A Synthesis Approach of Cu Nanoparticles Using Polyimide As a Template and Their Application on a Printed Circuit Board

Abstract

Electroless deposition process has been commonly used for the metallization of through holes of a printed circuit board (PCB). It is well-known that Sn/Pd colloid is widely used as the catalyst for catalyzing Cu electroless deposition onto the sidewalls of the through holes, composted of glass fiber and epoxy resin. However, Pd is very expensive. In addition, if IC substrate is fabricated using a semi-additive process (SAP), the residual Pd catalysts on the resin surface of the IC substrate, which has catalyzed a layer of copper electroless film, have to be removed from the resin surface after copper electroplating to prevent short between two copper lines. The SAP cost is accordingly high. To overcome these issues, copper nanoparticles (CuNPs) were synthesized using a heterogeneous reaction rather than a homogeneous reaction. Polyimide (PI) film was employed as a template to store copper ions. The CuNPs were gradually formed after the Cu2+-doped PI was transferred into a solution, containing a reducing agent and a ligand. The CuNPs were characterized by UV-Vis, FE-SEM, HR-TEM, ESCA, FT-IR, Zeta potential and XRD. Their mean particle size was smaller than 10 nm and varied from 4 to 6 nm and has a strong Cu (111) orientation. Therefore, they were able to perform a high catalytic activity for Cu electroless deposition.