Characterisation of FR-4 substrate with various plasma treatment conditions

Abstract

The effects of plasma treatment on the surface of the flame resistant-4 (FR-4) substrate with underfills under various treatment conditions (operating gas, operating time, operating power) are investigated by using contact angle measurement, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The plasma treatment on substrate surfaces increased the oxygen containing functional groups or the polar component of the surface free energy, improving the wetting characteristics of the underfills/FR-4 substrates. The plasma treatment conditions which minimised the contact angle between the underfills and FR-4 substrates were an operating power of 300 W and operating time of 180 s under Ar gas atmosphere.     

Improvement of Adhesion Between Liquid Crystalline Polyester Films by Plasma Treatment

Surface modification of thermotropic liquid crystalline aromatic polyester (LCP) films was carried out by low-pressure plasma treatment to improve the initial adhesion as well as the long-term adhesion reliability, a measure of durability between the LCP films used as substrates for printed circuit boards. Plasma irradiation was carried out in various plasma gases with different plasma modes such as reactive-ion-etching, and direct-plasma (DP) with pressures ranging from 6.7 Pa to 26.6 Pa. The introduction of polar groups on the film surface such as phenolic hydroxyl groups and carboxyl groups enhanced the initial adhesion by increased chemical interaction. However, if the concentration of polar groups became too high, the longterm adhesion reliability estimated by the pressure cooker test was degraded due to the acceleration of the penetration of water molecules into the interface. A large surface roughness was also effective in preventing the decrease in the long-term adhesion reliability. However, too much increase in surface roughness decreases the long-term adhesion reliability. The DP-treatment in the O₂ atmosphere at a gas pressure of 6.7 Pa was found to be the best plasma condition for both the initial adhesion as well as the long-term adhesion reliability between the LCP films.     

Influence of precursors on formation of TiO2–CrTaO4 rutile solid solutions

Abstract

Rutile solid solutions Cr_x Ti_1-2xTa_xO₂ (0 < x < 0·5) have been synthesised by: firing mixtures of Cr₂O₃ , Ta₂O₅ , and TiO₂ (anatase); firing colloidal gels obtained from TiCl₄ , TaCl₅ , and CrCl₃ . 6H₂O; and firing polymeric gels prepared from Ti⁴⁺ isopropoxide, Ta⁵⁺ethoxide, and Cr³⁺ acetylacetonate at 300–1300°C. Samples were characterised by XRD, differential thermal and thermogravimetric analysis, UV visible spectroscopy, Cielab colour parameter measurements, and electron microscopy. In samples synthesised from oxide mixtures, CrTaO₄ (rutile structure) appeared as an intermediate phase in the formation of the solid solutions and a positive departure from Vegard's law was observed. Ta₂O₅ segregation in gel samples seems to prevent the formation of material consisting only of rutile. The distortion of MO₆ octahedra varies as x increases. The chemical, structural, and thermal stability, and the colouration obtained on glazes containing 3 wt-%samples, indicate their potential for use as ceramic pigments. Under the experimental conditions used, the materials prepared by sol–gel synthesis were not found to be better than those prepared from oxide mixtures.     

Effect of talc and bauxite on sintering,microstructure, and refractory properties of Egyptian dolomitic magnesite

Abstract

Refractories produced from mixes of Egyptian dolomitic magnesite with talc and low cost Chinese bauxite have been assessed as potential substitutes for the high temperature basic refractory bricks currently used in steelmaking and other industries. Fifteen batches of different compositions were prepared by firing for 2 h up to 1580° C. Six samples were selected for further investigation on the basis of their phase composition and densification parameters. The mineralogical composition and microstructure, pore size distribution, and mechanical and refractory properties of these samples were investigated. All six samples consisted mainly of MgO and MA spinel refractory phases, plus some calcium silicates and aluminoferrite phases. The latter phases contribute to densification during firing by promoting liquid phase formation. Most samples showed high refractoriness under load, good spalling resistance, better mechanical properties than current refractories, and compact microstructure. It is concluded that these new refractories are good candidate materials for the production of shaped linings for industrial kilns and furnaces.     

Current status of supersaturated surface engineered S phase materials

Abstract

The present paper reviews the scientific development of the understanding of S phase. It is now known that S phase formation is an example of paraequilibrium phenomena. A necessary but not sufficient condition for S phase formation is the presence of a face centred cubic (fcc) structure at least in part with structure in the starting alloy. An essential requirement is for a nitride forming element to be present, particularly Cr. After surface engineering with carbon, nitrogen or carbon and nitrogen to generate supersaturated solid solutions, the various tribological, corrosion, mechanical and microstructural studies are reviewed for the various alloy systems. The current industrial status of S phase technology on an international basis is examined and the potential for its acceptance in China is discussed.     

Improvement of paint adhesion to a polypropylene bumper by plasma treatment

Improvement of the paint adhesion to a polypropylene (PP) bumper has been investigated without using a primer by treating the bumper surface with O₂, H₂O, and acetylene plasmas. All the plasma treatments resulted in an increase of the adhesion strength in dry conditions. The adhesion strength could be increased up to a value comparable to that obtained by applying a primer. The treated surfaces were quite stable for 7 days in air. After exposure to wet conditions, however, the adhesion strengths for both O₂ and H₂O plasma-treated samples decreased significantly, while the adhesion strength for the acetylene plasma-treated sample did not change much.     

Nanoparticle removal from substrates with pulsed-laser induced plasma and shock waves

Removing particles with nanometer scale diameters from substrates is a challenging task with numerous critical applications. A novel removal method for nanoparticles is developed and tested. The technique, which is dry and non-contact, takes advantages of shock wavefronts initiated by plasma formation under a focused laser beam pulse and its interaction with the substrate. Experimental results indicate that silica particles down to 500 nm on silicon wafers can be removed without substrate damage. In the reported experiments, a Q-switched Nd : YAG pulsed laser with a 5-ns pulse width and 360-mJ pulse energy at 1064 nm wavelength is employed as a plasma generation source. It is reported that the traditional dry laser cleaning method based on the rapid thermal expansion under direct laser irradiation often results in surface damage in the nanometer scale due to light diffraction around nanoparticles and/or stress localization in the thermal skin. This occurs when the characteristic dimensions of the particles are comparable to the wavelength of incident beam. In the laser plasma method, various mechanisms are responsible for the removal effect. The strong shock wave in air generates complex pressure wavefields resulting in both drag/lift on the particle and acceleration of the substrate. However, shock waves are not transmitted to the solid substrate due to a large difference between the relevant wave phase speeds in the two media. The effects of the number of shots and the distance between the surface and the plasma boundary on the removal efficiency are reported.     

A study of paint adhesion to polymeric substrates

In order to explore the fundamental mechanism of paint adhesion to polymer substrates the surface of polypropylene- ethylene propylene rubber (PP-EPR) blends was modified by flame or plasma treatments. The changes in surface composition and properties were investigated and discussed in light of the results of simple adhesion tests. The topography and surface properties of the PP-EPR samples were studied by employing various surface sensitive techniques. Additionally, the surface properties of the pre-treated PP-EPR were compared with the model polymers poly(methyl methacrylate) (PMMA) and polycarbonate (PC) displaying a poor and an excellent paint adhesion, respectively. Differential scanning calorimetry (DSC) measurements showed that the miscibility of the polymer substrate with paint components was an essential factor for the understanding of the adhesion mechanism. A general model of paint adhesion to polymer surfaces is proposed, where the degree of interdiffusion of the polymer chains of the substrate and paint in the interphase determines the adhesion strength.     

Argon-plasma-assisted graft polymerization of thick hydrogels with controllable water swelling on Chronoflex

Chronoflex, a polyurethane, is a suitable material for use in polymeric tracheobronchial stents. A controlled release layer on the stent is required for effective localized delivery of cancer drugs to the tumor cells. This paper reports on the investigation of coating Chronoflex with acrylated oligomers by argon plasma assisted UV graft polymerization. Coatings of poly(ethylene glycol) diacrylate (PEGDA) with molecular weight 700 or a 50 : 50 mixture of PEGDA with poly(propylene glycol) diacrylate (PPGDA) with molecular weight 900 which were tens of micrometers thick were shown to have good adhesion to Chronoflex. No photoinitiator was added. Formulations containing photoinitiator or a trifunctional crosslinker which increases strength and decreases water swelling showed poor adhesion to Chronoflex. The degree of water swelling of grafted PEGDA coating reached about 709%, making it suitable for use as a hydrogel coating for controlled drug release on Chronoflex. Adding PPGDA to PEGDA was shown to decrease the degree of water swelling. Hence, removal of the photoinitiator, use of oligomeric diacrylate with high molecular weight per acrylate group and a clean Chronoflex surface are found to be important factors for ensuring adhesion between the thick hydrogel coating and Chronoflex.     

Enhanced Cell Adhesion to Helium Plasma-Treated Polypropylene

Materials used for biomedical applications are required to have suitable surface properties since they depend more on the surface properties than on the bulk properties. Surface properties greatly influence the cell adhesion and its behavior either directly by guiding cell spreading or indirectly by controlling proteins adsorption and their structural rearrangement on the material. Modulation of physical and chemical properties of polymers by various treatments can render the substrates adhesive for cells in a culture. In the present study, polypropylene surface was modified using helium plasma to enhance cell adhesion to its surface. The experiments were run according to the central composite design of response surface methodology to optimize the process conditions. The effects of the process variables, namely, RF power, pressure, flowrate and treatment time on surface energy and percentage weight loss were studied through central composite design (CCD). A statistical model relating the process variables and the responses was developed. The improved hydrophilicity of polypropylene through helium plasma treatment was observed from its surface energy data. Changes in surface chemistry and surface morphology were studied by Fourier transform infrared spectroscopy and scanning electron microscopy, respectively. Enhanced cell adhesion to polypropylene treated with helium plasma at the optimum conditions, obtained from the statistical design, was observed from cell adhesion test and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay with L929 mouse fibroblast cells.