Silver Metallization of Polyimide Surfaces Using Environmentally Friendly Reducing Agents

Efficient and Adhesiveless Metallization of Flexible Polyimide by Functional Grafting of Carboxylic Acid Groups

“…19,37 The pH level of the reducing agent can also influence the morphology and distribution of the reduced metal nanoparticles in the modified PI film. 17 In an acid environment, the Ag + ions complexed with the carboxylate groups were reduced to the Ag nanoparticles by the reducing agent (ascorbic acid), and the carboxylate groups were converted to the carboxylic acid groups. The latter is the acid−base neutralization reaction, which drives ascorbic acid continuously diffuses into the hydrolyzed PI film and reduces the Ag + ions to form the Ag nanoparticles embedded in the PI film.…”

“…The pH level of the reducing agent can also influence the morphology and distribution of the reduced metal nanoparticles in the modified PI film . In an acid environment, the Ag + ions complexed with the carboxylate groups were reduced to the Ag nanoparticles by the reducing agent (ascorbic acid), and the carboxylate groups were converted to the carboxylic acid groups.…”

“…FPCB is based on a copper clad laminate (CCL), which is typically a trilayer structure; the bottom is a flexible polymeric substrate, the top is electrodeposited (or rolled annealed) Cu foil, and the middle is an epoxy adhesive responsible for the adhesion. To further downscale the packaging volume, development of the dual-layer “adhesiveless” laminate based on direct metallization on a polymeric substrate − or polymerization on metal foil − is imperative. The removal of the intermediate adhesive layer can also avoid the reliability problems caused by thermal instability and mechanical hole drilling of the adhesive layer.…”

“…Conventional surface functionalization methods include plasma treatment, − silanization, − and alkaline hydrolysis. − Alkaline hydrolysis has been investigated extensively due to the process simplicity and wide suitability for various metals. In the alkaline hydrolysis process, PI was immersed into a KOH or NaOH solution − during which the nucleophilic attack of hydroxyl ions (OH – ) on a carbonyl carbon of the imide ring occurs, followed by the cleavage of a C–N bond to form poly­(amic acid) (PAA). The cleavage of the imide ring simultaneously generates the hydrophilic carboxylate anions as the ion exchangeable sites for the incorporation of metallic ions.…”

“…Although the start-up imide ring cleavage reaction plays a crucial role in activating inert PI for subsequent deposition of the metal film, ,,, it has a fatal drawback that the mechanical property of PI deteriorates due to the formation of a PAA layer . A comprehensive review of previous reports indicates that the imide ring cleavage reaction was performed in a concentrated alkaline solution (5 M KOH) ,,,,, so as to induce the acuter nucleophilic attack of OH – on the imide ring to ensure the formation of abundant active sites for ion exchange. However, an excess of ring cleavage reaction results in the formation of a thicker PAA layer, which may raise the mechanical risks.…”