Study on the structure and adhesion of copper thin films on chemically modified polyimide surfaces - Polyimides and Other High Temperature Polymers - page 329

Study on the structure and adhesion of copper thin films
on chemically modified polyimide surfaces

LEE LEE LAU, YIN XIONG and LIANG HONG ∗
Department of Chemical and Environmental Engineering, National University of Singapore,
10 Kent Ridge Crescent, Singapore 119260

Abstract—Upilex-s [BPDA-PDA, poly(biphenyldianhydride-p-phenylenediamine)] and 6FDA-
ODA [4,4'-(hexafluoroisopropylidene)diphthalic anhydride-4,4'-oxydianiline] polyimide sheets
were subjected to wet treatment using ethylenediamine (EDA) and hydrazine as the base. The re-
sults of wet treatment were evaluated in terms of elemental analysis (N/C atomic ratio) obtained us-
ing XPS as well as surface morphologies determined using AFM and SEM. Furthermore, a copper
layer was deposited onto the modified surface via electroless plating. The adhesion strength between
the copper layer and the modified surfaces was assessed by the tape-peel test. A large adhesion en-
hancement was achieved when copper was plated onto the modified surfaces of PI sheets as com-
pared to the untreated samples.

Keywords : Polyimide; surface modification; wet treatment; adhesion; copper plating.

1. INTRODUCTION

Polyimides (PIs) have been widely used in microelectronic packaging due to their
low dielectric constant, good thermal and mechanical stability and excellent
chemical resistance, for example, its use as an insulator in the multi-chip module
(MCM) is being investigated [1-2]. However, the adhesion of the polyimide to
metals is normally rather poor, this is probably due to its rigid molecular structure
and the fact that low surface energy component (aromatic rings) overwhelms the
high surface energy component (polar groups) in the surface phase. The smooth
surface also contributes to the low adhesion property [3].
In the past decades, many surface treatment methods have been developed to
enhance the interfacial adhesion between metals or polymers and a polyimide
film. The aim of modification is to introduce polar functional groups as well as
micro-roughening to the polyimide surface. This can be done by employing either
the dry process, in which the surface is subjected to reactions with gaseous spe-
cies, such as plasma, particle beams, corona discharge, X-rays, ion beams or γ -