1. SYNTHESIS AND CHARACTERIZATION
OF ULTRA-THICK NEGATIVE PHOTOSENSITIVE POLYIMIDE
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

2. Contents Introduction Materials and Methods Results and Discussion
Conclusions

3. Introduction

4. Polyimides Polyimides are a polymer of imide monomers.
Figure 1 Structure of an imide group.
Polyimides are polymers formed by the condensation reactions
of dianhydrides and diamines.
Figure 2 Aromatic polyimides repeating unit.

5. 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 nm
and have relatively higher dielectric constants over 3.0.

6. synthesis of polyimides[[
synthesis of polyimides
Two-step method polymerization
via poly(amic acids)
One-step method polymerization
High-temperature solution polymerization
polyimides
Low-temperature solution polymerization

7. synthesis of polyimides[[
synthesis of polyimides
Two-step method polymerization via poly(amic acids)
polyimides
Figure 3 Reaction mechanism of imide formation.

8. Photosensitive Polyimides
Figure 4 Process simplification opportunity using photosensitive polyimide as compared with conventional nonphotosensitive polyimide.

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

10. Negative Photosensitive polyimide precursors
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

11. 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.

12. Materials and Methods

13. 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)
Materials
Dianhydride
3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)
Diamine
4,4′-Oxydianiline (ODA) Hexamethylenediamine (HMDA)

14. Materials Photosensitive precursor 2-hydroxyethyl methacrylate (HEMA)
Photosensitive initiator
Bis (2,4,6-trimethylbenzoyl) phenyl phosphine oxide (Irgacure-819)

15. Materials Solvents γ – butyrolactone N-methyl-2-pyrrolidinone (NMP)
Copper clad (size= 5x5 cm) was grateful provided by Mektec Manufacturing Corporation (Thailand) Ltd.

16. Preparation of the negative photosensitive poly (amic acid)
NMP solvent
BPDA:HMDA:ODA
1:0.3 :0.7 by mole ratio
PAA
Stirred 30 min
under Ar atmosphere
Irgacure-819
HEMA
Negative PAA
PAA
PAA

17. Scheme 1 Preparing negative photosensitive poly (amic acid)

18. Patterning of the negative photosensitive polyimidex
Patterning of the negative photosensitive polyimide
Negative PAA
Copper
dried at 55 oC for 2 h
NPSPI film
cured at 250 oC for 30 min
UV radiation for 200 s
Mask
developed by
γ – butyrolactone

19. Results and Discussion

20. Thickness of PI and NPSPI films Polymer Solution* (ml)
Table 1: Thickness of PI and NPSPI films
No.
Polymer Solution* (ml)
Film thickness after
cured 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

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

22. TGA curves of the NPSPI and PI film
Type
NPSPI PI
Td 5 % (°C)
281
269
Figure 8 TGA curves of the NPSPI and PI at the heating rate of 10°C/min.

23. The film thickness and the size opening of NPSPI films by Stylus profiler
3 mm
Photograph of
NPSPI films
Figure 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

24. Morphology of NPSPI films on copper foil
Figure 10 Morphology of NPSPI films on copper foil.

25. Conclusions

26. Conclusions
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 % which is acceptable.
The prepared negative photosensitive polyimide could have potential applications for patterned electronic and optoelectronic devices.

27. Acknowledgements
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.

28. Thank you for your attention