Polybenzoxazole Research Articles

Diffusion barrier effect of Ta/Ti bilayer in organic dielectric/Cu interconnects

This study describes a Ta/Ti bilayer to improve the adhesion between Cu and a dielectric material and to enhance the barrier effect for Cu interconnects in electronic circuits. The addition of Ti improves the adhesion between Ta and Polybenzoxazoles (PBO) from the industry standard of 0B (worst level) to 5B (best level), as evaluated via a peeling test. The results of a comparative study demonstrate that a Ta/Ti bilayer (40 nm/10 nm) enables a higher annealing temperature vs. pure films of either Ta or Ti (50 nm respectively) by preventing diffusive mixing of Cu/Si. Using an accelerated high-temperature testing system, the results show stable annealing at 550 °C for the bilayer as compared to 500 °C for Ta and 350 °C for Ti. Under accelerated low-temperature and long-term conditions, both material systems (Cu/Ta/Ti/PBO/Si and Cu/Ta/Ti/Si) remained stable and reliable. The results suggest the improved diffusion barrier property of the Ta/Ti bilayer is due to the strong Ta/Ti interface and the greater oxygen attraction by the Ti layer. The Ta/Ti bilayer is a promising candidate for use as a diffusion barrier and an adhesion promoter, especially in applications in which the insulation layer exhibits poor adhesive properties.

Gas transport properties of polybenzoxazole–silica hybrid membranes prepared with different alkoxysilanes

The gas transport properties of polybenzoxazole (PBO)–silica hybrid membranes were investigated. The PBO–silica hybrid membranes were prepared with poly(o-hydroxy amide) (PHA) as a precursor and various alkoxysilanes via thermal oxazolization and sol–gel processes. The thermal decomposition temperature of the hybrid membranes increased with increasing silica content, indicating that the thermal stability was improved by hybridization with silica. The gas permeabilities of the PBO–silica hybrid membranes also increased with increasing silica content and thermal treatment temperature. It is worth noting that the hybrid membranes prepared with tetraethoxysilane (TEOS) as the selected alkoxysilane showed simultaneous enhancements in CO2 permeability and CO2/CH4 selectivity with increasing silica content and thermal treatment temperature. The prominent CO2/CH4 separation ability of the PBO–silica hybrid membranes prepared with TEOS might be attributable to free volume holes created around the polymer/silica interfacial area and increased intermolecular chain distance, which improved size-selective CO2/CH4 separation. The gas transport properties of polybenzoxazole (PBO)–silica hybrid membranes were investigated. The gas permeability of the PBO–silica hybrid membranes increased withincreasing silica content and thermal treatment temperature. The hybrid membranes prepared with tetraethoxysilane (TEOS) showed simultaneous enhancements in CO2 permeability and CO2/CH4 selectivity with increasing silica content and thermal treatment temperature. The prominent CO2/CH4 separation ability might be attributable to free volume holes created around the polymer/silica interfacial area and increased intermolecular chain distance.

Synthesis of thermotropic polybenzoxazole using 3-amino-4-hydroxybenzoic acid

Bio-based polybenzoxazoles (PBOs) are prepared by polycondensation of diacid monomer derived from 3-amino-4-hydroxybenzoic acid with a series of aliphatic diamines. Resulting bio-based PBOs have high weight average molecular weight ranging 5.70–7.20 × 104 g/mol and show ultrahigh thermal resistance with T 10 values over 400 °C and T g values over 170 °C, which are higher than those of conventional bio-based polymers, polyamides 11 (around 60 °C) or poly(lactic acid) (56 °C). Especially hydrazide group of the bio-based PBO were cyclized to form diazole ring by annealing at 330 °C for 20 min. The resultant PBO show liquid crystalline (LC) behavior to spin fiber in a melting state. The resultant PBO fibers showed high values of Young’s modulus and mechanical strength as compared with conventional polymers polyamide 11 and poly(lactic acid) (PLA).

Synthesis and gas permeation properties of a novel thermally-rearranged polybenzoxazole made from an intrinsically microporous hydroxyl-functionalized triptycene-based polyimide precursor

A hydroxyl-functionalized triptycene-based polyimide of intrinsic microporosity (TDA1-APAF) was converted to a polybenzoxazole (PBO) by heat treatment at 460 °C under nitrogen atmosphere. TDA1-APAF treated for 15 min (TR 460) resulted in a PBO conversion of 95% based on a theoretical weight loss of 11.7 wt% of the polyimide precursor. The BET surface area of the TR 460 (680 m2 g−1) was significantly higher than that of the TDA1-APAF polyimide (260 m2 g−1) as determined by nitrogen adsorption at −196 °C. Heating TDA1-APAF for 30 min (TRC 460) resulted in a weight loss of 13.5 wt%, indicating full conversion to PBO and partial main-chain degradation. The TR 460 membrane displayed excellent O2 permeability of 311 Barrer coupled with an O2/N2 selectivity of 5.4 and CO2 permeability of 1328 Barrer with a CO2/CH4 selectivity of 27. Interestingly, physical aging over 150 days resulted in enhanced O2/N2 selectivity of 6.3 with an O2 permeability of 185 Barrer. The novel triptycene-based TR 460 PBO outperformed all previously reported APAF-polyimide-based PBOs with gas permeation performance close to recently reported polymers located on the 2015 O2/N2 upper bound. Based on this study, thermally-rearranged membranes from hydroxyl-functionalized triptycene-based polyimides are promising candidate membrane materials for air separation, specifically in applications where space and weight of membrane systems are of utmost importance such as nitrogen production for inert atmospheres in fuel lines and tanks on aircrafts and off-shore oil- or natural gas platforms. Mixed-gas permeation experiments also demonstrated good performance of the TR 460 membrane for natural gas sweetening with a CO2 permeability of ∼1000 Barrer and CO2/CH4 selectivity of 22 at a typical CO2 wellhead partial pressure of 10 bar.

Polybenzoxazole (PBO)-based gas separation membranes thermally derived from blends of Ortho-functional polyimide and polyamide precursors

Abstract This study investigates the physical properties and gas separation performance of a series of PBO-based membranes derived from thermal conversion of blends containing ortho -OH polyamide (PHA) and polyimide (API) precursors. Homogeneous films were obtained in varying PHA/API molar ratios before and after thermal conversion, indicating good compatibility between the two precursors and resulting PBOs. This study reveals that PBO conversion efficiency, fractional free volume and gas transport properties of the resulting PBO-based blend films show an unexpected non-linear dependence on the blend composition (i.e., PHA/API ratio), due to an interplay between API thermal rearrangement (TR) process and PHA cyclodehydration process. Particularly, the B11 blend membrane, containing API and PHA in 1:1 M ratio, showed an optimal combination of gas separation performance and mechanical robustness, while the B31 blend (PHA:API = 3:1) showed little degradation of separation performance relative to both constituent polymers. This is possibly because of the localization of the excess PHA fraction that discourages the formation of inter-connected diffusive transport pathways. In summary, physical blending of API and PHA precursors at an optimal composition is demonstrated to be a simple yet instrumental approach to mitigate the mechanical deterioration issue of API-TR process while greatly improving the separation performance of the PBOs derived from the PHA cyclodehydration process.

Low Temperature Curable PI/PBO for Advanced Packaging

Photo-definable polyimides (PI) and polybenzoxazoles (PBO) have been widely used as dielectrics for re-distribution layers in wafer level chip size packages (WL-CSP). These materials can simplify the manufacturing process and ensure high reliability owing to their good mechanical properties and high thermal stability. For next generation electronic components fabricated by utilizing advanced packaging technologies such as 3D-stacking using TSV, package-on-package, fan-out WL-CSP etc., the most important requirements for dielectric materials are high lithographic performance, high adhesion to Cu RDL, high chemical resistance and low temperature curability. In this paper, we will report on our novel low temperature (<200C) curable PBO and PI. A novel alkaline positive tone PBO was developed by re-designing key components of the formulation to enhance lithographic performance, Cu adhesion and chemical resistance. It was found that the new PBO material showed higher lithographic performance than conventional PBOs due to its high dissolution contrast and which resulted in a resolution of 2micron (L/S) with a 7μm cured thickness and 3micron (L/S) with a 15micron cured thickness, respectively. This material also produced strong Cu adhesion and high chemical resistance at curing temperatures <200C with no delamination from the Cu RDL being observed after a 168hr Pressure Cooker Test (PCT). Furthermore, the new formulation showed high TCT resistance due to its high elongation below 0C. In addition, a novel solvent negative tone PI was also developed by incorporating a cross-linker to accelerate low temperature curability as well a photo-initiator to improve lithographic properties. As a result, the novel PI when cured at 175C for 1hr showed high Cu adhesion after 168hr PCT as well as high film properties. The new PI also showed excellent lithographic properties with a resolution of 6micron (L/S). Furthermore, the low temperature curable PI and PBO materials were used as dielectrics to fabricate WL-CSPs for both chip and board level reliability testing. The test results indicated that both the novel PBO and PI showed excellent reliability after thermal cycling (TCT) due to the significant improvements made to Cu adhesion and chemical resistance. These materials are expected to be promising for next generation WLP applications. Details are described in the presentation.

高強度化学繊維によるワイヤ駆動のための基礎的検討

Synthetic fiber ropes, which are lightweight and have high tensile strength and flexibility, have attracted attention as an alternative to stainless steel wire rope. This study clarifies various physical characteristics of synthetic fiber ropes to design a tendon-driven mechanism and this paper focuses on creep of ropes. We first designed and constructed a creep testing machine for ropes. Second, we performed experiments with three types of synthetic fiber ropes and one stainless steel wire rope. As a result, in stainless steel wire rope, creep was not observed. In addition, Polyarylate(PAR) fiber rope and Poly-phenylene-Benzobisoxazole(PBO) fiber rope have much higher creep resistance than Ultra High molecular weight Polyethylene(UHPE) fiber rope.

Erosion characteristics and mechanical behavior of new structural hybrid fabric reinforced polyetherimide composites

In this work, a new structural hybrid fabric reinforced polyetherimide composite was prepared using a solution impregnation method. The effects of fabric orientation, i.e., the angle between the projected line of the impact path of the solid particle on the specimen surface and the axis of the polybenzoxazole (PBO) fibers, and weft density on the erosion behavior of the prepared hybrid composites were investigated. The results show that the erosion rates of the hybrid composites decreased with increasing fabric orientation angle and weft density. No obvious crimp of carbon fibers was observed in the cross-section of a hybrid fabric prepreg sheet, therefore composites with excellent mechanical properties can be obtained. The carbon fibers were covered with PBO fibers and resin, and these protect the carbon fibers from damage well. The prepared hybrid composites showed better erosion resistance than carbon fiber reinforced thermoplastics and better mechanical properties than PBO fiber reinforced thermoplastics. Dynamic mechanical analysis showed that the prepared hybrid composite has high heat resistance.

Highly Selective Wet Silicon Etch Chemistry and Process for Advanced Semiconductor Packaging

Abstract A wet silicon etch chemistry and a process using the chemistry as a simple and cost-effective alternative to the polish/plasma etch silicon thinning process are presented in this paper. The new etch chemistry improves the Si etch rate over traditional etchants such as tetramethylammonium hydroxide (TMAH). The chemistry has very high silicon etch selectivity (ratio of Si etch rate to another film etch rate) over SiO2 and over copper films, with etch selectivity greater than 8000:1 and 2500:1 respectively. Chemical compatibility with typical packaging materials such as polybenzoxazole (PBO) and polyimide (PI) are also discussed. Additionally, real production TSV wafers have been successfully processed on an advanced single wafer etch tool using the chemistry. High uniformity and smooth surface finishing have been achieved.

Synthesis and gas transport properties of hyperbranched polybenzoxazole – silica hybrid membranes

Gas transport properties of hyperbranched polybenzoxazole (PBO) – silica hybrid membranes were investigated. The hyperbranched PBO – silica hybrid membranes were prepared via in-situ silylation method and sol-gel reaction. Thermal decomposition temperature of the hybrid membranes increased with increasing silica content, indicating improved thermal stability brought by the hybridization with silica. The hyperbranched PBO – silica hybrid membranes showed higher gas permeability than corresponding linear-type PBO – silica hybrid membranes with similar chemical structure. It was worth noting that both CO2 permeability and CO2/CH4 selectivity of the hyperbranched PBO – silica hybrid membranes were increased with increasing silica content across the upper bound trade-off line for CO2/CH4 separation. The prominent CO2/CH4 separation ability of the hyperbranched PBO – silica hybrid membranes might be achieved by large amounts of free volume holes, that were fundamentally brought by a characteristic hyperbranched structure and additionally crated around polymer/silica interfacial area, equipped with unique distribution and interconnectivity advantageous for a size-selective CO2/CH4 separation.

Spirobisindane-based polyimide as efficient precursor of thermally-rearranged and carbon molecular sieve membranes for enhanced propylene/propane separation

High performance thermally-rearranged (TR) and carbon molecular sieve (CMS) membranes made from an intrinsically microporous polymer precursor PIM-6FDA-OH are reported for the separation of propylene from propane. Thermal rearrangement of PIM-6FDA-OH to the corresponding polybenzoxazole (PBO) membrane resulted in a pure-gas C3H6/C3H8 selectivity of 15 and C3H6 permeability of 14 Barrer, positioning it above the polymeric C3H6/C3H8 upper bound. For the first time, the C3H6/C3H8 mixed-gas properties of a TR polymer were investigated and showed a C3H6 permeability of 11 Barrer and C3H6/C3H8 selectivity of ~11, essentially independent of feed pressure up to 5bar. The CMS membrane made by treatment at 600°C showed further improvement in performance as demonstrated with a pure-gas C3H6/C3H8 selectivity of 33 and a C3H6 permeability of 45 Barrer. The mixed-gas C3H6/C3H8 selectivity dropped from 24 to 17 from 2 to 5bar feed pressure due to a decrease in C3H6 permeability most likely caused by competitive sorption without any evidence of plasticization.

Polybenzobisoxazoles-based nanocomposites with high microwave absorption performance and excellent thermal stability

A microwave absorption nanocomposite is prepared by polyaniline (PANI) coated Fe3O4 nanoparticles and polybenzobisoxazole (PBO), the latter being a conjugated polymer with high mechanical strength and outstanding thermal and oxidative stability. Fe3O4@PANI nanoparticles are well dispersed in the PBO matrix to form PBO/(Fe3O4@PANI) nanocomposite, which has excellent thermal stability (high char yield above 55 wt% at 800 °C under nitrogen). Attributed to the conductive polymer PANI as shell and the good compatibility of PANI with PBO matrix, PBO/(Fe3O4@PANI) nanocomposite with 8 wt% of Fe3O4@PANI exhibits a minimum RL value of −28.6 dB at 10.1 GHz and below −10 dB in 9.3–15.4 GHz at the film thickness of 3.5 mm. This demonstrated the potential applications of PBO/(Fe3O4@PANI) nanocompositeas a low-density microwave absorbing material in extreme environments.

Experimental investigation on masonry arches strengthened with PBO-FRCM composite

Abstract In the last two decades, Fiber Reinforced Polymer (FRP) composites were effectively used for increasing the load-carrying capacity of masonry arches and for improving their mechanical response against the most critical arch failure mechanisms. More recently, Fabric Reinforced Cementitious Matrix (FRCM) composites are appearing significantly promising for the strengthening of masonry arches, providing an alternative to the FRP composites, but only few experimental contributions are available to date. In the present paper, the structural performance of masonry arches strengthened both at intrados and at extrados by using a polybenzoxazole (PBO) fabric reinforced cementitious mortar composite was experimentally investigated. Results, in terms of load-carrying capacity, post peak behavior and failure mechanism, were compared with those determined by using a Carbon Fiber Reinforced Polymer (CFRP) composite. The present experimental study contributes to improve the knowledge of the innovative PBO-FRCM composites and it provides mechanical data useful for defining masonry strengthening design guidelines.

Synthesis and thermal properties of polyhydroxyamide copolymer and its derivatives

We synthesized a polyhydroxyamide (PHA) copolymer via low-temperature solution polymerization of 3,3'-dihydroxybenzidine with terephthaloyl chloride (80.0 mol%) and isophthaloyl chloride (20.0 mol%) in N,Ndimethylacetamide with the aid of LiCl. We prepared the PHA copolymer derivatives containing the fluorine-based substituents and investigated their solubility, cyclization behavior, and thermal properties using a differential scanning calorimeter (DSC), a thermogravimetric analyzer (TGA), and the simultaneous thermogravimetric analyzer coupled with a mass spectrometer (STA-MS). The chemical structures of the PHA copolymer and its derivatives, as well as the polybenzoxazoles (PBOs) obtained through thermal cyclization of the copolymer and derivatives, were determined by a fourier transform infrared (FT-IR) spectroscopic analysis. The PHA copolymer could be dissolved in organic solvents only with the aid of LiCl, while its derivatives were readily soluble in DMAc and NMP without LiCl at room temperature. The DSC and TGA results demonstrated that the PHA copolymer derivatives could be converted to PBOs at a lower temperature than the PHA copolymer.

Preparation and gas transport properties of triptycene-containing polybenzoxazole (PBO)-based polymers derived from thermal rearrangement (TR) and thermal cyclodehydration (TC) processes

Triptycene-containing PBO-based polymers with ultrafine microporosity promoting ultrafast and highly selective gas transport.

Hyperbranched polybenzoxazoles incorporated polybenzoxazoles for high‐performance and low‐Kmaterials

ABSTRACTThis paper reports an effective approach for the fabrication of low‐kpolybenzoxazole (PBO) by covalent incorporation of hyperbranched PBO (HBPBO). Solubleo‐aminophenol‐terminated HBPBO was first synthesized by a one‐pot polycondensation, then covalently bonded to poly(hydroxyamide) ended with carbonyl chloride groups, PBO was finally obtained by thermal conversion of the precursor polymers. It was demonstrated that the thermal stability of PBO was not influenced by the incorporation of HBPBO due to their similar chemical compositions, while the glass transition temperature, elastic modulus and hardness were improved because of the linking effects of HBPBO to linear PBO chains. The dielectric constant of PBO was significantly reduced due to the disturbed chain packing of PBO by the globular HBPBO, and the intrinsic cavities in HBPBO, which increased free volume in the materials. Moreover, the material also exhibited reduced coefficient of thermal expansion as compared to neat PBO and low water absorption. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem.2016,54, 1623–1632

Gas permeation and mechanical properties of thermally rearranged (TR) copolyimides

Gas transport and mechanical properties are reported for a series of copolyimides and their corresponding thermally rearranged (TR) analogs. Random copolyimides of APAF/HAB-6FDA with various compositions were synthesized via chemical imidization from 2,2′-bis (3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF), 3,3′-dihydroxy-4,4′-diaminobiphenyl (HAB), and 2,2′-bis-(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA). These copolyimides were thermally treated at temperatures between 350 °C and 450 °C to prepare TR polybenzoxazoles (PBOs). Pure gas permeabilities of H2, CH4, N2, O2, and CO2 were measured at 35 °C with upstream pressures ranging from 3 to 17 atm. In general, gas permeability increased and selectivity decreased as TR conversion increased. Gas permeability also increased with increasing APAF content in the polyimides as a result of higher fractional free volume (FFV) imparted by the extra hexafluoroisopropylidene group in APAF. Stress–strain relationships were recorded for the polyimides and their TR analogs. As polyimides underwent thermal rearrangement, samples became more rigid, and tensile stress and elongation at break decreased. A similar trend in mechanical properties was also observed as APAF content increased, which was attributed to the lower molecular weight of APAF-containing polymers, resulting from the lower reactivity of APAF relative to that of HAB.

Optical Studies of Poly(hydroxy imide) to Polybenzoxazole Thermal Rearrangement

Studies of the optical properties of poly(hydroxy imide) (HPI) exposed to stepwise heating from room temperature up to 400 °C are reported in this work. It is demonstrated that this new method can be used to monitor thermal rearrangement (TR) of HPI to polybenzoxazole (PBO). Temperature dependences of the absorption edge parameters (Urbach energy and energy gap) are obtained and used to estimate the changes in the defects states and conjugation within the polymer chain associated with its TR to PBO. It is shown that the conversion temperatures determined based on the optical studies correspond to those received from the thermogravimetric analysis (TGA) investigations. Moreover, it is demonstrated that transition to PBO is accompanied by an 11‐fold increase in nitrogen permeability associated with only a slight decrease in O2/N2 selectivity from 8.8 to 7.2. image

TCT Reliability of Organic Passivation Layer for WLCSP

Wafer level chip scale packages (WLCSP) have been increasingly used in portable electronic products such as mobile phones. Solder bumps with redistribution layer (RDL) are typical interconnect technology for WLCSP applications. One of the major concerns in joint reliability is the failure by temperature cyclic stresses. In addition, in terms of heat tolerance or device yields, process temperature of RDL dielectric is limited around 200deg.C in some packaging applications. According to our board level reliability test for temperature cycle test (TCT), photosensitive polyimide (PI) which is 200deg.C curable material has lower fail rate than polybenzoxazole (PBO) by TCT. In this study, we compared the actual board level test and Finite Element Analysis (FEA) during temperature cycle test, and correlated the mechanical and fatigue properties of passivation layer material with TCT reliability.

Synthesis and Characterization of Fluorinated Polybenzoxazole Copolymers

Synthesis and Characterization of Fluorinated Polybenzoxazole Copolymers