Fine solder

Fine solder is an alloy of two parts of tin and one of lead. It melts at 360". Coarse solder, which melts at 500", contains one part of tin and three of lead. Hard solder, for copper, is a compound of copper and zinc, the latter metal being in excess. 

FIGURE 33.1 An example of fine solder dams, or webs, imaged between fine pitch SMT pads. 

The Fe, Co, and Ni deposits are extremely fine grained at high current density and pH. Electroless nickel, cobalt, and nickel—cobalt alloy plating from fluoroborate-containing baths yields a deposit of superior corrosion resistance, low stress, and excellent hardenabiUty (114). Lead is plated alone or ia combination with tin, iadium, and antimony (115). Sound iasulators are made as lead—plastic laminates by electrolyticaHy coating Pb from a fluoroborate bath to 0.5 mm on a copper-coated nylon or polypropylene film (116) (see Insulation, acoustic). Steel plates can be simultaneously electrocoated with lead and poly(tetrafluoroethylene) (117). Solder is plated ia solutioas containing Pb(Bp4)2 and Sn(Bp4)2 thus the lustrous solder-plated object is coated with a Pb—Sn alloy (118). 

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). 

Automated soldering operations can subject the mol ding to considerable heating, and adequate heat deflection characteristics ate an important property of the plastics that ate used. Flame retardants (qv) also ate often incorporated as additives. When service is to be in a humid environment, it is important that plastics having low moisture absorbance be used. Mol ding precision and dimensional stabiUty, which requites low linear coefficients of thermal expansion and high modulus values, ate key parameters in high density fine-pitch interconnect devices. 

Plate Thickness. Thickness of the plate should always be specified as should the locations on the work where the thickness is to be measured. Generally, thicker deposits perform better, but there are notable exceptions. Mating parts, eg, fasteners having fine machine threads, are not usable if over plated. Machine-threads are usually plated to 10 p.m or less, depending on tolerances. Additionally, gold-plate over nickel does not solder well if too thick thus, gold is usually 1—2 pm or less. Chromium, plated for decorative purposes from the conventional chromic acid bath, tends to macrocrack above about 0.7—1.0 pm. 

Metal Casting Techniques. Many ancient cast metal objects were made by the cire perdue (lost wax) casting process, which involves pouring molten metal into a one-piece mold and letting it solidify modem fakes are usually cast in two halves that are then joined. A casting fin, or a fine line of filed solder on a cast object, usually reveals that the casting is modem. 

The manufacture of a sandwich fusehead proceeds in the following manner. Brass or other metal foils are fixed on each side of a sheet of pressboard with a suitable adhesive. The pressboard is then stamped into combs of the shape shown in Fig. 10.3 and steps are cut in the tips of the heads. Fine resistance wire is stretched across the heads and soldered to the foil on each side of the pressboard. These operations were originally all carried out by hand now many are carried out mechanically. 

Occasionally leaks can also be located or detected by means of chemical reactions which result in a discoloration or by penetration of a dye solution into fine openings. The discoloration of a flame due to halogen gas escaping through leaks was used earlier to locate leaks in solder joints for refrigeration units. 

Metal powder can also be coated onto the workpiece. The 3M Company has developed a cold welding technique in which the workpiece, the metal powder, water, glass shot and additives are tumbled together in a barrel. Coatings are limited to ductile metals such as Cd, An, Sn, Pb, In, Ag, Cu, brass, and tin/lead solder the method is generally suitable only for small parts, and it doesn t produce a fine surfaced, cosmetic coating. Costs are comparable to those for electroplating with afterbake (Kirk-Othmer 1981). 

A design for a still suitable for this preparation is shown in Fig. 24. The vessel is made of copper, nickel, or monel metal. The copper exit tube A is silver soldered or brazed to the cover D. At the cover, it should be 1 to 2 cm. in diameter. Ten to twenty centimeters above the cover, it may be constricted to about 5 mm. At some distance from the cover, it may have a chamber containing a mass of fine copper wire to remove salt spray. However, this is Pennsylvania State College, State College, Pa. f University of California, Berkeley, Calif. 

Silver is an excellent conductor of heat and electricity and a good reflector of light. It is relatively immune to oxidation but becomes tarnished by exposure to sulfur compounds in exceedingly small concentrations. It is an excellent electroplating metal and can also be deposited in thin films by evaporation. In Dewar flasks and other vacuum glassware, it is deposited from an aqueous medium by the Brashear process. Silver is an excellent brazing material and an important constituent of silver solder. The term silver is often applied to alloys of silver with copper for example Sterling silver contains 7.5 percent copper. Fine silver is 99.9+ percent silver. 

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