Pd-Ni Coating Profile for Cu Bonding Wire Bond Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Cu bonding wires with Pd-coating layers face galvanic corrosion in high-temperature environments, leading to poor bond reliability, while bare Cu wires lack sufficient FAB shape and compression-bonding quality for high-density mounting.
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 Ni concentration near the surface, and optionally Au, to enhance bond reliability and FAB shape.
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 coating structure with different compositions at different depths: a Pd-rich layer at the surface for oxidation resistance, a Ni-containing layer in the intermediate region (depth 0.3d to 0.7d) to suppress galvanic corrosion, and a Cu-rich core for electrical conductivity. This local differentiation of material properties resolves the contradiction between oxidation protection and corrosion resistance.
Solution Approach 2:
The bonding wire uses a composite structure combining Cu core material with a multi-layer coating of Pd and Ni. This composite material approach allows the wire to simultaneously achieve oxidation resistance from Pd, galvanic corrosion suppression from Ni, and electrical conductivity from Cu, resolving the reliability issue in high-temperature environments.
2Reliability
If bare Cu bonding wire is used to avoid galvanic corrosion, then galvanic corrosion is eliminated, but FAB shape and compression-bonding quality deteriorate for high-density mounting
Solution Approach 1:
The patent creates a localized Ni-containing region at specific depths (0.3d to 0.7d) within the coating layer, rather than uniformly distributing Ni throughout. This localized placement suppresses galvanic corrosion at critical interfaces while maintaining the overall coating structure needed for FAB formation and compression bonding quality.
3Object-affected harmful factors
If Ni concentration is increased in the coating layer to suppress galvanic corrosion, then galvanic corrosion resistance is improved, but the coating layer structure becomes less stable
Solution Approach 1:
The patent confines the Ni-containing region to a specific depth range (0.3d to 0.7d) rather than distributing Ni uniformly throughout the coating layer. This localized placement achieves galvanic corrosion suppression at critical interfaces while maintaining Pd-rich regions for oxidation resistance and overall coating stability.
Solution Approach 2:
The patent optimizes the Ni concentration within the coating layer to fall between 0.02-0.7 mass%, and positions the maximum Ni concentration at specific depths (0.3d to 0.7d). This parameter optimization balances galvanic corrosion suppression with coating layer stability, preventing excessive Ni from compromising the protective function of the Pd-rich surface layer.
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 reduces galvanic corrosion, ensuring high bond reliability in high-temperature environments, suitable for on-vehicle and power devices.
Implementation Method 1
Cu has the drawback of being more susceptible to oxidation than Au. As a method of preventing the surface oxidation of the Cu bonding wire, there has been proposed a structure in which a surface of a Cu core material is coated with a metal such as Pd and Ni
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') through surface tension
Implementation Method 3
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') through surface tension
Implementation Method 4
In the 2nd bonding, 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 without forming the ball
Data Source
AI summary
The bonding wire for semiconductor devices 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. 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, the thickness d (nm) of the coating layer is 10≤d≤130, a ratio of a concentration CNi (mass %) of Ni to a concentration CPd (mass %) of Pd relative to the entire wire is 0.02<CNi/CPd≤0.7, and a position indicating a maximum concentration of Ni which is 10 atomic % or more, 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.