Improvement in the adhesion of polyimide/epoxy joints using various curing agents

An improvement in the adhesion strength of polyimide/epoxy joints was obtained by (1) introducing a functional group on the polyimide surface, (2) improving the mechanical properties of the epoxy adhesive, (3) increasing the curing temperature, and (4) using polyamic acid as an adhesion‐promoting layer. The functional group on polyimide was introduced via treatment with aqueous KOH. An adhesion‐promoting layer was formed by spin coating polyamic acid onto a modified polyimide surface. The maximum adhesion strength of the polyimide/epoxy joint was obtained using polyamic acid as both the adhesion‐promoting layer and as the curing agent. The surface energy of the modified polyimide was examined using contact angle measurements and Fourier transform infrared spectroscopy, and the peel strength was determined by the T‐peel method. The peeled surfaces were analyzed using scanning electron microscopy and X‐ray photoelectron spectroscopy.© 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 812–820, 2002     

Long-term stability of Cu/Pd nanoparticles and their feasibility for electroless copper deposition

Poly-vinylpyrrodione (PVP) protected Cu/Pd nanoparticles synthesized with citric complexing agent were developed as activator for electroless copper deposition in printed-circuit boards (PCBs) industry. Cu/Pd nanoparticles in different molar ratio were employed in electroless copper deposition and found that the catalytic activity was influenced not only by the amount of Pd content or particle size but also by the surface protected PVP layer. From the time-resolved electroless copper deposition, we suggested that the catalytic efficiency should be evaluated by both initial activity and the structure of deposited copper film. As a result, the Cu/Pd nanoparticles of molar ratio = 1/2 was found to have best catalytic activity which was comparable to traditional Pd/Sn or pure Pd activator. In regard to the most concerned stability issue of Cu-content system, a surprising slow galvanic corrosion of Cu was found when Cu/Pd nanoparticles were exposed to the open air. Besides, slightly oxidation of Pd was found after air-exposure. Surprisingly, these Cu/Pd colloids maintain part of activity and well suspension even after 6-month exposure, suggesting well long-term stability as activator. In short, Cu/Pd nanoparticles synthesized with citric complexing agent with high catalytic activity and long-term stability was a promising activator for electroless copper deposition.     

Development and thermal durability of an interfacial bond between electrolessly deposited metals and a fluorinated polyimide

The oxygen content of a fluorinated polyimide surface can be increased by exposure to an oxidant such as an alkaline permanganate solution. Deposition of an electroless metal layer on this oxidized surface results in the formation of an interfacial bond which is predominantly chemical in nature. The level of adhesion achieved depends both on the surface oxidation conditions and post-plating heating. Adhesion maxima are obtained by heating to 200°C for an electroless Cu deposit and to 300°C, the cure temperature for the polyimide film, for deposited electroless Ni. The fluorinated polyimide used in this study was derived from the reaction of 2,2-bis(4-(4-aminophenoxy)phenyl)hexafluoropropane with pyromellitic dianhydride and was obtained from Ethyl Corporation as Eymyd® L30N resin.     

Electroless plating of copper on fluorinated polyimide films modified by surface graft copolymerization with 1‐vinylimidazole and 4‐vinylpyridine

Electroless plating of copper via a tin‐free activation process was carried out effectively on two types of fluorinated polyimide (FPI) films modified by UV‐induced surface graft copolymerization with N‐containing monomers, such as 1‐vinylimidazole (VIDz) and 4‐vinyl pyridine (4VP). The graft copolymerization of VIDz and 4VP was carried out on the argon (Ar) plasma‐pretreated FPI films via a solvent‐free process under atmospheric conditions. X‐ray photoelectron spectroscopy (XPS) results showed that the VIDz graft‐copolymerized FPI surface (the VIDz‐g‐FPI surface) and 4VP graft‐copolymerized FPI surface (the 4VP‐g‐FPI surface) were much more susceptible to the electroless deposition of metals via the Sn‐free process than the pristine FPI surfaces, and the FPI surfaces modified by Ar plasma pretreatment alone. T‐peel adhesion strengths above 9 N/cm were achieved for the electrolessly deposited copper on both VIDz‐g‐FPI surfaces (the Cu/VIDz‐g‐FPI assemblies) and 4VP‐g‐FPI surfaces (the Cu/4VP‐g‐FPI assemblies). These adhesion strength values were much higher than those obtained for assemblies involving electrolessly deposited copper on pristine or on Ar plasma pretreated FPI films. The high adhesion strength of the Cu/VIDz‐g‐FPI and Cu/4VP‐g‐FPI assemblies was attributed to the synergistic effect of spatial interactions of the grafted VIDz or 4VP polymer chains with the copper atoms, and the fact that the VIDz or 4VP polymer chains were covalently tethered on the FPI surfaces. XPS results also revealed that the Cu/VIDz‐g‐FPI and Cu/4VP‐g‐FPI assemblies delaminated by cohesive failure inside the FPI films.     

Correlation of residual stress and adhesion on copper by the effect of chemical structure of polyimides for copper‐clad laminates

BACKROUND: Polyimide films coated on copper are a potential new substrate for fabricating printed circuit boards; however, adhesion between the copper and polyimide films is often poor. The relations between residual stress and adhesion strength according to the development of molecular orientation of polyimide films with different chemical backbone structure coated on copper were studied. RESULTS: The effect of chemical structures on properties including the residual stress and the adhesion strength were widely investigated for four different polyimides. Diamine 4,4′‐oxydianiline (ODA) and dianhydrides 1,2,4,5‐benzenetetracarboxylic dianhydride (PMDA), 4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) were used to synthesize polyimide. In an attempt to quantify the interaction of thermal mismatch with the polyimide films depending on various structures, residual stress experiments between polyimide film and Cu? Si wafer were carried out over a range of 25–400 °C using in situ thin film stress analysis. A universal test machine was used to conduct 180° peel test (ASTM D903‐98) of polyimide film from cooper foil. The residual stress on Cu? Si (100) wafer decreased in the order 6FDA‐ODA > BTDA‐ODA > ODPA‐ODA > PMDA‐ODA, and the interfacial adhesion strength decreased in the order BTDA‐ODA (5 N mm^?2) > ODPA‐ODA > PMDA‐ODA > 6FDA‐ODA. The results may suggest that the morphological structure, degree of crystallinity of chain orientation and packing significantly relate to the residual stress and adhesion strength in polyimide films. Wide‐angle X‐ray diffraction was used for characterizing the molecular order and orientation and X‐ray photoelectron spectroscopy was used for the analysis of components on copper after polyimide films were detached to confirm the existence of copper oxide chemical bonding and to measure the binding energy of elements on the copper surface. CONCLUSION: In this research, it is demonstrated that BTDA‐ODA polyimide has a low residual stress to copper, good adhesion property, good thermal property and low dielectric constant. Therefore, BTDA‐ODA would be expected to be a promising candidate for a two‐layer copper‐clad laminate. Copyright © 2007 Society of Chemical Industry     

Electroless copper plating on acrylonitrile butadiene styrene material surfaces without chromic acid etching and a palladium catalyst

Hydrolysis modification of nitrile groups on acrylonitrile butadiene styrene (ABS) plate surfaces into carboxylic acid groups was investigated to find a new recipe for electroless copper plating of ABS plate surfaces without etching reactions using chromic acid and also without a palladium catalyst. Hydrolysis modification of nitrile groups was successfully conducted in an aqueous sodium hydroxide (NaOH) solution (70 wt %) at 80°C for more than 72 h, and nitrile groups were modified into carboxylic acid groups. The hydrolysis modification was accelerated by the addition of dioxane as a supplement to the aqueous NaOH solution. The modification, when an aqueous mixture solution of NaOH (35 wt %) and dioxane (10 wt %) was used as a reagent, was accomplished at 65°C in 30 min. The hydrolyzed ABS plate surfaces were successfully metalized by electroless copper plating. A silver catalyst, instead of a palladium catalyst, was usable in the electroless copper‐plating process. Adhesion between the deposited copper metal and ABS plate surface was perfect for the Scotch tape test. Consequently, we propose a new recipe for an electroless copper‐plating process without an etching process using chromic acid and without a palladium catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

Antireflective coatings using organically modified silica and polyimide via solution casting method

Antireflective (AR) coatings were prepared using a polyimide and two types of organically modified silica colloids via a solution casting method. The optically transparent polyimide was prepared from 2,2′‐Bis[4‐(3,4‐dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 4,4′‐oxydianiline (ODA). The silica colloids were driven to the coating‐air interface by either the fluorinated alkyl group or PDMS (Polydimethylsiloxane) segment tethered onto the silica colloids. The amount of fluorinated alkyl groups and the molecular weight of the siloxane grafted on the silica colloid were varied. The PDMS‐silica and fluorosilica colloids were characterized by TEM (Transmission Electron Microscopy), DLS (Dynamic Light Scattering), FTIR (Fourier Transform Infrared Spectroscopy), solid‐state ¹³C NMR (Nuclear Magnetic Resonance) and solid‐state ²⁹Si NMR. The AR coatings were characterized by UV–vis (Ultraviolet–Visible Spectroscopy) transmittance spectra, AFM (Atomic Force Microscope), and SEM (Scanning Electron Microscope). The effects of modified silica loading and type of solvent on AR properties were studied. An enhancement in AR activity was observed for 1 wt% PDMS‐modified (low molecular weight) silica coatings and 3 wt.% fluorosilica‐10 in dimethylacetamide (DMAc). In comparison with cyclopentanone (CPT), DMAc favors migration of silica particles toward coating‐air interface giving higher transmittance. The migration of particles to the surface and consequently increased surface roughness was observed by SEM. POLYM. ENG. SCI., 53:2228–2241, 2013. © 2013 Society of Plastics Engineers     

Formation of polyimide- Cu complexes: improvement of direct Cu-on-PI and PI-on-Cu adhesion

Polyimides containing triazole or imidazole functionalities have been synthesized. Poly(3,3',4,4'-benzophenone tetracarboxylic dianhydride-3,5-diamino-1,2,4-triazole) (BTDA-TADA) contains triazole groups as repeat units and poly(4,4'-oxydiphthalic anhydride-1,3-aminophenoxybenzene-8-azaadenine) (ODPA-APB-8-azaadenine) consists of triazole (8-azaadenine) groups as the end caps. While the BTDA-TADA polyimide starts to decompose at 350°C, the ODPA-APB-8-azaadenine polyimide is thermally stable at 400°C. The peel strength of copper to BTDA-TADA polyimide without surface modification is 200-400 J/m². For the adhesion of polyimide to copper, ODPA-APB-8-azaadenine polyisoimide (1.0 μm) and poly(pyromellitic dianhydride-oxydianiline) (20 μm) were coated onto the copper substrate and then the two layers were cured together to polyimides at 400°C. Peel strengths of 500-800 J/m² were obtained. The failure of the copper/polyimide interface by peeling either the copper or the polymer layer occurred in the near-interface region of the polymer. Both PI/Cu and Cu/PI adhesion was enhanced due to the formation of Cu-polyimide complexes. In the case of PI/Cu adhesion, the polymer chain flexibility of ODPA-APB-8-azaadenine polyimide also plays a significant role in improving adhesion.     

Effects of current density on adhesion of copper electrodeposits to polyimide substrates

To provide protection, electrical conductivity, or a decorative finish, plastic components are often metallized by a three-step process: deposition of a catalytic palladium layer followed by electroless and electrolytic plating. In this paper we focused on determining the relationship between applied current density used to electrodeposit copper and adhesion of the metal to a polyimide substrate. To test a range of current densities on a single sample, we deposited a series of copper strips on a planar sheet of the polyimide material and electrodeposited copper in a modified Hull cell. From peel tests we found that strips subjected to higher current density adhered more strongly to the substrate. This experimental procedure should be generally applicable to other metal-polymer systems.     

多壁碳纳米管/聚酰亚胺复合材料制备及其性能研究

聚酰亚胺的前聚体,聚酰胺酸,是通过4,4-二氨基二苯醚(ODA)与3,3,4,4二苯甲酮四羧酸二酐(BTDA)反应制备的。未改性的、酸改性和胺改性的多壁碳纳米管(MWCNT)被分别地单独加入到聚酰胺酸溶液中,并加热至300℃,从而制成聚酰亚胺/碳纳米管复合材料。扫描型电子显微镜(SEM)和透射电子显微镜(TEM)的显微照片表明,酸改性的多壁碳纳米管和胺改性多壁碳纳米管在聚酰亚胺基体中被均匀一致地分散开。通过对酸和胺改性的多壁碳纳米管MWCNTS对多壁碳纳米管/聚酰亚胺复合材料的表面和体积电阻率的影响进行了研究。了解到该纳米复合材料的表面电阻率ITES从1.28×10^(15)Ω/cm^(2)(纯聚酰亚胺),降到7.59×10^(6)Ω/cm^(2)(26.98%的未改性的多壁碳纳米管含量)。除此之外,添加多壁碳纳米管影响了纳米复合材料的玻璃化转变温度。改性多壁碳纳米管意义就是提高了纳米复合材料的机械性能。多壁碳纳米管/聚酰亚胺复合材料的拉伸强度从10^(2)MPa(纯的聚酰亚胺)增加到134 MPa(6.98%酸改性多壁碳纳米管/聚酰亚胺复合材料)。     

Metallization of polyimide film by wet process

The interfacial adhesion strength of metallized polyimide (BPDA/ODA/PDA) has been studied with respect to polyimide surface molecular structure, reactions during electroless nickel deposition, baking, copper electroplating, and thickness of polyimide film. Each factor is discussed in terms of its influence on the peel strength. For practical application, operation at optimized conditions for each step of the metallization process is essential for sustaining the mechanical integrity of the copper/polyimide laminate. © 1994 John Wiley & Sons, Inc.     

Gold wire bondability of electroless gold plating using disulfiteaurate complex

Generally, contact or terminal areas are coated with nickel as a barrier layer; subsequently, gold plating is performed to maintain reliability of electrical interconnection. Treatment using dilute solutions of palladium ions have been applied to initiate electroless nickel plating on copper substrates because copper has no catalytic action for the oxidation of hypophosphite. However, trace amounts of palladium ions may remain on the unwanted areas and extraneous nickel deposits are often observed. We confirmed that nickel films without extraneous deposits can be formed using the activation solutions containing dimethyl amine borane (DMAB). Bondability on the electrolessly deposited gold was greatly influenced by the phosphorus contents of the deposited nickel films as the underlayer. Bonding strength after electroless gold plating was increased with increasing phosphorus contents in the nickel films. Stabilizers in the electroless gold plating also influenced the bonding strength. Baths containing cupferron or potassium nickel cyanide as a stabilizer showed superior bondability. Gold deposits having strong orientation with Au(220) and Au(311) indicated high bond strength.     

Surface modification of polyimide by combining swelling and TiO2 photocatalytic treatments for adhesion improvement of electroless Cu

In order to enhance the adhesion strength between the PI film and the electroless copper film, a combination of swelling and TiO₂ photocatalytic treatments was used to modify polyimide (PI) film. The effects of the swelling solution composition and TiO₂ photocatalytic condition on the surface performance were investigated. After the optimal swelling and photocatalytic treatment, the surface contact angle of the PI film decreased from 85 to 28.7°, and the surface average roughness of the PI film only increased from 1.3 to 13.6?nm, indicating no obvious change for the surface topography of PI film after the photocatalytic treatment. However, the adhesion strength between electroless copper film and the PI film reached to 0.6?KN·m^?1. The FT-IR spectra and XPS analyses indicated that –COOH group was formed on the PI surface after the treatment, and the surface hydrophilicity was improved, which improved the adhesion strength between the PI film and the electroless copper film.     

All-wet fabrication process for ULSI interconnect technologies

“All-wet process” for fabrication of Cu wiring on a silicon chip was proposed as a novel ultra-large scale integration (ULSI) interconnect technology for integrated circuits (ICs) applications. Electroless-NiB film was deposited on SiO₂/Si substrate modified by self-assembled-monolayer (SAM) activated with PdCl₂. The NiB film formed by this method has highly uniform, with good adhesion to the substrate and with good diffusion barrier characteristics against Cu diffusion. Cu was electrodeposited directly on the electroless NiB film that acted as a seed layer. This was done without any conventional conductive or adhesive layer that is conventionally formed by physical vapor deposition (PDV). The thermal stability of electroless NiB layer as a barrier preventing copper from diffusing into the SiO₂/Si substrate was evaluated by secondary ion mass spectroscopy (SIMS) and sheet resistance measurement at several annealing temperatures. It was confirmed that the electroless NiB film blocked Cu diffusion and kept the layer integrity under annealing temperatures of up to 400 °C for 30 min. The same process of electroless NiB was used for the capping layer that was also formed by “wet process”, as the electroless NiB film deposited selectively onto a surface of Cu wiring was also applicable to a capping layer. We conclude that the proposed process is very promising for sub-100 nm technologies as it offers a variety of desirable properties: it has good step coverage while showing good barrier and seed layer properties.     

Supercritical fluid‐assisted electroless metal plating onto aramid films: The influence of thermal treatment

Although the production of electro‐conductive aramid fibers is efficient, the method needs to be modified before it can be applied to aramid films. Whereas impregnation of an aramid film with a metal complex using supercritical CO₂ is achievable, the relatively low adhesion strength of the metal layer applied using electroless copper plating is problematic. To solve this problem, thermal treatment was conducted before, after, or both before and after electroless plating. The rationale for using thermal treatment to improve the adhesiveness of the plated layer was based on the findings that (1) an aramid film contains a significant amount of water (about 3.5 % w.o.f.), which might have a negative impact on adhesion; and (2) because an impregnated metal complex liberates metal catalyst by thermal decomposition during impregnation, a supplementary thermal action might liberate more catalyst and thereby improve adhesion. We found that thermal treatment improved adhesion of the metal layer to the aramid film. Moreover, we discovered that with respect to electroless copper plating, a short time‐lag was crucial to obtaining a thin and homogeneous metal layer with strong adhesion. In addition, we demonstrate the affinity of an aramid film for Pd(acac)₂. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Microwave‐assisted synthesis and characterization of polyimide/functionalized MWCNT nanocomposites containing quinolyl moiety

Polyimide‐MWCNT nanocomposites were prepared by the reaction of a heterocyclic diamine monomer of bis(4‐amino‐3,5‐dimethylphenyl)‐2‐chloro‐3‐quinolylmethane (BACQM), pyromellitic dianhydride (PMDA) with unmodified MWCNT (MWCNT), acid‐functionalized MWCNT (acid‐MWCNT) or amine‐functionalized MWCNT (amine‐MWCNT) using microwave irradiation as well as by the conventional method. The structure of the monomer was confirmed by FTIR, ¹H‐NMR, and ¹³C‐NMR spectral techniques. The glass transition temperature (T_g) of the MWCNTs/polyimide nanocomposite was found to be higher than that of the unfilled polyimide system. The T_g's of both systems were higher when prepared with the microwave method than the conventional synthesis. The T_g's of the nanocomposites using acid and amine functionalized MWCNTs are greater than 300°C, in both methods. This is attributed to the presence of hydrogen bond and strong covalent bond in both the acid‐MWCNT/polyimide and amine‐MWCNT/polyimide systems. The morphological studies of the nanocomposites synthesized using microwave irradiation show that a distinct MWCNT nanofibrillar network is formed in the matrix when MWCNT or acid‐MWCNT is used. A homogeneous morphology, without distinct nanotube domains is seen when the amine‐MWCNT is covalently linked to the polymer. POLYM. COMPOS., 37:2417–2424, 2016. © 2015 Society of Plastics Engineers     

Double‐shell surface modifications of large poly(methyl methacrylate) spheres

Two reactive shells were polymerized on poly(methyl methacrylate) (PMMA) spheres to improve the compatibility of the spheres with a paint binder. By adjusting the buoyancy of the polymerization medium, PMMA, retroreflective spheres with an average diameter of 600 μm were successfully modified with a thin cross‐linked layer together with an amine functional layer outside on the surface. The cross‐linked layer was polymerized by methyl methacrylate and ethylene glycol dimethacrylate by suspension polymerization. After that, a second monomer with functional amine group was polymerized and a functional layer was formed on the surface. The amine groups on the modified spheres can react with the enamine groups of acetoacetate already formulated in the binder and connected the spheres and the paint by chemical bond. The structure of the modified spheres was studied using transmission election microscopy, FTIR, DSC, and other tests. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 829–836, 2005     

Electrochemical formation of bi-metal (copper-palladium) electrocatalyst supported on poly-3,4-ethylenedioxythiophene

Bi-metal modification of poly-3,4-ethylenedioxythiophene (PEDOT) layers by combining palladium and copper deposition is studied. Initial reference measurements are performed on electrodriven deposition and electroless precipitation of palladium, showing the existence of Pd nanocrystals on the PEDOT surface. It is established that by using the electrodeposition sequence - Cu (first step) - Pd (second step) only palladium remains available in the PEDOT layer. By reversing the deposition sequence - Pd (first step) - Cu (second step) a bi-metal modification of PEDOT is achieved. Depending on the parameters potential and time of the copper electroreduction the Pd nanocrystals coexist with either Cu-PEDOT-stabilized species or both Cu crystals and Cu-PEDOT-stabilized species. The voltammetric response of the modified PEDOT electrodes is tested for nitrate electroreduction in neutral solution. It is found that the bi-metal modified PEDOT shows a marked electroactivity for this reaction.     

TiB2表面镀铜工艺

利用化学镀覆技术成功在TiB2颗粒表面均匀化学镀覆铜。透射电子显微镜观察表明：通过严格的镀前预处理工艺的优化设计以增加活化点,对传统镀液配方的调整以降低镀速,能够成功地在TiB2颗粒表面镀覆一层铜,从而培强了其和铜基体之间的界面结合力,为TiB2在复合材料领域之中的应用打下了坚实基础。