Electronics lead-free solder

Similarly, the various EU directives that mandate substance bans have initiated wide scale research and development of alternative materials. Lead is a case in point. Lead has been widely used in the electronic industry in solders. Lead-free solders have existed for many years but it was the mandate in the Restriction of use of certain Flazardous Substances Directive (RoHS) to have products free of lead by July 2006 that spurred industry research, planning and adoption of the substitutes. Annex I lists examples of Green Chemistry case studies where research was stimulated in response to legislation targeting hazardous materials. 

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... 

In spite of a tremendous amount of effort for the search of lead-free C4s, no industry standard has evolved as yet. Commonly cited lead-free solders are Sn-rich alloys for which electroplating processes are available. The most popular lead-free solder among them is Sn3.9AgO.6Cu with a melting temperature of 217°C. This solder is recommended by National Electronic Manufacturing Initiative (NEMI) and has been extensively studied and characterized by NIST. However, applicability of this solder as a C4 material in chips with advanced ILD is not known. 

Joints between metals, including those in electronic components, have traditionally used SnPb solders. However, in the European Union, new environmental legislation aims to phase out this use of lead by 2006 or 2007 a move to lead-free solders is also being made in Japan and the US. Eutectic SnPb solder exhibits many desirable properties... 

Typical environmentally regulated substances are arsenic, cadmium, mercury, and lead. Presently, there are few products including mercury. Some electronic devices include arsenic or cadmium, and are used in a computer and so on. Lead is used in the battery of a car, and its alloys are used as solders. In addition, it is included in polyvinylchloride (PVC) cables as a stabilizer. The battery has been treated appropriately. The solder was replaced by a lead-free solder after the RoHS directive. However, a lead-free solder includes lead below 1000 (mass) ppm. The quantity of lead in PVC cables has been decreased. The consumption of the environmentally regulated material seems to decrease, but the discarded products may be the products produced before the enactment of the regulations. 

If the reactive blending is stopped at an intermediate stage, the micelles and the shrunken particles coexist and a bimodal particle distribution is realized, as shown in Fig. 8.39. In the case of Fig. 8.39, PA-6 was mixed with polyethylene (PE) modified with a small amount of MAH (0.1 wt%) and glycidyl methaciylate (3-12 wt%), at a 70/30 (PA/PE) blend ratio. The bimodal system can be easily crosslinked by electron beam irradiation at a low dose level, the same as that used for neat PE (Pan et al. 2002). The crosslinked PA/PE alloy shows good heat resistance in a lead-free solder test thus, it may be applied in making construction parts with melt-down resistance in fires, e.g., a window frame. 

The recommended lead-free solder formulation is Sn-Ag-Cu for board assembly but there are other formulations such as Nickel-Palladium (NiPd), or Nickel-Palladium with Gold flash (NiPdAu). Passive components, to be compatible with a lower temperature Lead process (which is 215°C for 50/50 Tin/Lead formulations and 230°C for 40/60 formulations) and the higher lead-free process of up to 260°C, use pure matte Tin for their contacts. The use of lead in solder is partially based on several potential reliability issues. Pure Tin component leads have been shown to result in inter-metaUic migration in the termination of the electronic component and the growth of tin whiskers which could cause short circuits (which is why there is a exemption for military use (only) components). 

The UK Cookson Group s, Cookson Electronics subsidiary has negotiated licences with the patent holders of various lead-free solders. These enable it to manufacture globally and supply them as a patent holder, making royalty payments on sales. The alloys concerned are Senju Sn/Ag/Cu (Senju-... 

A more comprehensive list of mechanical material properties of lead-free solders and other materials used in electronic packages can be found in Reference 22. 

Darveaux, Robert, Shear Deformation of Lead Free Solder Joints, Electronic Components and Technology Conference, 2005, pp. 882-893. 

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