Pd-Ni Coated Cu Bonding Wire for Stable FAB and Hot Bonding
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Solution Overview
Problem
Conventional Cu bonding wires with Pd-coating layers face galvanic corrosion in high-temperature environments, leading to unreliable bond reliability, while bare Cu wires without coatings result in poor FAB shapes and inadequate compression-bonding for high-density mounting, especially in on-vehicle and power devices.
Innovation Solution
A Cu bonding wire with a coating layer containing Pd and Ni, where the coating layer has a specific thickness and composition profile, including a region with a high concentration of Ni and Pd, and optionally Au, In, or Ag, to enhance bond reliability and prevent galvanic corrosion.
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 galvanic corrosion occurs in high-temperature environments leading to poor bond reliability
Solution Approach 1:
The patent applies a multi-layer composite coating structure consisting of Pd, Ni, and Au layers on Cu core material. This composite structure combines the oxidation resistance of Pd with the galvanic corrosion resistance of Ni and Au, achieving both protection functions simultaneously while maintaining bond reliability in high-temperature environments.
Solution Approach 2:
The patent creates different functional zones within the coating layer by controlling the distribution of Pd, Ni, and Au elements. The coating has varying composition and thickness at different depths, with specific elements concentrated in specific regions to provide localized protection against different types of degradation (oxidation at surface, galvanic corrosion at interface).
2Object-affected harmful factors
If a Pd-coating layer is applied to Cu bonding wire, then oxidation resistance is improved, but the coating layer exfoliates during bonding process exposing Cu core material to corrosion
Solution Approach 1:
The multi-layer composite coating structure with Pd, Ni, and Au provides enhanced adhesion and structural stability. The different materials in the composite layers have complementary properties that prevent exfoliation, with each layer providing mechanical and chemical bonding support to the others during the bonding process.
Solution Approach 2:
The patent optimizes the thickness and composition parameters of each coating layer to prevent exfoliation. By controlling the thickness of Pd, Ni, and Au layers within specific ranges and adjusting their compositional ratios, the coating maintains structural integrity and adhesion strength during bonding operations.
3Reliability
If bare Cu bonding wire is used without coating, then galvanic corrosion is avoided, but FAB shape deteriorates and compression-bonding quality becomes insufficient for high-density mounting
Solution Approach 1:
The composite coating structure with optimized Pd, Ni, and Au composition provides the right balance between protection and manufacturability. The specific ratios of these elements in the coating layers enable proper FAB formation during bonding while maintaining corrosion resistance, achieving both reliability and manufacturing precision simultaneously.
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 wire achieves a favorable FAB shape and improved bond reliability in high-temperature environments, ensuring reliable connections for on-vehicle and power devices, even at elevated temperatures beyond 200°C.
Implementation Method 1
the coating layer has a region containing Pd as a main component on a core material side, and has a region containing Ni and Pd
Implementation Method 2
a tip end of wire is heated and melted by arc heat input to form a free air ball (FAB: Free Air Ball; hereinafter also simply referred to as 'ball' or 'FAB')
Implementation Method 3
heated and melted by arc heat input to form a free air ball (FAB: Free Air Ball; hereinafter also simply referred to as 'ball' or 'FAB') through surface tension
Implementation Method 4
the wire part is compression-bonded (hereinafter referred to as 'wedge-bonded') onto the external electrode by applying ultrasonic waves and load to the wire part
Data Source
AI summary
There is provided a novel Cu bonding wire that achieves a favorable FAB shape and achieves a favorable bond reliability of the 2nd bonded part even in a rigorous high-temperature environment. The bonding wire for semiconductor devices is characterized in that the bonding wire includes: a core material of Cu or Cu alloy; and a coating layer containing conductive metal other than Cu formed on a surface of the core material, wherein the coating layer has a region containing Pd as a main component on a core material side, and has a region containing Ni and Pd in a range from a wire surface to a depth of 0.5 d when a thickness of the coating layer is defined as d (nm) in a thickness direction of the coating layer, the thickness d of the coating layer is 10 nm or more and 130 nm or less, a ratio CNi/CPd of a concentration CNi (mass %) of Ni to a concentration CPd (mass %) of Pd relative to the entire wire is 0.02 or more and 0.7 or less, a position indicating a maximum concentration of Ni is present in the range from the wire surface to a depth of 0.5 d in a concentration profile in a depth direction of the wire, and the maximum concentration of Ni is 10 atomic % or more, and at least one of the following conditions (i) and (ii) is satisfied:(i) a concentration of In relative to the entire wire is 1 ppm by mass or more and 100 ppm by mass or less(ii) a concentration of Ag relative to the entire wire is 1 ppm by mass or more and 500 ppm by mass or less.