Silver-Coated Copper Bonding Wire for Low-Force Wedge Bonding
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Solution Overview
Problem
Existing bonding wires face challenges in wedge bonding due to high bonding forces, susceptibility to oxidation, and compatibility issues with new semiconductor materials like SiC and GaN, leading to reduced assembly lifetime and potential damage to substrates.
Innovation Solution
A copper core wire with a silver coating and an intermediate layer, where the intermediate layer consists of materials from both core and coating, enhances adhesion and reduces bonding forces while maintaining high conductivity and corrosion resistance, suitable for wedge bonding with WBG semiconductors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If copper wires are used for bonding, then electrical conductivity is improved, but wedge bonding becomes more difficult and oxidation susceptibility increases
Solution Approach 1:
The patent employs a composite wire structure with a copper core and aluminum coating layer. The copper core provides superior electrical conductivity, while the aluminum coating enables easier wedge bonding and oxidation resistance. This composite material approach resolves the contradiction by combining materials with complementary properties in a single wire structure.
Solution Approach 2:
The aluminum coating layer acts as a protective barrier that creates an inert environment for the copper core, preventing oxidation. The coating layer contains aluminum oxide and other compounds that form a protective surface, eliminating the need for complex oxidation prevention measures during storage and processing.
2Ease of manufacture
If aluminum coated copper wires are used, then wedge bonding ability is improved, but material migration accelerates at high temperatures reducing lifetime
Solution Approach 1:
The patent carefully controls the thickness of the aluminum coating layer and the composition of the intermediate layer to optimize performance. By adjusting these parameters, the wire achieves good wedge bonding ability while minimizing material migration at high temperatures. The intermediate layer acts as a diffusion barrier that slows down material migration rates.
Solution Approach 2:
The intermediate layer serves as a mediator between the copper core and aluminum coating. It consists of copper-aluminum alloy compounds that reduce the direct contact between pure copper and aluminum, thereby slowing down the material migration process at high temperatures while still allowing effective wedge bonding.
3Strength
If high bonding forces are applied during wedge bonding, then bond strength is improved, but substrate damage increases
Solution Approach 1:
The patent optimizes the aluminum coating thickness and intermediate layer composition to achieve strong bonding at lower forces. The controlled parameters allow the wire to form strong bonds with substrates like SiC and GaN without requiring excessive bonding forces that would cause substrate damage.
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 provides strong bondability with low bonding forces, improved reliability, and extended lifetime, suitable for high-temperature operations, and is compatible with advanced semiconductor materials, ensuring minimal substrate damage and increased assembly durability.
Implementation Method 1
an intermediate layer, arranged between the copper core and the coating layer, wherein the intermediate layer comprises only material of the copper core and material of the coating layer
Data Source
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AI summary
The invention relates to a wire, preferably for bonding in power electronics, comprising a copper core with a surface and a coating layer superimposed over the surface of the copper core, wherein the coating layer comprises silver, and an intermediate layer, arranged between the copper core and the coating layer, wherein the intermediate layer comprises only material of the copper core and material of the coating layer. The wire has a diameter in the range of 100 µm to 600 µm and the intermediate layer has a thickness in the range of 0.1 to 5 µm. The invention further relates to a process to manufacture such a wire, to a wire obtainable by said process, to an electronic assembly comprising at least two electronic elements and at least aforementioned wire, and to a process of connecting two elements through afore mentioned wire by wedge-wedge-bonding.