Photosensitive Polyimide Research Articles

Investigation of Photosensitive Polyimide With Low Coefficient of Thermal Expansion and Excellent Adhesion Strength for Advanced Packaging Applications

Investigation of Photosensitive Polyimide With Low Coefficient of Thermal Expansion and Excellent Adhesion Strength for Advanced Packaging Applications

Tribological and AO irradiation resistant properties of 3D printing polyimide-POSS composites

To address the requirements of polyimide (PI) parts in the harsh Low Earth Orbit (LEO), a 3D printable PI composite with superior tribological and atomic oxygen (AO) irradiation resistant properties was proposed by employing methacryloxypropyl polyhedral oligomeric silsesquioxane (MPA-POSS) as a crosslinking agent in the photosensitive PI inks to obtain POSS-contained PI composite (PI-POSS composite). The resultant PI-POSS exhibits unique comprehensive performance including excellent AO irradiation resistance of an erosion yield of 2.86 × 10−24 cm3/atom, 50 % lower than that of PI without POSS, and anti-wear and friction reducing properties with a coefficient of friction of 0.1 and a wear rate of 4.4 × 10−6 mm3/N∙m. Importantly, the PI-POSS inks have excellent VP 3D printability, enabling the creation of complex, AO irradiation resistant, self-lubricating PI-POSS parts. These findings highlights the significant potential of such PI-POSS composite in aerospace applications within LEO.

Fast and scalable production of crosslinked polyimide aerogel fibers for ultrathin thermoregulating clothes

Polyimide aerogel fibers hold promise for intelligent thermal management fabrics, but their scalable production faces challenges due to the sluggish gelation kinetics and the weak backbone strength. Herein, a strategy is developed for fast and scalable fabrication of crosslinked polyimide (CPI) aerogel fibers by wet-spinning and ambient pressure drying via UV-enhanced dynamic gelation strategy. This strategy enables fast sol-gel transition of photosensitive polyimide, resulting in a strongly-crosslinked gel skeleton that effectively maintains the fiber shape and porous nanostructure. Continuous production of CPI aerogel fibers (length of hundreds of meters) with high specific modulus (390.9 kN m kg−1) can be achieved within 7 h, more efficiently than previous methods (>48 h). Moreover, the CPI aerogel fabric demonstrates almost the same thermal insulating performance as down, but is about 1/8 the thickness of down. The strategy opens a promisingly wide-space for fast and scalable fabrication of ultrathin fabrics for personal thermal management.

Recent Study Advances in Flexible Sensors Based on Polyimides.

With the demand for healthy life and the great advancement of flexible electronics, flexible sensors are playing an irreplaceably important role in healthcare monitoring, wearable devices, clinic treatment, and so on. In particular, the design and application of polyimide (PI)-based sensors are emerging swiftly. However, the tremendous potential of PI in sensors is not deeply understood. This review focuses on recent studies in advanced applications of PI in flexible sensors, including PI nanofibers prepared by electrospinning as flexible substrates, PI aerogels as friction layers in triboelectric nanogenerator (TENG), PI films as sensitive layers based on fiber Bragg grating (FBG) in relative humidity (RH) sensors, photosensitive PI (PSPI) as sacrificial layers, and more. The simple laser-induced graphene (LIG) technique is also introduced in the application of PI graphitization to graphene. Finally, the prospect of PIs in the field of electronics is proposed in the review.

A strategy to prepare low-temperature curable photosensitive polyimide with good comprehensive performance

Low-temperature curable photosensitive polyimide (PSPI) materials have attracted widespread attention in advanced packaging, serving as key insulating dielectric materials in redistribution layer (RDL) to avoid wafer warpage. Considering PSPI and copper together formed the core RDL part, the adhesion between PI and copper need to be concerned to realize high reliability. However, the exploration of novel diamines with desirable characteristics such as low temperature curing ability, improved adhesion and excellent lithography properties was limited. We designed a new diamine with fluorine-containing pyridine side group named PyFNH2, which facilitated preparation of low-temperature curable polyimide (at 200 °C) with remarkable degree of imidization (≥95.9 %). Secondly, the coordination interaction between pyridine side group and copper enhanced adhesion strength. Thirdly, the PI films cured at 200 °C exhibited favorable dielectric properties compared to control films without PyFNH2, because of the introduction of electronegative fluorine atoms and rigid side groups. Apart of these, the PI films possessed fairly good thermal and mechanical properties. Significantly, negative-tone PSPI employing the precursor poly (amic ester) with PyFNH2 was successfully prepared and cured at 200 °C, enabling precise lithography patterns with line resolutions down to 3 µm. Our findings highlight promising application potential of PyFNH2 in photolithography technology, offering a feasible strategy for structure designs of low-temperature curable diamine.

Synthesis of poly (amic ester) with controlled molecular weight for photosensitive polyimide in advanced package

Photosensitive polyimide (PSPI) with excellent lithography patterning and superior comprehensive properties have emerged as a very promising material for the advanced electronic package in IC field. Thereinto, poly (amic ester) (PAE) with highly sensitive groups and suitable molecular weight becomes the most important component in PSPI. Herein, a series of PAEs are synthesized by 4,4-oxydiphthalic anhydride, 4,4′-oxydianiline, and 2-hydroxyethyl methacrylate. The molecular weight of PAE was carefully controlled by using phthalic anhydride as the end-capping agent ranging from 9 000–20 000 g/mol. With the cooperation of photoinitiator and crosslinker, high-performance PSPIs were obtained. The results showed that the PAE with a molecular weight of 15 000 g/mol showed the best performance of lithography with resolution of 10 µm. The further increase of the molecular weight resulted the residues after developing, while lower molecular weight exhibited partially imidization during the pre-baking process, leading to a decrease in the solubility of PAE, as well. Additionally, as-prepared PSPIs also performed excellent thermal, mechanical, and dielectric properties, showing tensile strength of 120 MPa, elongation at break of 8%, glass transition temperature and the temperature of 5% weight loss of 260 °C and 430 °C, respectively. All these results exhibit a great application potential for high performance advanced packaging.

Thermal, Mechanical, and Electrical Stability of Cu Films in an Integration Process with Photosensitive Polyimide (PSPI) Films.

Photosensitive polyimides (PSPIs) have been widely developed in microelectronics, which is due to their excellent thermal properties and reasonable dielectric properties and can be directly patterned to simplify the processing steps. In this study, 3 μm~7 μm thick PSPI films were deposited on different substrates, including Si, 50 nm SiN, 50 nm SiO2, 100 nm Cu, and 100 nm Al, for the optimization of the process of integration with Cu films. In situ temperature-dependent resistance measurements were conducted by using a four-point probe system to study the changes in resistance of the 70 nm thick Cu films on different dielectrics with thick diffusion films of 30 nm Mn, Co, and W films in a N2 ambient. The lowest possible change in thickness due to annealing at the higher temperature ranges of 325 °C to 375 °C is displayed, which suggests the high stability of PSPI. The PSPI films show good adhesion with each Cu diffusion barrier up to 350 °C, and we believe that this will be helpful for new packaging applications, such as a 3D IC with a Cu interconnect.

Additive manufacturing patterned self-lubricating polyimide surfaces

Surface patterning has been widely utilized in structure enhancement, bionics, and surface lubrication. Drawing inspiration from the layer-by-layer forming principle of additive manufacturing and the Yin-Yang theory of traditional Chinese culture, we herein tailor patterned surfaces with various stripes of width using photosensitive polyimide and photosensitive polyimide-polytetrafluoroethylene composites that exhibit tough and lubricated properties by changing inks. To further optimize the self-lubricating surfaces, we present an accurate screening of the tribological data using machine learning (ML) and the optimized surfaces demonstrated the exceptional comprehensive properties. The combination of ML design and vat photopolymerization 3D printing is believed to enhance toughness and lubrication of surfaces, has the potential to the applications of the mechanical engineering, space equipment, and automobile manufacturing.

Quaternary copolymerized polyimides and negative photosensitive polyimides: preparation and properties

Photosensitive polyimide (PSPI) have been developed base on polyimide (PI). PSPI can be used as insulating and protective materials in the microelectronics industry due to the excellent insulating properties, thermal stability, and chemical stability. In this work, we designed a synthetic method to improve the regularity of the polymer chain segment sequence. Quaternary block copolymerized precursors were prepared using condensation polymerization of poly (acid amid). A photosensitive poly (acid amid) salts (co-PAS) was also synthesized to produce patterns with photochemical reaction. After imidization, the resolution of copolymerized PSPI (co-PSPI) pattern was in the range of 16 μm–110 μm. Partial photoreactive cross-linking structure was maintained to improve the thermal stability of co-PSPI. The co-PSPI exhibited higher glass transition temperatures (327.0°C–358.8°C) than copolymerized PI (307.4°C–332.9°C). This work provides the study on the synthesis and properties of quaternary copolymerized PI and PSPI.

A robust lateral shift free (LSF) electrothermal micromirror with flexible multimorph beams

Electrothermal bimorph-based scanning micromirrors typically employ standard silicon dioxide (SiO2) as the electrothermal isolation material. However, due to the brittle nature of SiO2, such micromirrors may be incapable to survive even slight collisions, which greatly limits their application range. To improve the robustness of electrothermal micromirrors, a polymer material is incorporated and partially replaces SiO2 as the electrothermal isolation and anchor material. In particular, photosensitive polyimide (PSPI) is used, which also simplifies the fabrication process. Here, PSPI-based electrothermal micromirrors have been designed, fabricated, and tested. The PSPI-type micromirrors achieved an optical scan angle of ±19.6° and a vertical displacement of 370 μm at only 4 Vdc. With a mirror aperture size of 1 mm × 1 mm, the PSPI-type micromirrors survived over 200 g accelerations from either vertical or lateral directions in impact experiments. In the drop test, the PSPI-type micromirrors survived falls to a hard floor from heights up to 21 cm. In the standard frequency sweeping vibration test, the PSPI-type micromirrors survived 21 g and 29 g acceleration in the vertical and lateral vibrations, respectively. In all these tests, the PSPI-type micromirrors demonstrated at least 4 times better robustness than SiO2-type micromirrors fabricated in the same batch.

3D Printing by Two‐Photon Polymerization of Polyimide Objects and Demonstration of a 3D‐printed Micro‐Hotplate

AbstractPolyimides are polymeric materials with outstanding thermal, chemical, and mechanical properties. For this reason, they find applications in several engineering sectors, including aerospace, microsystems, and biomedical applications. For realizing 3D structures made of polyimides, 3D printing is an attractive technique because it overcomes the limitations of polyimide processing using conventional manufacturing techniques such as molding and subtractive manufacturing. However, current polyimide 3D printing approaches are limited to realizing objects with the smallest dimensions of the order of a few hundred micrometers. 3D printing of polyimide objects featuring sub‐micrometer resolution using two‐photon polymerization by direct laser writing is demonstrated here. A negative photosensitive polyimide is applied that is widely used in microsystems applications. To demonstrate the utility of this polyimide 3D printing approach and the compatibility of the 3D objects with operation at elevated temperatures, a micro‐hotplate is 3D printed and characterized at operating temperatures of above 300 °C.

Positive-tone chemically amplified photosensitive polyimides with controllable taper angles

Current methods for tuning the taper angle of photosensitive polyimide (PSPI) often require additional equipment or materials, and has limited achievable angle tuning range while maintaining resolution. To overcome these limitations, a positive tone chemically amplified photosensitive polyimide (p-CA-PSPI) was prepared from tert-butylcarbonate-protected polyimide (t-Boc-PI), photoacid generator (PAG), other additives, and solvent. By optimizing the protection ratios of t-Boc-PI resins, the p-CA-PSPI achieved a high film retention rate and wide processing window. The photo-patterning conditions were able to manipulate the sidewall profile and taper angle within the range of 11–53°, maintaining a resolution of 3 μm for patterns with taper angles higher than 28° at 1.5 μm film thickness, by controlling the acid diffusion. The thermally cured polyimide films demonstrated excellent mechanical properties, including a tensile strength of 95.7 MPa, tensile modulus of 2.9 GPa, and elongation at breakage of 24.2%, high thermal stability with a glass transition temperature of 343 °C, decomposition temperature of 409 °C, and good chemical resistance. This novel taper angle tuning method has the potential to optimize the internal stress of semiconductor devices and advance the development of display devices, MEMs, and multifunctional electronics that require a single package containing multiple or unique taper profiles.

Investigating the structure–sensitivity relationship of photosensitive polyimide formulated by using a photobase generator

AbstractPhotosensitive polyimides (PSPIs) have been widely used in the buffer coating layer and insulation layer due to their excellent thermal and mechanical stability. In this work, a series of negative‐type PSPIs based on poly(amic acid) (PAA) and a photobase generator (PBG) have been developed. Two diamines of 4,4′‐oxydianiline (ODA), 3,3′‐diaminodiphenyl sulfone (SDA), and four dianhydrides of pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and cyclobutene‐1,2,3,4‐tetracarboxylic dianhydride (CBDA) are copolymerized to PAA through polyaddition, and the PAA is further thermally imidized to polyimide (PI). Through scrutinizing the structure–sensitivity relationship of these PIs, we find that the rigidity and transparency of the PAA/PI backbone play an important role in the sensitivity and contrast of PSPI. Accordingly, PSPI (SDA‐ODPA), possessing high optical transparency and a low rigidity represented by the low glass transition point, is capable of providing good photosensitivity of 30 mJ/cm2, a high contrast of 2.46, and an excellent pattern resolution of 4 μm after optimizing the prebaking (100°C for 5 min), exposure dose (380 mJ/cm2), post‐exposure baking (130°C for 7 min), and development parameters. This work provides the concept of structural design for negative‐type PSPI in the microelectronic application.

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Negative-tone photosensitive polyimide with high transparency

Negative-tone photosensitive polyimides (n-PSPI) with high transparency at visible wavelength region (400–700 nm) were prepared by dissolving photosensitive polyimide precursor -poly(amide ester)(PAE) resins, photoinitiator, photocrosslinker and other additives in organic solvents. The PAE resins were synthesized by polycondensation of a fluorinated aromatic diamine with an aromatic diester dichloride or its mixture. The n-PSPI coating solutions showed good photolithographic performance with resolution of 8 µm (via) and 7 µm (line) at 5 µm of the thermally cured film thickness. After thermally cured at 350 °C/1h, the typical PSPI film exhibited excellent thermal properties with Tg of 344 °C and Td5 of 525 °C, respectively. The mechanical properties with elongation at breakage of as high as 42.2% and tensile strength of 133.7 MPa were also measured. Additionally, the thermally cured PSPI films exhibited excellent transparency with UV cuttoff wavelength of 362 nm, transmittance of 90.5% at 450 nm, and 95.5% at 550 nm, as well as yellowness indices of less than 6.55. Furthermore, theoretical simulations were used to prove that trifluoromethyl group in the backbone structure of PSPI precursor resin can effectively improve the transparency of PSPI films.

Low-Temperature Curable Negative-Tone Photosensitive Polyimides: Structure and Properties.

Low-temperature curable negative-tone photosensitive polyimide (n-LTPI) viscous solutions were prepared by dissolving photo-crosslinkable poly (amic ester) (pc-PAE) resin, photophotocrosslinker, photoinitiator, and the heteroaromatic base as curing catalysts, and other additives in organic solvents. Among them, the pc-PAE resin was synthesized by polycondensation of aromatic diacid chloride and diester of 2-ethoxymathacrylate, aromatic diamines in aprotic solvents. After being spun-coated on a silicon wafer surface, soft-baked, exposed to UV light, and developed, the n-LTPI with 2% of imidazole (IMZ) as a curing catalyst produced high-quality photo-patterns with line via resolution of 5 μm at 5 μm film thickness. The photo-patterned polymer films thermally cured at 230 °C/2 h in nitrogen showed 100% of the imidization degree (ID) determined by in situ FT-IR spectroscopy. The thermally cured polymer films exhibited great combined mechanical and thermal properties, including mechanical properties with tensile strength of as high as 189.0 MPa, tensile modulus of 3.7 GP, and elongation at breakage of 59.2%, as well as glass transition temperature of 282.0 °C, showing great potential in advanced microelectronic packaging applications.

A water-borne photo-sensitive polyimide precursor for an eco-friendly process of preparing organic thin film transistors

A water-borne photo-sensitive poly(amic acid) salt for the micropatterned polyimide layer of a microelectronic device.

Aminoquinoline-functionalized fluorographene quantum dots for low-temperature curable and low-dielectric photosensitive polyimide nanocomposites

Photosensitive polyimide (PSPI) is widely used in the electronic packaging of integrated circuits (IC), organic light-emitting diodes (OLED), and optoelectronic devices. However, low-temperature curable and low-dielectric PSPI is currently required to meet new applications in electronic packaging. Herein, a multifunctional aminoquinoline-functionalized fluorographene quantum dots (QL-FGQDs) nanofiller is carefully designed to achieve these goals. The results demonstrated that the in-situ polymerized QL-FGQDs/PI nanocomposites cured at 200 °C exhibit a low dielectric constant (Dk) of 2.65@1 MHz and a dissipation factor (Df) of 0.009@1 MHz. In addition, the nanocomposites also have excellent optical, mechanical, and thermal properties (the transmittance at 550 nm is above 90%, Young's modulus is 2.95 GPa, and T5% can achieve as high as 517.2 °C), which are better than those of pure PI cured at 300 °C. Furthermore, QL-FGQDs are demonstrated to be applied as a nanofiller for PSPI with a high resolution of 3 μm under an exposure light of 365 nm. Therefore, QL-FGQDs nanofiller and PI nanocomposites exhibit excellent application potential in next-generation electronic packaging.

Alicyclic Dianhydrides and Polyimides Containing Double-Bond Bridged Cyclohexanes and Investigations on Their Retro Diels–Alder Reaction

In this study, two alicyclic dianhydrides, bicyclo[2.2.2]oct-7-ene-2-exo,3-exo,5-exo,6-exo,7-methyltetracarboxylic-2,3:5,6-dianhydride (MBTA) and bicyclo[2.2.2]oct-7-ene-2-exo,3-exo,5-exo,6-exo,7,8-dimethyltetracarboxylic-2,3:5,6-dianhydride (DMBTA), containing methyl substituents on the double-bond bridged cyclohexane structures were successfully synthesized by Diels–Alder reaction. The chemical structures of these dianhydrides with exo-exo configuration were fully characterized by NMR spectroscopy and X-ray single crystal diffraction. Alicyclic polyimides were prepared from these dianhydrides and diamines, such as 4,4′-oxydianiline (4,4′-ODA) and 2,2′-bis(trifluoromethyl)benzidine (TFMB). The introduction of methyl substituents on the double-bond bridges exhibits enhancements in various properties compared with their nonsubstituted analogs. These polyimides with high molecular weights can form flexible, transparent, and colorless films with superior optical transmittance at wavelength 400 nm (T400) of 86–88% and yellow indices (b*) of 0.32–0.87. They also showed high thermal stability with the degradation temperature at 5% weight loss (Td5%) of 423–447 °C in nitrogen and glass transition temperature (Tg) of 372–417 °C. These polyimides are good candidates as substrates for flexible electronic application. These polyimides also showed excellent solubility in organic solvents. Especially, PI-MBTA/TFMB and PI-DMBTA/TFMB are soluble even in low-boiling-point solvents such as cyclopentanone (CPN), implying the potential application as negative photosensitive polyimides (PSPIs) using CPN as the developing solvent. The double bonds of the bridges of MBTA and DMBTA cannot be hydrogenated with hydrogen pressure of 1–4.5 kg cm–2 using palladium on carbon as the catalyst at room temperature for 1–5 days. This could be attributed to the steric hindrance of the methyl substituents on the double bond. From the results of model compounds and the addition of strong dienophile (maleic anhydride), we conclude that the double-bond bridged cyclohexane system cannot undergo retro Diels–Alder reaction at 360 °C.

알칼리 수용액에서 현상이 가능한 네거티브 형태의 폴리이미드 공중합체의 합성과 광 형상화 연구

광반응기로 메타아크릴로일 그룹인 hydroxyethyl methacrylate(HEMA)를 곁사슬로 가지며 알칼린 수용액에 현상이 가능한 네거티브 광감성 폴리(아믹 에스테르) 공중합체를 pyromellitic dianhydride(PMDA), 4,4’-oxydianiline(ODA)와 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane(Bis-APAF)를 기반으로 합성하였다. 합성된 광감성 폴리(아믹 에스테르) 공중합체는 열적 이미드화 방법에 의하여 폴리이미드로 전환되며, 높은 열안정성을 가짐을 확인하였다. 광감성 폴리(아믹 에스테르) 공중합체, 광개시제 및 가교제 등의 광감성 조성물의 광 형상화 연구에서 고분자 합성에 투입된 ODA와 Bis-APAF의 조성에 따라 자외선 노광에 따른 현상 속도 및 형상화에 차이를 보임을 확인하였다. 전자주사현미경을 이용하여 알칼리 수용액에서의 현상 및 열적 이미드화 후의 표면을 분석하였으며, 광감성 폴리(아믹 에스테르) 공중합체 합성 시 투입된 ODA와 Bis-APAF의 조성에 따른 특성을 분석하였다.