Lead-free solder supply

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-... 

Lead-Free Solder Alloys. Because of the toxicity of lead and the concern that the lead in electronic products may end up in landfills, and ultimately in the water supply, the electronic industry is exploring alternative solder alloys that do not contain lead. These alternative solder alloys are typically composed of tin (Sn), with one, two, or three additives such as copper (Cu), silver (Ag), bismuth (Bi), antimony (Sb), zinc (Zn), or indium (In). Typical tin lead-free candidate solder alloys include Sn-Cu, Sn-Ag, Sn-Ag-Cu, Sn-Ag-Cu-Sb, Sn-In, and Sn-Cu-Bi-Sb. Some of these are more suitable for wave solder... 

D. Shangguan, Supply China Impact of Lead-Free Soldering, Global SMT Packaging, Jan 2005, p 8... 

D. Shangguan, Supply Chain Readiness for Lead-Free Soldering and Environmental Compliance, Proceedings of IPC/JEDEC Eighth International Conference on Lead Free Electronic Components and Assemblies, San Jose, California, April 2005... 

These are just a few issues of concern regarding the transition to lead-free solder. Many questions still remain. This is evident in the multitude of studies, experiments, workshops and conferences available focusing on reliability, inspection, rework, alloy selection, and exemptions, as well as labeling and materials declarations. As the deadline draws near, most of the kinks should be worked out. It seems most U.S. companies are taking the EU dates seriously. No one is shirking their duties, says NEDA s Martin. No one said, No big deal, they ll slip those dates. The best advice, adds Martin, is to prepare and keep your eyes on the EU s laws as each member state completes their laws. Companies can do things in anticipation, but it all trickles down and it seems that time will tell how lead-free plays out for the entire SMT supply chain. Until then, maybe we should still keep our eyes on the price of duct tape. 

Science (NCMS) estimated that replacing Pb in electronic assemblies will result in a material cost of US 140-900 million dollars in the United States alone, with supply chain costs likely to run in the tens of billions of dollars [66]. Cost issues are related to materials (solders, components, boards, protective atmospheres during processing, additional energy consumption due to the higher process temperatures required for most lead-free solders, and operational costs). 

In most cases, food is not a significant avenue of lead exposure. Lead-free solder is used in canneries to ensure that lead is not leached from the canning materials by acidic foodstuffs. One area that lead can pose a hazard to the food supply is lead-coated cookware and tableware. In many countries lead continues to be used as a pottery colorant and glaze. Acidic foods can leach and absorb lead from these decorated surfaces. Crops can absorb lead and other metals into their edible parts. Table 4 lists some examples of metal contamination in crops. 

The manufacturing processes for soldering electronic assemblies were developed over decades as electronics technology advanced. The substitution of lead-free solders for the standard tin-lead alloys has a considerable deleterious effect on manufacturing methods, the entire supply chain of materials and parts, and the environment. The main contributing factor is the higher temperature required to melt and use the lead-free solder alloys. Development and performance testing of... 

Many North American companies are concerned that lead-free components and assemblies will not meet the reliability or functionality requirements necessary for high-end equipment supplied to banks, air traffic control systems, web-based businesses, and other mission-critical applications. Accordingly, manufacturers of aerospace and military electronics have no plans to introduce lead-free solders. There are too many reliability concerns to utilize lead-free solder materials in high-reliability equipment related to the mechanical characteristics of the materials themselves and the effects of high temperatures to process them. The effect of new and modified intermetallic compound phases within solder joints and at the interfaces is yet an additional concern, and there are many more. 

While an increasing number of environmentally friendly products continue to be introduced in Japan and Europe, some North American companies have taken a wait and see approach while others are pacing themselves based on market demands and supply line availability to the lead-free issue. Many Japanese companies have adopted the use of lead-free solder and lead-free components. The use of green labels helps to promote lead-free product introduction using guidelines established by the Japan Electronics and Information Technology Industries Association (JEITA). 

A concern has been raised with regard to the replacement of Pb with Bi metal in current Pb-Sn solder applications. Since the major source of Bi metal is as a by-product of Pb refining [40], the replacement of Pb with Bi would lead to the dilemma of drastically increasing the amount of refined Pb metal. However, since the amount of Pb used in electronics is less than 2% of the total Pb consumption, the mining of Pb for automobile batteries which utilizes approximately 80% of the Pb consumed would provide a sufficient supply of Bi metal. The final report of the National Center for Manufacturing Sciences (NCMS) on Lead-Free Solder Project has raised a serious... 

Volume production of the lead-free assembly has been underway since June 1, 2001. Visteon produces about 7000 units a day with lead-free processing. The next level of complexity for future products will incorporate double-sided reflow, selective soldering, and wave soldering process implementation. Visteon received approval from Ford Motor Company to manufacture and supply its Passive Anti-Theft System transceiver module using lead-free solder [37]. 

Environmental legislation such as the European Union s Restriction of Hazardous Substances (RoHS) directive has a profound impact on all levels of the electronics supply chain, including these components. RoHS restricts the use of lead, which is an element in the solder used for component assembly onto printed circuits. The impact on the base materials and components is primarily the result of higher assembly temperatures that are associated with lead-free assembly. Table 7.1 summarizes the key issues for base material components. RoHS issues will be discussed further in Chap. 10. 

The PCB needs to be supplied at a quaUty level that is capable of withstanding the assembly process, as it will undergo several operations to mount and rework components and connectors. This assembly and rework process has gotten more complicated and damaging to the PCB, especially with the introduction of lead-free products. The acceptability criteria should attempt to anticipate the conditions of the soldering process to ensure the PCB wiU survive the assembly and rework process and stiU function as intended. 

Managing the compatibility issues is critical to lead-free transition. These include materials compatibility (solder, components and PWB), process compatibility (reflow, wave soldering, rework, equipment, and yield), design compatibility, reliability compatibility, and business compatibility (cost, supply chain, and operations). 

In order to turn the entire electronics industry around from its more than 40 years of lead-tin solder assembly practices, a close working relationship is required with the supply chain, i.e., the vendors that provide materials, parts, and assembly services. The industry must come to some consensus concerning lead-free materials, particularly solders and component lead finishes. Vendors cannot be expected to provide multiple versions of individual part numbers. In addition, consensus will allow price reductions that result from economies of scale. As always, companies that desire products from vendors that lie outside the de facto standards (i.e., the industry consensus) must be prepared to bear the burden of additional costs, sourcing issues, and, in some cases, long lead times. 

The ability of the supply chain to manage multiple PNs, BOMs for leaded, lead-free, and mixed configurations must be addressed. Given the fact that there is no standard alloy that will be utilized to replace eutectic Sn-Pb solder, and that the many OEMs and contract manufacturers are working to different schedules, this is a daunting task. It will be necessary to implement quality standards considering the nuances of each alloy. Standards must also be established to classify the specifications and limitations of each component as well as the components forward and backward compatibility. 

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