Soldering is essential for fabricating printed circuit boards (PCBs). Without solder, connections between components on the board would be unreliable or nonexistent. Depending on the type of PCBs produced, lead-based or lead-free solder is used to create reliable electrical connections.
Lead-based solder has been around for decades and is still a popular choice for many PCB applications. However, with the advancement of modern technology, lead-free solders are gradually gaining in popularity. They are fast becoming a viable option for many industries seeking to reduce their environmental impact and design a more reliable and safe PCB.
With the many advantages and disadvantages to each type of solder depending on its end goal, electronics engineers and PCB manufacturers need to understand the differences to help decide which solder is best for their PCBs.
Lead Solder Properties
We can attribute the benefits of using lead solder to the compound’s chemical composition. More specifically, the 60% tin to 40% lead ratio creates special advantages that make it suitable for applications such as electronics repair, HVAC, and LEDs.
Lead Solder Pros
Most importantly, lead solder is far easier to use than lead-free options. This characteristic means it is perfect for manual soldering applications, as the low melting point reduces any risk of overheating PCB components and damaging the board.
Lead solder also has more efficient wetting compared to its lead-free counterpart. Wetting is the ability of the solder to flow and cover the PCB components, creating a secure connection. Lead solder’s higher wetting enhances this process and ensures reliable electrical connections with minimal flux or other additives.
Finally, the solid joint formation often has those in the repair, plumbing, and general electronics industries reaching for lead solder when working on PCBs. The strong joint is mainly due to the alloy ratio of the lead solder, creating a bond that is more reliable and less susceptible to damage from rough handling.
Lead Solder Cons
Overall, the largest drawback to using lead solder lies in its composition — lead is a toxic substance to humans and the environment. Over the past few years, many countries have drastically curtailed its use in electronic products due to regulations concerning hazardous materials.
In addition to toxicity issues, lead solder also has heat dissipation issues. This can be a problem in high-power applications, as the higher temperatures may translate less efficiently from component to component due to lead solder’s lower heat dissipation rate. As such, lead solder may not provide ideal PCB results for those in metal, glass, or ceramic-making industries.
Flammability is also a concern with lead solder, as the compound can ignite at high temperatures. This hazard can damage nearby components and also produce dangerous fumes that may harm individuals working on wiring and soldering.
A company’s bottom line is also at risk when using lead solder as the compound is more expensive than lead-free solders and can result in higher waste output.
Lead-Free Solder Properties
The benefits and drawbacks of lead-free solder are directly related to its composition. Most PCB lead-free solder is made from a tin and copper or tin and silver alloy, but it is also available in alloy compositions that include antimony, bismuth, nickel, and zinc. No matter the composition, lead-free solder has proven a viable option for many PCB applications.
Lead-Free Solder Benefits
The most notable advantage of using lead-free solder is its non-toxicity and safety for use in any environment. The alloy contains no innately-hazardous materials, making it more eco-friendly and health-conscious than lead solder.
Various manufacturers often report lead-free solder makes the soldering process easier. This aspect is due to its higher melting point, which prevents component damage from overheating while reducing the risk of metal being pulled away from the joint due to heat stress.
Electronics manufacturers usually rejoice at the price of lead-free solder compared to lead solder — it is far cheaper than the latter and is ideal for PCB production runs that need to stay within budget.
Finally, lead-free solder is also far less likely to catch fire than its lead counterpart. This property makes it safer for all applications, especially those in the industrial and automotive fields.
Lead-Free Solder Disadvantages
The major disadvantage associated with lead-free solder is its reduced thermal conductivity. This attribute can often cause problems when repairing or reworking solder on PCBs and may require higher temperatures to ensure a secure bond between components.
Lead-free solder is also known to have lower surface tension. This lack of tension may result in poor wetting, making it difficult to form a reliable connection without additional flux or other additives.
Those working on extended or delayed timelines will find that the shorter shelf life of lead-free solder is a hindrance. The compound is known to oxidize quickly, which could lead to manufacturing errors that affect adhesion quality.
Lastly, whiskers, voids, and other mechanical issues may occur if you use lead-free solder. This outcome is due to the structure of the alloy, which is often prone to cracking and other structural flaws over time.
Choose Your Best Solder Option
The choice between lead-based or lead-free solder will ultimately come down to your project’s needs and local regulations.
Lead solder is an excellent option for those needing PCBs with more reliable connections and less effort involved in soldering. On the other hand, lead-free solder is the better choice for those with environmentally sensitive applications or projects requiring more durable, heat-resistant joints.
Remember that solder is the lifeblood of most PCBs, so it is essential to understand the properties and differences between lead-based and lead-free solder before making any decisions. Taking this action can guard your PCB components against catching fire, losing contact, or failing due to a bad solder connection.
No matter which type of solder you use, always follow the best PCB manufacturing practices and safety guidelines as advised by experienced professionals. Following this precaution will ensure you complete your project confidently and efficiently with the desired results. Read one of our other articles to learn more about how to choose PCB materials.