Thin Layer Of Epoxy Research Articles

Epoxy polymer surface modification through wet-chemical organic surface synthesis for adhesion improvement in microelectronics

Wet-chemical surface synthesis reactions were performed on thin epoxy layers for usage as a build-up layer in microelectronics. The synthesis reactions, based on heterocyclic organic coupling agents, were used to imprint iminodiacetic acid and imidazole groups at the surface of the epoxy polymer, based on nucleofilic substitution reactions. The synthesized surfaces are examined by means of XPS and ATR-IR measurements. XPS measurements illustrate that the identity of the chemical groups near the interface (top 10 nm of the polymer surface) has been altered by the procedure. After the synthesizing procedure, copper was electrochemically deposited using an electroless/electroplating scheme. The type of groups located at the surface of the polymer has a pronounced influence on the adhesion strength of electrochemically deposited copper. Hence the interface between the copper and epoxy determines the adhesion properties between both. The surfaces of the peeled polymer layers and the backs of the copper strips were examined by XPS after the peeling procedure in order to determine the interface failure mechanism.

Design and fabrication of a 40-MHz annular array transducer

This paper investigates the feasibility of fabricating a five-ring, focused annular array transducer operating at 40 MHz. The active piezoelectric material of the transducer was a 9-microm thick polyvinylidene fluoride (PVDF) film. One side of the PVDF was metallized with gold and forms the ground plane of the transducer. The array pattern of the transducer and electrical traces to each annulus were formed on a copper-clad polyimide film. The PVDF and polyimide were bonded with a thin layer of epoxy, pressed into a spherically curved shape, then back filled with epoxy. A five-ring transducer with equal area elements and 100-microm kerfs between annuli was fabricated and tested. The transducer had a total aperture of 6 mm and a geometric focus of 12 mm. The pulse/echo response from a quartz plate located at the geometric focus, two-way insertion loss (IL), complex impedance, electrical crosstalk, and lateral beamwidth all were measured for each annulus. The complex impedance data from each element were used to perform electrical matching, and the measurements were repeated. After impedance matching; fc approximately equal to 36 MHz and -6-dB bandwidths ranged from 31 to 39%. The ILs for the matched annuli ranged from -28 to -38 dB.

Failure initiation in an epoxy joint between two steel plates

An Irwin-like criterion, initially developed to predict crack initiation in monolithic v-notched specimens, is used to examine the failure of two steel plates bonded together by an epoxy joint. It is based on an estimate of the critical value of the intensity factor of the elastic singular fields appearing in some regions of the structure, due to the geometry and to the elastic mismatch of the components. The analysis is worked out at two scales: a macroscopic one ignoring the thin epoxy layer and considering the two plates as perfectly bonded along an idealized interface and a microscopic one taking into account the elastic fields within the joint. It is shown that these two approaches are equivalent and that a macroscopic failure criterion can be developed. The characteristic failure parameter is a macroscopic critical intensity factor. It can be derived from the knowledge of microscopic data such as the strength and the toughness of the epoxy.

Fracture testing of Brazilian disk sandwich specimens

The reliability of a joint subjected to mechanical and thermal loads during processing and service constitutes a major technical problem. Joints contain flaws. The observed strength of a joint depends upon the location and size of the flaws, as well as the crack path through the joint. The aim of this investigation is to measure the fracture toughness of a crack in an adhesive joint, as well as to observe its path through the bond. Sandwich Brazilian disk specimens made of two aluminum adherends joined by a thin layer of epoxy are employed in the testing. A thin paraffin notch is located within the adhesive layer. Numerical analyses are carried out to calibrate the specimens. It is seen that asymptotic expressions for the energy release rate and phase angle of a sandwich specimen with a thin layer are inappropriate in this investigation. A wide range of mixed modes is attained with this specimen. Values of the critical energy release rate Gc are obtained as a function of the phase angle ψ. A fracture criterion is compared to the results. During testing, all cracks divert from within the layer and grow toward and into the interface. Comparison of crack path direction is made to two theories.

Experimental Study of the Local Convection Heat Transfer From a Wall-Mounted Cube in Turbulent Channel Flow

This paper presents some results of the experimental investigation of the local convective heat transfer on a wall-mounted cube placed in a developing turbulent channel flow for Reynolds numbers between 2750 < ReH < 4970. Experiments were conducted using a specially designed cubic assembly made of heated copper core and a thin epoxy layer on its surface. The distribution of the local heat transfer coefficient was obtained from the surface heat flux evaluated from the heat input and computed temperature field in the epoxy layer, and from the surface temperature distribution acquired by infrared thermography. In parallel, the flow field was studied using laser doppler anemometer and flow visualizations, aimed at correlating the local heat transfer with the flow pattern and turbulence field. The complex vortex structure around the cube, in particular at the top and the side faces, caused large variation in the local convective heat transfer. The largest gradients in the distributions of the surface heat transfer were found at locations of flow separation and reattachment. Areas of flow recirculation are typically accompanied by a minimum in the heat transfer coefficient. It is argued that the local temperature rise of the air in the recirculation zone is caused by the trapped vortex, which acts as an insulation layer preventing the removal of heat from the surface of the cubes. In contrast, the intermittent reattachment of the low-temperature shear flow was found to produce large heat transfer coefficients.

Electrical conduction models for isotropically conductive adhesive joints

An electrical conduction model for silver filled isotropically conductive adhesives (ICA) was developed. The model combines the microscopic resistance of the bulk silver particles and the contact between silver flakes with the macroscale resistor network calculation by percolation theory. The resistivities of the composites were calculated by resistor network simulations considering both contact effects and particle size effects. Three different types of film typically exist on the silver surface: residual organic films; tarnish films; and a thin epoxy layer. The contact resistance between silver flakes can be due to a constriction resistance, to the tunneling resistance through insulating films, or to the resistance of more conductive layers. The constriction resistance is produced by the restriction of the current flow by small contact spots and is controlled by the actual contact spot area (metallic contact), which is dependent on the contact force between flakes. The tunneling resistance is caused by the very thin layer which may reside on the silver flakes between the metallic contact spots, and is dependent on a barrier film thickness and potential. Oxide and sulfide tarnish films are typically degenerate semiconductors. Two- and three-dimensional (2-D and 3-D) computer simulations were performed to predict the effects of particle sizes, shapes, and distribution on the percolation conduction thresholds and cluster sizes. The model predicts that the percolation threshold decreases with broad particle size distributions and high aspect ratio particles. The effective resistivity of the adhesive depends on the thickness dimension of the adhesive pad geometry, with very thin layers resulting in high percolation thresholds and high resistivities. Resistivity does not change with the pad thicknesses greater than a certain thickness level. Silver flake orientation on the surface increases the resistivity of the conductive adhesive pads, but in the same magnitude range. The resistivities of the materials are controlled by silver flake sizes and the nature of the contacts.

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties. III. Longitudinal (0°) Compressive Properties of Graphite/Epoxy Composites

An experimental investigation was performed to quantify the relationship between fiber-matrix adhesion as determined by single fiber interfacial shear strength tests with the compressive properties and failure modes of unidirectional graphite/epoxy com posites. The compression tests were conducted on three identical sets of composites differ ing only in their fiber-matrix interfacial shear strength. The interfacial shear strength was varied by using the same graphite fibers with different surface treatments, namely un treated, surface treated, and surface treated and coated with a thin layer of epoxy. The sur face treatment changed the interfacial shear strength by more than a factor of two, while the properties of the fibers remained unchanged. The experimental results show that the fiber surface treatment affects the compressive modulus only marginally. However, the compressive strength and maximum compressive strain were highly sensitive to the fiber surface treatment. Both the strength and maximum strain increased with the interfacial shear strength. The fracture surface analysis revealed that when the fiber-matrix inter facial shear strength was low the compressive failure occurred due to delamination and global delamination buckling. At intermediate values of the interfacial shear strength, the compressive failure occurred due to shear failure driven by inphase microbuckling of fibers. The composites having the highest values of the interfacial shear strength yielded "stepped" fracture surfaces showing compressive failure of fibers in several planes perpen dicular to the fiber axis.

Structure and properties of a new κ-phase organic metal: (BEDT-TTF) 2Cu 2(CN) 3

The electro-synthesis, structure and conductivity of a new κ-phase organic metal (BEDT-TTF) 2Cu 2(CN) 3 are described [BEDT-TTF = bis(ethylenedithio)tetrathiafulvalene C 10H 8S 8]. Partially oxidized BEDT-TTF cations form a structure similar to that found in the κ-phase superconductors, while Cu 2(CN) 3 −1 anions form infinite two-dimensional sheets which alternate with layers of BEDT-TTF cations along the crystallographic a axis. The morphology and conductivity of the crystals are dependent on the electrocrystallization conditions. Samples prepared under certain conditions show a semiconductor-to-metal transition in the 10–30K range, while others have an immeasurably large resistance in this temperature range, even though the room-temperature crystal structures are identical, and EDX shows all samples to have the same composition. However, application of a thin layer of epoxy induces the transition in all samples, and enhances the low-temperature conductivity of some samples by a factor of about 100. Low temperature crystallographic measurements of the unit cell change on cooling indicate the epoxy-coating to reduce the thermal contraction of the samples, in particular in the direction of the crystallographic a-axis.

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties: I. Inplane and Interlaminar Shear Behavior of Graphite/Epoxy Composites

An experimental investigation was performed to establish the relationships between fiber-matrix adhesion as determined by single fiber interfacial shear strength tests with the inplane and interlaminar shear properties of graphite/epoxy composites. ±45°-tension, Iosipescu, and short beam shear tests were conducted on three identical sets of composites differing only in their fiber-matrix interfacial shear strength. The fiber-matrix interphase and consequently the interfacial shear strength was varied by using the same graphite fiber was different surface modifications, namely untreated, surface treated, and surface treated and coated with a thin layer of epoxy. The surface modification changed the interfacial shear strength by more than a factor of two, while the properties of fibers remained unchanged. The experimental results showed that both inplane and interlaminar shear strengths increased approximately in the same ratio as the interfacial shear strength, however, the inplane shear modulus was relatively insensitive to the fiber surface modifications. The fracture surface analysis revealed that when the fiber matrix interfacial shear strength was increased from low to intermediate to high values, the major failure modes changed from primarily interfacial failure to a combination of interfacial and matrix failure to primarily matrix failure, respectively, in a manner identical to that observed with the single fiber fragmentation tests.

Effects of oxygen and ammonia plasma treatment on polyphenylene sulfide thin films and their interaction with epoxy adhesive

X-Ray photoelectron spectroscopy (XPS) and infrared reflection absorption spectroscopy (IRRAS) were used to study the chemical modification of polyphenylene sulfide (PPS) thin films on exposure to both oxygen and ammonia plasmas. The XPS results for the oxygen plasma treatment indicated a large oxygen increase with the incorporation of various oxidized carbon species as well as oxidized sulfur. For the ammonia plasma, both nitrogen and oxygen were incorporated. IRRAS proved to complement the XPS results, showing a wide range of C-O and C=O functionalities incorporated on oxygen plasma exposure. For the ammonia plasma treatment, an increase in hydrocarbon, alkene-type fragments, and possibly amine groups was detected. Both the XPS and IRRAS results indicated that exposure of plasma-treated surfaces to epoxy with subsequent carbon tetrachloride washes removed most of the modification originally present after plasma treatment. IRRAS analysis showed that a thin layer of epoxy remained after repeated solvent w...

Development and testing of a new alpha radiac

A new, state-of-the-art alpha radiac has been developed to monitor for alpha contamination in both laboratory and field operations. The detector is a 7.6 cm (3 inch) diameter circular diffused-junction semiconductor with an active detection area of 42.6 cm 2. Its surface is coated with aluminum and a thin layer of epoxy to provide light shielding and protection against abrasion during decontamination. The modular design of the detector-preamplifier, the probe processor unit and the detector interface unit allows for ease in replacement. The electronic components are contained in the probe housing so that only the processed, digitized detector signal is sent to a separate, detached display device. An external computer and IEEE connector are used to set the detector threshold levels and operational parameters, e.g. various calibration factors. Additional enhancements include shock hardening of the detector assembly, shielding from electromagnetic interference, and a removable decontamination shield. Testing and evaluation of prototype units were performed at several military and civilian laboratories to determine the detector's limitations and abilities to monitor alpha radiation, and to determine its capabilities under various operational conditions. These tests indicate that the radiac meets or exceeds the requirements.

A ruggedized ZnS(Ag)/epoxy alpha scintillation detector

An alpha scintillation survey instrument has been developed which is more rugged and efficient than conventional alpha scintillation detectors that use aluminized Mylar ∗∗ ∗∗ Mylar is a trademark of E.I. du Pont de Nemours & Co., Inc., Wilmington, DE, USA. radiation entrance windows. This new detector consists of a mixture of ZnS(Ag) phosphor and optically transparent epoxy. The scintillator mixture is poured into a preformed mold to provide a thin layer of phosphor after the particles settle to the clear epoxy surface. After partial curing, an optically transparent light pipe is coupled to the ZnS(Ag)/epoxy film by using an additional thin epoxy layer, forming a monolithic scintillator assembly. Experimental results indicate that the new probe is 44% efficient (2π) for a large-area 239Pu alpha source; resistant to scratches, tears, and corrosives; watertight; and temperature independent between −20°C and 54°C.

Slow waves, boundary conditions, and reflection and transmission coefficients

Biot's theory of acoustics in fluid-saturated porous media predicts a “fast” compressional wave, a unique “slow” compressional wave, and a shear wave. Experimental work by the authors demonstrated that Biot theory correctly predicts the measured speeds of all three waves. The boundary conditions, however, which must include an additional condition beyond those postulated by elasticity theory to describe the “slow” wave, have not been adequately studied experimentally. Measurements have been made of reflection and transmission coefficients (including velocities and attenuations) at the plane interfaces between water and a water-filled porous slab at ultrasonic frequencies. At these frequencies, the slow wave is a propagating mode and is readily measurable, but only if the porous medium has a carefully chosen pore structure. By using either an open pore surface or a sealed (thin layer of epoxy) surface, the excitation of the slow wave can be controlled. Slow waves are generated in the solid even when the interface is sealed. These measurements are compared to predictions using the “open” and “sealed” interface boundary conditions of Deresiewicz and Skalak.

Attempts to improve the bond between cement paste and aggregate

Because there are many coatings on the surface of coarse aggregate particles that reduce the concrete strengths through the reduction of the bond between cement paste and aggregate, a laboratory work is presented whose objective was to find such aggregate coating that improves the concrete strength. To achieve this, coarse aggregate particles were coated with a thin epoxy layer, with or without an adhesive promoter, in which either fine sand particles, or unhydrated Portland cement particles were embedded to make the surface rougher, or chemically more reactive, or both. After the hardening of the epoxy, concrete was made with the coated aggregate and concrete strengths were tested. The test results obtained show that the attempts to increase strength were unsuccessful because even the most effective coating, that with unhydrated Portland cement, produced only small increases in strength.