Adhesion Of Copper Research Articles

A Low-Cost Hands-On Laboratory for an Undergraduate Microwave Course

A low-operating-cost microwave laboratory for undergraduate students is presented, which emphasizes fundamental concepts while enabling students to gain practical experience with the design and measurement of microwave circuits. By training the students in the proper use of modern microwave test equipment, students are able to test hand-built circuits, made of adhesive copper tape, using modern vector network analyzers. Additional experiments with waveguides, and several systems applications, such as radar experiments, provide students with an exciting laboratory experience.

Experiences with peel strength

PurposePeel strength numbers are part of a laminate's specifications and should characterize the specific bond performance (copper adhesion) under test conditions. Unfortunately, from both a theoretical and a practical point of view they are not able to do that. This study seeks to address this issue.Design/methodology/approachThis paper has been written to show the main impacts on the measured peel strength numbers in the IPC‐TM‐650 peeling test. From an extensive database regarding peel numbers for diverse foil types, foil thicknesses and treatment roughnesses it is possible to show the influence of prepreg type, foil thickness and roughness on the measure peel strength.FindingsCopper adhesion to laminating resin is insufficiently described by peel strength data because of the impacts of foil thickness, stiffness on bending (physical bending work, stress distribution underneath the peeling line) and the treatment roughness. The latter works reinforcing regarding the (low) resin strength and this influence is measured on resin strength instead of real bond. Fracture due to peeling is cohesive, mostly with a totally intact copper‐resin interface. This is especially true in high performance laminates that show low peel strengths not because of bad copper bonding but because of brittle resins (filled and unfilled).Originality/valueUsers have to understand the limited benefit of the IPC peel test in characterizing copper‐resin bonds. Peel increase on (low bond) high performance resins by increased foil roughness is not a practical way in the field because of no bond improvement (interface) and heavy disadvantages in dielectric thickness (HiPot tests at thin core laminates), respectively.

Effects of Polymer Architecture and Composition on the Adhesion of Poly(tetrafluoroethylene)

Poly(glycidyl methacrylate), PGMA, chains in linear and arborescent structures were incorporated onto surfaces of poly(tetrafluoroethylene), PTFE, films by hydrogen plasma and ozone treatment and atom transfer radical polymerization. The epoxide groups of the PGMA chains were further reacted with acetic acid (AAc), oxalic acid (XAc), allyl amine (AA), and ethylenediamine (EDN) to introduce hydroxyl and amine groups to the surfaces of the PTFE films. Surface characterizations performed by Fourier Transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the surface modification and the chemical structure. The PGMA chains in arborescent structures show a high effectiveness for the enhancement of the adhesion of PTFE films. The adhesion of PTFE films was also significantly enhanced by ring-opening reactions of the PGMA epoxide groups with acetic acid and amine compounds. A high value of 9.5 N cm(-1) in the optimum 180 degrees peel strength test was observed with PTFE/copper assemblies.

Enhancement of Epoxy Resin/Copper Heterojunction by Introduction of Sulfur‐Containing Polymers

AbstractSummary: Epoxy resins are widely used in electronics and electric industries because of their superior properties. In recent years, excellent bonding properties for metals (e.g., copper, gold, aluminium, silver, etc.), to which it is hard to adhere, have become desirable for epoxy resins in the electric and electronics industrial fields. However, epoxy resins have only poor bonding strength to the metals. In order to increase the heterojunction strength between epoxy resins and copper, the introduction of sulfur, providing strong interactions with metals, was investigated. TDP polyester and MPS polythioesters containing sulfur moieties were employed as the sulfur‐containing modifiers for the epoxy resin. Epoxy resins containing a modifier (5–20 phr) and a curing agent were cured between copper plates at 120 °C for 2 h and at 170 °C for 2 h. The effect of the added modifiers was evaluated by the lap‐shear testing method. It could be demonstrated that MPS polythioesters have a beneficial effect on the enhancement of the epoxy resin/copper heterojunction. The most effective example was the addition of 20 phr of the MPS_7 polythioester, which increased the lap shear strength from 5.7 to 17 MPa.Improvement of lap shear strengths of adhesive copper joints by sulfur‐containing modifiers.magnified imageImprovement of lap shear strengths of adhesive copper joints by sulfur‐containing modifiers.

Ab initio modeling of copper adhesion on regular BaTiO 3(0 0 1) surfaces

Ab initio calculations have been performed for copper adsorption on a regular, defect-free TiO 2- and BaO-terminated (0 0 1) surfaces of a cubic BaTiO 3, using a posteriori HF-CC method as implemented into the CRYSTAL-03 computer code. To clarify the nature of the interfacial bonding, we use slab models of the Cu/BaTiO 3(0 0 1) interfaces with different one-side substrate coverages, varied from 1/8 monolayer (ML) up to 1/2 ML, over both TiO 2- and BaO-terminated surfaces. TiO 2 termination has been found to be energetically more favorable for the adsorption of copper atoms. In agreement with previous experimental and theoretical data, our calculations indicate essential contribution of atomic polarization into the interaction between Cu atoms and surface O 2− ions. An increase of substrate coverage by copper simultaneously reduces the binding energy (per adatom) and enhances the interatomic interactions inside growing metallic film.

Applications of electron-beam generated plasmas to materials processing

Nonequilibrium (T/sub e//spl Gt/T/sub ion,gas/) plasma processing often allows for greater process control with reduced environmental impact when compared to other materials processing methods, and therefore presents tremendous opportunities in the areas of thin film development and surface modification. The U.S. Naval Research Laboratory's "Large Area Plasma Processing System" (LAPPS) has been developed based on the high-energy (2 keV) electron-beam ionization process, with the goal of maximizing the benefits of plasma processing over large areas (/spl sim/1 m/sup 2/). This system has been shown to be: 1) efficient at producing plasma in any gas composition; 2) capable of producing low-temperature plasma electrons (<0.5 eV) in high densities (10/sup 9/-10/sup 12/ cm/sup -3/); and 3) scalable to large area (square meters). In this paper, the progress of a number of applications using LAPPS is discussed. Nitride growth in stainless steel was investigated, which demonstrated high rates (over 20 /spl mu/m/h/sup 1/2/) at low temperatures (/spl les/462/spl deg/C). Complementary mass spectrometry showed that the nitriding results correlated to the flux of atomic ions delivered to the substrate. LAPPS was also combined with magnetron sputtering sources to form hybrid systems for thin film deposition of nitrides. The simultaneous operation of LAPPS with a titanium magnetron sputter source increased the growth of the <200> orientation in TiN films, due to the increased atomic nitrogen ion flux. Polymer pretreatment studies were also initiated in these systems; polytetrafluoroethylene substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. Similarly dramatic fluorination of polyethylene was demonstrated with plasmas generated in Ar/SF/sub 6/ mixtures.

Influence of the polymer pre-treatment before its electroless metallization

In order to activate polyvinylidene fluoride (PVDF) surfaces, a mixed Pd-Sn colloidal solution is used for further copper deposition. The plasma pre-treatment is performed using N2 or N2/H2 reactive gases. The conditions to prepare the colloidal solution like reaction temperature and growth time of colloids as well as the plasma processing conditions are studied in order to establish the elaboration and treatment parameters that allow obtaining the highest concentration of metallic palladium and also the good adhesion of copper onto the PVDF surface. This study is essentially supported by X-ray photoelectron spectroscopy (XPS) analysis.

Adhesive copper films for an air-breathing polymer electrolyte fuel cell

A design for an air-breathing and passive polymer electrolyte fuel cell is presented. Such a type of fuel cell is in general promising for portable electronics. In the present design, the anode current collector is made of a thin copper foil. The foil is provided with an adhesive and conductive coating, which firstly tightens the hydrogen compartment without mask or clamping pressure, and secondly secures a good electronic contact between the anode backing and the current collector. The cathode comprises a backing, a gold-plated stainless steel mesh and a current collector cut out from a printed circuit board. Three geometries for the cathode current collector were evaluated. Single cells with an active area of 2 cm 2 yielded a peak power of 250–300 mW cm −2 with air and pure H 2 in a complete passive mode except for the controlled flow of H 2. The cells’ response was investigated in steady state and transient modes.

Plasma enhanced surface treatments using electron beam-generated plasmas

NRL has developed a ‘large area plasma processing system’ (LAPPS) utilizing a high energy (∼2 keV) modulated electron beam to drive the plasma ionization. This system has been shown to be (1) efficient at producing plasma in any gas composition, (2) capable of producing low temperature plasma electrons (<0.5 eV) in high densities (10 9–10 12 cm −3) and (3) scalable to large area (square meters). In this work, the progress of a number of applications using LAPPS is discussed. Nitride growth in stainless steel was investigated, which demonstrated high rates (up to 20 μm/h 1/2) at low temperatures (≤462 °C). Complementary mass spectrometry showed that the nitriding results correlated to the flux of atomic ions delivered to the substrate. LAPPS was also combined with magnetron sputtering sources to form hybrid systems for surface pretreatments of polymers for metallization and thin film deposition of nitrides. In these systems, Teflon® substrates pretreated with an oxygen LAPPS exposure demonstrated a significant increase in copper and aluminum film adhesion compared to untreated substrates, with the dominant factor believed to be the changed surface morphology. The simultaneous operation of LAPPS with a titanium magnetron sputter source increased the growth of the 〈200〉 orientation in TiN films, due to the increased atomic nitrogen ion flux. Additional LAPPS systems are also discussed.

Replacement of pickling with shot blasting for wire rod preparation

An oxide scale layer covers steel wire rod produced by hot rolling. This oxide is often removed by pickling before wire drawing; otherwise, hard oxides will be impressed into the wire surface and give an inferior surface quality. Stricter pollution regulations increase the incentive to replace pickling with mechanical descaling. This paper gives results from tests on carbon steels by using shot blasting to descale wire rod. The tests include: (i) shot blasting experiments in an industrial full‐scale in‐line shot blasting machine, (ii) laboratory drawing experiments on shot blasted wire rod, (iii) industrial trials on shot blasted wire rod at the drawing plants. There are differences in the appearance of surfaces between shot blasted and pickled wires, but no differences in the drawing process were observed in the laboratory experiment. In the industrial trials the wear of dies were more severe when drawing shot blasted wire of one of the steel grades. In the downstream processes, problems were recorded with the cleanness of the surface of another grade and adhesion of copper coating on a third grade.

A comparative study of Ag and Cu adhesion on an MgO(001) surface

Ab initio calculations were performed on 2D slab models of copper and silver adhesion on a perfect MgO(001) surface using density functional theory (DFT) combined with the localized atomic wave functions, as implemented in both CRYSTAL-98 and CRYSTAL-03 computer codes. To clarify the nature of the interfacial bonding, we consider slab models of the Ag/MgO(001) and Cu/MgO(001) interfaces with six different substrate coverages, varied from 1 4 monolayer (ML) up to 2 ML. The dependence of several key interface properties on the substrate coverage is analyzed. For all coverages, the most favorable sites for the adsorption of metal atoms are found to be above the surface O 2− ions, whereas Cu atoms are found to be more strongly bonded on a magnesia substrate, with shorter bond lengths z Cu – O 2 − . Our calculations indicate that a weak atomic polarization induces the interaction between the metal atoms and the defect-free MgO substrate and gives the dominant contribution to the bonding on the regular interfaces. Growth of metal coverage simultaneously reduces the binding energy with substrate per adatom and enhances the interatomic interaction inside the metal adlayer.

Ab initio Calculations of Copper Nanostructures of MgO Substrate

Ab initio slab simulations were performed for copper adhesion to a perfect MgO(001) surface using the DFT-LCGTF method as implemented in CRYSTAL98 computer code. In order to clarify the nature of interfacial bonding, we considered a slab model of the Cu/MgO(001) interface with regular 1/4 monolayer (ML), 1/2 ML, 1 ML and 2 ML substrate coverages and verified the results of our calculations. In particular, the dependences of the adhesion energy per Cu atom, projections of multipole moments as well as total and projected densities of states (DOS) on the substrate coverage by a metal are analyzed. Computer simulation indicated that physical adsorption makes the dominant contribution to bonding on the regular Cu/MgO(001) interface.

First principles slab calculations of the regular Cu/MgO(0 0 1) interface

Ab initio slab calculations are performed for the copper adhesion over magnesium ions on the perfect MgO(0 0 1) surface with 1/4 monolayer (ML), two types of 1/2 ML and 1 ML substrate coverages. Results of our calculations are compared with various experimental and theoretical data. Both small atomic polarization and charge redistribution give the dominant contributions to the physisorption bonding on a regular Cu/MgO(0 0 1) interface.

Susceptibility of low-density lipoprotein to oxidation and circulating cell adhesion molecules in young healthy adult offspring of parents with type 2 diabetes*1

Relatives of subjects with type 2 diabetes carry an increased risk for diabetes and cardiovascular disease. Oxidative modification of low-density lipoprotein (LDL) and proinflammatory processes are believed to have central roles in atherogenesis. We have investigated the susceptibility of LDL to oxidation and circulating cell adhesion molecules in healthy, glucose-tolerant adults (aged 18 to 38 years) with (12 men, 2 women) and without (controls; 12 men, 2 women) a parental history of type 2 diabetes. From fasting blood samples, oxidation of LDL was initiated with copper ions and adhesion molecules were measured using immunoassays. Groups were similar with respect to age, body mass index (BMI), blood pressure, plasma glucose, and serum lipids. Resistance of LDL to oxidation was reduced in offspring of parents with type 2 diabetes (time to Vmax, 80.1 ± 2.2 v 91.4 ± 2.6 minutes, P = .003). Plasma hydroperoxides did not differ between groups (1.2 ± 0.1 v 1.1 ± 0.1 μmol/L). Soluble intracellular adhesion molecule-1 (sICAM1) was elevated in offspring compared with controls (571 ± 20 v 447 ± 20 μg/L, P = .0002). Soluble vascular cell adhesion molecule-1 (sVCAM-1) (1,184 ± 76 v 1084 ± 56 μg/L, P = .31) and E-selectin (53 ± 8 v 53 ± 7 μg/L, P = .98) did not differ between groups. Reduced resistance of LDL to oxidation and increased circulating sICAM-1 in young healthy adult offspring of parents with type 2 diabetes may be intrinsic to increased risk of atherosclerosis in these subjects.

Copper/polyimide fabrication process for above-IC integration of high quality factor inductors

This paper reports on a technological process that combines copper and a low-k dielectric to provide high Q inductors for radio-frequency (RF) integrated circuits (ICs). Using a 4–8 μm-thick Cu and polyimide as dielectric (εR=2.9), we target quality factors in excess of 10 over a wide frequency range: 0.8–10 GHz. This performance cannot be obtained with standard Al/SiO2 or even with more advanced thin-Cu/low-k interconnects currently available in ICs. We demonstrate successful fabrication results with various inductor geometries (horizontal-plane spirals) in terms of: (i) excellent gap filling (down to 2 μm), (ii) very good adhesion of copper to tantalum barrier and (iii) sharply defined copper/polyimide interface using one-metal-level CMP process on thick electroplated copper films (>4 μm).

Susceptibility of low-density lipoprotein to oxidation and circulating cell adhesion molecules in young healthy adult offspring of parents with type 2 diabetes

Relatives of subjects with type 2 diabetes carry an increased risk for diabetes and cardiovascular disease. Oxidative modification of low-density lipoprotein (LDL) and proinflammatory processes are believed to have central roles in atherogenesis. We have investigated the susceptibility of LDL to oxidation and circulating cell adhesion molecules in healthy, glucose-tolerant adults (aged 18 to 38 years) with (12 men, 2 women) and without (controls; 12 men, 2 women) a parental history of type 2 diabetes. From fasting blood samples, oxidation of LDL was initiated with copper ions and adhesion molecules were measured using immunoassays. Groups were similar with respect to age, body mass index (BMI), blood pressure, plasma glucose, and serum lipids. Resistance of LDL to oxidation was reduced in offspring of parents with type 2 diabetes (time to Vmax, 80.1 ± 2.2 v 91.4 ± 2.6 minutes, P = .003). Plasma hydroperoxides did not differ between groups (1.2 ± 0.1 v 1.1 ± 0.1 μmol/L). Soluble intracellular adhesion molecule-1 (sICAM1) was elevated in offspring compared with controls (571 ± 20 v 447 ± 20 μg/L, P = .0002). Soluble vascular cell adhesion molecule-1 (sVCAM-1) (1,184 ± 76 v 1084 ± 56 μg/L, P = .31) and E-selectin (53 ± 8 v 53 ± 7 μg/L, P = .98) did not differ between groups. Reduced resistance of LDL to oxidation and increased circulating sICAM-1 in young healthy adult offspring of parents with type 2 diabetes may be intrinsic to increased risk of atherosclerosis in these subjects.

Copper/polyimide fabrication process for above-IC integration of high quality factor inductors

This paper reports on a technological process that combines copper and a low- k dielectric to provide high Q inductors for radio-frequency (RF) integrated circuits (ICs). Using a 4–8 μm-thick Cu and polyimide as dielectric ( ε R=2.9), we target quality factors in excess of 10 over a wide frequency range: 0.8–10 GHz. This performance cannot be obtained with standard Al/SiO 2 or even with more advanced thin-Cu/low- k interconnects currently available in ICs. We demonstrate successful fabrication results with various inductor geometries (horizontal-plane spirals) in terms of: (i) excellent gap filling (down to 2 μm), (ii) very good adhesion of copper to tantalum barrier and (iii) sharply defined copper/polyimide interface using one-metal-level CMP process on thick electroplated copper films (>4 μm).

Adhesion of Copper to Teflon ® poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) Surfaces Modified by Vacuum UV Photo-oxidation Downstream from Argon Microwave Plasma

ABSTRACTGood practical adhesion of sputter-deposited Cu is achieved to poly(tetrafluoroethylene-co-perfluoropropyl vinyl ether) (PFA) surfaces at short treatment times of vacuum UV (VUV) photo-oxidation downstream from Ar microwave (MW) plasma. Factors contributing to the adhesion include: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; (4) cross-linking at the surface and (5) incorporation of oxygen as CF-O-CF2, CF2-O-CF2 and CF-O-CnF2n+1 moieties. With long treatment times, a cohesive failure occurred within the modified PFA and not at the Cu-PFA interface due to extensive chain scission weakening its mechanical properties.

Adhesion of copper to poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces modified by vacuum UV photo-oxidation downstream from Ar microwave plasma

Poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) surfaces were exposed to vacuum UV (VUV) photo-oxidation downstream from Ar microwave plasma. The modified surfaces showed the following: (1) an improvement in wettability as observed by water contact angle measurements; (2) surface roughening; (3) defluorination of the surface; and (4) incorporation of oxygen as CF—O—CF2, CF2—O—CF2 and CF—O—CF3 moieties. With long treatment times, a cohesive failure of copper sputter-coated onto the modified surface occurred within the modified FEP and not at the Cu–FEP interface.

Effects of surface treatment on the adhesion of copper to a hybrid polymer material

The effects of various surface pretreatments on the adhesion of electroless and sputter-deposited copper metallizations to a hybrid polymer material were investigated. Without pretreatment, the adhesion between copper and the polymer was virtually zero. The adhesion of electroless copper to the polymer was poor regardless of the pretreatment used. However, the wet-chemical pretreatment of the polymer surface markedly increased the adhesion of sputtered copper to the polymer. It preferentially removed the inorganic part of the polymer and formed micropores on the surface. The plasma and reactive ion etching pretreatments, in turn, selectively etched away the organic part of the polymer and noticeably increased the hydrophilicity. Although this resulted in even higher increase in the surface free energy than was achieved with the chemical treatment, the granular surfaces became mechanically brittle. With the help of x-ray photoelectron spectroscopy, scanning electron microscopy, atomic force microscopy, and contact-angle measurements and with the recently developed pull test, the physicochemical changes of the wet-chemically pretreated polymer surfaces were demonstrated to have significant effects on the adhesion.