Lead Free Solder: Introduction, Types, Advantages and Disadvantages
Today, more than two decades after its invention, lead free solder has gained popularity so much so that 70% of the consumer electronics manufactured today use lead free solders in their components like circuit boards, etc.
Lead free solder is an alternative to the traditional lead solders that were prevalent ever since the inception of the soldering process. Many factors give the lead free solders an edge over their alternatives. However, the most significant factor is its lack of the toxic component- Lead.
Since the choice of solder influences the entire soldering process and affects the outcome of the process as well. Therefore, it is imperative for commercial and hobbyists solders alike to choose the right solders for their applications.
This article will give a brief but concise introduction of the star of the electronics industry: the lead free solder. But first, what is a Solder?
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What is a Solder?
In simpler terms, solder is the glue that holds two metallic parts together. Now, glue is just an analogy, and to put things into perspective, let us give a more technical definition of a solder.
Solder is a metal alloy that solderers (or people who perform soldering) use to join parts of metal together. It comes in the form of thin wires wrapped into a spool. The thickness of the wire required is determined by the finesse of the application.
Now, a question may arise that why can’t they use average metal glue-like Epoxy? Epoxy is a non-metallic, non-conductive insulating material. It is ideal for joining two pieces of metal together but don’t expect it to let the current flow between the two metals.
On the other hand, most electronic components require a mechanical bond between two different metals that can let current flow from one metal component to the adjoining metal part.
Solders provide an electrically conductive mechanical bond. It keeps the two metal pieces intact while ensuring current flows through it.
How does a solder work? A solderer melts the solder wire with a soldering iron. The metal melts and flows over the parent metal, cools, and hardens to create a strong metallic bond.
Normally, metals have a very high melting point. But solders are specially curated to melt at lower temperatures so that they can easily melt using a soldering iron. A typical Tin-Lead solder melts between 170-190 °C.
Traditional solders, which were (and still are to some extent) prevalent are a mixture of tin (Sn) and Lead (Pb). A typical Sn-Pb solder carries 60% tin and 40% lead and this mixture is called a Eutectic Mixture.
Lead Free Solder
Now that you know what a solder is, you might guess what a lead free solder is by its name. That’s right. Lead free solder is a soldering material that does not contain lead.
Does it only contain Tin then? Yes and no. Lead free solders contain more than 95% of tin and, depending upon the type of solder, other metals like Bismuth, Indium, Cadmium, Copper, and Silver make up the rest of the composition.
The Lead free solders have a higher melting point due to the addition of metals such as copper. Therefore, they are often touted to be more difficult to melt and handle. However, their health and environmental safety factors give them a leg up over their counterparts.
What Lead to the Development of Lead Free Solders?
After the studies relating lead with serious health issues and researches highlighting the adverse effects that it has on the environment, efforts to eliminate lead from consumer electronics picked up the pace.
These efforts turned fruitful in 1996 when Professor and Metallurgist Iver Anderson invented and patented lead free solders. Later on, courtesy of stringent government regulations, Lead free solders started gaining popularity.
Furthermore, what lead to the popularity of lead free solders that it enjoys today were the restriction put by the European Union Waste Electrical and Electronic Equipment (WEEE) directory and Restriction of Hazardous Substances directory in 2003.
These authoritative regulations and restrictions fuelled the race of innovations in lead free solders. Currently, there are many different variations in the composition of lead free solders available today.
Types of Lead Free Solders:
For the sake of this article, we will restrict our discussion to two of the most common types of lead free solders. These are:
Tin-Copper Solders
Tin-copper solders are the most common type of lead free solders available today. These soldering materials have a typical composition of 99.3% tin and 0.7%, copper. Because of an excessive amount of tin, these solder joints are more likely to develop Tin Whiskers, but more on that later.
Sn-Cu solders are most often used in plumbing applications because lead leaching into drinking water has severe health effects. These solders may also be used while soldering stainless steel.
Tin-Silver-Copper Solder
The tin-silver-copper solder contains 3-5% silver, 0.5-0.7% copper, and around 95% tin. The Sn-Ag-Cu solder has adequate thermal fatigue. The most common Sn-Ag-Cu composition is 3% Silver and 0.5% Copper and is called the SAC305.
However, the amount of silver in the solder is proportional to its price. Cheaper Sn-Ag-Cu alternatives include SAC307 that has 0.3% Silver and 0.7% Copper.
Other Alternatives
Aside from the common Sn-Cu and Sn-Ag-Cu solders, many other lead free alloys come as soldering wires. These include Tin-Bismuth (Sn-Bi), Tin-Indium (Sn-In), Tin-Antimony (Sn-Sb), and Tin-Zinc (Sn-Zn).
Advantages of Lead Free Solders
We have been going on about lead free solder trumping leaded solders. Now, we will highlight some of the key advantages that have helped them outshine their counterparts.
RoHS Compliance
The government regulations authorities do not have tight restrictions for hobbyist solderers regarding the use of leaded solders. However, commercial manufacturers, especially those who want to trade in Europe are required to produce lead-free component.
Lead-free solder is RoHS compliance. Therefore, top-notch manufacturers and suppliers use lead free solders to be able to trade openly and freely throughout Europe and the rest of the world.
Human Health and Environment Protection
Lead is a toxic element. When exposed to the atmosphere, it runs a high risk of polluting the air, that humans, animals, and plants breathe. When mixed in water bodies, lead harms marine life. And being a neurotoxin, if ingested, lead can lead to adverse effects on human health.
Many manufacturing companies believe in green manufacturing. That means they prioritize the production and retail of material that do not harm the environment. Moreover, B2B companies also advertise their environment-friendly manufacturing principles to attract other businesses that put environment safety before everything else.
Lead free solders allow all such electronics companies to stay true to their motto of environment-friendliness. Moreover, soldering with lead free solders keep the employees safe from lead toxication.
Soldering with leaded solders can be dangerous even for hobbyists because the scale of a soldering project does not minimize the adverse effects that it has on human and environmental health. Therefore, more and more at-home solderers are now shifting towards using lead-free solders.
Better Soldering
In some cases, like soldering a printed circuit board (PCB), a lead-free solder may prove to be more promising than the leaded ones. Because soldering with lead free solders may minimize the common faults associated with conventional solders, such as voids.
Reliability
Lead free solders create harder joints. Therefore, the bonds form with these solders are more reliable, less susceptible to fatigue, and more capable of bearing external stress.
High-Temperature Soldering
Lead free solders melt at around 220 °C. So, these solders are often chosen for high-temperature soldering because they are capable of performing well at elevated temperatures.
Disadvantages of Lead Free Solders
Since lead free solders are still pretty young, therefore, they fall behind the older and traditional leaded solders in some fields. Some of the demerits of lead free solders include:
Difficulty in Handling
Lead free solder is more difficult to work with as compared to leaded solders. Therefore, many new solderers and those under no restriction by the government often prefer using leaded solders because of their ease of use.
Higher Melting Temperature
While lead free solder’s higher melting temperature is an advantage for high temperature soldering, it becomes its shortcoming when soldering heat sensitive material. The high temperature required to melt and sold lead free solder runs a risk of damaging the sensitive circuitry and other small components.
Tin Whiskering
As we mentioned above, tin is susceptible to whiskering. Whiskering of tin is a phenomenon where small, needle-like crystals grow on the tin joints.
Since lead free solders contain a greater composition of tin, therefore they are more susceptible to this electroconductive crystalline growth, otherwise known as whiskers.
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Conclusion
After being invented in 1996, lead free solder has gradually secured its position at the top. Lead free solder by eliminating lead from its composition makes it safe for human and environmental exposure.
Moreover, these solders comply with most government regulatory authorities that restrict lead usage in consumer goods. Therefore, it is a go-to choice for commercial manufacturers.
However, because it is still fairly new, it lacks some of the qualities that the traditional solders feature. But research is going on and we can expect astounding innovations in lead free solders that will help eliminate lead from the world of soldering.
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