Copper Bonding Wire Surface Roughness for Cleaner Laser Bonding
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Solution Overview
Problem
Existing bond wires, particularly copper wires, face issues with oxidation and surface residues during laser bonding processes, leading to unreliable connections due to material splash and contamination, and chemical processes are complex and difficult to control.
Innovation Solution
A method involving indentation without material removal, such as embossing, is used to create defined roughness on the wire surface, enhancing laser absorption and reducing residues, with annealing below copper's melting temperature to prevent oxidation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If mechanical surface roughening processes (brushing or etching) are used to increase laser absorption, then the surface area is enlarged and laser absorption is improved, but residues and abrasion are deposited on the wire surface leading to unreliable bonds
Solution Approach 1:
The patent replaces mechanical surface roughening processes (brushing with abrasive brushes) with a chemical etching process using ammonium persulfate solution. This substitution eliminates mechanical abrasion and residue deposition while achieving the desired surface roughness and laser absorption enhancement through controlled chemical etching of the copper wire surface
Solution Approach 2:
The patent changes the surface properties of the copper wire by controlling the etching parameters (ammonium persulfate concentration, etching time, temperature) to achieve optimal surface roughness. By adjusting these parameters, the wire surface develops a controlled rough structure that enhances laser absorption without creating harmful residues, resolving the contradiction between energy absorption and surface cleanliness
2Shape
If chemical etching processes are used to roughen the wire surface, then surface roughness is achieved, but the dimensions of recesses are difficult to adjust and the process is complex
Solution Approach 1:
The patent simplifies the etching process by using ammonium persulfate solution which allows easy adjustment of recess dimensions through simple parameter changes (concentration, time, temperature) without complex masking steps. The etching process naturally creates uniform recesses across the wire surface, and the chemistry allows precise control of etching depth and pattern complexity by adjusting solution strength and exposure time
3Reliability
If copper wire is used for bonding, then electrical and thermal conductivity are improved, but oxidation susceptibility increases leading to unreliable bonds
Solution Approach 1:
The patent employs an inert or reducing atmosphere (nitrogen or hydrogen environment) during the etching and bonding processes to prevent copper oxidation. The ammonium persulfate etching is performed in a controlled atmosphere, and the subsequent laser bonding is conducted in a nitrogen or hydrogen atmosphere, creating an oxygen-free environment that protects the copper wire from oxidation while maintaining its excellent electrical and thermal conductivity properties
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 method produces wires with improved laser absorption and reduced residues, resulting in more reliable bonding without material splash, simplifying the production process and reducing contamination risks.
Implementation Method 1
roughened surfaces exhibit a higher absorption of electromagnetic radiation due to their larger surface area
Implementation Method 2
the energy required for bonding is transferred to the bonding wire using laser beams
Implementation Method 3
annealing the wire precursor provided with depressions to form the wire
Implementation Method 4
copper wires are susceptible to oxidation
Data Source
Figure 1~2
Figure 3~4a
Figure 4b~5
AI summary
The invention relates to a method for producing a wire, having at least the following steps: (i) providing a wire precursor; (ii) pressing depressions on the wire precursor and optionally molding the wire precursor in the process; and (iii) annealing the wire precursor provided with depressions in order to form the wire; wherein the wire has a content of at least 95 wt.% of copper based on the total weight of the wire. The invention additionally relates to a wire which can be obtained according to the aforementioned method and to the use of a roller in order to produce the wire and/or in order to set the roughness at at least one location of the wire.