Surface modification of polyimide films by argon plasma for copper metallization on microelectronic flex substrates

Surface modification of polyimide films such as Kapton E(N) and Upilex S by argon plasma was investigated because of the enhanced adhesive strength with sputtered copper. Peel tests demonstrated this improvement, with a peel strength of 0.7 and 1.2 g/mm for unmodified Kapton E(N) and Upilex S, respectively, and 110.3 and 98 g/mm for argon plasma–modified Kapton E(N) and Upilex S, respectively, in certain plasma conditions. This study showed that the enhanced adhesive strength of polyimide films with sputtered copper by argon plasma was strongly affected by the surface characteristics such as surface morphology and surface energy of polyimide films. Atomic force microscopy and the sessile drop method indicated that the surface roughness and surface energy of the polyimide films were greatly increased by argon plasma, resulting in highly increased peel strength of the polyimide films with sputtered copper. It was observed in electron spectroscopy for chemical analysis (ESCA) that the increased surface energy of the polyimide films from argon plasma was a result of more of the surface being composed of O and N and of the increased number of C? O, C?O, and C? N chemical bonds. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 744–755, 2006     

Plasma modification of poly(oxybenzoate-co-oxynaphthoate) film surfaces for copper metallization

Poly(oxybenzoate-co-oxynaphthoate) (POCO) film surfaces were modified by four plasma gases, Ar, O₂, N₂ and NH₃, and the effects of the plasma modification were investigated in order to understand the adhesion with copper metal. The Ar, O₂, N₂ and NH₃ plasmas converted the POCO surfaces from hydrophobic to hydrophilic. The effect of the plasma on the hydrophilic modification was in the order: Ar plasma > O₂ plasma > N₂ plasma > NH₃ plasma. The plasma modification contributed to the adhesion between the deposited copper metal and the POCO film. The NH₃ plasma was most effective in improving the adhesion, and the Ar plasma was ineffective. The plasma-modified POCO film surfaces showed quite different C_ls spectra from that of the original POCO film. There were large differences in the C_ls and N_ls spectra between the NH₃ and Ar plasma modifications. The NH₃ plasma modification did not show C_ls component #5 due to π–π^* shake-up satellite, but the Ar plasma modification did show this component. Furthermore, NH₃ plasma modification led to a new N_ls spectrum. The plasmas caused etching of the POCO film surfaces, and the etch rate depended on what plasma was used and how much RF power was used. The NH₃ plasma-modified POCO film surface showed a larger R _a (25.5 nm) than the other plasma-modified surfaces (R _a = 16.4–19.0 nm), which were comparable to that of the original surface (R _a = 14.8 nm). The NH₃ plasma led to a highly-undulated surface, and the other plasmas did not alter the surface roughness. The roughened surfaces showed contribution to enhancement of the adhesion to the deposited copper metal.     

Surface modification and metallization of polyimide using gold colloids as a seed layer

Herein we report on metallization of Cu on to surface‐modified polyimide resin, the method of which relies on potassium hydroxide‐induced modification of the polyimide surface to introduce carboxylic acid groups and incorporation of gold colloids as a seed layer through reduction of chloroauric acid. The contact angle of modified polyimide surface with water changed from 70 to 35° due to the hydrolysis of polyimide. Secondary amine group on the surface was detected with attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectrophotometry, suggesting that tertiary amine group has turned into secondary group. In addition, on the basis of hydrophilic behavior, we succeeded in depositing gold colloids on the chemically modified surface. SEM image of copper electroless plated on polyimide surface indicated that copper particles were compact and about ～ 300 nm in diameter. It showed that gold colloids provide an excellent conductive layer to catalyze the electroless plating of Cu on polyimide surface. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Surface modification of tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) by plasmas for copper metallization

Tetrafluoroethylene–perfluoroalkyl vinylether copolymer (PFA) sheet surfaces were modified with argon, helium, oxygen, and hydrogen plasmas. How the four plasmas modified the PFA sheet surfaces was investigated. All plasmas modified the PFA surfaces and at the same time initiated degradation of the PFA polymer chains. The balance between modification and degradation was strongly influenced by the magnitude of the discharge current in the plasmas. Efficiency of the plasmas in modification was hydrogen plasma > oxygen plasma > argon plasma > helium plasma. The modification involved defluorination of CF₂ carbons into CHF and CH₂ carbons and oxidation into O? CH₂, O? CHF, and O? CF₂ groups. The surface‐modification technique (a combination of hydrogen plasma treatment and silane coupling treatment) proposed in this study was applied for copper metallization of the PFA surface. The utility of the technique was confirmed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1087–1097, 2002     

Hydrophilic modification of a polyimide film surface

The surface of a polyimide [poly(biphenyl 3,3′,4,4′-dianhydride-p-phenylene diamine)] film was modified with an O₂ glow plasma and subsequent treatment with polyethyleneimine (PEI) and poly(maleic anhydride-co-vinyl methyl ether) (PMAVM). The density of peroxide groups formed on the surface after O₂ plasma exposure was determined with 1,1-diphenyl-2-picrylhydrazyl and was found to level off to 1.2 nmol/cm² within the plasma exposure time of 20-60 s. The peroxide groups formed were utilized to immobilize PEI covalently onto the plasma-treated polymer film. After that, PMAVM was immobilized on the surface through the formation of amide bonds between the amino groups of PEI and the anhydride groups of PMAVM. The water contact angle on the modified films showed that the hydrophilic durability of the PMAVM-PEI-modified polyimide film was superior to that of the polyimide film treated by O₂ plasma alone.     

Surface modification of polyimide and polysulfone membranes by ion beam for gas separation

The surface carbonization of polyimide (PI) and polysulfone (PSf) by ion beam has been performed to adapt the carbon molecular sieve properties on the skin of the polymeric membranes without the deformation of the membrane structure. In order to control the structure of membrane skin and to improve gas transport properties, the irradiation conditions, such as the dosage and the source of ion beams, have been varied. The ideal separation factor of CO₂ over N₂ through the surface‐modified PI and PSf membranes increased threefold compared to those of the untreated, pristine membranes, whereas the permeability decreased with almost two orders of magnitude. This appears to be due to the fact that the structure of membrane skin has been changed to a barrier layer. The formation of barrier layer was confirmed by comparing the calculated values of a simple resistance model with the experimental results, and the estimated permeability of this barrier was 10⁻⁴ barrer. It was concluded that ion beam irradiation could provide a useful tool for improving selectivity for gas separation membranes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1554–1560, 2000     

Plasma surface modification of poly(phenylene sulfide) films for copper metallization

Poly(phenylene sulfide) (PPS) films were modified by Ar, O₂, N₂ and NH₃ plasmas in order to improve their adhesion to copper metal. All four plasmas modified the PPS film surfaces, but the NH₃ plasma modification was the most effective in improving adhesion. The NH₃ plasma modification brought about large changes in the surface topography and chemical composition of the PPS film surfaces. The peel strength for the Cu/plasma-modified PPS film systems increased linearly with increasing surface roughness, R _a or R _rms, of the PPS film. The plasma modification also led to considerable changes in the chemical composition of the PPS film surfaces. A large fraction of phenylene units and a small fraction of sulfide groups in the PPS film surfaces were oxidized during the plasma modification process. Nitrogen functional groups also were formed on the PPS film surfaces. The NH₃ plasma modification formed S—H groups on the PPS film surfaces by reduction of S—C groups in the PPS film. Not only the mechanical interlocking effect but also the interaction of the S—H groups with the copper metal may contribute to the adhesion of the Cu/PPS film systems.     

Surface modification of ABS by photocatalytic treatment for electroless copper plating

Surface roughness of acrylonitrile–butadiene–styrene (ABS) resin prior to metallization is treated generally with sulphuric/chromic acid system. However, the presence of chrominum (VI) ion imposes serious environmental problems. In this work, TiO₂ photocatalytic treatment was used to enhance the adhesion strength between the ABS surface and the electroless copper film. Effects of the TiO₂ content, irradiation time and UV power upon the surface topography, surface characterization and the adhesion strength were investigated. The results indicated that the surface hydrophilicity of ABS resin and the adhesion strength between the electroless copper film and ABS surface increased with an increase in the UV power and a prolongation in irradiation time, and did not increase linearly with an increase of TiO₂ content. Though the surface topography of ABS changed little, the adhesion strength reached 1.25?kN/m, which was higher than that in the optimal H₂SO₄–MnO₂ colloid. The surface chemistry results indicated that –COOH and –OH groups formed with the photocatalytic treatment and the absorption strengths increased with the UV power. XPS analysis results further demonstrated that the contents of C=O and –COOH reached 6.4 and 4.9% with the photocatalytic treatment, which was much higher than that of the H₂SO₄–MnO₂ colloid (3.9 and 3.1%). The high contents of C=O and –COOH groups enhanced the surface hydrophilicity of the ABS resin and improved the adhesion strength between the electroless copper film and ABS resin. The results indicated that the photocatalytic treatment was an environment-friendly and effective method to replace the commercial wet chemical process for ABS surface modification.     

Plasma surface modification of polyimide for improving adhesion to electroless copper coatings

The influences of oxygen plasma treatment of polyimide (PI) films on the adhesion of electroless copper coatings as well as on the chemical composition of the film surface and the PI surface morphology were investigated. The plasma operating parameters were 1800 W forward power with O₂ flowing at a rate of 300 cm³/min at a pressure of 200 mTorr. The peel strength increased with decreasing plasma treatment temperature. However, extension of the treatment time at higher temperatures had a positive effect on adhesion. A correlation between the enhancement in peel strength and the content of oxygen-containing groups at the PI surface (investigated using XPS) was observed. A change in the morphology as a result of plasma etching was also observed, in the formation of pits in the film surface. The pits ranged from 3 to 6 μm in depth and the diameter varied from 10 to 200 μm. Comparison of the data obtained after plasma treatment with the results of chemical etching in alkaline solutions of permanganate showed approximately the same adhesion increase (to 0.6 kN/m) in both cases. However, chemical etching did not affect the surface morphology and increased the oxygen content at the PI surface less than the plasma treatment.     

Surface modification studies of Kapton® HN polyimide films

Surface imide hydrolysis of Kapton HN polyimide films in a 1 M KOH aqueous solution was studied using dynamic contact angle measurements, X‐ray photoelectron spectroscopy (XPS) and time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS). The surface energy of Kapton HN increased quickly upon KOH treatment due to the formation of polar polyamate. Prolonged treatment led to a jump in surface energy that we ascribe to the onset of etching causing increased surface roughness. Potassium depth profiles of treated Kapton HN samples measured by XPS and TOF‐SIMS demonstrated that during the first 10 minutes of 1 M KOH treatment the modification depth increased rapidly. Thereafter the thickness of the modified layer no longer increased. For Kapton H films, however, the development of etching was much slower and a steady increase in modification depth was observed even after long treatment times. The different behaviours between Kapton HN and Kapton H films in alkali solutions are analysed and discussed. Copyright © 2003 Society of Chemical Industry     

Surface modification of aromatic polyamide film by remote oxygen plasma

Surface modification of poly(p-phenylene terephthalamide) (PPTA) film by a remote oxygen plasma treatment has been investigated from a viewpoint of comparison with a direct oxygen plasma treatment. We call the modification procedure in a space far away from the oxygen plasma zone “the remote oxygen plasma treatment,” and the modification procedure in a space just in the oxygen plasma zone (a conventional oxygen plasma treatment) “the direct oxygen plasma treatment.” In a space far away from the plasma zone, oxygen radicals rather than electrons and oxygen ions are predominant, and the PPTA film can be modified by the remote oxygen plasma treatment into a hydrophilic surface without heavy degradation of the PPTA film. The PPTA film surfaces modified by the remote oxygen plasma treatment were analyzed with contact angle measurement, scanning microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 831–840, 1997     

Surface modification of aromatic polyamide film by aminoethanethiol solution for silicon rubber composites

The surface modification of poly(p-phenylene terephthalamide) (PPTA) film with 2-aminoethanethiol (AET) to adhere to silicon rubber was investigated. The combination of the AET treatment and the silane coupling treatment is an effective surface modification of the PPTA film for this adhesion. The x-ray photoelectron spectroscopy (XPS) analyses show that the AET treatment does not generate sulfur functionalities at the surface of the PPTA film but does generate oxygen functionalities. In the AET treatment process, a part of the amide groups near the surface of the PPTA film is hydrolyzed to form carboxylic acid groups and amino groups. The oxygen functionalities are condensed at the film surface, and nitrogen functionality is diluted at the film surface. The C(O)O moiety at the PPTA film surface may be a key factor for the adhesion with silicon rubber. The C(O)O moiety is mobile from the bulk of the PPTA film to the film surface. Hot water treatment of the original PPTA film makes the impossible adhesion with the silicon rubber possible. The hot water treatment, however, is not as powerful a surface modification as the AET treatment. © 1995 John Wiley & Sons, Inc.     

稀土复合偶联剂对氢氧化镁的表面改性研究

对超细无机阻燃粉体氢氧化镁进行表面改性可大大改善其与有机高聚物的相容性和加工流动性.选择稀土偶联剂/螯合磷酸酯钛偶联剂作为氢氧化镁的复合改性剂,采用湿法改性处理氢氧化镁.通过表面分析技术测定改性氢氧化镁粉体表面性质;利用差热分析技术(DTA)测定其热起始分解温度;利用傅里叶变换红外光谱仪(FT-IS)证实了氢氧化镁表面改性层的存在.通过实验,得到稀土偶联剂/螯合磷酸酯钛偶联剂复合改性剂表面处理氢氧化镁的最佳工艺条件:浆料质量分数为30%,改性剂稀土偶联剂与螯合磷酸酯钛偶联剂质量比为1.9∶ 1,改性剂用量为2.5%,改性温度为80 ℃,搅拌速率为760 r/min,改性时间为30 min.在此条件下,改性氢氧化镁的吸油值从0.499 7 g/g降至0.336 5 g/g,活化指数从0上升到99.86%,热起始分解温度从341.1 ℃升至366.5 ℃.     

Adhesion enhancement of thin copper film on polyimide modified by oxygen reactive ion beam etching

Polyimide (PI) films were modified by O₂ reactive ion beam etching (RIBE) to enhance the adhesion of subsequently deposited copper films. The adhesion of evaporated copper on the O₂ RIBE-modified PI consisted of three different regimes. The first regime involved chemical reaction between PI and Cu atoms; the second regime involved the mechanical interlocking of the grass-like structure of the modified PI with Cu; and in the third regime, overetching was observed. The locus of failure was also analyzed to understand the adhesion mechanism of Cu on the PI. A 10% decrease in adhesion strength was observed after thermal cycling. Furthermore, humidity tests showed that the adhesion enhancement by mechanical interlocking of the grass-like structure is not affected by the presence of moisture.     

Filling mechanism in microvia metallization by copper electroplating

This work explores the mechanism of microvia filling by copper electroplating using a printed circuit board (PCB) with a specific pattern design. The microvias employed in this work had no sidewall copper layer. The outer and inner copper layers of these microvias that had no sidewall copper layer were together connected to the cathode during electroplating in order to clarify the mechanism of bottom-up filling. A plating formula that was composed of CuSO₄, H₂SO₄, polyethylene glycol (PEG), bis(3-sulfopropyl) disulfide (SPS), Cl⁻ and Janus Green B (JGB) was employed as a model formula for studying the filling mechanism. The results showed that bottom-up filling stemmed from two crucial factors. One was the sidewall growth of the microvia, increasing the surface coverage of an accelerator; the other was the convection-dependent adsorption (CDA) of additives, leading to different copper deposition rates on the outer and inner copper layers. When a leveler was present in the plating solution, CDA behavior dominated the filling mechanism, regardless of whether a sidewall copper layer was present. On the other hand, the mechanism of coverage accumulation of the accelerator was dominant only when the microvia possessed a sidewall copper layer and no leveler was present in the plating solution.     

聚酰亚胺薄膜表面无钯活化化学镀铜

为了增加聚酰亚胺薄膜表面与化学镀铜层的结合力,采用NaOH溶液对其表面进行化学改性,然后在其表面制备出具有催化活性的银微粒,进而化学镀铜。使用傅里叶变换衰减全反射红外光谱仪(FTIR-ATR)和能谱分析仪(EDS)对聚酰亚胺的表面结构和组成进行了表征和分析,利用X射线衍射(XRD)及扫描电子显微镜(SEM)表征铜镀层的结构及表面微观形貌。结果表明,聚酰亚胺表面在NaOH溶液中发生水解,在AgNO3溶液中实现Ag+与Na+间的离子交换,Ag+通过化学吸附附着在聚酰亚胺表面。在镀铜液中,Ag+先被甲醛还原成银微粒,从而引发化学镀铜反应的发生,并可获得结合力良好的化学镀铜层。     

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.     

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.     

Surface modification of Inconel-600 by growth of a hydrous oxide film

In this study, Inconel-600 (Ni–Cr–Fe alloy) was modified by repetitive potential cycling in 1M NaOH solution. This procedure induced the growth of a hydrous oxide film, following the same mechanism as previously reported for pure nickel in alkaline solution under similar experimental conditions. The electrode, modified by 30 repetitive potential cycles, exhibited about one order of magnitude lower current density in both the active and passive ranges of the anodic polarization curve. Selective dissolution of nickel and iron in acid solution was determined by rotating ring–disc electrode measurements. This process resulted in chromium enrichment as shown by use of X-ray electron spectroscopy. The proposed model for the enhanced stability of the modified electrode agrees with the percolation model of passivity of stainless steels and Fe–Cr alloys.     

Surface modification of Inconel-600 by growth of a hydrous oxide film

In this study, Inconel-600 (Ni–Cr–Fe alloy) was modified by repetitive potential cycling in 1M NaOH solution. This procedure induced the growth of a hydrous oxide film, following the same mechanism as previously reported for pure nickel in alkaline solution under similar experimental conditions. The electrode, modified by 30 repetitive potential cycles, exhibited about one order of magnitude lower current density in both the active and passive ranges of the anodic polarization curve. Selective dissolution of nickel and iron in acid solution was determined by rotating ring–disc electrode measurements. This process resulted in chromium enrichment as shown by use of X-ray electron spectroscopy. The proposed model for the enhanced stability of the modified electrode agrees with the percolation model of passivity of stainless steels and Fe–Cr alloys.