Pd-Ni Coated Cu Bonding Wire for 2nd-Bond Corrosion Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional Cu bonding wires with Pd-coating layers face issues such as partial exfoliation of the Pd-coating layer during the bonding process, leading to galvanic corrosion and inadequate bond reliability, especially in high-temperature environments. Additionally, bare Cu bonding wires without Pd-coating suffer from poor FAB shape and insufficient bondability at the 1st bonding part.
Innovation Solution
A novel alloy-coated Cu bonding wire with a coating layer having a total concentration of Pd and Ni of 90 atomic % or more, where the coating layer's thickness is between 10 nm and 130 nm, and the average Pd to Ni concentration ratio (CPd/CNi) is between 0.1 and 35.0, with at least 50% of measurement points within 0.3X of the average ratio. The wire also includes one or more elements selected from a specific group, with a total concentration of 5 ppm to 450 ppm, and optionally contains Au on its surface with a concentration of 0.5% by mass or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a Pd-coating layer is applied on Cu core material to prevent oxidation, then oxidation resistance is improved, but the coating layer may partially exfoliate during bonding process causing galvanic corrosion
Solution Approach 1:
The patent applies a composite coating structure with multiple layers (Pd layer, Ni layer, and intermediate layer) on the Cu core material. This composite structure prevents direct contact between Pd and Cu, eliminating galvanic corrosion while maintaining oxidation resistance. The specific layer configuration and thickness control ensure both protective functions are achieved simultaneously.
Solution Approach 2:
The patent introduces an intermediate layer between the Pd coating and Cu core material to prevent direct galvanic interaction. This intermediate layer acts as a mediator that blocks the electrochemical cell formation while still allowing the Pd outer layer to provide oxidation protection, thus resolving the contradiction between corrosion prevention and bond reliability.
2Reliability
If a Pd-coating layer is applied to improve bond reliability, then galvanic corrosion is reduced, but the adhesion at the 2nd bonding part is insufficient
Solution Approach 1:
The patent applies different coating layers with specific properties at different locations and depths. The Pd layer provides oxidation resistance at the surface, the Ni layer provides adhesion enhancement at the bonding interface, and the intermediate layer provides corrosion protection. This local quality differentiation resolves the contradiction between overall bond reliability and specific adhesion strength.
Solution Approach 2:
The patent controls specific parameters including coating layer thickness (10-130 nm), Pd/Ni concentration ratio (0.1-35.0), and additive element concentrations (5-450 ppm). By optimizing these parameters, the coating structure achieves both high bond reliability and strong adhesion at the 2nd bonding part simultaneously.
3Reliability
If bare Cu bonding wire is used without Pd-coating layer, then galvanic corrosion does not occur, but FAB shape is poor and bondability is insufficient
Solution Approach 1:
The patent uses a thin Pd-coated structure that provides necessary protection during bonding but does not interfere with FAB formation. The controlled thickness and composition allow the coating to serve its protective function temporarily during the bonding process while enabling proper FAB shape formation, effectively balancing protection needs with bonding performance.
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 alloy-coated Cu bonding wire achieves a favorable FAB shape, improved initial bondability at the 2nd bonding part, and reduced galvanic corrosion in high-temperature environments, thereby enhancing the overall bond reliability of the 2nd bonding part.
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
Implementation Method 2
a tip end of wire part extended from the capillary (hereinafter also referred to as 'tail') 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') through surface tension
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') through surface tension
Implementation Method 4
the wire part is compression-bonded (hereinafter also referred to as 'wedge-bonded') onto the external terminal by applying ultrasonic waves and load from the capillary to the wire part without forming the ball
Data Source
AI summary
There is provided a novel alloy-coated Cu bonding wire that achieves a favorable FAB shape and also a favorable initial bondability of a 2nd bonding part including adhesion of the 2nd bonding part, and that reduces a galvanic corrosion in a high-temperature environment to achieve a favorable bond reliability of the 2nd bonding part. The alloy-coated Cu bonding wire includes a core material of Cu or Cu alloy, and a coating layer having a total concentration of Pd and Ni of 90 atomic % or more formed on a surface of the core material. The bonding wire is characterized in that:in a concentration profile in a depth direction of the wire obtained by performing measurement using Auger electron spectroscopy (AES) so that the number of measurement points in the depth direction is 50 or more for the coating layer,a thickness of the coating layer is 10 nm or more and 130 nm or less,an average value X is 0.1 or more and 35.0 or less, the average value X being defined as an average value of a ratio of a Pd concentration CPd (atomic %) to an Ni concentration CNi (atomic %), CPd/CNi, for all measurement points in the coating layer,the total number of measurement points in the coating layer whose absolute deviation from the average value X is 0.3X or less is 50% or more relative to the total number of measurement points in the coating layer, andthe bonding wire satisfies the following condition (A):(A) the bonding wire contains one or more elements selected from the group consisting of Ti, V, Cr, Mn, Fe, Co, Zn, Zr, Nb, Mo, Ru, Rh, Sn, Ta, W, Os, Ir, Pt, Au and Bi (hereinafter referred to as “first additive element”), and the total concentration of the first additive element relative to the entire wire is 5 ppm by mass or more and 450 ppm by mass or less.