Improving interfacial adhesion between copper foil and resin using amino acid in printed circuit board industry

The corrosion inhibitor of nitrogen-containing amino acid histidine (His) has been applied in brown oxidation solutions and the relationships between brown oxidation solutions with the various concentrations of His and the adhesion strength of copper/resin laminates have been systematically studied by various testing techniques, including electrochemical impedance spectroscopy (EIS), peeling strength and field emission scanning electronic microscope. The result obtained from EIS suggested that His exhibited excellent anti-corrosive performance which contributed to a higher stability of the organic metallic film post brown oxidation process treatment. The roughness surface like honeycomb structure was gained and peel strength of the Cu/resin laminates was raised up to 0.71 kg/cm by altering the concentration of His in brown oxidation solutions. Moreover, theoretical calculations manifested that the studied inhibitor was almost adsorbed in parallel on the copper surface and X-ray photoelectron spectroscopy (XPS) declared that the value of adhesion strength was related to the surface chemistry of copper foil and resins after the lamination process which may attribute to chemical reactions at the copper/resin interface.     

Analysis of the Molecular Structure at the PPS/Copper Interphase and its Role in Adhesion

X-ray photoelectron spectroscopy (XPS) was used to examine the interfacial chemistry in polyphenylene sulfide (PPS)/copper bonded laminates. Several surface pretreatments were studied including a simple methanol wash, two acid etches, thermal oxidation and chemical oxidation. Peel test analysis showed poor adhesion to the methanol-washed and acid-etched foils, giving a peel strength of only 3-5 g/mm. XPS analysis of the failure surfaces revealed a large amount of inorganic sulfide at the interface with reduction of the copper oxide. Chemical oxidation using an alkaline potassium persulfate solution gave a matt-black surface consisting of primarily cupric oxide. These samples showed improved adhesion and XPS analysis of the failure surfaces revealed fracture through a mixed PPS/cuprous oxide layer. A simple thermal oxidation yielded a cuprous oxide surface layer and laminates bonded to these surfaces showed a more than ten-fold increase in peel strength. XPS analysis of the failure surfaces showed much lower amounts of interfacial copper sulfide and it was postulated that excess sulfide at the interface was responsible for the poor adhesion observed for other pretreatments.     

Effect of the microstructure of copper oxide on the adhesion behavior of epoxy/copper leadframe joints

The thermal oxidation of copper leadframe was carried out at 175°C and the adhesion behavior of the epoxy/copper leadframe joint was analyzed by investigating the microstructure changes of copper oxide with the thermal oxidation time of copper. The peel strength increased sharply at an early stage of oxidation (~20 min) followed by a slight increase. After further oxidation (120 min), the peel strength showed a slight decrease. The contact angles of water and diiodomethane decreased sharply at an early stage of oxidation with negligible change afterwards. As the oxidation time increased, X-ray photoelectron spectroscopy (XPS) results revealed that the chemical composition of copper oxide had changed (Cu/Cu₂O → Cu₂O → CuO); this change improved the wettability of the copper surface, which affected the peel strength. Increase of the surface roughness of copper oxide, investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM), causes the epoxy resin and copper oxide to undergo mechanical interlocking, which increases the peel strength. Failure analysis by SEM and XPS indicated that failure was largely in the copper oxide, and the amount of copper oxide on the peeled epoxy increased as the oxidation time increased, due to the weak mechanical strength of the oxide layer. However, a small portion of the epoxy resin was also fractured during the failure process, regardless of the oxidation time. Consequently, fracture proceeded mainly in the copper oxide close to the epoxy resin/copper oxide interface.     

Oxidation of the copper alloy with pure copper plating

The oxidation failure of a copper alloy lead frame with/without a copper plating layer was investigated. The oxidation rate and adhesion strength of oxide films on copper alloy substrates were studied by measuring the thickness and by carrying out peel tests. The adhesion strength of the oxide film was mainly influenced by the composition but not the thickness of the oxide film. The highest adhesion strength was obtained when the oxide film was composed mainly of Cu₂O. When the thickness of the copper preplated layer was over 0.165?μm, the Cu atoms of the preplated copper were available for oxidation. Thus the oxidation process was within the copper preplated layer, and the main product of the oxidation was Cu₂O. It was found that the large column grain of the oxide film on the copper alloy with a copper plated layer, favored the diffusion of copper or oxygen atoms that led to the formation of Cu₂O, and lead to higher adhesion strength. This indicated that the oxidation resistance of a copper alloy lead frame can be effectively improved by electroplating copper.     

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。     

A New Approach to the Copper/Epoxy Joint Using Atmospheric Pressure Glow Discharge

A new approach for adhering copper to an epoxy resin was studied. In this new approach, the copper surface was first treated with hydrogen plasma generated by the atmospheric pressure glow (APG) discharge. Then a thin film of γ-aminopropyltriethoxysilane (γ-APS) was formed on the treated copper surface. The copper oxide formed by air on the copper surface deteriorated the adhesion by forming a weak boundary layer, part of which could separate from the surface. This oxide layer was reduced when an APG hydrogen plasma was applied for a couple of minutes at a frequency of 13.56 MHz and a power input of 200 W. The resulting peel strength at the copper/epoxy interface increased up to ca. 0.9 Kg/cm. Curing temperature of γ-APS was also an important factor in obtaining good adhesion at the copper/epoxy interface, with the highest value of peel strength occurring at a curing temperature of 120°C.     

Temperature effect on PI/Cu interface

The interfacial reaction and peel strength of polyimide with copper foil at various cure schedules have been investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and peel test to determine the temperature effect on polyimide/copper interface diffusion and adhesion. SEM studies indicate that the polyimide/copper interfaces are fairly smooth for all samples studied in this experiment. The TEM microstructure reveals the existence of a copper-polyimide interaction zone at the interface when it is cured at a temperature higher than 250°C, which also results in a high peel strength. XPS spectra revealed higher copper and carbonyl carbon contents at the polyimide interface when it is cured at a high-temperature schedule (350°C). From the results of these interface studies, it is concluded that chemical bonding resulting from the interaction of copper oxide and polyimide carbonyl group provides the binding force for polyimide and copper foil. © 1993 John Wiley & Sons, Inc.     

Adhesion and interface studies between copper and polyimide

The adhesion and interface structure between copper and polyimide have been studied. Polyimide films were prepared by spinning a polyamic acid solution (Du Pont PMDA-ODA) in an NMP solvent onto a Cu foil, followed by thermal curing up to 400°C. The adhesion strength was measured by a 90° peel test. The peel strength of 25 μm thick Cu foil to 25 μm thick polyimide substrate was about 73 g/mm with the peel strength decreasing with increasing polyimide thickness. Cross-sectional TEM observation revealed very fine Cu-rich particles distributed in the polyimide. Particles were not found closer than 80-200 nm from Cu boundary. These Cu-rich particles were formed as a result of reaction of polyamic acid with Cu during thermal curing. We attribute the high peel strength to interfacial chemical bonding between Cu and polyimide. This behavior is in contrast to vacuum-deposited Cu onto fully cured polyimide.     

Adhesion of Polyethylene to Metals: The Role of Surface Topography

Previous work established the importance of the fibrous substrate topography in obtaining good adhesion of polyethylene to matt black oxide films formed on copper in alkaline solution. In this paper the effect of the very rough surface topography is shown to be general. Anodising treatments for copper and zinc and a high temperature oxidation for steel are described which give a very rough surface consisting (respectively) of fibrous, dendritic and blade-like growths. The peel strength of polyethylene to these substrates is high even under circumstances, for example when the polymer is stabilised with anti-oxidant, where adhesion to a chemically similar smooth surface is low. The high peel strength is associated with large amounts of energy being dissipated during peeling in plastic deformation of the polymer near the interface. It is suggested that this is caused by the development of high shear stress concentration at the fibre ends causing yielding in a large volume of polymer.     

Spray Deposition Methods for Improving Interfacial Strength of Copper–Epoxy Systems

A simple spray method using a plain orifice atomizer has been developed for depositing γ-aminopropyltriethoxysilane (APS) from solutions in water and in methanol onto copper surfaces. The evaporative patterns of the sprayed droplets were studied to determine the distribution of deposited APS and the percent coverage of the surface. The peel strengths between copper foil and epoxy resin were measured with and without APS deposition. It was shown that the application of APS resulted in a considerable increase in interfacial adhesion. APS applied from a 1 wt% solution in methanol resulted in a higher peel strength than when applied from a 1 wt% aqueous solution; the opposite was true with 0.2 wt% APS solutions, indicating a trade-off between deposited APS film thickness and surface coverage. In all cases, a higher concentration of APS gives a higher peel strength. APS was very effective when chemisorption occurred at the surface but much less effective when only physisorption took place. A study of the fracture surfaces showed cohesive failure inside the epoxy layer, and that the deposited APS on the copper surfaces had a long-range effect which was seen deep into the epoxy layer, well away from the copper surface.     

Improving interfacial adhesion between thermoplastic polyurethane and copper foil using amino carboxylic acids

A chemical methodology to improve the adhesion between copper foil and a thermoplastic polyurethane (TPU) matrix is reported. The copper foil (0.127 mm thickness) was treated with aminocarboxylic acid‐based coupling agents such as 6‐aminohexanoic acid and 4‐aminobenzoic acid. 3‐Aminopropyl trimethoxysilane was also used as a conventional silane coupling agent for comparative studies. The interfacial adhesion between copper foil and laminated TPU was examined by means of peel adhesion test, scanning electron microscopy, and attenuated total reflection‐infrared spectroscopic methods. The treatment of copper foils with 6‐aminohexanoic acid resulted in improved adhesion, which was equal to that of the silane‐treated system. The mechanism of how the coupling agents strengthen the interfacial adhesion between TPU and copper foil is discussed. The solution concentrations of the coupling agents were optimized with respect to the peel adhesion of the interface. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Improved adhesion between Kapton film and copper metal by silane-coupling reactions

Kapton film, poly[(N,N′-oxydiphenylene)pyromellitimide], was modified by silane-coupling reactions using 3′(trimethoxysilyl)propoxy-2-hydroxypro-pyl-1,3-diazole (Si–imidazole) to improve the adhesion with copper metal. The Kapton film surface was first treated with argon plasma for 30 s, then dipped into a methanol solution of Si–imidazole (0.01 wt %), followed by heating at 110°C for 90 min. The Kapton surfaces, modified by the argon plasma and Si–imizadole coupling reactions, were analyzed by water contact-angle measurement, atomic force microscopy, and XPS. The Si–imidazole modification showed a large increase in adhesion between the copper metal and the Kapton film. The peel strength of the copper metal/Kapton film joint increased from 0.94 to 2.4 N/5 mm. The failure occurred at the interface between the Si–imidazole and the Kapton film layer. We conclude that the Si–imidazole modification is an effective treatment for improvement of the adhesion between copper metal and Kapton film. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1645–1654, 1999     

Effects of Surface Modifications on the Peel Strength of Copper Based Polymer/Metal Interfaces with Characteristic Morphologies

This paper summarizes a study on the effect of changes in surface chemistry on the peel strength of copper/polymer interfaces. Two different surface topographics were created and evaluated, one produced by cleaning and etching in sodium persulfate, the other by etching then mechanically roughening using 180 grit sandpaper. Both surfaces were then oxidized in an alkaline/oxidizing treatment to form cupric oxide. Ion implantation and benzotriazole priming modified the surface chemistry of the cupric oxide samples. After lamination to form an epoxy/copper interface, peel strength measurements were taken. The results showed that ion implantation degraded the peel strength while priming with benzotriazole improved the peel strength compared with the unmodified cupric oxide. In a separate comparison study, peel strength measurements were taken on interfaces formed from copper oxides with the same oxide structure but with widely different gross morphologies, “As laminated” adhesive strength was virtually the same. The bonded interfaces were aged at elevated temperature and the peel strength obeyed first order degradation kinetics. Two terms can be determined from the degradation studies, the first is the long term peel strength, A(∞), and the other is Ω, the degradation rate with units of time^-1. A value of A(∞) was 3.0 lbs/in for etched copper interfaces while A(∞) was 0.5 lbs/in for the sanded interfaces.     

Adhesion to Sodium Naphthalenide Treated Fluoropolymers. Part III. Mechanism of Adhesion

Adhesion of fluoropolymers to copper and to other polymers is examined using a range of fluoropolymer types (PTFE, PFA, extruded, skived and cast films), surface modification techniques such as sodium naphthalenide (Na/naphth), acid stripping and lamination to produce surfaces of controlled roughness, and three tests of adhesion (90 degree peel tests, torsional shear tests and stripping of transmission electron microscopy (TEM) replicas). A combination of chemical and physical modification is required to produce good adhesion, with the relative importance of each dependent upon the specific adhesion test used. For relatively smooth-surfaced films, Na/naphth appears to function by increasing both the chemical functionality and the mechanical integrity of a surface layer. Untreated PTFE and PFA show interfacial failure and negligible adhesion. Smooth-surfaced PTFE with superficial surface modification, e.g. after lamination to shiny copper foil or after acid stripping of defluorinated material, often fails by fibrillation of the fluoropolymer surface. For short sodium etch times, adhesion is improved and the failure mode is interfacial. For long etch times, there is a mixed mode of failure. Fibrillation in smooth-surfaced PFA systems was not observed. Adequate adhesive strength in these systems could only be achieved by an increase in the surface roughness. The best adhesion could be achieved by surface roughening, followed by Na/naphth treatment. For such PTFE surfaces plated with copper, peel and shear tests showed a mixed mode of failure, with copper and fluoropolymer found on both failure surfaces by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDS). Extensive fibrillation occurred at the locus of failure. Provided chemical modification is adequate to allow wetting, the roughness of the surface dominates the properties of the adhesive bond. Prolonged Na/naphth treatment (e.g. one hour) causes a reduction in peel strengths.     

Surface modification of thermotropic poly(oxybenzoate‐co‐oxynaphthoate) copolyester by remote oxygen plasma for copper metalization

Poly(oxybenzoate‐co‐oxynaphthoate) (POCO) film surfaces were modified with remote oxygen plasma, and the effects of the modification on the adhesion between the copper layer and POCO were investigated. The remote‐oxygen‐plasma treatment led to a noticeable decrease in the contact angle, which was mainly due to the C? O functional groups on the surface. The modification of the POCO surface by remote oxygen plasma was effective in improving the adhesion with copper metal. The peel strength for the copper metal/POCO system was enhanced from 10 to 127.5 mN/5 mm by the surface modification. The failure mode of the copper metal/POCO system was an interface layer between the oxidized micro‐POCO fibril surface and the copper metal layer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2400–2408, 2003     

Adhesion to Sodium Naphthalenide Treated Fluoropolymers. Part III. Mechanism of Adhesion

Adhesion of fluoropolymers to copper and to other polymers is examined using a range of fluoropolymer types (PTFE, PFA, extruded, skived and cast films), surface modification techniques such as sodium naphthalenide (Na/naphth), acid stripping and lamination to produce surfaces of controlled roughness, and three tests of adhesion (90 degree peel tests, torsional shear tests and stripping of transmission electron microscopy (TEM) replicas). A combination of chemical and physical modification is required to produce good adhesion, with the relative importance of each dependent upon the specific adhesion test used. For relatively smooth-surfaced films, Na/naphth appears to function by increasing both the chemical functionality and the mechanical integrity of a surface layer. Untreated PTFE and PFA show interfacial failure and negligible adhesion. Smooth-surfaced PTFE with superficial surface modification, e.g. after lamination to shiny copper foil or after acid stripping of defluorinated material, often fails by fibrillation of the fluoropolymer surface. For short sodium etch times, adhesion is improved and the failure mode is interfacial. For long etch times, there is a mixed mode of failure. Fibrillation in smooth-surfaced PFA systems was not observed. Adequate adhesive strength in these systems could only be achieved by an increase in the surface roughness. The best adhesion could be achieved by surface roughening, followed by Na/naphth treatment. For such PTFE surfaces plated with copper, peel and shear tests showed a mixed mode of failure, with copper and fluoropolymer found on both failure surfaces by x-ray photoelectron spectroscopy (XPS) and energy dispersive x-ray spectroscopy (EDS). Extensive fibrillation occurred at the locus of failure. Provided chemical modification is adequate to allow wetting, the roughness of the surface dominates the properties of the adhesive bond. Prolonged Na/naphth treatment (e.g. one hour) causes a reduction in peel strengths.     

氮化铝陶瓷覆铜基板的研制

通过高温热氧化的方法,在ＡＩＮ陶表面形成一薄层ＡＩ２Ｏ３作为过渡层,成功地将铜与ＡＩＮ陶瓷键合在一起,研制出性能优越的ＡＩＮ陶瓷覆铜基板。研究了ＡＩＮ热氧化时间及温度对键合质量的影响,提出子较佳的儿得的键合力可达１１０Ｎ／ｃｍ,同时,运用扫描电镜（ＳＥＭ０、电子能谱（ＥＤＸ）对键合结构作了分析和研究。ＡＩＮ衬底上的氧化物相对键合过程中上重要作用。     

Surface modification of polyimide film by coupling reaction for copper metallization

In this study, Upilex-S [poly(biphenyl dianhydride-p-phenylene diamine)], one of polyimide films, was modified by coupling reactions with N,N-carbonyldiimidazole (CDI) to increase adhesion to copper for flexible copper clad laminate (FCCL). Imidazole groups show strong interaction with copper metal to make charge transfer complexes. Because polyimide film did not have active site with coupling agent, the film surfaces were modified by aqueous KOH solutions and reacted with dilute HCl solutions.Surface modified Upilex-S was analyzed by X-ray photoelectron spectroscopy (XPS) to examine the surface chemical composition and film morphology and investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Changes in the wettability were evaluated by measuring contact angle with the sessile drop method. After deposition of copper on surface modified Upilx-S, the adhesion strength of the copper/polyimide system was measured by a 90° peel test using the Instron tensile strength tester. The peel strength of the copper/polyimide system increased from 0.25 to 0.86 kg_f/cm by surface modification. This result confirmed that the CDI coupling reaction is an effective treatment method for the improvement of the adhesion property between copper metal and polyimide film.     

Improvement in the adhesion between copper metal and polyimide substrate by plasma polymer deposition of cyano compounds onto polyimide

The surface modification of Kapton film by means of plasma polymer deposition is discussed from the viewpoint of improving the adhesion between copper metal and Kapton film substrate. Plasma polymers of AN (acrylonitrile) and FN (fumaronitrile) were used for the surface modification, and the adhesion between the copper metal and the plasma polymer-coated Kapton film was evaluated by the T-peel strength measurement. The surfaces of peeled layers were analyzed by X-ray photoelectron spectroscopy (XPS) and the failure mode is discussed. The plasma polymer deposition of AN and FN shows an effective improvement in the adhesion between the copper metal and Kapton film; in particular, the AN plasma polymer deposition increased the peel strength 4.3 times. Failure occurred mainly in the Kapton film, and the adhesion between the AN plasma polymer and the Kapton film and that between the copper metal and the AN plasma polymer were found to be quite strong.     

The effect of water on the adhesion of organic coatings on aluminium

Water normally decreases the strength of adhesive joints. In the case of epoxy coatings on aluminium, however, after an initial decrease the adhesive strength increased with the time of exposure to water. It is suggested that this increase is caused by the hydration of aluminium oxide adjacent to the adhesive joint, thus enabling additional hydrogen bonding between the organic coating and its support.

Results obtained by measuring adhesion with peel and tape tests on aluminium foil and an alloy with different surface pretreatments and different curing conditions have been compared. It is shown that the tape test is useful for the semi-quantitative determination of the stability towards water of an adhesive joint.