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Survey on Lead Free Solder Systems

10 Toxicological evaluation of solders and fluxes

Reflow soldering (Pastes)
62Sn36Pb2Ag and flux
96.5Sn3.5Ag and flux
95.5Sn4Ag0.5Cu and flux
Evaluation
Wave-soldering (Alloys)
63Sn37Pb Alloy and Flux
95.5Sn3.8Ag0.7Cu Alloy and Flux
Evaluation
Hand-soldering (Wires)
60Sn40Pb and Flux
96.5Sn3.5Ag and Flux
Evaluation
Summary of toxicology
Occupational considerations
Consumer considerations
Environmental considerations
Conclusion and recommendations

In this chapter the products used in the project are presented one by one. A toxicological evaluation has been made of each substance in each product. The ingredients of the products are all assigned an identification code in order to be able to identify each single substance in the Annex 1: Toxicological Profiles.

By the end of each subchapter there is a comparative toxicological summary evaluation of the products in each type of soldering process (reflow, wave and hand soldering).

The identity and precise amount of ingredients/components in the products is confidential and only known to DTC.

Reflow soldering (Pastes)

62Sn36Pb2Ag and flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part:

Flux:

According to the Danish regulation the product should not be classified as there is no content of lead compounds, only metallic lead. The classification of the flux, would be: Xi (Irritant): R36/38 Irritating to eyes and skin (1,2).

Lead poses high human toxicity and moderate toxicity towards aquatic organisms. Silver has low human toxicity but is much more toxic to aquatic organisms than lead. Tin has low human toxicity and the aquatoxicity of inorganic tin compounds is comparable to that of lead.

The flux is irritating to the skin and eyes on direct contact.

At room temperature (20 ° C) lead, tin and silver will remain, as metals and the flux is not volatile at this temperature.

The range of the soldering temperature is 235 ° C – 250 ° C. When tin, lead, and silver is heated in air to temperatures in this range they may be oxidized to tin-, lead-, and silver oxides and to a little extent become airborne.

In products, if lead oxides are included as an ingredient with equal or more than 5 weight-% the product would be classified as: T (Toxic), N (Dangerous for the environment): R61 May cause harm to the unborn child, R62 Possible risk of impaired fertility, R20/22 Harmful by inhalation and if swallowed, R33 Danger of cumulative effects, R 50/53 Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment (1,2).

The chemical composition of the flux fumes at soldering temperature has not been determined by the producer. The flux is a non-corrosive flux, based on rosins. By heating the flux to soldering temperatures (235 ° C – 250 ° C), it is likely that the rosin derivatives will form fumes containing a complex mixture of resin acids, aldehydes and carbon oxides. Furthermore, by heating the flux there is a small risk of evaporation of small amounts of nitrogen oxides, ammonia, bromides and fluorides. Chemical reactions between one or more of the components are likely to take place, but these have not been established.

Inhalation of the airborne metals (especially lead) and the flux fumes is of relevance for the working environment. Inhalation of the airborne metals, may cause metal dust lungs, and lead may affect the central and the peripheral nervous systems and the haeme synthesis, i.e. the product ion of haemoglobin and may cause anaemia. Furthermore exposure to lead may cause chromosomal aberrations, impair the fertility and cause preterm delivery of babies and minor malformations. The evidence for lead being carcinogenic is ambiguous.

The flux fumes given off at soldering are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause sensitization and occupational asthma.

The emission to the air from the solder process to the environment may contain metal oxides of tin, lead and silver. Furthermore small amounts of e.g. CO_x, NO_x, resin acids, aldehydes, ammonia and fluorides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the product should be considered as toxic to the aquatic environment. Lead is toxic to aquatic organisms, the toxicity though, depends on the water hardness. Lead is more toxic in soft water than in hard water. Silver ions are lethal to bacteria, and is very toxic aquatic organisms. The aquatoxicity of inorganic tin compounds is comparable to that of lead.

The biocompatibility of lead is smaller in hard water than in soft water. The bioaccumulation is low.

96.5Sn3.5Ag and flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part:

Flux:

The classification of the product, according to the producer is:

Xi, Irritant; R43 May cause sensitization by skin contact (1,2).

The paste has low acute toxicity, is irritating to the skin and the eye and may cause severe damage on the eye in case of contact. Prolonged or repeated contact with skin may cause itching and soreness and possible sensitization. Furthermore the product may de-fat the skin and lead to irritation and dermatitis. Exposure to dust may cause gastrointestinal irritation.

A small part of the product is soluble in water. The product is slowly biodegradable and it has a tendency to bioaccumulate. It is rated as hazardous to aquatic organisms.

Silver has low human toxicity but is much more toxic to aquatic organisms than lead. Tin has low human toxicity and the aquatoxicity of inorganic tin compounds is comparable to that of lead.

At room temperature (20 ° C) or, when not in use (not heated), the product contains only substances with low volatility. During soldering the range of the temperature are 260 ° C – 270 ° C. The producer has not determined the chemical composition of the flux fumes at soldering temperature. By heating the product (metals plus flux) there is a small risk for evaporation of tin- and silver oxides from the metals, and a complex mixture of resin acids, aldehydes and carbon oxides from the rosin, which is the main ingredient in the flux. There will also be a small risk for formation of e.g. nitrogen oxides, phosphin, phosphide and phosphorous oxides. Most likely, chemical reactions between two or more components will take place, but these have not been established.

Inhalation of the airborne metal fumes (metals/metaloxides) and the flux fumes is of relevance for the working environment. The metal fumes given off at soldering may cause metal dust lungs. The flux fumes are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause pulmonary sensitization and asthma. Exposure to processing fumes may cause gastrointestinal irritation.

The emission to the air from the solder process to the environment may contain metal oxides of tin and silver. Furthermore small amounts of e.g. carbon oxides, nitrogen oxides, resin acids, aldehydes, phosphin, phosphide and phosphorous oxides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the paste should be considered as toxic to the aquatic environment. Inorganic tin compounds are toxic to aquatic organisms. The bioaccumulation is low. Silver ions are lethal to bacteria, and is very toxic to aquatic organisms.

A small part of the product is soluble in water. According to the producer the paste is slowly biodegradable and it has a tendency to bioaccumulate.

95.5Sn4Ag0.5Cu and flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part:

Flux:

The classification of the paste according to the producer is: Xi (Irritant): R43 May cause sensitization by skin contact (1,2).

The product has low acute toxicity, is irritating to the skin and the eye and may cause severe damage on the eye in case of contact. Prolonged or repeated contact with skin may cause itching and soreness and possible sensitization. Furthermore the product may de-fat the skin and lead to irritation and dermatitis. Exposure to dust may cause gastrointestinal irritation.

The paste has low volatility and a small part of the product is soluble in water. The product is slowly biodegradable and it has a tendency to bioaccumulate. It is not rated as hazardous to aquatic organisms.

Silver has low human toxicity but is much more toxic to aquatic organisms than lead. Tin has low human toxicity and the aquatoxicity of inorganic tin compunds is comparable to that of lead. Organic tin compounds are toxic to the aquatic ecosystems. Copper has low human toxicity and is moderate toxic to aquatic organisms.

At room temperature (20 ° C) when not in use (not heated) the product is not volatile.

The range of the soldering temperature is 260° C - 270° C. The chemical composition of the flux fumes at soldering temperature has not been determined by the producer. By heating the product (metals as well as the flux) there is a risk for evaporation of tin-, silver- and copper oxides from the paste. As the flux is identical with that for the flux used in connection with paste: 96.5Sn3.5Ag (4.1.2) and the range of soldering temperature is the same, the evaporation from this flux will also be the same: a complex mixture of resin acids, aldehydes and carbon oxides from the rosin, which is the main ingredient in the flux. There will also be a small risk for formation of e.g. nitrogen oxides, phosphin, phosphide and phosphorous oxides. Most likely, chemical reactions between two or more components will take place, but these have not been established.

Inhalation of the airborne metals (metals/metal oxides) and the flux fumes is of relevance for the working environment. The metal fumes given off at soldering may cause metal dust lungs. The flux fumes are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause pulmonary sensitization and asthma. Exposure to processing fumes may cause gastrointestinal irritation.

The emission to the air from the solder process to the environment may contain metal oxides of tin, silver and copper. Furthermore small amounts of e.g. carbon oxides, nitrogen oxides, resin acids, aldehydes, phosphin, phosphide and phosphorous oxides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards with water, the product should be considered as toxic to the aquatic environment. Inorganic tin compounds are toxic to aquatic organisms. Silver ions are lethal to bacteria, and are very toxic to aquatic organisms. Copper is cytotoxic, and inhibits algal growth.

A small part of the product is soluble in water. According to the producer, the paste is slowly biodegradable and it has a tendency to bioaccumulate.

Evaluation

The following table gives a summary overview of the possible exposure of workers and the environment to the products used in the reflow process.

Exposure

The process temperature is higher using the lead-free solders compared to the use of lead-containing solder. The tendency of chemicals to become airborne increases by increasing temperature. As a consequence the use of the lead-free solders in this project will possibly lead to an increase in the evaporation from the solders and fluxes compared to the use of the traditional lead-containing solder. Even though the process temperatures are relatively low, there will be a certain degree of thermic decomposition of the organic substances. The main fraction will consist of metal oxides and to a lesser extent resin acids, aldehydes, CO_x and NO_x. By using the lead-containing solder: 62Sn36Pb2Ag and flux, substances like ammonia and fluorides may be formed in very small concentrations. Whereas, the use of lead-free alternatives may result in the formation of very small concentrations of phosphin, phosphide and POx. These emissions will all enter the workplace or the environment unless necessary precautions are taken with containment, filters etc.

The composition of the drost from the production or the waste differs mainly due to the content of the metals.

The following table gives an overview of the main effects of the referred exposures of workers and the environment to the solders.

Effects of the metal parts of the alloys as metal compounds in vapor, fumes, waste water, etc.

[ ] = effects caused by compounds other than metal itself
( ) = effects are weak or uncertain
- = No
+ = Yes

Lead is very toxic to humans. The other metals in the solder are little to moderate toxic to humans. During the solder process fumes of metal and metal oxides may be formed and emitted to the air in the working environment, and inhaled by the workers. Especially lead may cause severe systemic effects.

Lead is moderate toxic to the environment. Silver appears to be much more toxic to aquatic organisms than the other metals in the solder, whereas the aquatoxicity of copper is moderate (in the order of lead). The lead-free solder contains more tin, silver and copper instead of lead.

Below is an overview of the toxicological effects of the fluxes used in the solder process.

Effects of the flux part of the alloy

( ) = effects are weak or uncertain
- = No
+ = Yes

Exposure to the fluxes, when not in use may cause irritation by skin contact. When heating the fluxes acrid vapors and fumes are formed, that are very irritating to the eyes and the respiratory system. Prolonged or repeated inhalation may cause asthma. Vapors and fumes may also irritate the skin. The fluxes in the lead-free solder pastes may cause skin and respiratory allergy.

The environmental effects of the fluxes is considered negligible compared to the environmental effects of the metals in the solders.

Wave-soldering (Alloys)

During wave soldering the assembled circuit boards, which have been pre-treated with solution of flux, are mechanically fed over a ’standing wave’ of molten solder. This method is used in automated large batch production and is usually enclosed (3).

The solders used in connection with wave soldering in this project consist of metal bars and fluxes that are separated. The fluxes are added separately during the solder process.

63Sn37Pb Alloy and Flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part:

Flux:

According to the Danish regulation the product should not be classified. Partly as the alloy is regarded as a material and because there is no content of lead compounds, only metallic lead.

The classification of the flux is: Xi (Irritant): R11 Highly flammable, R36 Irritating to the eyes, R43 May cause sensitization by skin contact (1,2).

It is possible though, that according to the Danish regulation the flux should be classified as a possible carcinogen (1,2). The content of benzene of one of the ingredients decides the classification with regard to the carcinogenicity.

Lead poses high human toxicity and moderate toxicity towards aquatic organisms. Tin has low human toxicity and the aquatoxicity of inorganic tin compounds is comparable to that of lead. Organic tin compounds are toxic to the aquatic ecosystems.

The flux contains high amounts of a solvent with high volatility. The solvent which has an ability to de-fat the skin, irritate the eyes, the skin and the respiratory tract. By inhalation of high concentrations it may cause headache, nausea and malaise. Prolonged or repeated exposure may affect the central nervous system, and cause sensitization to the skin.

The producer has informed that the flux is totally soluble in water, easily biodegradable and is not meant to be bioaccumulated. Furthermore the flux is evaluated to be non-toxic to water living organisms.

The range of the soldering temperature is 200 ° C – 210 ° C. As tin and lead is heated in air to temperatures in this range they may be oxidized to tin- and lead oxides and to a reduced extent become airborne.

In products, if lead oxides were included as an ingredient with equal or more than 5 weight-% the product would be classified as: T (Toxic), N (Dangerous for the environment): R61 May cause harm to the unborn child, R62 Possible risk of impaired fertility, R20/22 Harmful by inhalation and if swallowed, R33 Danger of cumulative effects, R 50/53 Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment (1,2).

The producer has not determined the chemical composition of the flux fumes at soldering temperature. By heating the flux, VOC´s will be emitted and there is a small risk for evaporation of a complex mixture of resin acids, aldehydes, carboxylic acid and carbon oxides. There will also be a small risk for formation of e.g. bromides. Most likely, chemical reactions between two or more components will take place, but these have not been established.

Inhalation of the airborne metals (especially lead) and the flux fumes is of relevance for the working environment. Inhalation of the airborne metals, may cause metal dust lungs, and affect the central and the peripheral nervous system and the haeme synthesis, i.e. the product ion of haemoglobin and may cause anaemia. Furthermore exposure may cause chromosomal aberrations, impair the fertility and cause preterm delivery of babies and minor malformations. The evidence for lead being carcinogenic is ambiguous. The flux fumes given off at soldering are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause sensitization and occupational asthma. High concentration of vapor may have narcotic effects.

The emission to the air from the solder process to the environment may contain metal oxides of tin and lead and VOC. Furthermore small amounts of e.g. carbon oxides, resin acids, aldehydes, carboxylic acid and bromides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the aquatoxicity of lead depends on the water hardness. The biocompatibility of lead is smaller in hard water than in soft water. Lead is toxic to aquatic organisms. The aquatoxicity of inorganic tin compounds is comparable to that of lead. The bioaccumulation is low.

95.5Sn3.8Ag0.7Cu Alloy and Flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part:

Flux:

According to the Danish regulation the metal alloy should not be classified (1,2).

According to the producer the flux is classified as: F (Highly flammable), Xi (Harmful): R11 Highly flammable, R36 Irritating to the eyes, R43 May cause sensitization by skin contact.

It is possible though, that according to the Danish regulation the flux should be classified as a possible carcinogen (1,2). The content of benzene of one of the ingredients decides the classification with regard to the carcinogenicity.

The flux contains high amounts of a solvent, which has an ability to de-fat the skin, irritate the eyes, the skin and the respiratory tract. By inhalation of high concentrations it may cause headache, nausea and malaise.

Prolonged or repeated exposure may affect the central nervous system, and sensitization of the skin.

The producer informs that the main part of the flux almost immediately mixes with water, is easily biodegradable and is meant not to be bioaccumulating. Furthermore the flux is evaluated to be mildly toxic to aquatic organisms.

Silver has low human toxicity but is much more toxic to aquatic organisms than lead. Tin has low human toxicity and the aquatoxicity of inorganic tin compounds is comparable to that of lead. Copper has low human toxicity and is moderate toxic to aquatic organisms.

The range of the soldering temperature is 235 ° C – 250 ° C. As tin, silver and copper is heated in air to temperatures in this range they may be oxidized to tin-, silver- and copper oxides and to a reduced extent become airborne. The producer has not determined the chemical composition of the flux fumes at the soldering temperature. By heating flux, VOC´s will be emitted and there is a small risk for evaporation of a complex mixture of resin acids, aldehydes, carboxylic acid, carbon oxides and for formation of e.g. bromides. Most likely, chemical reactions between two or more components will take place, but these have not been established.

Inhalation of the airborne metals/metal oxides and the flux fumes is of relevance for the working environment. The metal fumes given off at soldering may cause metal dust lungs. Prolonged or repeated exposure to the fumes may cause dermal and respiratory sensitization and occupational asthma. High concentration of vapor may have narcotic effects, and affect the central nervous system.

The emission to the air from the solder process to the environment may contain metal oxides of tin and lead and VOC. Furthermore small amounts of e.g. carbon oxides, resin acids, aldehydes, carboxylic acid and bromides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the product should be considered as toxic to the aquatic environment. The aquatoxicity of silver is high. Silver ions are lethal to bacteria, and are very toxic to aquatic organisms. Inorganic tin compounds are toxic to aquatic organisms. The aquatoxicity of inorganic tin compounds is comparable to that of lead. Copper is cytotoxic, and inhibits algal growth.

The metals in the alloy has a tendency to bioaccumulate.

Evaluation

The following table gives a summary overview of the possible exposure of workers and the environment to the products used in the wave soldering process.

Exposure

In the wave soldering process the use of lead-free solders requires higher process temperature than by the use of lead-containing solder. As a consequence the use of the lead-free solder will possibly lead to an increase in the evaporation from the solders and fluxes compared to the use of the traditional lead-containing solder. Even though the process temperatures are relatively low, there will be a certain degree of thermic decomposition of the organic substances. The main fraction will consist of metal oxides and to a lesser extent resin acids, aldehydes, carboxylic acids and CO_x. Bromides may be formed in very small concentrations. These emissions will all enter the workplace or the environment unless necessary precautions are taken with containments, filters etc.

The composition of the drost from the production or the waste differs mainly due to the content of the metals.

The following table gives an overview of the main effects of the referred exposures of workers and the environment to the solders.

Effects of the metal part of the alloys as metal compounds in vapor, fumes, smoke, waste water, etc.

[ ] = effects caused by compounds other than metal itself
( ) = effects are weak or uncertain
- = No
+ = Yes

Lead is very toxic to humans. The other metals in the solder are little to moderate toxic to humans. During the solder process fumes of metal and metal oxides may be formed and emitted to the air in the working environment, and inhaled by the workers. Especially lead may cause severe systemic effects.

Lead is moderate toxic to the environment. Silver appears to be much more toxic to aquatic organisms than the other metals in the solder, whereas the aquatoxicity of copper is moderate (in the order of lead). The lead-free solder contains more tin, silver and copper instead of lead.

Below is an overview of the toxicological effects of the fluxes used in the solder process.

Effects of the fluxes

( ) = effects are weak or uncertain
- = No
+ = Yes
* Depends on the content of benzene

Due to the high content of low-boiling solvents in both fluxes, they are very volatile also when the flux is not heated in soldering process. The solvents have an ability to de-fat the skin, irritate the eyes, the skin and the respiratory tract. By inhalation of high concentrations it may cause headache, nausea and malaise. Prolonged or repeated exposure may affect the central nervous system, and sensitization of the skin. The flux used in connection with the lead-containing solder is more volatile than the lead-free solder flux.

When heating the fluxes acrid vapors and fumes are formed, that are very irritating to eyes and the respiratory system. Prolonged or repeated inhalation may cause asthma. Vapors and fumes may also irritate the skin.

The environmental effect of the fluxes is considered negligible compared to the environmental effects of the metals in the solders.

Hand-soldering (Wires)

Hand soldering involves the use of a soldering iron. The iron is purely a means of applying heat to the solder so that it melts and forms the required joint (4). The solder used during the hand soldering process is solder wires with "built-in" flux.

60Sn40Pb and Flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part of wire:

Flux part of wire:

According to the Danish regulation the product should not be classified partly as the wire is regarded as a material and partly because there is no content of lead compounds, only metallic lead.

The classification of the flux, isolated from the metals would be: Xi (Irritant): R36 Irritating to the eyes, R43 May cause sensitization by skin contact (1,2).

Lead poses high human toxicity and moderate toxicity towards aquatic organisms. Tin has low human toxicity and the aquatoxicity of inorganic tin compunds is comparable to that of lead.

The flux is based on rosin and has low acute toxicity. The flux is irritating to the skin. Prolonged or repeated contact with skin may cause itching and soreness and possible sensitization.

The material in the wire has low volatility. The flux is totally soluble in water. The flux is easily biodegradable and it has no tendency to bioaccumulate. The flux is regarded as non-toxic to aquatic organisms.

At room temperature (20 ° C ) the product contains only substances with low volatility.

During soldering the range of the soldering temperature are 200 ° C – 210 ° C. The chemical composition of the flux fumes at soldering temperature has not been determined by the producer. By heating the product (metals as well as the flux) there is a small risk of evaporation of tin- and lead oxides from the metals, and a complex mixture of resin acids, aldehydes, ammonia, amines, carbon oxides, nitrogen oxides and chlorides from the flux. Most likely, chemical reactions between two or more components will take place, but these have not been established.

In products, if lead oxides were included as an ingredient with equal to or more than 5 weight-% the product would be classified as: T (Toxic), N (Dangerous for the environment): R61 May cause harm to the unborn child, R62 Possible risk of impaired fertility, R20/22 Harmful by inhalation and if swallowed, R33 Danger of cumulative effects, R 50/53 Very toxic to aquatic organisms, may cause long-term adverse effects in the aquatic environment (1,2).

Inhalation of the airborne metals (especially lead) and the flux fumes is of relevance for the working environment. Inhalation of the airborne metals, may cause metal dust lungs, and affect the central and the peripheral nervous system and the haeme synthesis, i.e. the product ion of haemoglobin and may cause anaemia. Furthermore exposure may cause chromosomal aberrations, impair the fertility and cause preterm delivery of babies and minor malformations. The evidence for lead being carcinogenic is ambiguous.

The flux fumes given off at soldering are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause pulmonary sensitization and asthma. Exposure to dust or processing fumes may cause gastrointestinal irritation via swallowing of inhaled dust/fumes.

The emission to the air from the solder process to the environment may contain small amounts of metal oxides of lead and silver. Furthermore small amounts of e.g. resin acids, aldehydes, ammonia, amines, carbon oxides, nitrogen oxides and chlorides may occur.

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the flux is totally soluble in water. The flux is easily biodegradable and it has no tendency to bioaccumulate. It is not rated as hazardous to aquatic organisms. The metals should be considered as toxic to the aquatic environment. Lead is toxic to aquatic organisms, the toxicity though, depends on the water hardness. Lead is more toxic in soft water than in hard water. The aquatoxicity of inorganic tin compounds is comparable to that of lead.

The biocompatibility of lead is smaller in hard water than in soft water. The bioaccumulation is low.

96.5Sn3.5Ag and Flux

In the following tables the ingredients are presented in weight-% of the entire product:

Metal part of wire:

Flux part of wire:

According to the Danish regulation the product should not be classified.

Tin has low human toxicity and the aquatoxicity of inorganic tin compunds is comparable to that of lead.

The flux is based on wax and has low acute toxicity. There is lack of data on some of the ingredients of the flux, which, makes the evaluation of the toxicity of the flux incomplete. Prolonged or repeated contact with skin may cause irritation.

The flux has low volatility and is practically insoluble in water. The flux is slowly biodegradable and it has a tendency to bioaccumulate. The flux is regarded as non-toxic to aquatic organisms.

Silver has low human toxicity but is much more toxic to aquatic organisms than lead. Tin has low human toxicity and the aquatoxicity of inorganic tin compounds is comparable to that of lead. Organic tin compounds are toxic to the aquatic ecosystems.

At room temperature (20 ° C) the product contains only substances with low volatility.

During soldering the range of the soldering temperature is 235 ° C – 250 ° C. The producer has not determined the chemical composition of the flux fumes at soldering temperature. By heating the product (metals as well as the flux) there is a small risk for evaporation of tin- and silver oxides from the metals, and a complex mixture of ammonia, amines, carbon oxides and nitrogen oxides. There will also be a small risk for formation of e.g. chlorides. Most likely, chemical reactions between two or more components will take place, but these have not been established.

Inhalation of the airborne metals (especially lead) and the flux fumes is of relevance for the working environment. Inhalation of the airborne metals may cause metal dust lungs. The flux fumes given off at soldering are irritating to the nose, throat and respiratory organs. Prolonged or repeated exposure to the fumes may cause asthma.

The emission to the air from the solder process to the environment may contain metal oxides of tin and silver. Furthermore small amounts of e.g. ammonia, amines, carbon oxides and nitrogen oxides may occur. There will also be a small risk for formation of e.g. chlorides

In case of the product entering the aquatic environment, e.g. by rinsing the circuit boards the flux is practically insoluble in water. The flux is slowly biodegradable and it has a tendency to bioaccumulate. It is not rated as hazardous to aquatic organisms. Silver ions are lethal to bacteria, and are very toxic to aquatic organisms. Tin is moderate toxic towards aquatic organisms.

Evaluation

The following table gives a summary overview of the possible exposure of workers and the environment to the products used in the hand soldering process.

Exposure

The process temperature is higher using the lead-free solders compared to the use of lead-containing solder. The tendency of chemicals to become airborne increases by increasing temperature. As a consequence the use of the lead-free solders in this project will possibly lead to an increase in the evaporation from the solders and fluxes compared to the use of the traditional lead-containing solder. Even though the process temperatures are relatively low, there will be a certain degree of thermic decomposition of the organic substances. The main fraction will consist of metal oxides and to a lesser extent resin acids, aldehydes, CO_x and NO_x. There is furthermore a small risk for formation of chlorides.

These emissions will all enter the workplace or the environment unless necessary precautions are taken with encapsulation, filters etc. There will be special requirements on the exhaust/ventilation as the wires are used in hand soldering processes.

The composition of the drost from the production or the waste differs mainly due to the content of the metals.

The following table gives an overview of the main effects of the referred exposures of workers and the environment to the solders.

Effects of the metal pars of the alloys as metal compounds in vapor, fumes, smoke, waste water, etc.

[ ] = effects caused by compounds other than metal itself
( ) = effects are weak or uncertain
- = No
+ = Yes

Lead is very toxic to humans. The other metals in the solder are low to moderate toxic to humans. During the solder process fumes of metal and metal oxides may be formed and emitted to the air in the working environment, and inhaled by the workers. Especially lead may cause severe systemic effects.

Lead is moderate toxic to the environment. Silver appears to be much more toxic to aquatic organisms than the other metals in the solder. The lead-free solder contains silver and more tin instead of lead.

Below is an overview of the toxicological effects of the fluxes used in the solder process.

Effects of the fluxes

( ) = effects are weak or uncertain
- = No
+ = Yes

When not heated, both fluxes are of low volatility. The flux in the lead-containing wire is allergenic.

When heating the fluxes acrid vapors and fumes may be formed, that is very irritating to eyes and the respiratory system, and the flux in the lead-containing wire is allergenic. Prolonged or repeated inhalation may cause asthma. Vapors and fumes may also irritate the skin.

The environmental effect of the fluxes is considered negligible compared to the environmental effects of the metals in the solders.

Summary of toxicology

Occupational considerations

During the solder process fumes of metals and metal oxides may be formed. The fumes may be emitted to the working environment and be inhaled. Especially lead may cause systemic effects, and vapors and gasses may irritate the mucosae of eyes and respiratory tract, and possibly cause respiratory diseases with symptoms like asthma and respiratory allergy. Skin contact during handling flux and solder materials may irritate the skin and in some cases cause development of skin allergy.

As the lead-free processes requires higher processing temperatures, the tendency of chemicals to become airborne increases. As a consequence the use of the lead-free solders will possible lead to an increase in the evaporation from the solder metals and fluxes compared to the use of the traditional lead-containing solders.

In general, regarding the fluxes, the concentration of activators seems to be higher (at least the double) in fluxes used in connection with lead-free solders as compared to the fluxes used in lead-containing solders (see figure below).

Fig.
Content of activators and antioxidants in the fluxes used in connection with resp. lead-containing and lead-free solders in w/w-%.

Furthermore, experience from the practical testing program in this project indicates that the flux of the lead-free solders is more corrosive to the materials. Combined with the fact that the lead-free soldering temperature is higher, developing more fumes and vapors this may indicate that the lead-free solder processes may develop more acrid, irritating and in some cases allergenic fumes and vapors than the traditional lead-containing solder processes.

From a working environmental point of view though, it seems justifiable to substitute the lead-containing solders by lead-free materials, as lead poses high human toxicity compared to tin, silver and copper. That is assuming humans are exposed. Whereas, if containment of the processes are very efficient, there will be no occupational exposure of solderers. There will though always be a risk of exposure, e.g. during maintenance, cleaning and reparation, which still may justify the substitution of lead-containing solders to lead-free.

Consumer considerations

Data indicates that neither of the solder technologies (lead-containing or lead-free) poses any nuisance to the consumer.

Environmental considerations

From a human toxicological point of view lead-free solder are to be preferred compared to lead-containing solders. Lead is moderately toxic to the environment, but it is uncertain whether lead metal, e.g. in solder, will be bioavailable from electronic equipment dumped in waste sites. If incinerated, lead will be present in smoke to some extent as lead metal and oxides.

The general-purpose lead-free solder contains in addition to tin silver and copper instead of lead, but in much lower contents, e.g. Sn95/Ag4/Cu1. Silver and copper are less toxic to humans than lead. Copper is an essential element. Silver appears to be much more toxic to aquatic organisms than the other metals in solder, whereas the aquatoxicity of copper is moderate (in the order of that of lead). However, as for lead, it is uncertain whether silver and copper metals will be bioavailable from electronic equipment dumped in waste sites.

If incinerated, these metals may be present to some extent in smoke as oxides and possibly also as metals. The content of copper in the incinerated metals may have a catalytic effect on the formation of dioxins (10).

In case electronic equipment is deposited there will be a risk for the metals and chemicals to leach into the environment. Some chemicals may also evaporate. Odense Renovationsselsskab A/S receives and treats electronic waste from the public and companies in Odense city. The waste is separated in fractions of materials and components. In 2001 84% were recycled, 10% incinerated and nothing was deposited (13). There is no information of the last fraction (6%). The numbers illustrate that it might be possible in the future to avoid depositing the electronic equipment, thus eliminating this disposal way as a source of emission.

The overall disposal of EE-products (except for refrigerators and deep freezers) in 1997 was 103.000 tons in Denmark. About 60.000 tons of these were electrical products and about 43.000 tons were electronic products.

The amount of electronic waste is expected to increase (10). Part of these are consumer electronics. The Danish Trade Organization for Consumer Electronics has estimated that the amount of disposed consumer electronics is expected to increase by 36% from 1997 to 2001 (total amount 14.000 tons). In 1994, 60% of the electronics was discarded. This amount was estimated to be 89% in the year 2001 (10). Unfortunately new figures are not yet available but are expected in a short period of time.

The European recycling industry for electrical and electronic products is expected to increase their turnover from 144 mio. USD in 1995 to 419 mio. USD in 2002 (12), which seems to be an essential increase. Question is weather it is possible to keep step with the increasing amount of electronic waste.

Conclusion and recommendations

In summary, lead poses high human toxicity and moderate toxicity towards aquatic organisms. Thus, substitution to lead-free solder seems justified with regard to human toxicity. However, the future general-purpose lead-free solder implies the use of silver, which has low human toxicity but is much more toxic to aquatic organisms than lead. The other metals (tin and copper) are little to moderately toxic to humans and of moderate aquatic toxicity. One has to bear in mind that a toxic hazard, e.g. as described in the toxicological profiles not necessarily implies a health risk. The toxic metal or formed compounds, e.g. oxide, must be present in (bio)available forms and in sufficiently high concentrations to result in toxic doses in humans or other organisms.

Lead is very toxic to humans and may cause serious chronic effects. The other metals (tin, silver and copper) have significantly weaker toxicological effects on humans than lead. From a human toxicological point of view it may seem justified to avoid lead in solders, if there is a risk of exposure. The use of modern technology, where the solder process takes place in full containment will reduce or eliminate the exposure of workers to solder vapors and fumes to nothing, regardless of the solders used (lead-containing or lead-free). There will though always be a risk of occupational exposure in connection with maintenance, reparation, etc., which still makes it justifiable from a human toxicological point of view to avoid lead in solders.

From an ecotoxicological point of view substitution to lead-free solders is more uncertain as emission and environmental fate are uncertain; exposure is therefore uncertain. In a life cycle perspective, the main environmental load will not be during the production/solder process, provided the production is optimized (e.g. with minimal losses during manufacturing), but after end of use.