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Article
Publication date: 1 January 1995

Victor P. Janule

Formulators must control coating transfer and adhesion by developing formulations that perform well under widely varying application speeds and operating conditions. There are…

Abstract

Formulators must control coating transfer and adhesion by developing formulations that perform well under widely varying application speeds and operating conditions. There are factors that can be controlled, and others that cannot be controlled. It is especially useful, and often essential, for the formulator to have an understanding of the principles and relationships of surface and interfacial tension, and surface energy or “wetting tension”. A review of these important principals and relationships, with a brief introduction to formulation variables sets the stage for introduction of an instrument that can easily measure the surface tension of coatings and the wetting tension of the surfaces or “substrates” to be coated.

Details

Pigment & Resin Technology, vol. 24 no. 1
Type: Research Article
ISSN: 0369-9420

Article
Publication date: 1 June 1996

Victor P. Janule

Water‐based inks and coatings require alcohols and surfactants to lower their surface tensions to acceptable levels, but have inherent problems of surface wetting, foaming, flow…

Abstract

Water‐based inks and coatings require alcohols and surfactants to lower their surface tensions to acceptable levels, but have inherent problems of surface wetting, foaming, flow and levelling common to water‐based systems. They are formulated quite differently from solvent‐based systems, which wet readily and transfer well on to most ink train materials. Surfactants used in water‐based systems tend to be highly surface‐active and can vary significantly with concentration and speed of diffusion depending on the surfactant type and molecular weight and structure compared with inherently low surface tension alcohols. A coating process is dynamic and, because active surfactants are utilized, surface tension will vary as application and press speed vary. It is the resulting variation in the speed of diffusion of the surfactant molecules that directly impacts on the quality of spreading and adhesion. Ink and coatings formulators must have knowledge of the principles of dynamic surface tension, and have instruments that can measure surface tension characteristics. Instruments must be simple to use, accurate, and as automatic as possible, to allow formulators to spend a minimum amount of time gathering necessary data.

Details

Pigment & Resin Technology, vol. 25 no. 6
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 1 December 1998

Charles M. Hansen

Surface tensions of polymers can be accurately determined by observing whether droplets of liquids spontaneously spread or not. The polymer surface tension will be higher than the…

991

Abstract

Surface tensions of polymers can be accurately determined by observing whether droplets of liquids spontaneously spread or not. The polymer surface tension will be higher than the surface tension of a liquid which spreads, and lower than that of a liquid which remains as a droplet.

Details

Pigment & Resin Technology, vol. 27 no. 6
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 7 August 2020

Elaine Lim, Tze Cheng Kueh and Yew Mun Hung

The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of…

Abstract

Purpose

The present study aims to investigate the inverse-thermocapillary effect in an evaporating thin liquid film of self-rewetting fluid, which is a dilute aqueous solution (DAS) of long-chain alcohol.

Design/methodology/approach

A long-wave evolution model modified for self-rewetting fluids is used to study the inverse thermocapillary characteristics of an evaporating thin liquid film. The flow attributed to the inverse thermocapillary action is manifested through the streamline plots and the evaporative heat transfer characteristics are quantified and analyzed.

Findings

The thermocapillary flow induced by the negative surface tension gradient drives the liquid from a low-surface-tension (high temperature) region to a high-surface-tension (low temperature) region, retarding the liquid circulation and the evaporation strength. The positive surface tension gradients of self-rewetting fluids induce inverse-thermocapillary flow. The results of different working fluids, namely, water, heptanol and DAS of heptanol, are examined and compared. The thermocapillary characteristic of a working fluid is significantly affected by the sign of the surface tension gradient and the inverse effect is profound at a high excess temperature. The inverse thermocapillary effect significantly enhances evaporation rates.

Originality/value

The current investigation on the inverse thermocapillary effect in a self-rewetting evaporating thin film liquid has not been attempted previously. This study provides insights on the hydrodynamic and thermal characteristics of thermocapillary evaporation of self-rewetting liquid, which give rise to significant thermal enhancement of the microscale phase-change heat transfer devices.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 31 no. 4
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 12 April 2013

Abdelraheem M. Aly, Mitsuteru Asai and Yoshimi Sonda

The purpose of this paper is to show how a surface tension model and an eddy viscosity based on the Smagorinsky sub‐grid scale model, which belongs to the Large‐Eddy Simulation…

Abstract

Purpose

The purpose of this paper is to show how a surface tension model and an eddy viscosity based on the Smagorinsky sub‐grid scale model, which belongs to the Large‐Eddy Simulation (LES) theory for turbulent flow, have been introduced into ISPH (Incompressible smoothed particle hydrodynamics) method. In addition, a small modification in the source term of pressure Poisson equation has been introduced as a stabilizer for robust simulations. This stabilization generates a smoothed pressure distribution and keeps the total volume of fluid, and it is analogous to the recent modification in MPS.

Design/methodology/approach

The surface tension force in free surface flow is evaluated without a direct modeling of surrounding air for decreasing computational costs. The proposed model was validated by calculating the surface tension force in the free surface interface for a cubic‐droplet under null‐gravity and the milk crown problem with different resolution models. Finally, effects of the eddy viscosity have been discussed with a fluid‐fluid interaction simulation.

Findings

From the numerical tests, the surface tension model can handle free surface tension problems including high curvature without special treatments. The eddy viscosity has clear effects in adjusting the splashes and reduces the deformation of free surface in the interaction. Finally, the proposed stabilization appeared in the source term of pressure Poisson equation has an important role in the simulation to keep the total volume of fluid.

Originality/value

An incompressible smoothed particle hydrodynamics is developed to simulate milk crown problem using a surface tension model and the eddy viscosity.

Details

International Journal of Numerical Methods for Heat & Fluid Flow, vol. 23 no. 3
Type: Research Article
ISSN: 0961-5539

Keywords

Article
Publication date: 1 October 1998

Charles M. Hansen

A procedure described in a new Nordtest method NT POLY 176 has been shown to determine relatively easily whether or not a surface is clean. One simply applies a well‐chosen…

197

Abstract

A procedure described in a new Nordtest method NT POLY 176 has been shown to determine relatively easily whether or not a surface is clean. One simply applies a well‐chosen droplet of liquid and observes whether or not it spreads. If it spreads the surface can be considered clean.

Details

Pigment & Resin Technology, vol. 27 no. 5
Type: Research Article
ISSN: 0369-9420

Keywords

Article
Publication date: 1 April 1996

M. Nowotarski and R. De Wilde **

The effects of oxygen on solder surface tension, wetting time and surface damping are presented. Oxygen levels greater than 10 ppm lower surfacetension, increase wetting time and…

283

Abstract

The effects of oxygen on solder surface tension, wetting time and surface damping are presented. Oxygen levels greater than 10 ppm lower surface tension, increase wetting time and increase surface damping. Decreased surface tension leads to higher misalignment defects in reflow soldering, but can lower the incidence of dewetting. Increased wetting times can increase non‐wetting defects in both wave and reflow soldering, especially when using no‐clean fluxes. Increased surface damping can lead to lower bridging rates in wave soldering, provided that the oxygen level and flux levels are properly balanced. Choosing the optimum oxygen level for production soldering is trade ‐ off between the stability and the versatility of the process. The most stable soldering processes will be those performed in an inert atmosphere with less than 10 ppm oxygen .These processes are insensitive to variations in soldering machine operating parameters (i,e. a larger process window).This is most desirable for manufacturers soldering large volumes of a given circuit board. The soldering process can be optimised by optimising the circuit board design. The most versatile soldering processes will be those performed in an inert atmosphere with controlled addition of oxygen in the range of 100 ppm to 10,000 ppm (1%). This will be most desirable to manufacturers soldering short runs of a large variety of circuit boards. The soldering process is best optimised by controlling the soldering machine operating parameters (oxygen, flux, preheat, conveyor speed, etc.).

Details

Soldering & Surface Mount Technology, vol. 8 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 1 January 1973

Shell Research Laboratories

A relatively new concept which is now playing a major role in the studies of organic surfaces is the characterisation of such surfaces by the measurement of critical surface

Abstract

A relatively new concept which is now playing a major role in the studies of organic surfaces is the characterisation of such surfaces by the measurement of critical surface tension, γc. The value of this property allows certain predictions to be made as to whether or not a given liquid will wet and spread on a particular solid surface.

Details

Pigment & Resin Technology, vol. 2 no. 1
Type: Research Article
ISSN: 0369-9420

Article
Publication date: 1 September 2005

Benlih Huang, Arnab Dasgupta and Ning‐Cheng Lee

Tombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead‐free soldering and the extensive adoption of…

1677

Abstract

Purpose

Tombstoning and voiding have been plaguing the surface mount assembly industry for decades. The recent global move toward lead‐free soldering and the extensive adoption of microvia technology further aggravate the problems. The present study investigates the impact of SnAgCu (SAC) alloy composition on these important issues.

Design/methodology/approach

In this study, tombstoning and voiding at microvias are studied for a series of SAC lead‐free solders, with an attempt to identify a possible “composition window” for controlling these problems. Properties which may be related to these problems, such as alloy surface tension, alloy melting pattern, and solder wetting behaviour, were investigated in order to assess the critical characteristics required to control these problems.

Findings

The results indicate that the tombstoning of SAC alloys is greatly influenced by the solder composition. Both the wetting force and the wetting time at a temperature well above the melting point have no correlation with the tombstoning frequencies. Because the tombstoning is caused by imbalanced wetting forces, the results suggest that the tombstoning may be controlled by the wetting at the onset of the paste melting stage. A maximum tombstoning incidence was observed for the 95.5Sn3.5Ag1Cu alloy. The tombstoning rate decreased with increasing deviation in Ag content from this composition. A differential scanning calorimetry (DSC) study indicated that this was mainly due to the increasing presence of the pasty phase in the solders, which result in a slower wetting speed at the onset of solder paste melting stage. Surface tension plays a minor role, with lower surface tension correlating with a higher tombstoning rate. The voiding rate at the microvias was studied by employing simulated microvias. The voiding level was lowest for the 95.5Sn3.8Ag0.7Cu and 95.5Sn3.5Ag1Cu alloys, and increases with a further decrease in the Ag content. The results indicate that voiding at microvias is governed by the via filling and the exclusion of fluxes. The voiding rate decreased with decreasing surface tension and increasing wetting force, which in turn is dictated by the solder wetting or spreading. Both low surface tension and high solder wetting prevents the flux from being entrapped within a microvia. A fast wetting speed may also facilitate reducing voiding. However, this factor is considered not as important as the final solder coverage area.

Research limitations/implications

In general, compositions which deviate from the ternary eutectic SAC in Ag content, particularly with a Ag content lower than 3.5Ag, exhibit a greater solid fraction at the onset of melting, resulting in a lower tombstoning rate, presumably due to a slower wetting speed. The SAC compositions with an Ag content lower than 3.5 per cent, such as 2.5Ag, resulted in a lower tombstoning rate with minimal risk of forming Ag3Sn intermetallic platelets. On the other hand, ternary eutectic SAC exhibits a lower surface tension resulting in an easier solder spread or solder wetting, and consequently exhibit a higher tombstoning frequency and a lower incidence of voiding.

Practical implications

Provides a solution to the tombstoning problem in lead‐free soldering.

Originality/value

The present study provided a solution to the tombstoning problem encountered in lead free soldering by controlling the SAC solder alloy compositions.

Details

Soldering & Surface Mount Technology, vol. 17 no. 3
Type: Research Article
ISSN: 0954-0911

Keywords

Article
Publication date: 8 February 2011

Z. Moser, P. Fima, K. Bukat, J. Sitek, J. Pstruś, W. Gąsior, M. Kościelski and T. Gancarz

The purpose of this paper is to investigate the influence of In additions on the wetting properties of the Sn2.86Ag0.40Cu (in wt%) eutectic‐based alloys, on a copper substrate, in…

Abstract

Purpose

The purpose of this paper is to investigate the influence of In additions on the wetting properties of the Sn2.86Ag0.40Cu (in wt%) eutectic‐based alloys, on a copper substrate, in the presence of a flux. The main goal was to find correlations between the results of the wetting balance (WB) and the sessile drop (SD) method, in relation to the contact angles.

Design/methodology/approach

The WB method was applied for the wetting measurements, at 250°C, in an air atmosphere and in the presence of a flux. The SD measurements were conducted at the same temperature, in the presence of the same flux, but in an Ar atmosphere, while the maximum bubble pressure (MBP) and dilatometric measurements were conducted in an Ar+H2 atmosphere. The density data from the dilatometric method were used for the determination of the surface tension by means of MBP, and the WB method was used to determine the surface and interfacial tension. Next, the surface tension data from these two methods were compared. The WB data were used to calculate the contact angles and the obtained indirect data were compared with the results of the direct SD measurements of the contact angle.

Findings

A higher In content in the alloy resulted in a lower contact angle on the copper, and the WB results agreed well with the results of the SD experiments. It was confirmed that, in liquid In‐Sn and the alloys containing In and Sn (Ag‐In‐Sn, Sn‐Ag‐Cu‐In, Sn‐Zn‐In), the improvement of the wettability was indicated only by the increase of the contact angle with the increasing In content.

Research limitations/implications

Further studies are necessary for the confirmation of practical application, but they should be directed to the soldering of high indium alloys on printed circuit boards, with different finishes and qualities of the solder joint performance.

Practical implications

Taking into account the contact angle data from the WB and SD methods, the best results of the SAC‐In alloy on copper were obtained for the alloy of the highest In content. It was found that the contact angles from SD after 4 s were higher (non‐equilibrium conditions) than the values calculated from WB after 3 s. In contrast, the contact angles from SD after 10 min (equilibrium conditions) were lower than those from WB after 3 s. The comparison suggests that the contact angles from WB are situated within the data from SD, showing the same lowering tendency with the increasing content of In, and they may be well accepted for practical purposes. On the other hand, the sample of the solder in the SD method, after a prolonged time – in order to get the equilibrium contact angle – may be used to study the interfacial phenomena with the Cu substrate. The differential thermal analysis results indicate that the melting temperature decreases with increasing tin concentration. Taking into account the results of this study and the available literature data, alloys containing 8‐10 wt% of In can be recommended for practical application.

Originality/value

The WB and SD methods were used for the contact angle determination of a wide range of solder compositions, in the same temperature and flux conditions. Also, the surface tensions for these alloys were determined with the use of two independent methods: the MBP and the WB methods. The results obtained made it possible to draw conclusions regarding the correlation between the output of different methods and the conditions in which a comparison of the results can be made. It is supposed that these observations apply to many other alloy systems.

Details

Soldering & Surface Mount Technology, vol. 23 no. 1
Type: Research Article
ISSN: 0954-0911

Keywords

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