Soldering - continued

The Pb-Sn solders continue to play a critical role in the Level 1, Level 2, and Level 3 interconnections of commercial and military electronics. The widespread availability of Pb and Sn ores and the relative ease of winning the elements from these ores have contributed to their low primary metal costs. However, the real attributes of the Pb-Sn system lie in the physical and mechanical properties of these alloys ... 

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. 

Bonded silver linings are fabricated for mild steel or copper vessels. They are soldered in situ to the walls of the vessel by means of a special tin-silver solder. The melting point of this solder is approximately 280°C, and 200°C is recommended as the maximum continuous operating temperature for linings bonded with it. Since the whole of the silver is firmly adherent to the vessel, bonded linings are suitable for operation under vacuum conditions, and provide excellent heat-transfer characteristics. 

Also, when tin-containing solder connections are made to copper, intermetaUic materials are formed. Those continue to grow to render weak surfaces. Again, a nickel layer between the substrate and the solder provides a solution to this problem. 

Tin is anther ancient metal that continues to have a variety of uses. The inorganic form is used in food packaging, solder, brass, and as an alloy with other metals. The organic forms of tin, triethyltin and trimethyltin, are used as fungicides, bactericides, and generally as antifouling agents for boats. 

Electroless nickel or nickel—lead alloys can improve the solderability and braisability of aluminum even when a continuous film is not present. Electroless nickel systems based on dimethylamineborane reducing agents are used to coat aluminum contacts and semiconductors (qv) in the electronics industry. Newer uses include corrosion-resistant electroless nickel topcoatings on electroless copper plating for radio frequency... 

Continue heating until the top piece appears to drop down. This indicates that the solder has begun to melt. A bright seam of metal can be seen around the edges. This means that the solder has flowed. 

When exposed to low doses of ionizing radiation (either gamma or electron beam), ETFE becomes cross-linked. Cross-linking improves its high-temperature properties, such as cut-through by a hot soldering iron, and increases the continuous service temperature from 150°C (302°F) to 200°C (392°F).29... 

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