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.     

Influence of Erroneous Data on the Results of Calculations From Acid–Base Surface Free Energy Theories. III. Solution of a Three-Equation Set in the Case of Homoscedastic Error

The van Oss–Chaudhury–Good theory (vOCGT) was checked for a large artificial set of work of adhesion input data calculated for 15 solids and 300 liquids. Numerical values of LW component and acid (A) and base (B) parameters were assigned to 15 solids. These 15 solids were grouped in 5 sets of 3 solids in each. Also numerical values of LW component and A and B parameters were assigned to 300 liquids (three sets of 100 liquids in each). Data for these solids and liquids were especially selected to represent real types of materials encountered in practice. For all 15 solids and 300 liquids the work of adhesion values were calculated and these values were assumed to be error-free. Next, new values of the work of adhesion were obtained by adding a random homoscedastic error (A vector of random variables is homoscedastic if it has the same finite variance.) of the normal distribution (Also called the Gaussian distribution — it is continuous probability distribution defined by two parameters: the mean and variance (standard deviation squared, σ ²).), belonging to 8 distributions of a mean value equal to the error-free work of adhesion value and standard deviations of 0.5, 1, 2, 5, 7, 10, 15 and 20 mJ/m². The LW components and A and B parameters for these solids were back-calculated for each error level. Two different methods for the solution of a 3-equation set were used and they gave practically the same results irrespective of the error level and liquids and solids used. It was found that there existed a linear correlation between the RMSE (root mean square error) of the solution and the standard deviation of the work of adhesion data. This correlation was highly significant (with a correlation coefficient higher than 0.999) and was true separately for LW component, A and B parameters as well as for the total solution vector (i.e., combinedly for the LW component, A and B parameters). The RMSE values of the total solution vector (having as elements values of the LW component, A and B parameters) as well as separately for LW component and A and B parameters were correlated with the condition number of a given 3-equation set. A very good correlation was found only for the total solution, much worse for A or B parameters, and practically there was a lack of correlation for the LW component. Based on the correlation between the RMSE and the standard deviation of the work of adhesion it was possible to determine what should have been the maximal standard deviation of the work of adhesion if the calculated value of a given LW component or A or B parameter did not differ by more than 1 mJ/m² from an error-free (true) value.     

33—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART II: CYLINDRICAL SNARLING

An account is given of an experimental investigation of the cylindrical snarling of highly twisted monofilaments.

The theory underlying cylindrical snarling is set out, and an expression is derived for calculating the critical twist level at which normal snarling will be replaced by cylindrical snarling. Experiments on rubber filaments are described, and it is shown that there is good agreement between the theoretical and experimental results. Further experiments, in which the specimen was allowed to contract freely or forced into other forms, are also described.

It is shown from these experiments that it is difficult to establish the true equilibrium behaviour, since the situation appears to be dominated by frictional effects or by direct barriers to relative movement.     

14—EQUIVALENT TWISTS IN TYRE CORDS

This paper describes an empirical method for choosing a twist level for a new tyre cord that will ‘match’ the twist in an existing successful cord, i.e., one that will give the same twist angle. The technique is based on published cord geometry and is shown to give reliable results. No knowledge of densities or packing factors is required, and the results are independent of the number of yarns in the cord. The method offers the possibility of calculating twist angles and related properties for cords at any twist once a sufficiently reliable value of one cord constant has been determined. A table of matched twists calculated in this way is given.     

32—THE SNARLING OF HIGHLY TWISTED MONOFILAMENTS. PART I: THE LOAD–ELONGATION BEHAVIOUR WITH NORMAL SNARLING

An account is given of an experimental investigation of the normal snarling of highly twisted monofilaments, those used being vulcanized rubber and nylon.

An earlier theoretical analysis is corrected, and the experimental results show that, after this correction, the theory put forward for the mechanical properties of the snarling mechanism holds reasonably well for elastic filaments. Although, as would be expected, there are larger deviations from the theory for viscoelastic filaments, the theory still gives a good indication of the behaviour of these filaments under torsion.     

Effects in Surface Free Energy of Sputter-Deposited VNx Films

Vanadium nitride (VN _x ) thin films have attracted much attention for semiconductor integrated circuit (IC) packaging molding dies, and forming tools due to their excellent hardness and, thermal stability. VN _x thin films with VN_0.45, VN_0.83, VN_1.22, VN_1.73, VN_2.06 were prepared using a radio frequency (RF) sputter technique. The experimental results showed that the contact angle at 20°C increases with increasing nitrogen content of the VN _x films, to 101.4° corresponding to VN_1.73 and then decreased. In addition, the contact angles decreased with increasing surface temperature, because an increase of the surface temperature disrupts the hydrogen bonds between water and the films and the water gradually vaporizes. The total surface fee energy (SFE) at 20°C decreased with nitrogen content of the VN _x films to 29.8 mN/m (VN_1.73) and then increased. This is because a larger contact angle means weaker hydrogen bonding which results in a lower SFE. The polar SFE component had the same trend as the total SFE, but the dispersive SFE component had the opposite trend. The polar SFE component is also lower than the dispersive SFE component. This is because hydrogen bonds are polar. The total SFE, dispersive SFE and polar SFE of the VN _x films all decrease with increasing surface temperature. This is because with increasing temperature, water evaporates from the surface, disrupting hydrogen bonds and hence increasing surface entropy. The film roughness has an obvious effect on the SFE and there is tendency for the SFE to increase with increasing film surface roughness. As a result the SFE and surface roughness can be expressed in terms of a simple ratio function.     

Investigation of the surface rearrangement of poly(imide-siloxane) using dynamic contact angle measurements

Dynamic contact angle measurements and X-ray photoelectron spectroscopy (XPS) were used to investigate the surface compositions and surface rearrangement of poly(imide-siloxane) with various molecular weights and contents of amine-terminated poly(dimethyl siloxane) (ATPDMS). Four different water contact angles were measured to study the poly(imide-siloxane) surface: the initial advancing angle, the equilibrium advancing angle, the initial receding angle, and the equilibrium receding angle. Poly(imide-siloxane) with 2350 and 4300 g/mol of ATPDMS showed higher initial and equilibrium advancing contact angles than those of poly(imide-siloxane) with 433 g/mol of ATPDMS. Since the mobility of ATPDMS segments depended on the chain length of ATPDMS, the molecular weight of ATPDMS determined the surface composition of poly(imide-siloxane), the rate of surface rearrangement, and the contact angle hysteresis. Poly(imide-siloxane)s with 2850 and 4300 g/mol of ATPDMS were mostly covered with ATPDMS even if just 1 wt% of ATPDMS was incorporated, while poly(imide-siloxane) with 433 g/mol of ATPDMS was mostly covered with polyimide segments and partially with ATPDMS. The rate of surface rearrangement and the contact angle hysteresis decreased with the increasing molecular weight as well as content of ATPDMS. The actual ATPDMS-enriched layer thickness was also investigated by XPS. The actual thickness of the ATPDMS-enriched layer was about 15 nm for 2850 g/mol and 4300 g/mol of ATPDMS-modified poly(imide-siloxane) and about 7.5 nm for 433 g/mol of ATPDMS-modified poly(imide-siloxane)     

Introduction of carboxylic groups on ethylene-co-tetra fluoroethylene (ETFE) film surfaces by CO2 plasma

ETFE film surfaces were modified by CO₂, O₂ and Ar plasmas in order to form carboxylic groups on their surfaces, and the possibility that carboxylic groups could be predominantly introduced into the CH₂–CH₂ component rather than the CF₂–CF₂ component in the ETFE polymer chains was investigated from the viewpoint of chemical composition analyzed by XPS. The CO₂ plasma modification was more effective in the selectivity of the CH₂CH₂ component for the introduction of carboxylic groups, as well as in the concentration of the carboxylic groups formed on the film surfaces than O₂ plasma modification. The concentration of carboxylic groups formed on the ETFE film surfaces by the CO₂ plasma modification was 1.40–1.50 groups per 100 carbons. Topographical changes on the ETFE film surfaces by the plasma modification were also investigated by scanning probe microscopy.     

Influence of the growth medium,suspending liquid and measurement temperature on the physico-chemical surface properties of two enterococci strains

A knowledge of the physico-chemical surface properties of a bacterium is important to predict the first step in the adhesion process of such a microorganism to biomaterials. In this work, hydrophobicity, surface free energy and surface charge of Enterococcus faecalis ATCC29212 and E. faecalis 72 bacterial strains have been analysed under the followings conditions, which were considered as criteria that could affect the thermodynamical parameters of the cell surface: culture medium was supplemented with serum and urine and the experiments were carried out in two different buffers (KPi and PBS) and at two temperatures (22 and 37 °C). MATH hydrophobicity does not seem to be affected by temperature but water contact angle increased with temperature for both strains. Serum and urine added to the culture medium made the strains more and less hydrophobic, respectively. The zeta potential was dependent on the addition to the culture medium of serum and urine, the experimental temperature and the buffer employed and it decreased with increasing ionic strength in all cases studied. The results reveal that physico-chemical surface properties of bacteria are greatly affected by the environmental conditions in which they are measured, indicating that experiments should be carried out under experimental conditions as similar as possible to the situation of clinical interest.     

Finite element analysis of steady rolling tyre with slip angle: effect of belt angle

Abstract

The purpose of the present research was to study the effect of different belt angles on the steady state rolling behaviour of a steel belted radial tyre with slip angle. To achieve this goal, a finite element model has been developed using ABAQUS computer software. The simulation started with an axisymmetric model to analyse the tyre under inflation pressure. Then a full 3D model was generated to model the tyre under static vertical load. Having obtained the tyre configuration under contact load, a steady state rolling analysis was conducted using a mixed Lagrangian/Eulerian technique. The final stage of the modelling was the inclusion of the slip angle in the model. Each set of simulations was repeated for three belt angles and the effect of the belt angle variation on the tyre structural variables, including contact pressure and area, lateral force, interlayer shear stress and total strain energy was examined. In addition, the computed value of the number of revolutions per kilometre was compared with experimentally reported data which confirms the accuracy of the present model.