Lead vs. Lead-Free Solder: Health and Environmental Impacts

Although lead-based alloys were the go-to solder for decades, presently, manufacturers widely use lead-free solder because lead is more destructive to human health and the environment than its substitutes.

What is Solder?

Soldering is a method for joining two metal components using an alloy with a lower melting point, called solder. The technique is vastly used in electronics on printed circuit boards (PCBs), as the metal connection allows for current flow.

In the recent past, companies used alloys containing lead solder because of their desirable properties, such as:

low melting temperatures;
good ductility; and
high wettability (the ability of the solder to spread on a solid surface).

However, as concrete evidence emerged surrounding health and environmental concerns, manufacturers sought alternatives to lead-based alloys.

The Problem with Lead Solder

Despite alloys between lead and other metals, especially tin, having favourable properties for soldering, a change to lead-free compositions was necessary.

Firstly, lead is highly toxic; Its presence in the body causes brain damage and impairs the nervous system. Long-term exposure leads to:

reduced fertility;
kidney damage;
high blood pressure;
cancer;
anemia;
seizures; and
death.

Young children are more susceptible, as they have softer tissues than adults, allowing them to absorb more toxins. Therefore, lead may impact their development.

Moreover, the heavy metal accumulates in the bones and can enter the bloodstream after years of exposure.

Finally, a 2019 study found a significant correlation between lead exposure in soldering workers and poor sleep quality and digestive disorders.

Source: Mahmoud Mohammadyan, Mahmood Moosazadeh, Abasalt Borji, Narges Khanjani, and Somayeh Rahimi Moghadam, “Exposure to lead and its effect on sleep quality and digestive problems in soldering workers”, Environ Monit Assess 191, 184 (2019).

Lead’s Environmental Impacts

Lead is detrimental to not only humans but countless organisms. Discarded electronics contaminate ecosystems. Then, wildlife consumes the heavy metal, hurting them and impairing their reproductive ability. Furthermore, lead is bioaccumulative. Thus, its negative impacts exponentially increase up the food chain.

Finding Alternatives to Lead-Based Solders

Due to the damaging effects of lead on human health and the environment, governments began to ban its use in the 20^th century.

In 2006, the European Union released the RoHS directive, restricting the use of lead in electronics, among other hazardous substances. Globally, several regulations were released, like

There are many factors to consider when selecting an appropriate alloy for soldering. Ideally, the melting point would be equal to or lower than the previously used tin-lead alloy (183°C) since engineers designed most PCB components to withstand that temperature. However, the melting point must be higher than the operating temperature, or it will melt during use.

Lead-free Solder Compositions

Common alloys used for soldering today are tin-copper, zinc-tin, and tin-copper-silver, though many more exist. These alternatives to the tin-lead composition have slightly higher melting points (e.g. 217°C for Sn-Ag-Cu), but they are still suitable.

Notably, there is no perfect solder as an alloy’s ideal properties depend on the application.

Environmental Impact of Lead-free Solder

Scientists can measure a substance’s impact on the environment by the Toxic Potential Indicator (TPI). The higher the TPI value, the more detrimental a toxin is. Lead has a TPI of 20.77. In comparison, copper and zinc have TPI values of 1.63 and 0.63, respectively. Tin, the most common substitute for lead, has a TPI of 1.2.

Though, these elements still cause damage, especially to aquatic ecosystems. Interestingly, silver has a TPI of 37.82, higher than lead. However, it also has much higher recyclability. Thus, if facilities recover electronic components, the silver can be reused, keeping it from being released into the environment.

Overall, lead substitution reduces toxic impacts from WEEE (Waste of Electrical and Electronic Equipment), also called e-waste.

Therefore, lead-free alloys are less harmful to the environment than lead-based ones.

Health Impacts of Lead-Free Solder

While other elements in the average solder also have detrimental effects on human health, they are not nearly as toxic as lead. Copper, zinc, tin, and silver may cause irritation, nausea, and liver damage, but exposure must be very high for it to be dangerous, while lead is harmful even in small amounts.

Overall, lead is more damaging to the body than its alternatives.

Summary of Lead vs. Lead-free Solder

Though the properties of lead make it advantageous to use in solder, it is detrimental to humans and the environment. Therefore, the metal became heavily regulated, and engineers explored alternatives. Though it may be more expensive, lead-free solder is a safer option.

Enviropass is here to assess your consumable materials in product assemblies:

solder, paste, paint, and more, against restricted chemicals.

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