Delivered by Ingenta to: Sung Kyun Kwan University IP : 115.145.209.71 Fri, 15 Jul 2011 04:44:39 RESEARCH ARTICLE Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 11, 5328–5333, 2011 Polyimide Surface Modification by Using Microwave Plasma for Adhesion Enhancement of Cu Electroless Plating Sang-Jin Cho, Trieu Nguyen, and Jin-Hyo Boo ∗ Department of Chemistry and Institute of Basic Science, SungKyunKwan University, Suwon 440-746, Republic of Korea Microwave (MW) plasma was applied to the surface of polyimide (PI) films as a treatment to enhance the adhesion between copper deposition layer and PI surface for electroless plating. The influences of nitrogen MW plasma treatment on chemical composition of the PI surface were investigated by using X-Ray photoelectron spectroscopy (XPS). The wettability was also investigated by water contact angle measurement. The surface morphologies of PI films before and after treatment were characterized with atomic force microscopy (AFM). The contact angle results show that was dra- matically decreased to 16.1  at the optimal treatment condition from 72.1  (untreated PI). However, the root mean square (RMS) roughness of treated PI film was almost unchanged. The AFM rough- ness was stayed from 1.0 to 1.2 with/without plasma treatment. XPS data show a nitrogen increase when PI films exposed to N 2 MW plasma. Electroless copper depositions were carried out with the free-formaldehyde method using glyoxylic acid as the reducing reagent and mixture palladium chlo- ride, tin chloride as activation solution. Adhesion property between polyimide surface and copper layer was investigated by tape test. Keywords: Polyimide, Adhesion, Copper Electroless Plating, Microwave Plasma, Surface Modification. 1. INTRODUCTION A PCB is the platform upon which electronic compo- nents such as integrated circuit chips and capacitors are mounted. It can be classified into rigid and flexible types. A flexible printed circuit board (FPCB) has many advan- tages compared to rigid boards because of their flexibility, especially in applications demanding more integrated elec- tronic devices. FPCB, which is used for slide type cellular phones, consists of flexible copper clad laminate (FCCL) and cover layer. Electric signals are conveyed via FCCL of FPCB between keypad and display panel. Polyimide (PI) films coated copper is used as FCCL in electronic indus- try. However, in spite of the extensive usage as well as the detailed characterization of the PIs, applications of the materials are limited by their hydrophobic surfaces, which result in poor wettability and adhesion. The adhesion of a metal to the PI film is generally poor, unless the PI surface is pretreated prior to metallization. Pretreatment of polymers with the purpose to change adhesion properties can be classified in two main meth- ods: chemical surface modifications and physical surface ∗ Author to whom correspondence should be addressed. modifications. Wet chemical processes are highly efficient but result in the disadvantage of a very strong substrate roughening. Among those modification methods, plasma and ion- beam treatments are being used to an increasing extent. The effects caused on the polymer surface by these tech- niques are the incorporation of functional groups, changes in the surface morphology, and alteration in the chain structure. Most previous plasma works on polyimide or other polymers focused on radio frequency (RF) plasma treatment. 1–3 While RF plasmas are currently used as the standard production for polymer modification; interest in microwave (MW) plasma has multiplied in the last few years. Characterized by their high density of active parti- cles are capable for etching the same material at the rate at least ten times greater than RF plasmas because of high ion density by MW plasma. 4 In this work, MW plasma was applied to the surface of polyimide (PI) films as a treatment to enhance the adhe- sion of electroless copper deposition layers. The influ- ences of nitrogen MW plasma treatment on characteristics of electroless copper coatings as well as on the chemi- cal composition of the PI film surface were investigated at 5328 J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 6 1533-4880/2011/11/5328/006 doi:10.1166/jnn.2011.3793