Pd-Ni Coated Cu Bonding Wire for Corrosion-Resistant FAB Formation
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Solution Overview
Problem
Conventional Cu bonding wires with Pd-coating layers experience galvanic corrosion in high-temperature environments, leading to poor bond reliability, while bare Cu wires fail to form a favorable FAB shape for high-density mounting.
Innovation Solution
A Cu bonding wire with a coating layer containing Pd as a main component, along with Ni and optionally Au, having specific concentration ratios and depth profiles, reduces galvanic corrosion and ensures a favorable FAB shape.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a conventional bonding wire is used, then the device structure is simple, but the heat dissipation performance is insufficient leading to hot spots
Solution Approach 1:
The bonding wire is segmented into multiple sections along its length, with each section having different physical properties (material composition, diameter, or crystal structure). This segmentation allows different portions of the wire to perform specialized functions: some sections optimize for electrical conductivity, others for heat dissipation, and others for mechanical flexibility, thereby improving overall heat dissipation performance without requiring a completely complex device structure
Solution Approach 2:
Different sections of the bonding wire are assigned different local qualities tailored to specific functional requirements. For example, sections closer to the semiconductor chip may have higher thermal conductivity for heat dissipation, while other sections may have optimized electrical conductivity or mechanical properties. This local differentiation resolves the contradiction by improving heat dissipation performance through targeted property optimization rather than uniform structural complexity
2Reliability
If the bonding wire has high electrical conductivity, then signal transmission is good, but heat dissipation capability deteriorates
Solution Approach 1:
The bonding wire is divided into functionally specialized sections where certain segments are optimized for electrical conductivity to ensure good signal transmission, while other segments are optimized for thermal conductivity to provide heat dissipation capability. This spatial segmentation of functions allows the wire to simultaneously achieve both reliable signal transmission and adequate heat dissipation without compromising either property
Solution Approach 2:
Different local regions of the bonding wire possess different quality characteristics: sections requiring excellent signal transmission have optimized electrical conductivity, while sections requiring heat dissipation have optimized thermal conductivity. This local quality differentiation resolves the contradiction by allowing each region to excel at its primary function without negatively impacting the other function in regions where it is not the priority
3Quantity of substance
If the bonding wire diameter is increased, then current carrying capacity improves, but flexibility and ease of handling deteriorate
Solution Approach 1:
The bonding wire is segmented into multiple sections with varying diameters along its length. Sections that require high current carrying capacity have larger diameters, while sections that require flexibility and ease of handling have smaller diameters. This segmentation allows the wire to achieve both high current capacity where needed and flexibility where needed, resolving the contradiction between these two opposing requirements
Solution Approach 2:
Different sections of the bonding wire are assigned different local diameters optimized for their specific functional requirements. Sections requiring high current carrying capacity have increased diameter locally, while sections requiring flexibility maintain smaller diameters. This local quality optimization resolves the contradiction by allowing the wire to have high current capacity in critical areas without sacrificing overall flexibility and ease of handling in areas where flexibility is more important
Data Source
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AI summary
There is provided a novel Cu bonding wire that achieves a favorable FAB shape and reduces a galvanic corrosion in a high-temperature environment to achieve a favorable bond reliability of the 2nd bonded part. 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 0.5d 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, and a position indicating a maximum concentration of Ni is present in the range from the wire surface to a depth of 0.5d in a concentration profile in a depth direction of the wire, and the maximum concentration of Ni is 10 atomic% or more.