Non-wettable Surfaces by Robin H A Ras download in ePub, pdf, iPad
In other words, only one thermodynamically stable contact angle exists. Differences in wettability between surfaces that are similar in structure are due to differences in the packing of the atoms. Knowing the critical surface tension of a solid, it is possible to predict the wettability of the surface. The bonding material may a solder or may include a eutectic-forming metal adapted to form a low-melting eutectic with surrounding metals. This liquid phase however does not spread along the length of the lead.
Therefore, when the tip region of the lead is exposed to a liquid bonding material, the liquid bonding material wets the tip region but it does not spread from the tip region onto the main region. Zero hysteresis implies the advancing and receding contact angles are equal.
The non-wettable surface desirably confines the bonding material to the tip end of the lead when the bonding material is applied. As the tendency of a drop to spread out over a flat, solid surface increases, the contact angle decreases.
The methods according to this aspect of the invention provide advantages as discussed above in connection with the components. The non-wettable surface of a lead need not be provided on all areas of the lead other than the tip region.
Most molecular liquids achieve complete wetting with high-energy surfaces. In the bonding processes discussed above, the bonding material is a solder and hence the liquid bonding material is a molten solder. Lower critical surface tension means a less wettable material surface. For example, a surface presenting photon-driven molecular motors was shown to undergo changes in water contact angle when switched between bistable conformations of differing surface energies. Substantially the same process can be used with eutectic forming materials other than tin.
Similarly, the terms omniphobic and omniphilic apply to both polar and apolar liquids. This low-melting eutectic forms a liquid bonding material. However, fluxes can be used with other non-wettable surfaces. This critical surface tension is an important parameter because it is a characteristic of only the solid.
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