Lead Soldering vs. Lead-Free Soldering for PCBs

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Jul 6, 2021|Technological Advancements and Materials

Solder is used to connect components of printed circuit boards and allow them to pass a current freely to allow them to function correctly. There are two types of solder used in today’s PCBs, which are lead and lead-free.

Each type has benefits and issues, so we’ll discuss the difference and dive into more detail about each and what makes it either ideal or inappropriate for use in specific applications.

What Is Solder?

Solder is a metal alloy used as a type of “glue” used to fuse together with electrical components on PCBs. The solder is traditionally a mixture of 60% tin and 40% lead heated and applied with a soldering iron to sections of a PCB.

The scientific terminology for solder is a Eutectic Mixture. However, there are also lead-free solder mixtures that combine elements such as tin and copper. The copper mixture percentage is a fraction of the lead/tin version at 99.3% tin.

Each type of solder has its uses and can either make soldering PCBs harder or easier depending on the circumstances. To perform a solder on a PCB, the technician needs to have the solder and a soldering iron.

Therefore, the individual performing the soldering job needs to be skilled and pay close attention to detail to get it right.

Benefits of Using a Lead-Free Solder

Using lead-free solder has a few main advantages. Primarily, both the technician’s health and safety use the solder, and consumers use electronics that require soldering.

Lead-solder can cause a variety of health issues for people of all ages. Lead poisoning can create a life-threatening situation that may prove lethal in some cases. Lead was frequently used in the past because it makes substances more durable or easier to work within a  PCB manufacturing setting.

Disadvantages of Using a Lead-Free Solder

The leaded solder has a few benefits, although more and more commercial companies have turned to use lead-free due to restrictions and regulations. Lead is a toxic substance known to cause serious health problems to adults, children, and pregnant women.

The health risks outweigh the benefits for items being mass-produced. However, hobbyists and individuals creating items in small batches prefer using leaded solder because it has a lower melting point, is softer, and doesn’t need as much material to get the job done.

What Are Lead and Lead-Free Solders Made Of?

Lead-free solder is a mixture of copper and tin; however, the copper is in minuscule amounts compared to the lead/tin mixture of leaded solder. It’s approximately 99.3% tin and .7% copper.

However, copper is just one example of another material mixed with tin. Some other common materials used for lead-free solder can include the following.

• Silver
• Copper
• Antimony
• Bismuth
• Cobalt
• Nickel

There’s a wide range of options on the market, and some materials work better for specific needs than others.
What is the Advantage of Lead-Free Solder?
The real advantage of lead-free solder is primarily from a safety standpoint. Lead-free is much harder to work with; however, it doesn’t cause life-threatening conditions like lead solder.

Most governments prohibit using lead solder due to its effects on humans and the environment.

Comparing the Properties of Lead vs. Lead-Free Solder

When comparing the properties of lead vs. lead-free solder, there are a few very noticeable differences. Primarily the way lead-free solder melts is less even and fluid than its counterpart. Some other major differences include the following.

• Lead-free oxidizes easier
• The high melting temperature of the lead-free solder can have an undesirable effect on the other components soldered and the surrounding materials.
• Lead-free solder is more likely to fail because it creates component stress.
• The lead-based mixture has a lower melting point than either substance alone.

On the surface, solder may seem very similar, but there are vast differences between lead-based and lead-free.

The Effect on Different Types of Soldering

Although soldering is easier and less problematic with lead-based, it poses a significant risk to humans that can’t be ignored.

This is why PCB manufacturers use lead-free and pay careful attention to design layout and protocol to reduce the impact on the components and prevent damage during reflow, which subjects the area to high heat for a longer time.

Performance Difference Between a Lead Solder vs. a Lead-Free Solder

When it comes to performance in  PCB soldering, there are several differences between lead and lead-free solder. One notable point mentioned previously is the melting point. Another is wettability.

This is a reference to the way the solder bonds with the components when it’s melted. Wettability is crucial to ensure the components operate properly. If wettability isn’t possible, it causes the PCB to malfunction for manufacturing use.

Lead-based solder performs much better than lead-free. It’s smoother, applies easier, and cools solid and without the defects that plague lead-free. However, lead-free can have a great outcome if the technician is highly trained and skilled.

Physical Differences Between Lead Soldering and Lead-Free Soldering

The main physical difference between lead-based and lead-free solder is the flux. The flux is essential to add lead solder paste, and it creates lead change. Therefore, if lead-free solder paste is the mixture, it goes by a different name-lead-free flux.

In terms of appearance, the leaded solder is shiny and clean-looking. Those using lead-free are dull and have a rough surface. The appearance of the soldered area is a giveaway.

And finally, when it comes to weight, lead solder is much heavier than lead-free. The difference is approximately 8.5G/m2 for leaded solder and 3.5G/m2 for lead-free.

Considerations When Switching to Lead-Free Solder

Some considerations to know about when switching to lead-free solder include the following. The most prevalent concern is tin whiskers or filament structures that stick out from the PCB surfaces.

These tin whiskers are a significant defect that can create short circuits. To make a PCB without tin whiskers, you need extensive training and practice.

There is also another issue with lead-free solder, and that’s the growth of metal dendrites. These dendritic-shaped deposits are composed of metal oxide and create a hazard for the circuit board. They are a direct result of tin whiskers and can also create a short circuit.

There is also the revision of conductive anode filaments. These CAFs result due to an electrochemical reaction. This can cause circuit failures as well.

How to Decide What the Best Solution Is?

Ultimately the decision to use lead vs. lead-free solder should be based first on whether or not you plan to use the product for personal or commercial use.

If you plan to use the product commercially, you’re bound to regulations that prevent you from legally using lead solder.

Should I use Lead or Lead-Free Solder?

If you plan to use lead-based solder, know that it can negatively impact the liver, lungs, and heart. This is also true of anyone who may contact the lead solder, such as pregnant women and children.

If you’re confident that no one will come in contact with the solder and you use appropriate safety precautions to create your project, you might consider a lead solder.

It’s much cheaper and easier to work with overall. In addition, you can find it quickly, and it produces less waste in the long term.