Abstract
Nickel (Ni) metallization of polyimide (PI) was performed using a solution-based process including imide-ring opening reactions, the implanting of Ni ions, the reduction of catalytic Ni nanoparticles, and the electroless deposition of a Ni film. The start-up imide-ring opening reaction plays a crucial role in activating inert PI for subsequent Ni implanting and deposition. A basic treatment of potassium hydroxide (KOH) is commonly used in the imide-ring opening reaction where a poly(amic acid) (PAA) layer forms on the PI surface. In this study, we report that the KOH concentration significantly affects the implanting, reduction, and deposition behavior of Ni. A uniform Ni layer can be grown on a PI film with full coverage through electroless deposition with a KOH concentration of 0.5 M and higher. However, excessive imide-ring opening reactions caused by 5 M KOH treatment resulted in the formation of a thick PAA layer embedded with an uneven distribution of Ni nanoparticles. This composite layer (PAA + Ni) causes wastage of the Ni catalyst and degradation of peel strength of the Ni layer on PI.
Highlights
Wearable and portable technologies have attracted considerable attention because multiple functions such as communication, internet, sensor, navigation, and media, can be integrated in a small and light-weight device [1,2,3,4,5,6,7,8,9]
Excessive imide-ring opening reactions caused by 5 M KOH treatment resulted in the formation of a thick poly(amic acid) (PAA) layer embedded with an uneven distribution of Ni nanoparticles
It was found that KOH concentration was crucial for metallization uniformity
Summary
Wearable and portable technologies have attracted considerable attention because multiple functions such as communication, internet, sensor, navigation, and media, can be integrated in a small and light-weight device [1,2,3,4,5,6,7,8,9]. Sputtering can produce a dense and uniform metallic layer with good adhesion on PI, deposition [6,13,24,25,26,27,28]. Sputtering can produce a dense and uniform metallic layer with good adhesion but the high-vacuum operational environment makes cost-down difficult to achieve. After forming a catalytic nanoparticle layer on the PI surface, a thin alternative catalyst [30,31]. The base treatment of KOH is a ring-opening reaction which can implant the K+ ions into the uppermost sublayer of PI to form a potassium salt poly(amic acid) (PAA) layer [1,4,8,10,32]. The effect of the layer plays an important role for the subsequent metallization process.
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