Lead vs lead free soldering in electronics production

14.09.2022Przemysław Prolejko

Lead solder is, or rather was, the most widely used material in the production of PCBA due to its low cost, low melting point and ease of use.

However, concerns about lead neurotoxicity and the health and environmental effects of lead solders vs lead free solders contributed to the change in July 2006 of the EU regulations on the use of hazardous substances in electrical and electronic equipment (RoHS). Therefore, over the past two decades, soldering techniques with alternative tin-based solder materials have developed rapidly and contractual Electronics Manufacturing Services providers are shifting to lead free soldering.

Lead soldering

Lead solder (also known as SNPB solder) is a metal alloy whose basic components are lead (Pb) and tin (Sn). However, there is a growing awareness of the occupational risks associated with lead soldering, and lead solder is increasingly beginning to be considered a health hazard in the workplace. Especially since the dusts and vapours generated during lead soldering are considered neurotoxic when inhaled.

Therefore, lead solder is systematically removed from production procedures due to its negative effects on the environment and health. And this is despite its many undoubted advantages.

Advantages of lead solders

Lead solder:

  • It has a lower melting point (183°C) than lead free solder (217°C), causes fewer joint quality problems and poses a lower risk of adverse thermal effects on soldered components.
  • Cooling lead solder has a brighter colour than lead free solder, which makes it easier to detect potential problems such as oxidation.
  • It is cheaper and easier to use than lead free solder as the price of lead solder is 1/10 of tin-based alternative solders. This also makes it more accessible.

Disadvantages of lead solders

However, companies focused on protecting the health of workers and the environment are aware that the main reason for using lead free solder is the neurotoxic properties of lead.

  • Lead can accumulate in the human body even with slight but long-term exposure.
  • Lead can penetrate the body quickly through the skin, mouth or nose, and in industries with high lead emissions from production processes workers are constantly exposed to lead hazards because they can inhale lead vapours or lead can penetrate the body by simply touching contaminated surfaces.

This is why the use of lead-based paints has been abandoned, unleaded petrol has been introduced and EMS service providers are shifting to lead free soldering. Especially as the European Union (EU) adopted the RoHS directive (Restriction of Hazardous Substances) in 2006, and the United States followed suit by granting tax credits to companies that reduced the use of leaded solders.

Lead free soldering

Non lead solders are an alternative to conventional 60/40 and 63/37 SnPb lead solders. The lead free solders used today have different compositions and can contain copper, tin, silver, nickel, zinc, bismuth and antimony. This creates a high quality solder alloy, especially since the addition of trace metals ensures very good mechanical properties.

However, the most popular lead free soldering compound is tin-copper, which has a melting point of 217°C and consists of 99.3% tin with 0.7% copper.

Advantages of lead free solders

  • Non lead solders are, above all, better for the environment and human health and, therefore, more environmentally friendly.

This is why an increasing number of EMS manufacturers and service providers are switching to lead free soldering.

Disadvantages of lead free solders

Having said that the use of lead solders had its quite rational justification because lead free solders:

  • Are more difficult to use than lead solders
  • Have worse surface wettability than lead solder
  • Cannot guarantee as high joint reliability as lead solder because lead is softer and simply easier to solder.    
  • Form surface oxides, flux contamination and alloy deposits that can cause poor contact resistance. Therefore, switching from lead solder to lead free solder does not provide the same electrical and mechanical properties of the solder.
  • Some manufacturers using lead free solders are replacing tin with silver, which makes them even more expensive.
  • In addition, the wire flux core and lead free fluxes often contain harsh reducing agents that are highly irritating to the mucous membranes, leading to irritation of the sinuses, throat and eyes of workers.

Lead solder has many advantages in the production of electronics. However, the change is inevitable and all sectors that use solder in large quantities are likely to switch to lead free soldering soon. If they have not already done so.

Moreover, the governments of various countries enforce the use of environmentally friendly materials, which paradoxically leads to a shortage of lead solders used by hobbyists.

It should also be remembered that the lower resistance of lead free alloys to mechanical stress reduces the life time of devices using the PCBA soldered in this way. And, while it does not matter much in consumer electronics, where devices are quickly replaced with new ones due to the constant technological progress, the use of lead free solders becomes problematic in specialized devices such as medical equipment or systems used in railways. Especially because the durability of solders is strongly dependent on the temperature fluctuations to which lead solders are resistant.

Therefore, for contractual EMS service providers during the production process it is necessary to constantly choose between lead vs lead free soldering, which is a difficult task that only a good EMS provider can handle.



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