Development of a novel adamantane
cross-linker
K. Tsubaki
Osaka Organic Chemical Industry LTD., Katayama-Cho, Kashiwara City, Osaka, Japan
Abstract-- Cross-linked polymers with multi-functional (meth)acrylate such as DPHA and TMP-3A show higher thermal andchemical stabilities as well as excellent mechanical strength. However, water absorption property and dielectric constant of theseconventional cross-linkers were far from satisfactory. We recently developed a novel adamantane cross-linker having low water
absorption property and low dielectric constant. We introduce characteristics of this adamantane cross-linker.
Fig. 2. Thermal gravimetric analysis of cross-linkers.

I. INTRODUCTION
The multi-functional (meth)acrylate is well known as
chemical and mechanical strength improve agent, so that
it is used in various applications. However, water
absorption property and dielectric constant were high inthe conventional multi-functional (meth)acrylate, and its
application was limited [1]. On the other hand, thecompound having adamantyl structure has high heatresistant, low water absorption property and low
dielectric constant [2]. We produce a lot of(meth)acrylates having adamantyl structure and provide
these materials for electronic materials application.
Recently,
wedeveloped new
multi-functional(meth)acrylate having adamantyl structure. In this paper,
we report the characteristics of these adamantane crosslinkers.

ADAMANTATE XA-202 (red line), DARTMA (blue line),
TCDDA (black line)

II. PREPARATION

III. EVALUATION AS CURED FILM

The chemical structure of adamantane cross-linkers(ADAMANTATE XA-202 and DARTMA) are shown inthe Fig.1. Those materials were synthesized fromADAMANTATE E-201.

First, photo or thermal curable formulations were
coated onto a glass substrate to target film thickness(10~15 um), then baked at 90
for 2 min on the hotplate. In the case of photo curable formulations, coatingfilms after baking were irradiated at 3,000 mJ/cm 2 withintensity of 300mW/cm 2 at 365 nm. In the case of thermal
curable formulation, coating film after baking was baked
at 150for 60 min.
Properties of cured films using different cross-linkers
are shown in Table 1.

Fig. 1. Chemical structures of adamantane cross-linker.

Table 1. Properties of photo or thermal cured films.
curetype

reactionrate

pencilhardnessheat
resistancewater absorption
rate

dielectric
constant

ADAMANTATE XA-202

photo54%

HB

298

4.6%

3.62

DARTMA

photo30%

HB

340

1.6%

3.37

DARTMAthermal

77%

H

315

0.1%

-TCDDA

photo87%

H

363

0.6%

3.45

cross-linker

As a result of thermal gravimetric analysis (Fig.2.),
ADAMANTATE XA-202 and DARTMA show low
volatility than that of Tricyclodecane dimethanol
diacrylate (TCDDA) which are widely used as low water
absorptivity cross-linker.

DPHA

photo52%4H360

1.7%

4.14

DPHA/DATRMA = 80%/20%

photo38%

4H363

1.1%-DPHA/DATRMA = 40%/60%

photo35%

2H357

0.6%

-Photo curable formulation: cross-linker / Omnirad 379EG / Toluene= 39% / 1% / 60%
Thermal curable formulation: cross-linker / Perbutyl_P / Toluene= 39% / 1% / 60%

The pencil hardness of ADAMANTATE XA-202,
DARTMA and TCDDA cured film is lower than that of
Dipentaerythritol hexa/pentaacrylate (DPHA). The lowpencil hardness of adamantane cross-linkers can be
explained by acryl equivalent weight.
The heat resistance that mean 5% mass reduction
temperature of ADAMANTATE XA-202 and DARTMA
is lower than that of general cross-linkers. The low heatresistance of adamantane cross-linkers is considered to be
due to low crosslinking density.
The water absorption rate (Fig.3.) was obtained bythermal gravimetric analysis of cured film which dippedin the water at 23for 24 hr. The water absorption rateof ADAMANTATE XA-202 cured film is higher those ofother cross-linkers. ADAMANTATE XA-202 has twohydroxyl groups. These hydroxyl groups negatively
effect the water absorption property. The waterabsorption rate of DARTMA thermal cured film is very
low, but that of DARTMA photo cured film isn t. The
difference is due to the reaction rate of acryl group. TheDARTMA photo cured film has improved the waterabsorption property by combining with DPHA. This
results indicate that crosslinking density positively effects
the water absorption property.
The dielectric constant of DARTMA cured film islower than that of other cross-linkers.

Item

Table 3. Standard process conditions
Process condition

Film thickness
Soft bake10 um
902 min.

Exposure

200 mJ/cm2 at I line 20 mW/cm 2Development

60 sec. / 2.38% TMAH aq.

Hard bake230

30 min.

Fig.4. shows the water absorption rate of negative toneacrylic resist film. The water absorption rate of PR-3 isvery low and PR-3 shows good insulation reliability.
Also PR-3 shows good patterning ability.
Fig. 4. Water absorption rate of negative tone acrylic resist film.

Fig. 3. Water absorption rate of cured film.
PR-1 (black line), PR-2 (green line), PR-3 (blue line), Temperature (redline)

V. CONCLUSIONSIn this study, a novel adamantane cross-linker wasdeveloped to improve water absorption property ofacrylic curing film. The water absorption rate ofDARTMA thermal cured film is lower than conventionalcross-linkers.
ADAMANTATE X202 (purple line), DARTMA photo (blue line),
DARTMA thermal (blue broken line), TCDDA (black line), DPHA(green line), DPHA/DARTMA(80/20) (yellow line),
DPHA/DARTMA(40/60) (light blue line), Temperature (red line)

The negative tone acrylic resist used DARTMA shows
good water absorption property and insulation reliability.
Also this resist shows good patterning ability and it isexpected to be used as an insulating coating material.

IV. EVALUATION AS PHOTO RESISTAs application of DARTMA, We evaluated negative
tone acrylic resists shown Table 2.
Table 2. Negative tone acrylic resist formulations
Sample
PR-1
PR-2
PR-3
Acryl photo polymer
DPHA
TCDDA
DARTMA
Epoxy resin
Silane coupling agent
Photo initiator

54%
32%

54%
16%
16%

10%
1%
3%

10%
1%
3%

54%
16%
16%
10%
1%
3%

Negative tone acrylic resists were evaluated by thestandard process conditions shown Table 3.

REFERENCES[1] Gijutsujouhoukyoukai LTD, first ed.,How to choose,
how to use functional monomer casebook , pp. 133-141,
July 2017 ( in Japanese).

[2] Gijutsujouhoukyoukai LTD, first ed.,How to choose,
how to use functional monomer casebook , pp. 247-257,
July 2017 ( in Japanese).