Vol. 53 No. 2

Material Science and Technology of Japan, 53㸦2016㸧61㹼6323NoteSurface Nano-Roughness Enhanced Adhesion Strength of Electroless
Nickel-Phosphorus on Silicon Nitride-Aluminum-Polyimide Mixed
SubstratesTomiyuki ARAKAWA1, Nobuaki WATANABE2, Tatsunosuke NAKADA2
and Ichiro KOIWA2,*
1

Institute of Science and Technology, Kanto Gakuin University, 1-50-1 Mutuurahigasi, Kanazawa-ku,
Yokohama 236-8501, Japan

2

College of Science and Engineering, Kanto Gakuin University, 1-50-1 Mutuurahigasi, Kanazawa-ku,
Yokohama 236-8501, Japan

Received Dec. 10, 2015; accepted for publication Jan. 22, 2016
Abstract
Strong adhesion strength of electroless Ni-P on mixed-substrates of silicon nitride, aluminum and polyimide isrequired for a wafer-level chip size package. In this paper, the relation between the adhesion strength of electroless Ni-P on
silicon nitride, aluminum and polyimide substrates and the nano-roughness of substrate surface was discussed. The fractal
dimension which reflected the behavior of nano-roughness of substrate surface was adapted. Consequently, silicon nitride
provided the largest fractal dimension and adhesion strength among substrate surfaces after pretreatment.
Keywords: Electroless nikel-phosphorus, Silicon nitride-aluminum-polyimide mixed substrate, Fractal dimension, Adhesion strength1.

Introduction

adhesion strength of electroless copper deposits was increased by

Smaller as well as higher performance devices are desirable

argon plasma-pretreated polyimide which was subjected tofor mobile and wearable electrical apparatus. High density

UV-induced surface graft copolymerization [3]. Li et.al. has been

packaging technology has been developed in order to be realized

reported that alkaline etching and nickel salt activation enhanced

those. A wafer-level chip size package (W-CSP) is a promising

the adhesion strength of electroless nickel deposits to polyimide

candidate for reducing device size. A metallization is carried out

for metallization [4]. On the other hand, it has been known that

onto mixed surface which were composed of passivation of

the adhesion stregnth is improved by the anchor effect. The

silicon nitride and polyimide, pads of aluminum in W-CSP fabanchor effect is possible to be affected by the surface roughness

process. In general, the metallization is performed by electrolessof substrate. The behavior of surface roughness is reflected bydeposition on mixed substrates because silicon nitride andthe fractal dimension [6].
In this paper, the adhesion strength of electroless Ni-P topolyimide are dielectrics. The adhesion strength of metallizationis required to be enough to metalize on silicon nitride, aluminumsiliconnitride-aluminum-polyimide

mixed

substrates

isand polyimide mixed substrates. We have studied the influence

discussed from the point of view of the surface nano-roughnessof complexing agents on adhesion strength of electroless Ni-Pof substrates based on the relation between adhesion strength anddeposits to silicon nitride-aluminum-polyimide mixed substrates

fractal deimension.

[5]. The pretreatment method of substrate surfaces has provided
tightadhesion

ofelectroless

Ni-P depositsto2.

siliconExperimental method

carbide/aluminum composites [1]. The surface modification ofThree kinds of samples, silicon nitride, aluminum andargon plasma-pretreated polyimide has promoted enhancement

polyimide films were prepared in order to compare the adhesionof adhesion strength of electroless copper deposits [2]. The

strength of electroless Ni-P on them. Silicon oxides with the*Corresponding author: koiwa@ koiwa@kanto-gakuin.ac.jp(61)