The use of Surface Mounted Technology (SMT) and the miniaturization of the electronics equipment are demanding new lead-free materials in the soldering process, due to its high toxicity to human being and environmental concerns. Global competitiveness has been driving industries to technological development as challenges to the manufactures and there is an effort to use alternative materials for the soldering electronic components to find an environment-friendly process. This paper presents a literature review involving soldering processes and describes the lead toxicity from related residue. The main solder alloy that is nowadays used to substitute tin-lead and European Directives are also presented.74p.68-74Engenharia Mecânica, Engenharia Ambiental, Engenharia Elétric

Araí Augusta Bernardez Pécora

Eliane Maria Grigoletto

English

Repositorio da Producao Cientifica e Intelectual da Unicamp

Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
68 
Lead environmental issues and new solder alloys in 
electro-electronics equipment 
Eliane Maria Grigoletto 
Professor at the Salesian University Center of São Paulo (Unisal) – Campus Campinas / São José”. Almeida Garret, 
267, 13087-290. Campinas [SP], Brasil. <eliane@sj.unisal.br>. 
Araí Augusta Bernardez Pécora 
School of Mechanical Engineering (FEM), University of Campinas (Unicamp), 13083-970, Campinas [SP], Brasil. 
<arai@fem.unicamp.br>. 
 
 
XI Brazil-Japan International Workshop. IFSP-Caraguatatuba; Universidade Estadual de Campinas; Gifu University; Tokyo 
University of Agriculture and Technology. Caraguatatuba [SP], Brasil. 11/09/2013. [Conpadre n.16/2013]. 
Abstract 
The use of Surface Mounted Technology (SMT) and the miniaturization of the electronics equipment 
are demanding new lead-free materials in the soldering process, due to its high toxicity to human 
being and environmental concerns. Global competitiveness has been driving industries to 
technological development as challenges to the manufactures and there is an effort to use alternative 
materials for the soldering electronic components to find an environment-friendly process. This paper 
presents a literature review involving soldering processes and describes the lead toxicity from related 
residue. The main solder alloy that is nowadays used to substitute tin-lead and European Directives 
are also presented. 
Keywords 
RoHS directive, WEEE directive, lead-free solder, electro-electronic products. 
Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
69 
 
Introduction 
The advent of the integrated circuit and the utilization of Surface Mounted Technology (SMT)   
started and turned the miniaturization of electro-electronic equipment into reality SMT made 
possible to assembly electronic components on Printed Circuit Board (PCB) surface. 
Regarding the soldering process, the great diversity of electro-electronic products is 
demanding new materials that are lead-free in order to obtain electronic products and 
manufacturing processes environmentally cleaner. Modifications in the raw material as in the 
soldering process are currently occurring to reduce pollutant emissions (GRIGOLETTO, 
2003). 
The change in the solder alloy composition should present best results concerning the 
environmental impact when comparing tin-lead and lead-free solder alloys because the new 
alloys present lower toxicity than the lead ones (HWANG, 2004; GRIGOLETTO, 2003; 
MAESTRELLI; PFAHL, 2001). 
The usual tin-lead alloy applied in electro-electronics industries is made of 63%Sn and 
37%Pb. This composition has been chosen because it has a low value of the melting point 
temperature (183º C) and desirable mechanical, wetting and electrical properties. 
Furthermore, Pb is a cheap material when compared with others possible materials.   
The Sn-Ag-Cu (SAC) alloy in different compositions is the most used in both wave and reflow 
oven equipment for soldering. Some suppliers present solder alloys recycling program. In 
Brazil several electro-electronic industries are using lead-free solders. The SAC alloy 
composition most used presents 95.5%Sn, 3.8%Ag and 0.7%Cu. This solder alloy presents 
a higher melting point (217º C) than the tin-lead one which is a disadvantage (ANDERSON et 
al., 2007). 
The objective of the present paper is to show a literature review involving soldering process 
and lead toxicity from its residues. 
RoHS and WEEE Directives 
The Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic 
Equipment Directive (RoHS) (2002/95/EC) was elaborated by the European Parliament and 
the Council of the European Union.  This directive bans the manufacturing of new electrical 
and electronic equipment (EEE) containing lead, cadmium, mercury, hexavalent chromium, 
polybrominated biphenyl (PBB) and polybrominated diphenyl ether (PBDE) flame retardants. 
The RoHS directive is applied to equipment that was put in the market since July 1st 
(MAESTRELLI; GRIGOLETTO 2006). 
The purpose of WEEE Directive (2002/96/EC) is the prevention of electrical and electronics 
equipment waste.  The recycling, the reuse and other forms of recovery wastes are the 
objectives of WEEE Directive to reduce the disposal of such equipment. This directive also 
seeks to improve environmental performance of producers, distributors, consumers and 
those operators directly involved in the treatment of these kind of waste (MAESTRELLI; 
GRIGOLETTO, 2006). 
 
 
Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
70 
 
Lead as a contaminant 
Lead is currently an essential widely used metal in many industrial processes. In alloys and 
other different compounds, lead is used in the manufacture of highly technological products. 
Additionally, lead is used in batteries, paints, ceramics, cables and ammunition products. 
Lead presents desired physical-chemical properties such as malleability, low melting point, 
high resistance to corrosion, high electric conductivity and long working life, which gives it 
advantages over other metals, making it suitable for various industrial processes (LUND, 
1971). 
Lead is a very important chemical element for soldering processes as it can form alloys, 
generally composed by two or three metals, and it acts as a surface adhesion element. 
According to electronic industry, apart from promoting adhesion of components to the 
surface of the board, lead has the function of improving the electrical link between electro-
electronic components and circuits. 
Residues, generated by the lead obtention and its recycling process, may be added to the 
environment, contaminating air, water and soil. One environmental concern is that lead 
particles remain from seven to thirty days in the air. Topographical and meteorological 
factors present great influence on how long these particles remain in the air. Rain takes lead 
particles from the air and promotes their introduction into the soil and water bodies 
(GRIFFIN; KNELSON, 1975). 
Human contamination by lead can occur by ingestion of the compound in an organic or 
inorganic form. When ingestion occurs by organometallic derivatives, the absorption is fast. 
However, as soon as the exposition ceases, the levels of lead in the organism decrease 
quickly. On the other hand, ingestion of inorganic lead presents slow absorption and 
elimination by the organism (OGA, 1996). 
Long-term human intoxication in industry, which frequently is verified in lead related 
industries, is called saturnism or plumbism. It may take years for the illness’ symptoms to 
appear, caused by substitution, in the bones, of calcium by lead. Intoxication can occur either 
when a high amount of lead absorption is involved or after a long period of exposition to low 
concentrations of this metal (GOODMAN; GILMAN; GILMAN, 1983). 
Soldering process of electronic components on surfaces (SMT) 
The soldering of components SMT has been traditionally carried out with tin-lead alloys. 
Typically, two soldering processes are used: (i) double wave and (ii) reflow process.  
Regarding the double wave process, the solder alloy of tin-lead is used in solid bars, which 
will be melted to solder the Surface Mounted Components (SMC) and conventional 
components. On the other hand, the reflow process uses solder pastes made up of tin-lead 
alloy dispersed in solder flux and vehicle. The alloy composition used to be 60Sn/40Pb, 
63Sn/37Pb and 62Sn/36Pb/2Ag. The 63Sn/37Pb alloy is eutectic and it was widely used until 
2006. (HWANG, 1989). 
 
Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
71 
 
Soldering process by double wave 
The soldering process by double wave consists of passing the printed circuit board, 
containing the components, through two waves of melted alloy solder. The first wave is a 
turbulent flow and its function is to wet the terminals, the second one is a laminar flow and it 
aims at removing the possible solder excesses, which may have been deposited during the 
process. Soldering by double wave releases solder alloy residue and its oxides and the 
emissions from tin-lead alloy aerosols are liberated into the air (MEESEMAECKER; 
ROZUMEK; TARRIEU, 1989). 
The emission of residues in the double wave soldering process could occur during the 
soldering of components.  The volatilization of the solder flux steam and lead oxide emission 
into the air could cause residues in the environment. As the solder is in liquid form during 
soldering by double wave, a supernatant slag is produced, due to its contamination with 
copper, brass and other chemical elements coming from the terminals of the components. 
The solder used in the production of assembled boards is recycled by solder alloy producer, 
which commercializes it to be used again in the same soldering process. Boards, which 
possess minor defects, are reworked and, in this process, there is emission of solder 
residues into the environment. If the rework is not viable, the assembled plate is discarded. 
Figure 1 presents a conventional soldering scheme carried out by double wave (VELARDEZ; 
GRIGOLETTO, 1990). 
 
Figure 1. Scheme of the soldering machine by double wave. (VELARDEZ; GRIGOLETTO, 1990). 
 
 
 
Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
72 
 
Soldering process by reflow  
The soldering process of SMC components by reflow is carried out using a solder paste, 
which after being melted is the linking agent between the SMT components and the printed 
circuit board. The solder paste may be deposited on the printed circuit board by punctual 
deposition process or by serigraphy.  The punctual deposition occurs by means of syringes, 
which place the paste where the terminals will be soldered. The placing by serigraphy is 
carried out on a metallic screen covered by rosin like a mask or a stencil, containing the 
layout of the deposit places of interest. The screen is placed on the printed circuit board and 
the solder paste is pressed against it with a squeegee. The paste remains in specified places 
for the soldering of the component terminals. The components are placed on the wet paste 
either by manual, semi-automatic or automatic processes. The assembled board passes 
through a heating oven, which possesses temperature zones adequate to the paste outline, 
to the size of the components and according to the board to be soldered.  
Once the soldering process is finished, an examination is carried out where either the 
components presenting short circuits or placement problems are repaired or, if necessary, 
the board is rejected.  
The soldering process by reflow produces the following residues: solder paste removed from 
unsatisfactory deposits, solder rests in threads coming from the repair  process of solder 
boards, solder alloys solidified in assembled boards, and emissions of the tin-lead alloy into 
the air. Figure 2 presents a scheme of a heating oven used in the soldering of electronic 
components by reflow (VELARDEZ; GRIGOLETTO, 1990). 
 
Figure 2. Scheme of a heating oven (Velardez and Grigoletto, 1990). 
Lead emission in the manufacture of solder alloys and pastes 
According to studies carried out by the Environmental Protection Agency (EPA), the 
organization responsible for environmental conservation in the USA, the manufacture 
industry of solder alloys is not a very important source of lead emission.  
Research has identified two areas in the manufacture of solder alloys as potential sources of 
lead emission, which are lead melting and solder paste production. The lead emissions from 
these sources occur by the same lead emission mechanism as that one applied to the 
production of lead acid batteries. Nevertheless, the quantity of lead discharged is smaller, 
Revista Labor & Engenho                                                            L & E 
ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
73 
due to the low lead content of the produced alloy. In the production of solder paste, small 
lead emission is estimated because the particles in such material present size and density, 
which give them enough settling velocity to prevent their diffusion into the atmosphere.  
Lead emissions tend to present a reduction in the future due to the high demand of solder 
alloys and pastes, which do not include this element in their composition, such as Sn/Cu, 
Sn/Sb, Sn/Ag/Cu and Sn/Sb/Ag alloys. Also, effective control devices, such as bag filters and 
gas scrubbers (EPA, 1998) have increased for the removal of this kind of environmental 
contaminant as lead is emitted as particulate material in solder industry installations. 
Conclusions 
Lead is a used metal in industry and is present in the environment as a contaminant. 
Considering the refinement of mineral lead to obtain the finished product, this metal is a 
source of particulate materials. This metal always remains in the environment, as particulate 
material in the air, or as metallic lead in the soil and water. 
Heavy metals are generally highly toxic. Particularly for lead, it is important to ban it of the 
products, because this element competes with calcium in the organism of animals, the 
consequences of poisoning are serious. Intoxication caused by long-term exposition to low 
quantities of the metal is restricted to the industrial activities, which manipulate lead. The fact 
that this intoxication occurs in the working environment is exactly why lead control is 
extremely important, in order to protect the employees.  
SMC component soldering processes on printed circuit boards generate various residues, 
such as the solder paste that remains from wrong placing, or the solid solder alloy in printed 
circuit boards, which could not be recovered. 
The RoHS and WEEE European Directives helped the electro-electronic producers to 
achieve solutions to decrease environmental pollution due to the toxic elements traditionally 
used in the electro-electronic industry. The Directives are influencing the market and the 
recovery of electronic equipment as the recycling of different materials are been a reality.   
Brazilian electro-electronic industries that export to Europe are RoHS compliant. It should be 
interesting if there were financial incentives to recycling scraps and obsolets products. 
References 
ANDERSON, I. E.; WALLESER, J.; HARRINGA, J. L. Observations of nucleation catalysis effects 
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ISSN: 2176-8846                                                                                  v.7, n.4, 2013 
 
GRIGOLETTO, E. M.; PÉCORA, A. A. B. Lead environmental issues and new solder alloys in electro-electronics equipment. 
Labor & Engenho, Campinas [Brasil], v.7, n.4, p.68-74, 2013. Disponível em: <www.conpadre.org>. 
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Lead Environmental Issues And New Solder Alloys In Electro-electronics Equipment

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Lead Environmental Issues And New Solder Alloys In Electro-electronics Equipment

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