Tin-lead soldering

Solders are alloys that have melting temperatures below 300°C, formed from elements such as tin, lead, antimony, bismuth, and cadmium. Tin—lead solders are commonly used for electronic appHcations, showing traces of other elements that can tailor the solder properties for specific appHcations. 

Solders are cathodic to steel, zinc and cadmium, and anodic to Monel metal. Although tin or tin-coated metals may be used safely in contact with aluminium when they are not fused with it, a joint in aluminium made with a tin-lead solder is liable to destructive corrosion. The formation, on fusion, of the grain-boundary state, which, as already mentioned, makes aluminium so dangerous an impurity in tin, is responsible. Tin-zinc solders may be used the zinc gives a useful degree of protection. 

The effect of Oj, SOj, NOj, HjS, CI2, CO and NH3 on Sn/50%Pb in atmospheres of different relative humidity were investigated but only SO2 and NO2 were active at low concentrations (<100 ppm). An XPS study of Sn/50 7oPb solder exposed to O2, HjO and NO2 was conducted to establish both the surface species formed and the ratio of the concentration of each metal in the surface. Previous XPS studies had only considered the interaction of tin/lead solder with the air . 

Alloys are metallic materials prepared by mixing two or more molten metals. They are used for many purposes, such as construction, and are central to the transportation and electronics industries. Some common alloys are listed in Table 5.5. In homogeneous alloys, atoms of the different elements are distributed uniformly. Examples include brass, bronze, and the coinage alloys. Heterogeneous alloys, such as tin-lead solder and the mercury amalgam sometimes used to fill teeth, consist of a mixture of crystalline phases with different compositions. 

The properties of alloys are affected by their composition and structure. Not only is the crystalline structure important, but the size and texture of the individual grains also contribute to the properties of an alloy. Some metal alloys are one-phase homogeneous solutions. Examples are brass, bronze, and the gold coinage alloys. Other alloys are heterogeneous mixtures of different crystalline phases, such as tin-lead solder and the mercury-silver amalgams used to fill teeth. 

Tin-Lead Solder Stainless Steel Type 304 (active)... 

An example of using the LCA approach for informed substitution is the DfE LCA for tin-lead and promising lead-free solder alternatives for electronics. The alternatives assessment was conducted at the request of the electronics industry, as it prepared for compliance with the European Union (EU) Restriction of Hazardous Substances Directive, which includes a phase-out of the use of lead in electronic products. With estimates of worldwide tin-lead solder use at over 176 million lb (80 million kg) per... 

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). 

Results from electroless copper, tin-lead (solder) fluoborlc and tin-lead (solder) sulfonic applications will be discussed as they bscome available from installations planned for June and July, 1989. 

Corrosion by dealloying is common in brasses here the zinc component of the alloy is preferentially removed. Brasses with high proportions of the P phase are especially prone to this type of attack. The mechanism appears to be corrosion of both copper and zinc from the metal the zinc passes into solution but the copper is re-deposited with a porous structure of low strength. Aluminium bronzes also suffer dealloying of the aluminium component if incorrectly heat treated. Other metals which may be preferentially dissolved from their alloys are manganese from copper-manganese, nickel from copper-nickel, copper from either copper-silver or copper-gold, and tin from tin-lead (solders). It is evident from this list that it is the component which is anodic to the alloy which is removed. 

Heterogeneous alloys include tin-lead solder and mercury amalgams for dental fillings. 

Conventional tin/lead solders have the approximate composition Sn63/Pb37 by weight, corresponding to the eutectic mixture, which is close to SnsPb, with a melting point of 183 °C. Lead-free solders are often composed of tin with 3 % silver and 0.5-1% copper, and have a melting point of 215-220 °C. 

Lead based solders (tin/lead solders) contain up to 60 % of lead, which can be released into water through galvanic corrosion. The corrosion rate is increased by high concentrations of chloride and nitrate but is inhibited by sulfate, silicate and orthophosphate. Lead concentrations at the tap depend not only on the corrosion rate but also on the number of leaded joints in the plumbing, the area of solder exposed to water at each joint, and the water usage pattern (Gregory, 1990). 

Flip-chip devices have solder bumps, other metal bumps, or even conductive adhesive bumps on the face of the device for I/O connections. During assembly, the devices are flipped face down, then mated and bonded to corresponding solder or metal pads on the package or interconnect substrate. In the quest to eliminate tin-lead solders, electrically conductive epoxy adhesives are beginning to be used for the bumps. 

Tin-lead soldering Batch process. Requires flux... 

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