Surface Contact Angle Measurements Research Articles

Effect of the plasma cleaning process on plastic ball grid array package assembly reliability

Interface delamination is recognized as one of the major failures of microelectronics packaging. It can result from various factors, including stresses from mismatch of adherent materials, hygrothermal stress from the release of vapor pressure of moisture during soldering reflow process, and interface material adhesion strength. The failure mechanisms are associated with cyclic loads, temperature and moisture condition as well as interface adhesion strength degradation. This paper focuses on the evaluation of plasma cleaning on PBGA assembly, including resistance to interface delamination. Two different plasma systems, powered by radio frequency (RF) and microwave (MW) energy, are studied. The optimized plasma cleaning process parameters are obtained by surface contact angle measurements. The plasma cleaning results are also verified by scanning electron microscopy (SEM) as well as physical pull and shear tests. The test vehicles are 27/spl times/27 mm 292-ball PBGAs. The results from encapsulation peel tests, die and encapsulant pull tests, bonding wire pull tests and C-Mode SAM (C-SAM) examination are presented. It is clear that an optimal plasma cleaning process can be achieved with different plasma systems. The experimental results also demonstrate that plasma cleaning has little effect on wire bonding process and die attach pull strength for given substrates and assembly materials. In all the cases, optimal plasma cleaning steps improve PBGA resistance against interface delaminations for cases where plasma cleaning is carried out before encapsulation process. Moreover, different plasma cleaning techniques would affect the assembly productivity, investment and yield. This paper demonstrates that the optimized plasma cleaning process would enhance PBGA package qualification level and improve the process yields and productivity.

Synthesis and Surface Property Variations of Polypropylene-graft-poly(ethylene glycol)

Graft copolymers containing nonpolar main chains and polar side chains capable of acid–base interaction show surface property variations depending on the sample preparation methods. A series of polypropylene-graft-poly(ethylene glycol)s were synthesized and their surface property variations were studied using surface analysis techniques, such as surface contact angle measurement and X-ray photoelectron spectroscopic analysis. Molding against various substrates, dip-coating, vacuum annealing, and water-contact techniques were employed for the experiment. Different surfaces were obtained depending on the degree of acid–base interaction between the polymer surface and interfacing phase. These surface property variations were concluded to be the result of minimum interfacial free energy formation.

Evidence for surfactant contributing to the gastric mucosal barrier of the horse.

This study was undertaken to determine the hydrophobicity of the luminal surface of the equine stomach and to elucidate the ultrastructure of the lining imparting that property. Gastric and duodenal mucosal samples from 5 horses were collected immediately after euthanasia and subjected to surface contact angle measurement using a goniometer. Gastric mucosal samples from 4 horses and a foal were examined by electron microscopy following a fixation procedure known to preserve phospholipids and oligolamellar structures. Contact angles for the equine gastric glandular mucosal surface (mean +/- s.e. 78.0 +/- 11.0 degrees) were greater than for the duodenum (33.4 +/- 8.7 degrees), (P = 0.003). The contact angles for gastric squamous tissue (50.4 +/- 4.5 degrees) tended to be greater than for duodenum (P = 0.15). Electron microscopy revealed the existence of surfactant as abundant osmiophilic phospholipid material within both squamous and glandular gastric mucosae. These results indicate the hydrophobic nature of the equine gastric mucosae. We propose that the water-repellent nature of the stomach contributes to the 'gastric mucosal barrier' and is imparted by surface-active phospholipid adsorbed to the surface. Phospholipids may also be utilised as a physical barrier to back-diffusion of acid by lining intracellular canaliculi and oxyntic ducts where other defence mechanisms are absent.

Synthesis and properties of polyurethane modified with an aminoethylaminopropyl-substituted polydimethylsiloxane. II. Waterborne polyurethanes

A series of polyurethane (PU) emulsions modified with aminosilicone were synthesized, based on 2,4-toluene diisocyanate (TDI), poly(tetramethylene oxide) (PTMO), and dimethylolpropionic acid (DMPA) as a prepolymer which was chain-extended with aminoethylaminopropyl polydimethylsiloxane (AEAPS) in an aqueous emulsion. Their chemical compositions, structures, bulk and surface properties, and emulsion morphologies were investigated using Fourier transform infrared spectrum analysis (FTIR), tensile and surface contact angle measurements, electron spectroscopy for chemical analysis (ESCA), water swellablity, an emulsion stability test, and transmission electron microscopy (TEM). It was shown that the PU emulsions were stable and the siloxane chains were enriched on the PU surface. The water resistance of the PU film increased but the bulk tensile properties of the PU film were not changed significantly with a small amount siloxane modification up to 6 wt %. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 295–301, 2001

Contact angles of surfactant solutions in oil solvents on low energy solid surfaces

We have measured contact angles for a range of pure oils of different cohesive energy density and surfactant solutions in oil on polyethylene (PE) and polytetrafluoroethylene (PTFE) solid surfaces. For the pure oils, the measured contact angles are in approximate agreement with values calculated using dispersion force theory. Using measurements of surface tension and contact angle as a function of surfactant concentration, we have estimated surfactant adsorption isotherms at the oil/vapour surface and the ratio of the extents of adsorption at the oil/vapour and solid/oil surfaces. For alkylbenzenes in di-iodomethane (DIM) it is found that the extents of adsorption at the DIM/vapour and PTFE/DIM surfaces are similar whereas extents of adsorption at the PE/DIM surfaces are lower. n-Dodecyl pentaoxyethylene glycol ether (C12E5) adsorbs at the DIM/vapour surface but not at either the hexadecane (HD)/vapour or squalane (SQ)/vapour surfaces. For all the oils tested, C12E5 shows virtually zero adsorption at the solid/oil surface.

Styrenic surfmer in emulsion copolymerization of acrylic monomers. II. Copolymerization and film properties

Polymerizable styrenic surfactants (surfmers) and nonreactive analogs, have been applied in emulsion copolymerization of acrylic monomers in a seeded semibatch process. Stable core-shell latexes with low levels of coagulum and controlled particle size have been obtained; some of them, with either steric or electrosteric stabilization, display excellent stability to electrolytes, freeze–thaw cycles, and shear flocculation. In addition, the reactive surfactants lead to films with superior performance due to reduced migration of surfactant to the surface (contact angle measurements) and dimensional stability when the films are dipped in water, as well as less water uptake. Some differences also appear in particle morphologies. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4205–4217, 1999

Rivulet Formation in Surface-Water Flow on an Airfoil in Rain

The location of the onset of rivulet formation in the surface-water flow over a wing with a NACA 4412 airfoil in rainfall rates of 50-160 mm/h is calculated and compared with wind-tunnel experiments. A model is presented in which rivulets form when the surface-tension shear stress between the liquid and the airfoil surface equals the interface shear stress caused by aerodynamic forces on the liquid due to air motion. Surface-tension shear stresses are ohtained from measurements of surface tension and contact angle at the solid-water interface. Aerodynamic shear stresses are calculated by solution of Reynolds-averaged Navier-Stokes equations

Adsorption of PEO/PPO triblock co-polymers and wetting of coal

The adsorption characteristics of PEO/PPO/PEO triblock co-polymers on coal were investigated using surface tension and contact angle measurements. Although these surfactants have been widely used as wetting agents, it was observed that they increased the hydrophobicity of coal at concentrations below about 10 −6 M. Surface tension studies were carried out to explain the reasons for this behavior. The surface tension versus concentration profiles displayed three distinct regions. In region I, surface tension decreased linearly and monomers were proposed to be the dominant species. This region extended to a surfactant concentration of about 10 −6 M. In region II, a transition region between regions I and III, dimers, trimers, etc., were considered to form. In region III, micelles formed and surface tension was independent of concentration. The concentration at which monomers associate to form dimers, etc., is referred to as the critical association concentration (cac). The contact angle of coal increased when concentration was raised from low values to the cac. It decreased when the reagent concentration was above the cac. Finally, at concentrations above the cmc, the wetting of coal was complete and contact angle was zero.

Direct Surface Force and Contact Angle Measurements of an Adsorbed Polymer with a Lower Critical Solution Temperature

As an example of a polymer with a lower critical solution temperature, TLC, in water, we studied the phase behavior of a poly(N-isopropylacrylamide) copolymer. To adsorb it to a negatively charged surface, we introduced a positively charged comonomer. The combination of direct force measurements with the surface forces apparatus (SFA) and contact angle measurements reveal a lower TLC of the adsorbed layer than in bulk solution. At and above TLC the adsorbed polymer chains collapse and the adsorbed layers on the two opposing surfaces attract each other. The resulting adhesion is strongly dependent on the applied speed of separation, emphasizing the role of slow molecular relaxations and rearrangements above TLC. The results also point to the validity of the time−temperature superposition principle to this polymer system at T > TLC: at a low speed of separation the polymer layer is “liquid-like”, and at high speeds its behavior is more “solid-like”.

Calculation of Adsorption Isotherms on Hard Solid Surfaces Using Measurements of Surface Tensions and Contact Angles

The adsorption excess isotherms of binary mixtures adsorbed on hard solids were calculated by means of surface tension and contact angle measurements using the Gibbs adsorption isotherm equation. The calculation procedure is described in detail using the authors' own measurements of mixtures containing ethylene glycol(1)/water(2) on Teflon and poly(vinyl chloride), and water(1)/n-propanol(2) on Teflon. On the basis of these results and also from surface tensions and contact angles on hard solids published by other authors, all types of isotherms were found as given for porous adsorbents in the classification of Schay and Nagy. In addition to those, new isotherm types are proposed.

A quasi two-dimensional bubble method for surface tension and contact angle measurements at the crystal-melt interface. I. Theoretical background

A method for simultaneous determination of the surface tension of liquids and of the contact angle between liquid and solid is proposed, in view of studying the wettability of a crystal by its own melt. The method is based on the shape of a gas bubble captured at the solid-liquid interface inside a thin cell with plane-parallel walls. This quasi two-dimensional configuration simplifies the theoretical treatment of the bubble shape with respect to that in a three-dimensional space. It is stressed that contact angle is independent of dimensionality.

A quasi two-dimensional bubble method for surface tension and contact angle measurements at the crystal-melt interface. II. Physical realization

An experimental setup for simultaneous measurement of the surface tension of a liquid and of the contact angle at the solid-liquid interface between a crystal and its own melt, is described. The method is based on shape determination of a gas bubble captured at the crystal-melt interface inside a thin cell composed of two plane-parallel glass plates, in contact with a temperature gradient heating block. The feasibility of the method is demonstrated in the case of coumarin.

Use of surface insulation resistance and contact angle measurements to characterize the interactions of three water soluble fluxes with FR-4 substrates

Soldering flux chemistry and its interaction with the printed wiring board have been important reliability concerns for a number of years. Post Vietnam investigation of military hardware revealed corrosion in some areas. The test method most frequently used to assess the corrosion potential of flux residues is surface insulation resistance (SIR) testing. This paper gives some background on surface insulation resistance testing and reports on its application to three different water soluble fluxes. The appearance of surface dendrites is linked to test procedures that allowed water condensation on the board surface. Subsurface conductive anodic filament formation is associated with the use of fluxes which contained polyglycols. The use of contact angle measurements to assess the effect of the soldering flux residues on the board is demonstrated.

Ultrapure poly(vinyl alcohol) hydrogels with mucoadhesive drug delivery characteristics

Poly(vinyl alcohol) (PVA) hydrogels were prepared by treating 15 or 20% aqueous PVA solutions to repeated cycles of freezing for 6 or 12 h at − 20 °C and thawing for 2 h at 25 °C. The resulting gels did not contain any leachable toxic crosslinking agents or other residues. Their adhesive characteristics were examined using tensile experiments in contact with bovine submaxillary mucin. As the number of freezing/thawing cycles increased, the work of fracture (detachment) decreased due to the increase in the PVA degree of crystallinity. The PVA gels prepared from the 20 wt.% solution and exposed to two freezing/thawing cycles exhibited the largest work of adhesion. Surface contact angle measurements of the PVA gel in contact with water were used to evaluate their wettability. As the number of freezing/thawing cycles was increased and the degree of crystallinity increased, there was a decrease in the contact angle. The degree of crystallinity of PVA gels was determined by comparing the heat required to melt a PVA sample to the heat required to melt a 100% crystalline sample. The average degree of crystallinity of PVA samples prepared from 20 wt.% solutions was 19.3% on a dry basis. Oxprenolol and theophylline delivery studies were conducted using PVA samples prepared from a 20 wt.% solution and exposed to two, three or four cycles of freezing for 12 h followed by thawing for 2 h. Drug release was affected by the number of freezing/thawing cycles. Thus, the mucoadhesive characteristics and drug release could be optimized by controlling the freezing/thawing conditions.

Influence of the wetting properties of polymeric adhesives on the mechanical behaviour of cork agglomerates

A series of adhesives, polyurethane prepolymers with alkane chains of different functionalities, were used in the production of cork agglomerates. The polymeric structure varied from long, linear chains in adhesive M1 (14% isocyanate groups) to short, branched chains in adhesive M4 (30% isocyanate groups). The wetting properties of the adhesives were studied through surface tension and contact angle measurements of the polymeric liquids deposited on cork substrates. The mechanical behaviour of the cork agglomerates was studied through compression and three-point bending tests, and the agglomerate structure was analysed by scanning electron microscopy (SEM). The relationship between the structural and wetting characteristics of the adhesives and the mechanical properties of the agglomerates was investigated. The experimental results indicate that it is the work of adhesion for the adhesive/cork system, and not only the contact angle, which determines the mechanical resistance of the cork agglomerate.

Microbial Synthesis of Poly(β-hydroxyalkanoates) Containing Fluorinated Side-Chain Substituents

The preparation of novel fluorinated poly(β-hydroxyalkanoates), PHAs, was carried out using Pseudomonas oleovorans (ATCC 29347) and Pseudomonas putida (KT 2442) as biocatalysts. These organisms were first grown on 40 mM sodium citrate prior to studying polymer formation in the second stage using 1:1 molar mixtures of nonanoic acid (NA) and fluorinated acid cosubstrates. The following fluoro acids were synthesized and used in this study: 6,6,6-trifluorohexanoic acid (TFHxA), 6,6,7,7,8,8,8-heptafluorooctanoic acid (HpFOA), 6,6,7,7,8,8,9,9,9-nonafluorononanoic acid (NFNA), and 6,6,7,7,8,8,9,9,10,10,11,11,11-tridecafluoroundecanoic acid (TDFUDA). In general, the use of NA/fluoro acid cosubstrate mixtures instead of only NA in second-stage cultivations resulted in little to no cellular toxicity as measured by values of colony-forming units per milliliter. The mol percent incorporations of fluorinated side chains was determined by 1H and 19F NMR spectroscopies, and peak assignments were made using two-dimensional reverse-detected heteronuclear multiplet quantum correlation (HMQC) as well as 1H−1H correlation spectroscopy (COSY). P. putida formed PHA after a 3-day second-stage cultivation time with 17.3 mol % fluorinated side chains using NA/NFNA as cosubstrates. For shorter second-stage cultivation times (1 day) where product yields were relatively higher, 0.3 g/L of product was formed that contained 6.4 mol % fluoroalkanoate side groups using P. oleovorans as the biocatalyst and NA/HpFOA as cosubstrates. The incorporation of 12.4 mol % fluoroalkanoate repeat units resulted in products which showed melting at higher temperatures (55−80 °C), crystallized at faster rates from the melt, and had higher heats of fusion. Investigation of the surface free energy of products by surface contact angle measurements showed only a modest increase from 87 to 94° for PHAs containing 0 and 17.3 mol % fluorinated side chains.

A video-enhanced plate method for simultaneous measurements of surface tension and contact angle

The assumption of zero contact angle of the Wilhelmy plate method causes error for the surface pressure-area characteristics of some spread monolayers. To avoid this problem, a video-enhanced plate method is developed to monitor the dynamic surface tension and contact angle simultaneously. According to this method, the profile of the air–water interface adjacent to a flat plate is captured by an image digitization technique. The surface tension and contact angle are obtained from the best fit between the edge coordinates of the captured image and a theoretical equation derived from the Young–Laplace equation. Preliminary results show satisfactory agreement between the curve of the air–water interface obtained from experimental data and the theoretical curve for obtained values of surface tension and contact angle. Twenty tests for pure water at 25 °C give an average surface tension 72.0±0.2 mN/m, which confirms the accuracy of this method. A preliminary dynamic test also indicates that the effect of the contact angle in the Wilhelmy method can be corrected by dividing the apparent surface tension obtained from the Wilhelmy method by the cosine of contact angle measured by the present method.

Langmuir-Blodgett multilayers of native and synthetic glycerol-dialkylglycerol tetraether derivatives from archaea

Langmuir-Blodgett films of monosubstituted glycerol-dialkyl-glycerol tetraether with phosphomyoinositol group extracted from thermophilic archaebacterium Sulfolobus solfataricus are successfully deposited. However, the procedure of film deposition is rather complicated. Reproducibility of the results is not satisfactory. Non-uniform areas are often observed in the films despite the fact that the same optimum conditions of deposition are used. The films do not possess stability in water. To overcome these problems a series of semisynthetic archaeol lipids have been synthesized. The monosuccinilated and disuccinilated glycerol-dialkyl-glycerol tetraethers appeared to be the most promising compounds. Highly uniform films of barium salt of these lipids can be deposited by the Langmuir-Blodgett technique. The multilayers are stable in aqueous solutions. The quality of deposition of disuccinilated tetraether is similar to that of the usual fatty acid salts. The films are studied by optical microscopy, transmission electron microscopy, X-ray small-angle diffraction, and electron diffraction techniques. Contact angles for the deposited films are measured as well. Data obtained from the surface pressure-area isotherms, X-ray diffraction, and contact angle measurements show that the U-shape of molecules is preferred rather than the extended form.

Comparison of the efficiency of N 2 and NH 3 plasma treatments to improve the adhesion of PP films to in situ deposited Al coatings. Study of ageing phenomena in terms of acid-base properties

This paper reports on the characteristics of polypropylene (PP) treated at two different frequencies, 70 kHz and 13.56 MHz, in two plasma atmospheres, NH 3 and N 2 plasmas. Chemical modifications created on the plasma-treated material were investigated by different complementary surface analytical techniques (X-ray photoelectron spectroscopy (XPS) and contact angle measurements), which revealed a higher reactivity of the NH 3 plasma. The incorporation of nitrogen plays an important role as revealed by the adhesion study of thermally evaporated aluminium with treated PP: the measured peel strengths were two times higher for NH 3-treated surfaces than for N 2-treated ones, with XPS measurements showing a sharper increase of N/C ratio as a function of treatment time for the former treatment. Ageing of the PP pretreated in NH 3 was also studied in terms of surface acid-base properties. The work of adhesion, calculated from contact angle measurements, showed a distinct dependence on the pH value of the test liquids and good correlations were obtained with peel test results. The basic character of the NH 3-treated PP disappears with ageing, leading to an amphoteric surface.

Experimental characterization of permeability and fibre wetting for liquid moulding

Liquid moulding processes are unique in that resin is infused into a dry fibre preform. Appropriate wet-out of the reinforcing fibres is thus a necessity for the achievement of good composite properties. For this class of manufacturing methods, both macroscopic flow, as related to Darcy's Law and characterized by permeability, and microscopic flow, as related to fibre wet-out, are important. The current research investigates factors affecting permeability and fibre wet-out as related to liquid moulding. Specifically, it is shown that fabric permeability is dependent on the type of test fluid used. Surface tension and contact angle measurements indicate that interactions at the microscopic level between fibre and test fluid account for these differences in permeability. The investigation illustrates the competing nature of macroscopic and microscopic flow in liquid moulding.