by reducing the formation of corrosive intermetallic compounds and improving interfacial tension and wettability.
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
a thermal compressive bonding technique with the aid of ultrasound
Implementation Method 4
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 thereof, and the boding wire contains one or more elements of As, Te, Sn, Sb, Bi and Se in a total amount of 0.1 to 100 ppm by mass. 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 further contains one or more of Ni, Zn, Rh, In, Ir, Pt, Ga and Ge in an amount, for each, of 0.011 to 1.2% by mass, it is able to increase the reliability of a ball bonded part in a high-temperature environment of 170°C or more. When an alloy skin layer containing Au and Pd is further formed on a surface of the Pd coating layer, wedge bondability improves.