Chemistry Reference
In-Depth Information
2. EXPERIMENTAL
2.1. Synthesis of 6FDA-ODA film
The 6FDA-ODA
PI was synthesized via a two-step method: First, dried 4-4'-
oxydianiline powder (>99%, Aldrich) was dissolved in freshly distilled NMP (N-
methyl-2-pyrrolidinone) in a round-bottom flask under a nitrogen atmosphere at
room temperature. After the diamine was totally dissolved, an equimolar amount
of 4,4'-(hexafluoroisopropylidene)-diphthalic anhydride was added to the solution
with stirring to obtain a viscous poly(amic acid) (PAA) after eight hours of reac-
tion. The PAA solution was then spread on a Petri dish and the PAA was imidized
by heating in a forced-air oven at 100
o
C, 200
o
C and 300
o
C for one hour each with
a ramping rate of 2.0
o
C/min. The imidization extent of the PAA of 6FDA-ODA at
the three temperature points was characterized by FT-IR spectroscopy. The IR
peak at 1776 cm
-1
(the stretching vibration frequency of carbonyl group of imide)
was used as the main identification for the formation of the imide ring.
2.2. Samples preparation
Upilex-S
sheet
(BPDA-PDA, thickness = 50
m, obtained from UBE Industries,
Tokyo, Japan), EDA (99.5%, Aldrich), hydrazine hydrate (55%, Aldrich) and 2-
propanol (99%, Fisher Scientific) were used as received. The 6FDA-ODA PI
sheet was synthesized as mentioned before. The PI sheets were cut into small
pieces (about 2 cm
µ
2 cm) and washed in 2-propanol under ultrasonication for 15
min at room temperature, followed by rinsing with DI water and drying in air.
The purified PI pieces were soaked in an aqueous solution of either EDA or hy-
drazine at a given temperature for a certain period of time. The treated PI pieces
were washed successively with DI water and 2-propanol. Finally, the samples
were dried under vacuum for 12 hours at room temperature.
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2.3. Electroless copper plating and tape-peel test
The modified PI sheets were immersed in SnCl
2
-HCl
solution for 10 minutes and
then in DI water for 2 minutes. The PI sheet was then immersed in PdCl
2
solution
for another 10 minutes and washed finally in DI water for 2 minutes. After this
two-step pretreatment, metallic Pd colloidal particles were embedded into the sur-
face of PI sheet as the initiation sites for electroless copper deposition [13]. A
home-made electroless plating bath was prepared using the composition shown in
Table 1. Electroless copper plating was carried out at room temperature for 4
minutes and a copper layer with thickness of about 0.3
m was obtained accord-
ing to the SEM image. Extended plating will cause delamination of copper film;
this phenomenon has been studied recently by Choi et al. [14]. The plated PI
sheets were washed with DI water and dried in vacuum before characterization
and testing. The tape-peel test was conducted on a rectangular area (1
µ
3 cm) of
Cu layer on a PI sheet. The examined surface was carefully cleaned and then
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