Copper Surface Treatment for Fine Wiring Adhesion
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Solution Overview
Problem
Existing copper surface treatment methods struggle to maintain high bonding strength and precision in fine wiring formation, especially for multi-level wiring boards with line/space widths of 15 µm or less, due to issues like halation on glossy copper surfaces, low adhesive force between copper and resist, and insufficient bonding with insulating resins, leading to short circuits and transmission losses.
Innovation Solution
A copper surface treatment method involving the formation of nobler metals like gold or silver on the copper surface, followed by oxidation with an alkaline solution to create fine copper oxide irregularities, and subsequent dissolution with an acidic solution to achieve dense and even metallic copper irregularities, enhanced by treatments with pyrazole or azole compounds and electroless plating to improve bonding strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the copper surface is left glossy, then the surface is smooth and easy to manufacture, but halation occurs during light exposure and adhesive force with resist is low
Solution Approach 1:
The copper surface is pre-treated with an alkaline solution containing an oxidizing agent before resist application to form fine irregularities. This preliminary oxidation creates a surface structure that prevents halation and improves resist adhesion, resolving the contradiction between manufacturing precision and ease of manufacture.
Solution Approach 2:
The surface properties of copper are changed by controlling the oxidation process parameters (alkaline solution concentration, temperature, time) to create fine irregularities with specific characteristics. This parameter control allows optimization of both resist pattern precision and surface treatment efficiency.
2Strength
If irregularities larger than 1 µm are formed on copper surface, then adhesive force with resist is improved, but short circuits and transmission losses occur
Solution Approach 1:
The oxidation process parameters are precisely controlled to generate irregularities within the 0.003-1 µm range. By adjusting alkaline solution concentration, temperature, and treatment time, the irregularity size is optimized to provide sufficient bonding strength while preventing short circuits and transmission losses.
Solution Approach 2:
Instead of mechanical roughening methods that create large irregularities, chemical oxidation is used to generate fine irregularities at the molecular level. This substitution allows precise control of irregularity size to achieve optimal bonding without compromising wiring reliability.
3Strength
If conventional oxidation methods are used, then copper oxide is formed, but irregularities are not fine enough and bonding strength is insufficient
Solution Approach 1:
The oxidation process is optimized by adjusting multiple parameters simultaneously: alkaline solution concentration (0.1-10% w/w), temperature (20-80°C), and treatment time (1-60 minutes). These parameter changes enable precise control of irregularity size and distribution, achieving both fine surface structure and strong bonding.
Solution Approach 2:
The treatment solution uses a composite approach combining alkaline agents (NaOH, KOH) with oxidizing agents (NaClO, NaClO2, H2O2) to create synergistic effects. This composite chemical system produces finer and more uniform irregularities compared to conventional single-agent oxidation methods.
4Strength
If the copper surface is treated to remove glossiness, then adhesive force is improved, but the surface becomes rough and wiring precision decreases
Solution Approach 1:
The oxidation treatment parameters are controlled to create fine irregularities (0.003-1 µm) that remove surface glossiness while maintaining overall surface smoothness. This precise parameter control ensures improved adhesive force without compromising wiring precision in fine wiring formation.
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
This method ensures reliable bonding between copper and resist or insulating resins without forming irregularities larger than 1 µm, improving the reliability of copper wiring boards and reducing transmission losses, while maintaining precision and preventing short circuits.
Implementation Method 1
forming copper oxide on the copper surface by oxidation with an alkaline solution containing an oxidizing agent
Implementation Method 2
dissolving the copper oxide so as to be removed by using an acidic solution or a copper complexing agent
Implementation Method 3
the treatment for forming a baser metal than copper onto the copper surface is performed by electroless plating
Data Source
Figure 1(a)~1(b)
Figure 2(a1)~2(c2)
Figure 3(a1)~3(c2)
AI summary
An object of the present invention is to provide a copper surface treatment method capable of keeping certainly a bonding strength between a copper surface and a resist, or between a copper surface and an insulating resin without forming irregularities having sizes of more than 1 µm on the copper surface, and a copper treated with the method. The surface treatment method, comprising: a first step of forming, on a copper surfaces, a nobler metal than the copper discretely; a second step, subsequent to the first step, of forming copper oxide on the copper surface by oxidation with an alkaline solution containing an oxidizing agent; and third step of dissolving the copper oxide so as to be removed, thereby forming irregularities on the copper surface.