Double-Coated Silver Bonding Wire for Stable FAB and Looping
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Solution Overview
Problem
Existing silver-based bonding wires face challenges in preventing flowery bonded balls and ensuring stable looping behavior due to issues with wire softness, FAB formation, corrosion, and oxidation resistance.
Innovation Solution
A coated round wire with a silver-based wire core and a double-layer coating of palladium or nickel as the inner layer and gold as the outer layer, where the gold layer exhibits specific grain size and orientation properties to enhance wire bonding performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a silver-based wire core is used to maintain wire softness and FAB formation capability, then wire softness and FAB formation are improved, but corrosion and oxidation resistance deteriorate
Solution Approach 1:
The patent applies a composite material structure consisting of a silver-based wire core combined with a double-layer coating of palladium or nickel (inner layer) and gold (outer layer). This composite structure allows the silver core to provide wire softness and FAB formation capability while the coating layers provide corrosion and oxidation resistance, thus resolving the contradiction between ease of operation and reliability.
Solution Approach 2:
The double-layer coating acts as an intermediary between the silver-based wire core and the external environment. The inner layer of palladium or nickel provides a diffusion barrier, while the outer gold layer provides corrosion and oxidation resistance, protecting the silver core without affecting its mechanical properties.
2Ease of manufacture
If conventional coating structures are used, then manufacturing simplicity is maintained, but flowery bonded ball formation increases
Solution Approach 1:
The patent applies local quality by creating a double-layer coating structure where each layer has specific properties: the inner layer of palladium or nickel (1-100 nm) provides a diffusion barrier, and the outer gold layer (1-250 nm) with controlled grain size (0.1-0.8 μm) and orientation provides corrosion resistance and prevents flowery bonded ball formation. This localized functional differentiation resolves the contradiction between manufacturing simplicity and reliability.
Solution Approach 2:
The patent changes critical parameters of the gold layer including grain size (0.1-0.8 μm) and crystallographic orientation (60-100% <100> orientation) to prevent flowery bonded ball formation. These parameter changes are achieved through controlled deposition processes while maintaining a relatively simple double-layer structure.
3Reliability
If the gold layer thickness is increased to improve corrosion resistance, then reliability is improved, but manufacturing cost and complexity increase
Solution Approach 1:
The patent optimizes the thickness parameters of both coating layers to achieve the best balance between protection and complexity. The inner layer is maintained at 1-100 nm and the outer gold layer at 1-250 nm, with specific grain size (0.1-0.8 μm) and orientation (60-100% <100>) control. These parameter specifications provide effective corrosion resistance while avoiding excessive thickness that would increase manufacturing complexity.
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 coated round wire demonstrates improved prevention of flowery bonded balls and stable looping behavior, offering enhanced corrosion and oxidation resistance while maintaining wire softness and facilitating FAB formation.
Implementation Method 1
the inner layer is designed to act as a diffusion barrier between the wire core and the outer layer
Implementation Method 2
corrosion as well oxidation resistance
Implementation Method 3
corrosion as well oxidation resistance
Data Source
AI summary
A round wire comprising a wire core with a surface, the wire core having a coating layer superimposed on its surface, wherein the wire core itself is a silver-based wire core, wherein the coating layer is a double-layer comprised of a 1 to 100 nm thick inner layer of palladium or nickel and an adjacent 1 to 250 nm thick outer layer of gold, wherein the outer layer of gold exhibits at least one of the following intrinsic properties Al) and A2): A1) the average grain size of the crystal grains in the outer layer of gold, measured in longitudinal direction, is in the range of from-0.1 to 0.8 μm; A2) 60 to 100% of the crystal grains in the outer layer of gold are oriented in <100>direction, and 0 to 20% of the crystal grains in the outer layer of gold are oriented in <111>direction.