Photosensitive Polyimide Research Articles

New developments in intrinsic black photosensitive polyimide for advanced display applications

To meet the requirements of low power consumption, long endurance, and cost-efficiency for mobile phones, a polarizer-less technology (Pol-Less) OLED with a color-on-encapsulation (COE) structure has been proposed. In this groundbreaking technology, black photosensitive polyimide (PSPI) serves as the pixel definition layer (PDL) and plays a crucial role. However, the addition of inorganic pigments, such as carbon black, significantly compromises the dielectric insulation properties of the PDL. Therefore, exploring intrinsic black photosensitive polyimide with outstanding light shielding performance and high dielectric insulation properties has garnered increasing attention. In this study, a derivative of anthraquinone, namely 2,4,5,7-tetraamino-1,8-dihydroxyanthraquinone (4NADA) is incorporated into the photosensitive polyimide chains, successfully producing an intrinsic black photosensitive polyimide with broad absorption in the visible light range. Experimental results revealed that by copolymerizing 50 % moles of 4NADA in the diamines in the photosensitive polyamide acid ester, a black photosensitive polyimide with a high optical density (OD) of 0.89 and a relatively low dielectric constant of 3.6 at 1000 kHz was obtained. Furthermore.

Effect of hydrogen on the integration process of photosensitive polyimide and its feasibility in advanced packaging

To reduce the resistive-capacitive (RC) delay, low-k materials are employed in advanced packaging systems that cover the redistribution layers (RDL). Owing to its remarkable properties, photosensitive polyimide (PSPI) is one of the most widely used interlayer dielectric (ILD) materials. Industries usually employ the forming gas annealing (FGA) (5 % H2 / 95 % N2 at 350 °C) in processes which help to reduce the dangling bonds at interfaces of Si/SiO2. Considering this, we have studied the effect of FGA onto photopatterned PSPI films and compared it with nitrogen gas annealing. The imidization in films at different ambientes is confirmed by Fourier Transform Infrared Spectroscopy (FTIR). X-ray photoelectron spectroscopy (XPS), and Elemental Dispersive Spectroscopy (EDS) implied to study the compositional change in PSPI after different ambient annealing. Our study reveals that FGA causes more imidization, but it forms impurities in PSPI leading to reduction in its mechanical strength and causes carbon from PSPI to diffuse inside copper interconnects. We hope the proposed research will help to understand the adverse effect of FGA annealing on the PSPI. Interestingly, N2 gas annealing is more feasible for PSPI than that of FGA 350 °C.

A strategy to prepare high Tg and low CTE solder resist using alkali-soluble photosensitive polyimide

Photosensitive Solder resist (SR) materials require a high glass transition temperature (Tg > 170 °C) and a coefficient of thermal expansion matching that of copper (CTE≈17 ppm/°C) to meet the demands of manufacturing processes and application reliability. However, the commonly used epoxy resin in SR materials exhibits insufficient mechanical and thermal properties, failing to meet these requirements adequately. To address this issue, alkali-soluble photosensitive poly (amic ester) (PAE) materials were synthesized. By grafting a low-temperature curing accelerator, 6-([1,1′-biphenyl]–4-yl)–4-chloroquinoline (NQL), onto the hydroxyl groups of the PAE, the resultant grafted PAE resin was blended with an alkali-soluble photosensitive modified epoxy resin (APE) to enhance the mechanical and thermal properties of the SR composite. Research indicates that due to the low-temperature curing effect and electrostatic interactions of NQL, SR-2 (with a 10 % PAE addition) exhibits a Tg of 183 °C and a CTE of 16 ppm/°C, while SR-3 (with a 30 % PAE addition) achieves a Tg of 204 °C and a CTE of 20 ppm/°C. Furthermore, with the PAE addition of 5 %, the lithography quality of SR is enhanced, enabling SR-1 to achieve a pattern resolution of up to 40 μm. The modification method involving PSPI blending has been shown to enhance the thermal stability, dimensional stability, and lithographic performance of SR, indicating significant potential applications in solder resist materials.

Synthesis of Photosensitive Polyimides Incorporating Polydimethylsiloxane Segments and Studies on the Properties of their UV-Cured Films

Synthesis of Photosensitive Polyimides Incorporating Polydimethylsiloxane Segments and Studies on the Properties of their UV-Cured Films

Novel low‐temperature curable photosensitive polyimides with stable storage

AbstractIn this work, varieties of thermal base generators with nitrogen heterocyclic bases as curing catalysts were synthesized and further blended with photo‐crosslinking agents, and photoinitiators to achieve the research goal of the low‐temperature curable negative photosensitive polyimide (n‐LTPI) photoresist. Due to the addition of thermal base generators, the curing temperature was reduced to 200 °C. Adding 2% 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU) pyromellitic acid salt to the photoresist can completely iminate at 200 °C. Through field‐emission scanning electron microscope analysis, the film produced high‐quality photo‐patterns with line and via resolution of 2–5 μm at 5–6 μm film thickness. Compared with existing technologies, our article not only achieves low‐temperature curing of photoresists but also improved storage stability, which has great practical value in the field of advanced semiconductor packaging.

From Molecular Design to Practical Applications: Strategies for Enhancing the Optical and Thermal Performance of Polyimide Films.

Polyimide (PI) films are well recognized for their outstanding chemical resistance, radiation resistance, thermal properties, and mechanical strength, rendering them highly valuable in advanced fields such as aerospace, sophisticated electronic components, and semiconductors. However, improving their optical transparency while maintaining excellent thermal properties remains a significant challenge. This review systematically checks over recent advancements in enhancing the optical and thermal performance of PI films, focusing on various strategies through molecular design. These strategies include optimizing the main chain, side chain, non-coplanar structures, and endcap groups. Rigid and flexible structural characteristics in the proper combination can contribute to the balance thermal stability and optical transparency. Introducing fluorinated substituents and bulky side groups significantly reduces the formation of charge transfer complexes, enhancing both transparency and thermal properties. Non-coplanar structures, such as spiro and cardo configurations, further improve the optical properties while maintaining thermal stability. Future research trends include nanoparticle doping, intrinsic microporous PI polymers, photosensitive polyimides, machine learning-assisted molecular design, and metal coating techniques, which are expected to further enhance the comprehensive optical and thermal performance of PI films and expand their applications in flexible displays, solar cells, and high-performance electronic devices. Overall, systematic molecular design and optimization have significantly improved the optical and thermal performance of PI films, showing broad application prospects. This review aims to provide researchers with valuable references, stimulate more innovative research and applications, and promote the deep integration of PI films into modern technology and industry.

Development of a new type of highly effective etchant solution for glue residue in wafer-level packaging process

We synthesize an etchant solution designed to remove polydimethylsiloxane (PDMS) residues from semiconductor wafers during wafer-to-wafer processing in advanced semiconductor packaging (AVP). The etchant solution is produced by combining hexane, a nonpolar swelling solvent, with tetrabutylammonium fluoride (TBAF), a fluorine-based compound, to enhance PDMS etching. We evaluate the etching rate of PDMS using various solvent mixtures, including 1-vinyl-2-pyrrolidone, 1-methyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, and 1-octyl-2-pyrrolidone (NOP), with different concentrations of TBAF (1.0–5.0 wt%). Notably, NOP, which contains octyl groups, demonstrates the highest PDMS etching rate, particularly when combined with 70.0 wt% hexane. The optimized solution, F3-NOP/H70, achieves an etching rate of 85.7 μm/min. Further testing confirms that the F3-NOP/H70 solution effectively removes PDMS residues from wafer surfaces without damaging dielectric layers, such as the photosolder resist and photosensitive polyimide. These results indicate that the F3-NOP/H70 solution efficiently dissolves and removes PDMS residues and preserves the integrity of adjacent wafer components, making it a promising candidate for AVP applications. This study emphasizes the importance of selecting appropriate solvent systems for residue removal in semiconductor manufacturing and offers a practical solution to enhance device quality and reliability. This approach can potentially be applied at various stages of semiconductor processing, where residue management is essential.

A strategy for the preparation of low dielectric FGQD/PSPI composite films in wafer-level packaging

Advancement of wafer-level packaging (WLP) has heightened the requirements for photosensitive polyimide (PSPI) materials, where the low dielectric property is a key element to realize high frequency communication. Herein, a poly(amidate) (PAE) was prepared using Pyromellitic Dianhydride, 4,4’-diaminodiphenyl ether, and hydroxyethyl methacrylate as the photosensitive group. Specifically, the fluorinated graphene quantum dots (FGQD) was introduced into the PAE resin by in situ polymerization, and the prepared composite films of photosensitive polyimide-fluorinated graphene quantum dots (PSPI-FGQD) showed excellent dielectric constants and other comprehensive properties. Compared with pure PSPI, the dielectric constant of PSPI-FGQD decreases from 3.8 to 3.0 at 1 MHz; the tensile strength increases from 84.5 to 110.1 MPa, the elongation at break raises from 5.24 % to 17.3 %, and the Young's modulus increases from 2.68 GPa to 2.88 GPa. The glass transition temperature (Tg) is also increased to 420 °C with the introduction of FGQD. Apart of these, the fine patterning ability was observed for the FGQD/PSPI composite film, achieving a high photolithography resolution of 10 μm (L/S). To conclude, the preparation method of low dielectric FGQD/PSPI materials has promising potential applications in advanced packaging.

Development of Photosensitive Polyimides Compositions with Low Dielectric Property Corresponding to Semiconductor Back-End Processes

Development of Photosensitive Polyimides Compositions with Low Dielectric Property Corresponding to Semiconductor Back-End Processes

Rigid Photosensitive Polyimide Significantly Improves the Comprehensive Performance of UV-Curing Epoxy Acrylic Resins

Rigid Photosensitive Polyimide Significantly Improves the Comprehensive Performance of UV-Curing Epoxy Acrylic Resins

High-Porosity Sieve-Type Neural Electrodes for Motor Function Recovery and Nerve Signal Acquisition.

In this study, the effects of electrode porosity on nerve regeneration and functional recovery after sciatic nerve transection in rats was investigated. A sieve-type neural electrode with 70% porosity was designed and compared with an electrode with 30% porosity. Electrodes were fabricated from photosensitive polyimide and implanted into the transected sciatic nerves. Motor function recovery was evaluated using the Sciatic Function Index. The number of active channels and their signal quality were recorded and analyzed to assess the sensory neural signal acquisition. Electrical impedance spectroscopy was used to evaluate the electrode performance. The group implanted with the 70% porosity electrode demonstrated significantly enhanced nerve regeneration and motor function recovery, approaching control group levels by the fifth week. In contrast, the group with the 30% porosity electrode exhibited limited improvement. Immunohistochemical analysis confirmed extensive nerve fiber growth within the 70% porous structure. Moreover, the 70% porosity electrode consistently acquired neural signals from more channels compared to the 30% porosity electrode, demonstrating its superior performance in sensory signal detection. These findings emphasize the importance of optimizing electrode porosity in the development of advanced neural interfaces, with the potential to enhance clinical outcomes in peripheral nerve repair and neuroprosthetic applications.

High value-added use of waste photosensitive polyimide to develop low-shrinkage UV-curable inks for digital light projection technology

In the mass industrial production process of polyimide photoresists, waste generation is inevitable due to unqualified molecular weights, inappropriate ionic content of resins, or storage expiration. Consequently, the recycling and reuse of waste photosensitive polyimide (w-PSPI) is a growing concern in both scientific and industrial communities. In this work, w-PSPI was explored to prepare photocurable, fully crosslinked inks for digital light projection technology (DLP). For this purpose, suitable photoactive solvents and crosslinking agents were first screened to overcome the issue of large shrinkage caused by solvent volatilization. The formation of cross-linked network structures during DLP processing and subsequent imidization was also investigated. As a result, a polyimide DLP ink with minimum size shrinkage (less than 5 %) was proposed. For a given active solvent, the mechanical behavior and heat resistance of DLP-formed objects were significantly influenced by the ratio of short-chain and long-chain crosslinkers and the imidization temperature. By optimizing ink composition and imidization temperature, the DLP-formed objects showed high heat resistance (Td5 > 385 °C, Tg > 150 °C) and balanced mechanical properties of strength and toughness (Modulus ≥1 GPa, elongation at break >5 %). This w-PSPI ink has been successfully utilized to manufacture several complex 3D structures and vertical 3D microarrays with 100-µm on a limited-resolution DLP printer. This study not only points the direction for the high-added utilization of w-PSPI but also demonstrates the potential for expanding PSPI application from 2D lithography to 3D micro-manufacturing.

Synthesis and Characterization of Negative-Tone Photosensitive Polyimides with Low Coefficient of Thermal Expansion for Packaging Applications.

Negative-tone photosensitive polyimides (PSPIs) with a low coefficient of thermal expansion (CTE) were prepared by dissolving polyimide precursor-poly(amide ester) (PAE) resins, photoinitiators, photocrosslinkers and other additives in organic solvents. Using triamine as a monomer and dianhydride and diamine as polycondensates, tri-branched structure PAE resins with different molecular weights named PAE-1~5 were prepared. A series of corresponding PSPI films named PSPI-1~5 were prepared from PAE-1~5 resins with the same formulation, respectively. The PSPI-1~5 films prepared from resins of this structure have excellent mechanical, thermal and electrical properties after being thermally cured at 350 °C/2 h in nitrogen. The PSPI-1~5 films' coating solution also show good photolithographic performance and are able to obtain photolithographic patterns with a resolution of about 10 μm after homogenization, exposure and development. Among the PSPI-1~5 films, PSPI-2 has the most excellent lithographic properties with a weight average molecular weight (Mw) of 2.9 × 104 g/mol, a CTE of 41 ppk/°C, a glass transition temperature (Tg) of 343 °C and a 5% weight loss temperature (Td5) of 520 °C, making it suitable for industrial scale-up. The mechanical properties of elongation at breakage of 42.4%, tensile moduli of 3.4 GPa and tensile strength of 153.7 MPa were also measured.

The Impact of (Poly)glycerol in Developer on the Dissolution and Sensitivity of Positive-tone Photosensitive Polyimides

The Impact of (Poly)glycerol in Developer on the Dissolution and Sensitivity of Positive-tone Photosensitive Polyimides

Implementation of high‐performance, freestanding flexible film masks through photosensitive polyimide for arbitrary surface micropatterns creation

AbstractGiven the widespread presence of intricate surfaces, the development of electronics has generated a significant demand for surface patterning techniques capable of creating refined or novel patterns. Nevertheless, present surface patterning techniques suffer from complex processes, limited resolution, stringent conditions, and high manufacturing costs. Herein, we present a novel approach for arbitrary surface micropatterning using photosensitive polyimide (PSPI), enabling the in situ fabrication of electrodes without the need for a pattern‐transferring process. On this basis, we have implemented a high‐performance, freestanding flexible thin‐film mask with high optical transparency that facilitates precise alignment of microelectrode patterns with the target material. It also exhibits exceptional mechanical properties suitable for long‐term use and high‐temperature applications, with a notable glass transition temperature of up to 300°C. The fabricated masks with thicknesses of 5–20 μm are well‐suited for high‐resolution applications, including those requiring sub‐5 μm resolution. Furthermore, the creation of microelectrodes on a variety of surfaces utilizing the fabricated PSPI masks was successfully demonstrated. Our facile method provides a solid foundation for achieving efficient micropatterning for the fabrication of high‐performance flexible electronics on complex surfaces.

Photosensitive polyimide enabled simple, reversible and environmentally friendly selective metallization on diverse substrates

For breaking through the limitation of metal patterning in constructing conductive pathways of electronic devices, which is proposed to be an upgrade of traditional etching technique, a photo-reversible, transparent and soluble polyimide carrying spiropyran side chains is synthesized. The merocyanine isomers produced from the spiropyran moieties under digitalized ultraviolet irradiation bind the silver−histidine complexes in water, while the absorbed silver ions are in-situ reduced into metal silver seeds by the photo-generated radicals from histidine molecules, catalyzing copper deposition and yielding the desired copper patterns. Accordingly, the conventional time-consuming steps (like surface modification, immobilization of catalytic ions and (photo)chemical reduction) are simplified to a single one, and the environmentally unfriendly solvent and costly/toxic palladium reagent are excluded. The Cu patterns deposited on the polyimide show high resolution, electrical conductivity (1.785 × 10−6 Ω‧cm), adhesion strength (18.14 MPa) and fatigue resistance (> 2.6 million cycles of bending). Due to the absence of invasive surface treatments (e.g., surface hydrolysis and laser direct structuring), extremely low surface roughness of 7.83 nm is achieved. Besides, the developed strategy can be easily expanded to stretchable elastomer and other organic/inorganic substrates with irregular surfaces, showing promising application prospects. The solubility of the polyimide and ultraviolet/visible light triggered reversibility of the included spiropyran groups further enable repeated recycling, erasing and re-patterning.

Negative-tone Photo-definable Polyimide with High Thermal Stability and Thick Film Processability

High voltage power semiconductor requires higher polyimide insulation properties. We have designed a polyimide with high thermal stability, high light transparency and alkali dissolvable polyimide that is capable of passivating thick layer of polyimide with large topographys. A novel negavitve-tone photo-definable polyimide was formulated with cross linking reagent that can easily decompose during cure and a photo-initiator that initiates well during lithography. Our novel Negative photo sensitive polyimide, PSPI-1, has a patternable capability up to 16 mm thickness on silicon with 350 mj/cm2. PSPI-1 showed higher patternability than of the conventional polyimide. The cured film showed excellent properties as follows: 310C glass transition temperature (Tg), 500C 5% weight loss temperature, 40% elongation, no short observation during bias-HAST (130C. 96%, 100hr, 100V 15/30 mm line & space) and good adhesion to Si and Cu substrates. These results indicated a possibility for this novel PSPI-1 to be applicable for passivating power semiconductor.

Advancements in Synthesis Strategies and Optoelectronic Applications of Bio-Based Photosensitive Polyimides

With the rapid development of information, energy, and materials industries in China, the demand for high-performance polymers is gradually increasing. Photosensitive polyimide (PSPI) has emerged as an ideal choice for high-performance optoelectronic materials due to its outstanding thermal stability, mechanical strength, and low dielectric constant. In particular, bio-based photosensitive polyimide prepared from bio-based chemicals, as a green polymer material, not only reflects the advantages of environmental protection and resource efficiency but also contributes to carbon neutrality. However, how to improve the photolithography efficiency while maintaining the thermodynamic performance and environmental friendliness and how to balance the pros and cons of low-molecular-weight matrixes are still challenges in the research. This review systematically summarizes the synthesis and performance characteristics of photosensitive polyimides, bio-based polyimide, and bio-based photosensitive polyimides and further explores the future application prospects of bio-based polyimides in the field of high-performance optoelectronic materials.

Stress Analysis and Optimization on Saddle-shape Warpage by Direct Patterning of Stressed Film

As the stacks of the three-dimensional integrated circuits (3D-ICs) increases, the mechanical stress issues are challenging due to the increases in the asymmetry saddle-shape warpage. Various approaches to decrease asymmetric warpage were proposed by forming trenches of tens of micrometers or laser annealing treatment on the backside of wafer, but they had low throughput or lack of improved value. In this paper, we present a novel method to decrease the mechanical stress depending on the shape of the warpage by applying direct coating to the backside of wafer. The proposed method is to release the warpage by patterning a photo-sensitive polyimide (PSPI) with the inkjet-printing to adjust the surface characteristics and the steps, and then depositing tetraethylorthosilicate (TEOS) film with high compressive stress. We measured the changes in the asymmetric bow alongside the x-axis and y-axis before and after the process on the bare wafer by a finite element analysis using ABAQUS. Through the experiment and simulation, the x-y skew of about 230μm was obtained when 10μm-thick TEOS film was partially deposited on a 300mm wafer. In addition, by taking advantage of this process, the localized bow (warpage) can be released according to the changes in the thickness and area of the TEOS film. These results provide an effective guideline to solve unusual warpage caused by stacking process and can be applied to 3D integration in advanced packaging.

Next Level of 1/1 μm Line and Space Copper Redistribution Layer Fabrication with Organic Dielectric Materials

An electrical reliability of fine copper redistribution layer (RDL) with 1/1 μm line and space fabricated by using positive photosensitive polyimide (PSPI) has been demonstrated. The polyimide containing flexible molecular units in PSPI was introduced, in assumption to increase the entanglement of each polymer chain with a design concept of polymer backbone to enhance mechanical and thermal reliability. To conduct a series of tests, test vehicles with semi-additive copper RDL with 1/1 μm line and space were fabricated with Toray’s PSPI for electrical reliability test. Through a series of electrical reliability tests utilizing our test vehicles, PSPI out-performed the phenol-based resin, which has been proven to have excellent mechanical and thermal stabilities when compared with other resins. 1/1 μm line and space electrodes after electrical reliability tests were also observed and cross-sectioned. The observation of electrodes clearly showed oxidation-reduction of the electrodes on anode and cathode, respectively. On the cathode, copper particles of several nm in diameter were formed on the PI film surrounding the copper wiring. On the anode, copper oxide layers of about 100 nm thickness were observed on the copper wiring surface, which turned out to be Cu2O when analyzed with Electron Energy-Loss Spectroscopy (EELS) measurement.