Solderability, improving

Lea.d nd Le d Alloys. Selenium is reported to lower the surface tension of lead. The addition of 0.1% selenium and tellurium to solder improves its fluidity. 

In 2001, Mitsui Chemicals announced that it had developed a new grade of aromatic polyamide, which was designed to improve reflow solder resistance. In the electronics parts market, there is a shift from lead-eutectic solder to lead-free solder. Improvement of heat resistance is required for resins because lead-free solder has a higher melting point than conventional solder. 

The vapor blanket provides an oxygen-free environment during soldering, improving solderability. 

Recent advances in the development of TMF predictive models have included the incorporation of solder microstructure as a state variable in the constitutive equation [92,93]. A contour map (Fig. 30) shows the Pb-rich phase coarsening predicted in a leadless chip solder joint subjected to six thermal cycles having temperature limits of —50° and 80°C, ramp rates of 6°C/ sec, and dwell times of 10 min at both limits. The microstructure-based, viscoplastic constitutive equation for Pb-Sn solder improves the accuracy of solder fatigue strain predictions throughout the interconnection geometry. It provides a real-time adjustment of the local solder mechanical properties resulting from local changes in the solder microstructure (i.e., the Pb-rich phase). 

Uses. Lithium fluoride is used primarily in the ceramic industry to reduce firing temperatures and improve resistance to thermal shock, abrasion, and acid attack (see Ceramics). Another use of LiF is in flux compositions with other fluorides, chlorides, and borates for metal joining (17) (see Solders). 

The solder and ahoy market, including low melting or fusible ahoys, is a principal user of indium (see SoLDERS AND BRAZING ALLOYS). The addition of indium results in unique properties of solders such as improved corrosion and fatigue resistance, increased hardness, and compatibhity with gold substrates. To fachitate use in various appHcations, indium and its ahoys can be easily fabricated into wine, ribbon, foil, spheres, preforms, solder paste, and powder. 

Arsenic added ia amounts of 0.1—3% improves the properties of lead-base babbitt alloys used for beatings (see Bearing materials). Arsenic (up to 0.75%), has been added to type metal to increase hardness and castabiUty (21). Addition of arsenic (0.1%) produces a desirable fine-grain effect in electrotype metal without appreciably affecting the hardness or ductihty. Arsenic (0.5—2%) improves the sphericity of lead ammunition. Automotive body solder of the composition 92% Pb, 5.0% Sb, and 2.5% Sn, contains 0.50% arsenic (see Solders and brazing alloys). 

The compound MgGa204, when activated by divalent impurities such as Mn +, is used in ultraviolet-activated powders as a brilliant green phosphor. Another very important application is to improve the sensitivity of various bands used in the spectroscopic analysis of uranium. Minor uses are as high-temperature liquid seals, manometric fluids and heat-transfer media, and for low-temperature solders. 

The main use of elemental As is in alloys with Pb and to a lesser extent Cu. Addition of small concentrations of As improves die properties of Pb/Sb for storage batteries (see below ), up to 0.75% improves the hardness and castabilily of type metal, and 0 5-2.0% improves the sphericity of Pb ammunition. Automotive body solder is Pb (92%),, Sb (5 0%), Sn (2.5%) and As (0.5%). Intcrnxitallic compounds with Al, Ga and In give the 111-V semiconductors (p 255) of which GaAs and InAs are of particular value for light-emitting diodes (LEDs), tunnel diodes, infrared emitters, laser windows and Hall-effect devices (p. 258). 

Soldered joints present their own characteristic corrosion problems usually in the form of dissimilar metal attack often aided by inadequate flux removal after soldering. Such joints have always been a source of concern to the electrical industry. Lead-containing solders must be used with caution for some types of electrical connection since PbfOHjj.PbCOj may be found as a corrosion product and can interrupt current flow. Indium has been found to be a useful addition to Sn-Pb solders to improve their corrosion resistanceHowever, in view of the toxicity of lead and its alloys, the use of lead solders, particularly in contact with potable waters and foodstuff s, is likely to decline. 

Martin C, Solders G et al (2000) Antiretroviral therapy may improve sensory function in HIV-infected patients a pilot study. Neurology 54(11) 2120-2127 Masjuan J, Corral I et al (1997) Mycobacterial acute lumbosacral polyradiculopathy as the initial manifestation of AIDS. J Acquir Immune Defic Syndr Hum Retrovirol 15(2) 175 McArthur JC, Yiannoutsos C et al (2000) A phase II trial of nerve growth factor for sensory neuropathy associated with HIV infection. AIDS Clinical Trials Group Team 291. Neurology 54(5) 1080-1088... 

Lee, W. G. (1971) Improvement of solder connections by gold alloy plating. Plating, 58, 997-1001. 

Uses. Indium finds application in making low melting alloys the eutectic alloy indium-gallium (14.2 at.% In, 21.4 mass% In) melts at 15.3°C. In is used as an additive to solder alloys to improve malleability at low temperature and corrosion resistance it is also used in dental alloys, in the preparation of semiconductors, etc. 

In some instances, to improve solderability, tin is deposited on nickel surfaces. In a short time, however, interdiffusion of the two metals results in the growth of an inter-metallic NiSn3 compound that is much less amenable to soldering. For tin over elec-trolessly deposited nickel surfaces, the interdiffusion results in pores in both films. Pores are to be avoided, of course, if conductivity and/or contact resistance is an issue. 

Abrasion resistance and solder iron resistances are two other important properties required from a wire and cable insulator. These properties are critical for polymers used as sheathing or jacketing for hookup wire. Cross-linking improves both of thern. ... 

Tellurium—copper alloys are recommended for situations demanding a high production rate with no significant sacrifice in conductivity. These alloys can be soldered, brazed, or welded without incurring embrittlement. They are used in vacuum applications, forgings, screw-machine parts, welding-torch tips, transistor bases, semiconductor heat sinks, electrical connectors (qv), motor and switch parts, and nuts, bolts, and studs. Addition of tellurium significantly improves the surface of machined parts. 

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