Silver-Coated Copper Bonding Wire for High-Temperature Wedge Bonding
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Solution Overview
Problem
Existing bonding wires face challenges in high-temperature applications with WBG semiconductors due to material migration and require improved bondability, reliability, and resistance to oxidation, while maintaining low bonding forces and high conductivity.
Innovation Solution
A copper core wire coated with silver, having a specific aspect ratio and cross-sectional area share, with an optional intermediate layer, to enhance adhesion and conductivity, suitable for wedge bonding.
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 uses a composite wire structure with a copper core and silver coating layer. The copper core provides high electrical conductivity, while the silver coating layer improves wedge-bonding processability and oxidation resistance. This composite structure resolves the contradiction by combining materials with complementary properties.
Solution Approach 2:
The wire has different material properties at different locations: the core maintains high conductivity while the surface coating provides bonding facilitation and oxidation protection. This local differentiation of material qualities allows the wire to simultaneously achieve good conductivity and ease of bonding.
2Ease of manufacture
If aluminium coated copper wires are used, then wedge-bonding ability is improved, but material migration occurs at high temperatures reducing assembly lifetime
Solution Approach 1:
The patent replaces the aluminium coating with a silver coating on the copper core. Silver has superior high-temperature stability and does not exhibit the same migration issues as aluminium when bonded to WBG semiconductors. This composite structure maintains good wedge-bonding ability while eliminating the high-temperature degradation problem.
Solution Approach 2:
The patent changes the coating material from aluminium to silver, fundamentally altering the chemical and thermal properties of the wire. Silver's higher melting point and chemical stability prevent material migration at operating temperatures above 200°C, thereby extending assembly lifetime.
3Object-affected harmful factors
If bonding forces are reduced to avoid substrate damage, then substrate integrity is improved, but bonding strength may be compromised
Solution Approach 1:
The silver coating layer provides a surface with optimal properties for wedge-bonding, allowing strong bonds to form at lower forces. The coating's surface characteristics facilitate better adhesion between the wire and substrate, enabling reduced bonding forces while maintaining bonding strength.
Solution Approach 2:
The silver coating acts as an intermediary layer between the copper core and the substrate during bonding. It provides a surface that is easier to bond to than bare copper, enabling strong bonds to form at lower pressures and reducing the risk of 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 bonds at low forces, withstands high temperatures, and maintains conductivity, extending assembly lifetime and reliability.
Implementation Method 1
a copper core wire coated with silver
Implementation Method 2
withstands high temperatures
Implementation Method 3
maintains conductivity
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
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, wherein the aspect ratio between the shortest path and the longest path through the wire in any cross-sectional view is in the range of 0.8 to 1.0, wherein the wire has a diameter in the range of 100 µm to 600 µm and wherein in a cross-sectional view of the wire the area share of the coating layer is in the range of 10 to 60 %, based on the total area of the cross-section of the wire. 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. The invention further relates to an electronic assembly comprising a bonded wire with a copper core and a silver comprising coating layer, wherein the coating layer comprises a first and a second thickness in a contact area of the bonded wire, and wherein the first thickness is smaller than the second thickness.