Pd-Coated Copper Bonding Wire for Shrinkage Cavity Resistance
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Solution Overview
Problem
Palladium-coated copper bonding wires face issues with large shrinkage cavities and reduced bonding life, especially in high-temperature and high-humidity environments, due to oxidation and corrosion, which affect the reliability of ball bonding.
Innovation Solution
A palladium-coated copper bonding wire with a core material containing copper and a palladium layer, where the concentration of palladium is between 1.0 and 4.0 mass% and the sulfur group element concentration is between 5 and 50 mass ppm, forming a palladium-concentrated bonding region with a concentration of 2.0 mass% or more near the bonding surface, preventing shrinkage cavities and enhancing bonding reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a palladium-coated copper wire is used to reduce cost compared to gold wire, then the cost is reduced, but the wire surface oxidizes easily and bonding reliability deteriorates
Solution Approach 1:
The patent uses a composite structure with a copper core material and a palladium coating layer. The copper core provides cost advantage and electrical conductivity, while the palladium coating layer protects against oxidation. This composite material approach resolves the contradiction by combining materials with complementary properties to achieve both cost reduction and oxidation resistance.
Solution Approach 2:
The patent optimizes the palladium concentration in the coating layer to be between 1.0 and 4.0 mass%, and the sulfur group element concentration to be between 5 and 50 mass ppm. By precisely controlling these compositional parameters, the patent achieves adequate oxidation protection while minimizing coating thickness and cost, thereby resolving the contradiction between cost and reliability.
2Object-affected harmful factors
If the palladium concentration in the coating layer is increased to improve oxidation resistance, then oxidation resistance improves, but the formation of shrinkage cavities increases and bonding life decreases
Solution Approach 1:
The patent identifies an optimal parameter range for palladium concentration (1.0-4.0 mass%) and sulfur group element concentration (5-50 mass ppm). Within this range, the patent achieves sufficient oxidation resistance while preventing excessive palladium aggregation that would cause shrinkage cavities during ball bonding, thereby extending bonding life.
Solution Approach 2:
The patent introduces sulfur group elements as intermediary substances that modify the palladium coating structure. These sulfur group elements help distribute palladium more uniformly and prevent excessive aggregation, thereby reducing shrinkage cavity formation while maintaining oxidation resistance.
3Quantity of substance
If a palladium-coated copper wire is used for severe conditions such as automotive applications, then cost is reduced compared to gold, but the wire must withstand extremely severe and rapidly changing conditions which deteriorates reliability
Solution Approach 1:
The patent uses a composite material structure with copper core and palladium coating specifically designed for severe conditions. The optimized composition ratio and the presence of sulfur group elements enhance the wire's resistance to thermal cycling, vibration, and humidity, enabling it to withstand automotive severe conditions while maintaining cost advantage over gold wire.
Solution Approach 2:
The patent optimizes compositional parameters (palladium concentration: 1.0-4.0 mass%, sulfur group element concentration: 5-50 mass ppm) to enhance performance under severe conditions. This parameter optimization ensures the wire maintains structural integrity and bonding reliability during thermal cycling and vibration, meeting automotive application requirements.
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 solution significantly improves the bonding reliability and prevents shrinkage cavities, maintaining stable bonding even in severe conditions, suitable for automotive and high-temperature applications.
Implementation Method 1
an arc discharge is formed between the tip and a discharge torch using the Electronic Flame-Off (EFO) method, and by a discharge current, heat input is applied to the tip of the wire
Implementation Method 2
A molten metal rises through the wire due to its surface tension, and a spherical molten ball is formed at the tip of the wire to solidify
Implementation Method 3
the free air ball is crimped onto the electrode with ultrasonic waves being applied thereto while heating the electrode of the semiconductor element to about 140 to 300° C.
Data Source
AI summary
The bonding wire being a Pd-coated copper bonding wire includes: a copper core material; and a Pd layer and containing a sulfur group element, in which with respect to the total of copper, Pd, and the sulfur group element, a concentration of Pd is 1.0 mass % to 4.0 mass % and a total concentration of the sulfur group element is 50 mass ppm or less, and a concentration of S is 5 mass ppm to 2 mass ppm, a concentration of Se is 5 mass ppm to 20 mass ppm, or a concentration of Te is 15 mass ppm to 50 mass ppm or less. A wire bonding structure includes a Pd-concentrated region with the concentration of Pd being 2.0 mass % or more relative to the total of Al, copper, and Pd near a bonding surface of an Al-containing electrode of a semiconductor chip and a ball bonding portion.