Method for Forming Polyaniline Seed Layers for Metal Wiring Processes

Metal Wiring Process Replacing Electroless Plating Using Palladium Nanoparticle/Polyaniline Seed Layers

This technology forms a conductive polyaniline thin film on an insulating substrate, such as polyimide, via aqueous polymerization, and then creates a seed layer for electroplating by spray-coating a palladium nanoparticle catalyst layer on top. Metal wiring, such as copper, is then electroplated onto this metal catalyst/polyaniline seed layer.

Electroplating on the insulating material of a flexible printed circuit board requires a conductive seed layer. The electroless plating traditionally used for this purpose generates formaldehyde during the process, causing environmental issues. Furthermore, using only a metal seed layer has the limitation of insufficient adhesion strength between the insulating material and the copper conductor.

In this technology, the polyaniline thin film, which is doped simultaneously with oxidative polymerization, acts as an adhesive layer between the insulating substrate and the metal thin film. The palladium nanoparticles serve as growth nuclei, allowing electroplating to proceed smoothly even on high-resistance polymer surfaces. As a simple wet batch process, it is advantageous for utilizing existing equipment. It can be applied to flexible printed circuit boards for smartphones and tablets as well as semiconductor metallization processes, enabling the construction of formaldehyde-free, eco-friendly wiring lines while reducing conductor delamination defects.

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Key Features:

• A step of forming a polyaniline thin film on a substrate through simultaneous oxidative polymerization and doping by mixing aniline hydrochloride, an ammonium persulfate oxidizing agent, and a hydrochloric acid dopant
• A step of forming a metal catalyst layer by spray-coating palladium nanoparticles onto the polyaniline thin film using oleylamine as a dispersant
• A step of completing the metal catalyst/polyaniline seed layer by heat-treating in a furnace to remove the oleylamine dispersant
• A process of forming flexible printed circuit board wiring by electroplating a metal thin film, such as copper, onto the seed layer of a polyimide or polypyrrole substrate

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This invention was developed with support from the Ministry of Trade, Industry and Energy for the development of eco-friendly batch plating technology for 12-layer multi-flexible PCB wiring in wearable devices.

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