Spreading solder

Roughness has important implications in wetting applications. While the eutectic solder, SnPb, normally forms a contact angle of 15-20° with copper, it completely wets the surface of rough electroplated copper and forms a fractal spreading front [69]. 

Solders. In spite of the wide use and development of solders for millennia, as of the mid-1990s most principal solders are lead- or tin-based alloys to which a small amount of silver, zinc, antimony, bismuth, and indium or a combination thereof are added. The principal criterion for choosing a certain solder is its melting characteristics, ie, soHdus and Hquidus temperatures and the temperature spread or pasty range between them. Other criteria are mechanical properties such as strength and creep resistance, physical properties such as electrical and thermal conductivity, and corrosion resistance. 

Fluxes also contain agents that faciHtate appHcation, such as petroleum jeUy or alcohol. These bum or evaporate at elevated temperatures before the soldering temperature is attained, leaving behind a uniform coating of flux. Fluxes become molten before the joining process is reached. The molten flux flows or spreads to form a continuous coating over the surfaces to which they have been appHed. 

In addition to the deformation modes described above, there are some other modes of practical interest, for example, the cyclic spreading, recoiling, and oscillation mode typical of solder jetting process.[5°1 This mode leads to a final splat shape of multiple surface ripples at low substrate temperatures and hemispherical shape without surface ripples at high substrate temperatures. 

Preparation of Metal Surfaces for Soldering. Prior to soldering, thoroughly clean the surface of the metal with a file or emery paper. Such surface cleaning is not needed when soldering tinplate. Large metallic surfaces to be soldered should first be tinned. To do this, heat the metal article on the flame of a burner (300-350 °C), spread ammonium chloride over the surface to be soldered (for what purpose ), put a piece of tin on it, and spread the tin over the metal surface with an asbestos wad. 

F. G. Yost, F. M. Hosking, and D. R. Frear, The Mechanise of Solder Alloys Wetting and Spreading (Van Nostrand Reinhold, New York, 1993). 

F. G. Yost, "Fundamentals of Wetting and Spreading with Emphasis on Soldering", in The Metal Science of Joining. M.J. Cieslak, et al. Editor (The Minerals, Metal, and Materials Society, Warrendale, PA, 1992) p. 49. 

Soldering iron. 60 watt, with screwdriver-type tip Paint brush to spread caulk Drill, either hand or drill press Multimeter that can measure current... 

Use of ink-jet technology for printing of fuel cell components and packaging presents most of the same fluid/substrate interaction issues. The printing of Nafion , metal catalyst (e.g., Pt), solder, electrodes, etc. requires deposition of liquid onto a nonporous substrate (similar to printing an overhead transparency). For desired resolution, it is essential to control the spreading of the material. 

Spread or slump Observe three dots dispensed (0.65 mm diameter and 0.25 mm thick) cured and uncured. Measure uncured dots after 70 minutes <10% (5.6) Average of 1.8 0.2 mm dots on FR4 epoxy with solder resist. Check after 3 minutes uncured and cured. 

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