The wetting balance technique

The wetting balance technique is a variant of the maximum pull (or detachment) method used to measure liquid-vapour surface tensions (Keene 1993). It is nowadays widely employed in the electronics industry to quantify wetting of solders, but has also been used for wetting studies in metal/ceramic systems (Naidich and Chuvashov 1983b, Nakae et al. 1989, Rivollet et al. 1990). As compared to the sessile drop method which needs planar substrates, solids of various geometry can be studied by this technique. 

In the following, and for the sake of simplicity, the vertical translation rate of the solid in the liquid is supposed to be infinitely slow. Then, if the origin of the weight measurements is taken as the weight of the solid in the gas, the force f exerted on a solid partially immersed in a liquid, whose base is located at a level zb with respect to the flat horizontal surface of the liquid, is equal to the sum of the weight of the meniscus wm and the buoyancy force  

AP is the pressure difference between the sides of the liquid surface and in the case of a meniscus, AP is equal to the hydrostatic pressure. Ri and R2 are the 

The value of z being known, Ri and R2 have now to be determined. This is possible only in a few simple cases featuring a geometry of the solid with a high degree of symmetry. 

For a vertical blade of infinite width, the Laplace equation becomes  

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Table 3.3. Capillary properties of molten Sn/a-AhOj system measured by the wetting balance technique at 1370K using A12Oj cylinders (De Jonghe et al. 1990). fly is calculated by equation (3.22).

Table 3.4. Comparison of 0Y and

Vianco, P. An overview of the meniscometer/wetting balance technique for wettability measurements. In The Metal Science of Joining, Cieslak, M., Perepko, J., Kang, S., Glicksman, M., Eds. TMS Warrendale, PA, 1992 206-284 pp. 

The two most common techniques for the quantitative and qualitative assessment of the wetting and spreading performance of solders are the wetting balance and the sessile drop technique. Each method possesses certain advantages over the other and is discussed in Secs. 3.4 and 3.5. However, there are certain experimental conditions that are common to either method and merit brief consideration. 

Solder spread or ability to wet determines the shape of a fillet in a solder joint. Sattiraju et al. investigated the solderability of immersion tin, ENIG, electroless palladium, and OSP surface finishes with Sn-3.4Ag-4.8Bi, Sn-4.0Ag-0.5Cu, Sn-3.5Ag, and Sn-0.7Cu lead-free interconnection alloys both in air and nitrogen using sequential electrochemical reduction analysis (SERA) and wetting balance techniques. It has been reported that Ni/Au finish performed the best and OSP performed the worst in both nitrogen atmosphere and air environment, suggesting a preference for Ni/Au finish. The Sn-0.7Cu alloy was considered superior, whereas Sn-4.0Ag-... 

Semipermeable membranes and hollow fibers are produced from cellulose acetate. Dry-jet wet-spinning techniques are described to provide asymmetric and homogeneous hollow fiber membranes. Manipulation of spinning conditions leads to morphologies that permit higher rejection and higher fluxes. The excellent balance of the hydrophobic-hydrophilic characteristics for cellulose acetate makes this polymer useful for reverse osmosis [89-93]. Cellulose acetate membranes and hollow fiber membranes are commercially available for hemopurification. [94], for ultrafiltration [95], and for other commercial separation processes. 

Using the Wilhelmy technique the wetting tension (yiv-cos0) exerted by a liquid meniscus on a vertical fiber can be measured directly, using the balance ... 

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