Noppamas Wutikunprapan, Supakanok Thongyai, Piyasan Praserthdam

Center of Excellence on Catalysis and Catalytic Reaction Engineering

Department of Chemical Engineering Faculty of Engineering,

Chulalongkorn University, Thailand 1

SYNTHESIS AND CHARACTERIZATION OF ULTRA-THICK NEGATIVE

PHOTOSENSITIVE POLYIMIDE

Contents

2

Introduction

Materials and Methods

Results and Discussion

Conclusions

Introduction

3

Polyimides

4

Polyimides are polymers formed by the condensation reactions of dianhydrides and diamines.

Polyimides are a polymer of imide monomers.

Figure 1 Structure of an imide group.

Figure 2 Aromatic polyimides repeating unit.

Properties of polyimides

Polyimides (PIs) are outstanding polymers, which used in many microelectronics and aerospace industry such as high temperature insulators,

dielectrics, coatings, adhesives and advanced composite matrices.

PIs possessing thermal stability, excellent chemical resistance, good electrical and mechanical properties.

PIs strongly absorb under visible light with wavelength range about 400-700 nm

and have relatively higher dielectric constants over 3.0.

5

[[synthesis of polyimides

6

Two-step method polymerization via poly(amic acids)

One-step method polymerization

High-temperature solution polymerization

polyimidespolyimidesLow-temperature solution polymerization

[[synthesis of polyimides

7Figure 3 Reaction mechanism of imide formation.

Two-step method polymerization via poly(amic acids) Two-step method polymerization via poly(amic acids)

C

C

O

O

O + H2NC

COOH

O

HN

C

C

O

O

N

-H2O

polyimides

Photosensitive Polyimides

8Figure 4 Process simplification opportunity using photosensitive polyimide as

compared with conventional nonphotosensitive polyimide.

Types of photosensitive polyimide

9Figure 5 The principle of positive and negative photosensitive polyimide processing.

Negative Photosensitive polyimide precursors

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• The polyimide precursor is a polymeric resin that can be crosslinked by initiation step of “free radical”

• Crosslinked polymer becomes insoluble.

Figure 6 The ring closure reaction

Objectives

In this study, synthesis of negative photosensitive polyimides are investigated in order to create cover film with the thickness approximately controlled at 12.5 micron then the size opening of

cover film, the correlation of opening area and mask size are determined.

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Materials and Methods

12

Materials

Dianhydride

3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) Diamine

4,4′-Oxydianiline (ODA) Hexamethylenediamine (HMDA) 13

Photosensitive precursor

2-hydroxyethyl methacrylate (HEMA) Photosensitive initiator

Bis (2,4,6-trimethylbenzoyl) phenyl phosphine oxide (Irgacure-819)

14

Materials

Solvents

γ – butyrolactone N-methyl-2-pyrrolidinone (NMP)

Copper clad (size= 5x5 cm) was grateful provided by Mektec Manufacturing Corporation (Thailand) Ltd.

15

Materials

PAA

Preparation of the negative photosensitive poly (amic acid)

Preparation of the negative photosensitive poly (amic acid)

PAA

NMP solvent

BPDA:HMDA:ODA 1:0.3 :0.7 by mole ratio

PAAStirred 30 min

under Ar atmosphere

Irgacure-819 HEMA

Stirred 30 min under Ar atmosphere

Negative PAA

16

17Scheme 1 Preparing negative photosensitive poly (amic acid)

x

Negative PAA

Copper

dried at 55 oC for 2 h

Copper

NPSPI film

cured at 250 oC for 30 min

Copper

UV radiation for 200 s

Copper

Mask

developed by γ – butyrolactone

Patterning of the negative photosensitive polyimidePatterning of the negative photosensitive polyimide

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Results and Discussion

19

20

Thickness of PI and NPSPI filmsThickness of PI and NPSPI films

No.Polymer Solution*

(ml)

Film thickness aftercured at 250 °C (µm)

PI NPSPI**

1 0.4 24.1 12.3

2 0.5 27.7 22.0

3 1.0 42.4 39.7

4 1.5 67.4 56.6

5 2.0 85.9 72.3

*Conc. of PI = 17.17% wt./vol. **Negative photosensitive polyimide

Table 1: Thickness of PI and NPSPI films

21Figure 7 FTIR spectrum of Polyimide (PI) film.

1778 cm-1 (C=O sym. str.)

1726 cm-1 (C=O asym. str.)

1380 cm-1 (C–N str.)

FTIR spectrum of Polyimide (PI) filmFTIR spectrum of Polyimide (PI) film

22Figure 8 TGA curves of the NPSPI and PI at the heating rate of 10°C/min.

TGA curves of the NPSPI and PI filmTGA curves of the NPSPI and PI film

Type NPSPI PI

Td 5 % (°C) 281 269

23Figure 9 The film thickness and the size opening of NPSPI films by Stylus profiler as the film thicknesses of (a) 19.6, (b) 25.3 and (c) 21.6 µm

The film thickness and the size opening of NPSPI films by Stylus profiler

The film thickness and the size opening of NPSPI films by Stylus profiler

(a) (b) (c)

3 mm

(a) (b) (c)

Photograph of NPSPI films

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Figure 10 Morphology of NPSPI films on copper foil.

Morphology of NPSPI films on copper foilMorphology of NPSPI films on copper foil

Conclusions

25

Conclusions

26

The negative photosensitive polyimides with the thickness approximately controlled at 12.5 micron were successfully

prepared.

The ratio size of opening is in the range of 0.8 – 0.82 or 80 - 82 % which is acceptable.

The prepared negative photosensitive polyimide could have potential applications for patterned electronic and optoelectronic

devices.

Acknowledgements

27

Sincere thanks to Mektec Manufacturing Corporation (Thailand) Ltd. For using analysis & characterize instruments and financial

support with student’s scholarship.

Sincere thanks to Ciba Specialty Chemical Thailand Inc. for supplied Irgacure-819.

Thank you for your attention

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