Adhesion enhancement of polyimide on copper by Ar ion beam etching of copper

Ar ion beam etching (IBE) can be used to roughen a Cu surface and thus improve the adhesion of subsequently spin-coated polyimide (PI) films. During Ar IBE, the surface morphology of sputter-deposited Cu changes from round bumps to a rough cone structure. The ultimate tensile strength (UTS) of the PI/Cu interface is increased for certain specific beam conditions. Under optimal conditions, the UTS of the etched PI/Cu interface (6.2 MPa) is twice that of the unetched PI/Cu interface (3.1 MPa). Cu is detected in the deposited PI by Rutherford backscattering spectrometry (RBS). The amount of Cu at the top surface of the 2.5 μm thick PI film is 0.1 at. %; this is determined by RBS and XPS. While the Cu is dissolved by polyamic acid and diffuses into the PI, an oxygen-rich region is formed in the Cu. The oxygen-rich region in Cu grows from 50 A (approximately Cu₂O) before PI deposition to more than 2000 A (where the oxygen concentration is about 5 at. %) after PI deposition. The oxygen source is not the PI itself but either dissociated oxygen from the water vapor in the PI imidization process or a product of the chemical reaction between Cu and polyamic acid.     

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.     

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.     

Adhesion improvement of electroless copper to a polyimide film substrate by combining surface microroughening and imide ring cleavage

In order to enhance the adhesion strength of copper metal film to a polyimide (PI) film substrate, a method combining surface microroughness formation and imide ring cleavage was investigated. The results showed that imide rings were cleaved with a KOH treatment while carboxyl and amide groups were formed on the surface of the PI film. The surface micro-roughness did not change with the KOH treatment, and the adhesion strength of the copper metal film to the PI film was slightly improved to 30 g/mm, which could be attributed to the interaction of both carboxyl and amide groups with the copper atoms. When the PI films were successively treated with an alkaline permanganate and a KOH solution, many recesses were formed on the surface in an alkaline permanganate solution, and the size and depth of the recesses increased with alkaline permanganate treatment time. The results of the AFM measurements showed that the average roughness (R) increased from 3.54 to 10.23 nm after combined treatment with alkaline permanganate and KOH solutions. The adhesion strength of the copper metal film to the PI film reached 150 g/mm, which was five times greater than that achieved with the KOH treatment only.     

Use of high temperature and high humidity to test the adhesion of sputtered copper to a polyimide surface modified by an AC nitrogen glow discharge

We have used an extreme environmental stress test to study the adhesion of a thin sputtered copper film (0.5 μm) to flexible polyimide (PI) substrates between 25 and 125 μm thick. The polyimide types include Kapton (PMDA-ODA) and Upilex (BPDA-PDA). When there was no surface modification on the PI, the adhesion of the film to Upilex type S was better than the adhesion to Upilex type R or Kapton type HN. When the polymer surface was treated with a simple AC nitrogen glow discharge (NGD), there was an improvement in the adhesion of the film to each of these polyimides. This improvement in adhesion became apparent after the film/substrate combination was subjected to either boiling water or steam for 30 min or more; the difference became quite clear after 2 h. A simple tape test was used to quickly estimate a relative adhesion strength. In order to compare the effect of our AC NGD treatment with other substrate surface modification methods, we used it to improve the coupling of a thick (> 10 μm) layer of copper (via a thin intermediate chromium layer) to a rigid PI substrate, formed from spin coating its precursor onto a silicon wafer. Peel test results were within a factor of 2-3 of the corresponding results obtained with a radio frequency (RF) plasma and ion beam treatments.     

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.     

Interfacial behavior of polyimide/primer/copper system by preoxidation of the primer

The copolymers of vinyl imidazole (VI) and vinyl trimethoxy silane (VTS) were applied as the corrosion inhibitors and the adhesion promoters for the polyimide/copper system at elevated temperatures. The mol ratios of VI to VTS were 100 : 0, 70 : 30, 30 : 70, and 0 : 100. Preoxidation of the primer was performed to improve the reactivity of the primer on poly(amic acid). A peel test was performed to evaluate the adhesion strength of the polyimide/primer/copper system after heat treatment at 400°C in a nitrogen atmosphere. The effect of the preoxidation of the primer on corrosion protection and adhesion promotion were investigated by Fourier transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The adhesion strength of the polyimide/primer/copper system depended on not only the chemical interaction between polyimide and the preoxidized primer, but also the thermal stability of the primer. It showed the highest value when the mol ratio of VI to VTS was 30 : 70. The primer layer reduced or suppressed copper diffusion into the polyimide layer. The degree of corrosion protection by the primer was affected by its thermal stability and its reactivity on copper. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2518–2524, 2000     

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。     

Reduced copper diffusion in layered silicate/fluorinated polyimide (6FDA‐ODA) nanocomposites

The copper diffusion barrier properties of layered silicate/fluorinated polyimide nanocomposites were analyzed by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). It was found that the particles of copper are effectively retarded from penetrating into the polyimide matrix by layered silicates. The diffusion coefficients of layered silicate/polyimide nanocomposites are lower than that of the pure polyimide. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1422–1425, 2004     

Changes in the adhesion strength between copper thin films and polyimide substrates after heat treatment

The adhesion strength between a copper (Cu) thin film and a polyimide [pyromellitic dianhydride-oxydianiline (PMDA-ODA)] substrate is reduced by heat treatment at 150°C in air. In this work, we determined the changes in adhesion strength between Cu films and polyimide substrates using Auger electron spectroscopy (AES), attenuated total reflection Fourier-transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The analysis showed that the weak boundary layer (WBL) shifted towards the Cu interface as the heat treatment time was increased. To confirm this shift, we looked at two other polyimide substrates: biphenyl dianhydride-p-phenylene diamine (BPDA-PDA) and biphenyl dianhydride-oxydianiline (BPDA-ODA). Comparing the adhesion strength for the Cu thin film, the adhesion strength was high for the Cu/PMDA-ODA and Cu/BPDA-ODA laminates, but very low for the Cu/BPDA-PDA laminate. One of the possible reasons for this behavior could be that the ether moiety between the two benzene rings in ODA is related to the adhesion between a Cu film and an 0₂-plasma-treated polyimide (PI) substrate. The relationship between the adhesion strength and chemical bonding states is also discussed. We conclude that a Cu thin film sputtered onto a PI substrate is apt to peel at the oxidized interface, due to the heat treatment.     

Adhesion at copper- polyamide 11- copper and aluminum-poly amide 11-aluminum laminate interfaces: influence of metal surface oxidation

Adhesion at copper-polyamide 11-copper and at aluminum-polyamide 11-aluminum laminate interfaces was studied. Metal-polymer-metal laminates were prepared by compression molding using processing conditions similar to the normal melt processing of polyamide 11. The results show that the time of contact at the molding temperature required to reach a constant level of adhesion is significant. Mild oxidation of the metal prior to molding improves the adhesion of polyamide 11 to aluminum; with copper, a monotonic slow decrease in adhesion with the oxidation time is observed. The presence of a metal surface affects the crystallization behavior of polyamide. With a cooling rate of 40-50°C/min, an approximately 15 μm transcrystalline polymer layer is formed with a degree of crystallinity that is almost 10% higher than the material away from the interface. The metal substrate surface oxidation prior to molding does not change the crystallinity profile of the polymer in the bulk. The polymer surface crystallinity is also a function of the time of contact with the metal substrate. The cooling rate and the metal substrate structure and its nucleating activity are responsible for the surface/bulk crystallinity ratio. Although the highly-crystalline polymer surface layer improves the adhesion to some extent, the formation of active species on the polymer surface which are able to react with the metal surface is mostly responsible for the increase of adhesion with time and its ultimate strength.     

Water diffusion studies in polyimide thin films

The water diffusion behaviors and activation energies of PDA- and ODA-based polyimide thin films were quite dependent on both the chemical structure and the morphological structure in the films. The water diffusion coefficients of polyimide thin films increased with increasing temperature. The activation energies varied in the range of 5.81 to 9.27 kcal/mol and were relatively higher for the PDA-based polyimide thin films than for the corresponding ODA-based polyimide thin films. For the PDA- and ODA-based polyimide films, the differences in the morphological structures and the chemical affinity to water molecules might be reflected directly on the water diffusion behaviors. The PDA-based polyimide films exhibited a relatively more ordered morphological structure (high crystallinity and good in-plane orientation) than that of the corresponding ODA-based polyimide thin films, which may serve as impenetrable obstacles for the water diffusion in the out-of-plane direction. Consequently, it may lead to a relatively slower water diffusion and high activation energy in the PDA-based polyimide thin films. Additionally, the PDA-based polyimide films with relatively lower chemical affinity showed relatively low diffusion coefficients and high activation energies. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 731–737, 2001     

Adhesion improvement of epoxy resin/copper lead frame j oints by azole compounds

The adhesion strength of epoxy resin/copper joints is often very poor, due to the naturally formed copper oxide having a low mechanical strength. To improve the adhesion strength of epoxy resin/copper lead frame joints, copper lead frames were treated with azole compounds as adhesion promoters. The azole compounds used were benzotriazole (BTA), benzotriazole-5-carboxylic acid (CBTA), 8-azaadenine, imidazole, 2-methyl imidazole, urocanic acid, adenine, benzimidazole, and polybenzimidazole (PBI). The dependence of the adhesion strength of epoxy resin/azole-treated copper joints on the structure of the azole compound, the azole treatment time, and the azole treatment temperature was investigated. The surface coverage of azole-treated copper was examined by contact angle measurements, a surface defect test, optical microscopy, and scanning electron microscopy (SEM), and the locus of failure was studied by X-ray photoelectron spectroscopy (XPS). Triazole compounds such as CBTA and 8-azaadenine showed excellent adhesion strength; imidazole-based azole compounds did not improve the adhesion strength. However, the adhesion strength of CBTA- and 8-azaadenine-treated joints decreased with increasing treatment time, since thick porous Cu-azole complexes had a weaker mechanical strength when formed. The polymeric azole compound PBI showed the highest adhesion strength, 785 N/m, because of complete coverage of the copper surface. The thermal stability of azole compounds and epoxy resin/azole-treated copper joints was also investigated. CBTA and 8-azaadenine did not decompose up to 250°C, while PBI was stable up to 500°C in an air atmosphere.     

Adhesion promotion of the polyimide–copper interface using silane-modified polyvinylimidazoles

In order to promote the interfacial adhesion strength between polyimide (PI) and copper, the copper surface was treated with polyvinylimidazole (PVI) or silane-modified PVIs. They were prepared by the copolymerization of 1-vinylimidazole (VI) with the following silane coupling agents: 3-(N-styrylmethyl-2-amino-ethylamino)propyltrimethoxysilane (STS), vinyltrimethoxy silane (VTS), allyltrimethoxy silane (ATS), and γ-methacryloxypropyltrimethoxysilane (γ-MPS). The mole ratio of the silane coupling agent to VI was fixed at 1 : 1. The lap shear strengths between PI and copper were measured at the following different bonding temperatures: 290, 320, 350, and 380°C. In each case, the maximum adhesion strength was obtained at 350°C. VTS-modified PVI showed the best performance on adhesion promotion of the PI–copper interface. Fourier transform infrared spectroscopy was applied to investigate the thermo-oxidative degradation of PI and oxidation of copper. In addition, scanning electron microscopic analysis and contact angle measurements were performed for the investigation of the interaction between PI and silane-modified PVIs. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1343–1351, 1998     

The use of peel tests to examine the self adhesion of polyimide films

Peel tests were used to examine the adhesion between two layers of the polyimide pyromellitic dianhydride-oxydianiline (PMDA ODA). The main thrust of this work was to examine these tests with particular emphasis on yielding in bending of the peeled strips. Two peel geometries and a range of sample thicknesses were used to study interfaces whose strength could be varied over a wide range by changing the cure schedule. The peel strength varied with strip thickness and often reached a peak at an intermediate thickness. The results were shown to agree qualitatively with a combination of two theoretical models for the effects of yielding on peel tests. It was also found that a second problem of polyimide adhesion, the effect of solvent swelling, could significantly enhance the adhesion between polyimide layers.     

Electrochemical studies on aniline-pentamer-based electroactive polyimide coating: Corrosion protection and electrochromic properties

In this study, electrochemical investigations of corrosion protection and the electrochromic properties of an aniline-pentamer-based electroactive polyimide (AP-based EPI) coating prepared by oxidative coupling polymerization are presented. The in situ chemical oxidation of the reduced form of soluble, electroactive poly(amic acid) (EPAA) in N-methyl-2-pyrrolidone (NMP) was monitored by UV–Vis absorption spectra. Moreover, the electroactivity of the AP-based EPI was evaluated by performing electrochemical CV studies. Based on a series of electrochemical measurements in 3.5 wt% NaCl electrolyte, the AP-based EPI coating was found to exhibit enhanced corrosion protection effects on cold-rolled steel (CRS) electrodes as compared to the corresponding non-electroactive (NEPI) coating. A possible mechanism for the enhanced corrosion protection of EPI coatings on the CRS electrode has been proposed as follows: (1) EPI coatings may act as a physical barrier and (2) the redox catalytic properties of the aniline pentamer units in EPI may induce the formation of a passive metal oxide layer on the CRS electrode, as evidenced by SEM and ESCA studies. The electrochromic performance of EPI was investigated by measuring electrochromic photographs and UV absorption spectra.     

Local spin density investigation of the chromium / polyimide interface

Bonding of chromium to the polyimide, PMDA-ODA, surface is still the subject of debate. In an attempt to clarify this problem, we have performed density functional theory calculations on different model molecules, phthalimide, PMDA, and PAP (p-amino phenol), which represent the most functionalities of the polyimide (PMDA-ODA). If we consider only the low spin case, we find that chromium bonds preferentially to the phenyl ring. However, when we release the spin constraint and optimize the structure, we find that the absolute stable configuration is that of chromium in a quintet state, at a carbonyl group. The energy difference is 0.30 eV. The complete infrared spectrum has been calculated for phthalimide and compared with experimental spectra. The agreement is excellent. A vibrational analysis for the Cr/phthalimide system, in both configurations (Cr on C=O and Cr on phenyl), in their stable spin states, is presented. We find that the former yields better agreement with experiment than the latter.     

Adhesion between submicrometer polystyrene spheres

The sphere-substrate contact method was usually used to study adhesion theory because it is rather difficult to make two micrometer or submicrometer spheres contact precisely. Here, we used sphere-sphere contact method by a novel, simple process to investigate deformations of spheres. The polystyrene particles size ranges from 60 nm to 600 nm. We found that the polystyrene particles underwent plastic deformations due to van der Waals interaction. The contact radii were observed by the scanning electron microscope (SEM).     

聚丙烯薄膜与铜箔的粘接

通过聚丙烯薄膜和铜箔的表面处理和胶粘剂的选择,对它们的粘接进行了研究,经胶接接头的剥离强度和耐溶剂性能测试,筛选出粘接强度高、耐溶剂性能良好粘接接头,结果铜箔和聚丙烯薄膜的最高的剥离强度可达到14N/cm,与不经任何处理的空白试样相比,增加近7倍。     

Indentation test for adhesion measurement of polyimide films

An indentation technique was used to determine the adhesion of polyimide films on a ceramic substrate. Experimental results were obtained by indenting 13 μm thick polyimide films with a conical indenter at different indentation loads. Among the process variables investigated were the amount of adhesion promoter added to the polyimide and the exposure to temperature and humidity. The technique provides a measure of the bond strength, based on the analysis of indentation debonding of thin films. For well adhered films, no debonding could be induced, indicating the usefulness of the test only for the poorly bonded films.