Lead-free impact

Thomas M. Church. From Meteorites to Man The Patterson Geochemical Heritage. Unpublished manuscript. Source for the impact of Patterson s Ph.D. thesis on geologists few understood age of Earth work ocean sediments MIT sabbatical, Hardy and biology Goldberg s tip Schaule device and lead-free rats. 

Lead is present in most of the primary explosives and thus use of such primary explosives results in corresponding adverse environmental impact. Therefore, development of lead-free primary explosives is an important area of research. Several new explosives such as l,3,5-triazido-2,4,6-trinitrobenzene (TATNB) and... 

Lead Free Gasoline. The current rapidly developing move toward unleaded gasolines in the United States will have a further impact in enhancing the position of the heavier feedstocks. 

Lead and sulphur are derived from the fuel and there is a complex equilibrium dependent upon temperatures and gas composition controlling the absorption/desorption of these poisons. In the case of lead, extended trials have demonstrated the feasibility (ref. 20) of successful operation of oxidation catalysts on leaded fuel. However, it has been noted that in the decade since introduction of lead-free fuel in the USA, residual lead levels have fallen dramatically. In that market, where leaded and unleaded fuels are both available, incidents of poisoning reflect contamination of distribution equipment or deliberate misfuelling (refs. 21,22). Sulphur may also be derived from lube oil but its impact in the sense of poisoning is low on PGM catalysts. Interaction with catalyst components can, however, influence secondary/unregulated emissions of... 

The environmental issue has impacted the production system, accelerated the obsolescence of old technology of primary lead production from its ores and triggered the research of new products with lower lead content or absolutely lead-free.Therefore, pigments, paints and anti-detonating compoimds are now lead-free, while the lead content of hunting ammunition has been significantly reduced. 

With the implementation of the European Union (EU) directive on Restriction of Hazardous Substances (RoHS), the printed circuit industry has been forced to undergo a revolution in technology that is unprecedented in its history.The result is commonly called lead-free, a term that the reader will find used throughout this book, even though the restrictions are on several materials in addition to lead, as described in Chapter 1. The reason for this emphasis is that the biggest impact on the industry is the elimination of lead in the solder that is used for interconnection of the components and the board. 

In addition, the advent of the European Union s Restriction of Hazardous Substances (RoHS) directive and the lead-free assembly processes that result are redefining the requirements for base materials. RoHS has a severe impact on all aspects of base materials technology. The impact of lead-free assembly on base materials and a method of selecting materials for lead-free assembly are discussed in Chaps. 10 and 11. Requirements to support circuit densification, reliability, and electrical performance are also critical and will be discussed in Chap. 9. This chapter discusses grades and specifications of base materials, as well as the manufacturing processes used to make them. 

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. 

Historically, the properties that received the greatest amount of attention were the glass transition temperature, Tg, and the coefficients of thermal expansion, or CTEs, particularly in the z-axis. With the advent of lead-free assembly processes, other properties have increased in importance as well.The most notable is the decomposition temperature,Ta.These properties were described in more detail in Chap. 6, and will be discussed again in Chap. 10, which focuses on the impact of lead-free assembly on base materials. However, some additional information as well as examples of the test data are included here, as well as comparisons of some common material types. 

Comparisons of dicy-cured materials with non-dicy cured materials, especially the pheno-hc FR-4 materials developed for lead-free assembly, show that the elimination of dicy can have a positive impact on CAF resistance. This may be due to reduced moisture absorption when dicy is removed, or to the eUmination of an electrochemical reaction that may be promoted in the presence of dicy, or to both. 

THE IMPACT OF LEAD-FREE ASSEMBLY ON BASE MATERIALS... 

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