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Lead-free solder vs. Lead solder: A Comprehensive Guide You Should Know

Almost all electronics use solder as a glue that attaches components/parts to a circuit board. Whether lead-free solder vs. lead solder, the functions are nearly the same. But different products and applications may require other solders.
The choice of the solder may have an impact on the soldering process. If the alternative is wrong, then the soldering process will be challenging. All that’s needed is to get more theoretical knowledge on the choice and type of solder. With such, you’ll be in a position to carry out an easy soldering process.
Depending on what you want, you can choose between lead solder and lead-free options. There advantages and disadvantages that come with both methods. Therefore, if you want to ensure the quality of solder joints, you may have to find the best option for you.

(Automatic manufacturing of soldering iron tips for soldering and assembling printed circuit boards)

1. What is the Solder? 

So, what’s a solder? Why use lead-free solder as opposed to leaded solder? And are there any demerits associated with both of the two? This article highlights a lot to do with lead-free vs. lead solder. In the end, you’ll understand a lot about what you need to know about leaded-free and lead solder. 

But first, what is solder? Solder is a metal alloy consisting of lead and tin melted by use of a hot iron. The heating of the iron is under high temperatures of 600 Fahrenheit. The moment the iron cools, it creates a robust electrical bond. 

Traditional solder used for soldering across the electronics industry is a mixture of lead and tin. Of importance to note is that different types of solder find use in various purposes. Even across plumbing, there’s heavy usage of solder. 

In electronics, the type of solder that assemblers use is 40% lead and 60% tin. It goes by the name “Eutectic Mixture.” While this is a chemical term, mostly, this type of mixture does melt at temperatures well below that which you might expect. 

(The soldering process of and electronic circuit board with electronic components)

2. Lead-free Solder VS. Leaded Solder

So, now that you understand what solder is, what’s lead-free and leaded solder. What are the uses of lead solder? Here is a clear explanation between the two, and the primary benefits of leaded solder, especially in the electronics industry. 

With the drive towards reducing the amount of lead used in electronics, lead-free solder is now in use almost everywhere. Based on health and environmental reasons, some directives are banning the commercial use of information. It means that traditional solders containing lead won’t be available for any soldering exercise (especially for a hobbyist). 

Lately, traditional tin-lead solder is rapidly getting a replacement, especially by other lead-free solder types. There are several varieties currently appearing in the market. One contains 0.7% copper and 99.3% tin. 

However, such should not present problems to hobbyists or home constructors. These new lead-free solders perform in precisely the same way as traditional solders. 

Then there’s leaded solder.

Lead-based solder is the starting point of the electronics revolution. The lead-based mixture contains a mixture of (60% tin and 40% lead). Its blend with some melting point of around 170 – 190° C. Known casually as soft solder, the container is an obvious choice due to its lower melting point. The box is another material that prevents the growth of tin whiskers. 

There are plenty of reasons as to why we use lead solder. A majority of hobby solderers use lead-free solder in almost all their projects. Non-commercial projects or public purposes may be the use of lead solder. These projects don’t require strict regulations of RoHS. 

Lead solder is ideal for projects based on its high melting point. Here, there’s no requirement of the high heat as such. The cooling time is faster based on high melting points, meaning decreased chances of cold solder joints. 

With lead solder, hobbyists don’t have to spend too much solder. Unlike those commercial makers cooling time is faster based. Decreased use is a big reason why many hobbyists don’t face any restrictions. Based on its reduced use, there’s also a decrease in waste realized from the lead solder. 

(Lead-free solder, soldering tools, and a green printed circuit board)

3. Why do We Use Lead-free Solder?

Lead-free solder is better in comparison to leaded solder. Those PCBA assemblers who’ve switched to lead-free solder are full of its benefits. 

New RoHS regulations

First, wne use lead-free solder as a means of complying with RoHS guidelines. RoHS (Restrictions of Hazardous Substances) does affect the whole electronics industry. Also, it involves the manufacture of electronic products as well. With origins from Europe, these directives restrict the use of hazardous chemicals in manufacturing electronic products. 

Based on RoHS regulations, electronic manufacturers that don’t meet all the directives won’t do business. Since July 1, 2006, all the applicable products need to pass RoHS guidelines. Besides lead, other hazardous chemicals include Benzyl butyl phthalate, Hexavalent Chromium, and Diisobutyl phthalate. 

Protection of the environment

Besides RoHS regulations, assemblers tend to resort to the use of lead-free solders to protect the environment. Lead that finds its way to the ground does make its way to soils, air, and water. The information has the possibility of staying in the background for a long. 

The lead that we find in fuels brings about air population, especially in urban centers. Soils near freeways and highways accumulate over time. When dust blows, lead particles can find their way to lakes and the surrounding rivers. Lead may end up negatively affecting marine life and those living around the lakes. 

Drinking water that’s under the contamination of lead with time may be dangerous. High exposure to lead may cause weakness, anemia, brain, and kidney damage. For pregnant women, information can be hazardous. It can damage the nervous system of the developing baby. 

Better soldering of PCB

Finally, yet importantly, manufacturers use lead-free solder as it results in better PCB soldering. Lead-free solders don’t spread during reflow. It, therefore, means that the results are better during PCB soldering. During lead-free soldering, there’s no rapid stencil wear and other significant issues. 

Circuit manufacturers that use leaded solder are more than likely to experience voids and through-hole fillet lifting. All these are cases that occur, especially when using leaded solder. But the results on a PCB are excellent when using lead-free solder. 

If you compare the PCB results from lead-free and leaded solder, you’ll notice a huge difference. The products that you see from lead-free PCBs are perfect. All the components stick properly to the board when using lead-free solder. 

(A roll of a leaded solder wire on an isolated white background)

4. What are the Disadvantages of Lead-free Solder compared with Lead Solder?

Lead solder is easy to handle

While lead-free solder performs excellently, there are areas where lead solder performs better compared to lead-free solder. First, lead solder is relatively easy to handle. Even if a toddler ingests or eats it, the body absorbs it as toxic. 

Unlike lead-free solder, pure lead is straightforward to handle and rub off from hands. That’s not the case as of lead-free solder. Still, leaded solder is free to learn. If you want to know about much to do with solder, you’d mostly get training using leaded solder. 

Need lower temperature

Besides easy handling, leaded solder needs a lower temperature to melt. Lead-free solders tend to melt at high temperatures of about 217°C/422°F. But that’s not the case with lead-based solders. These require temperatures of 183°C/361°F. The electronic components and PCB materials must be in a position to withstand very high temperatures. 

Fewer quality problems with the head

With lead solder, there are also fewer quality problems with the head. The lead-free soldering process demands the use of high wattage soldering irons. With such, you may end up damaging your head. Again, such may bring about quality issues on your board. But that’s not the case when you choose to use lead solder. 

Based on the high soldering temperature required during lead-free soldering, you may have to remove the head quickly. However, you get to avoid such a scenario when you resort to lead soldering. Many circuit makers are well aware of this factor. 

Lack of surface tension

Arguably, the biggest demerit that comes with lead-free solder is the lack of surface tension. Lead-free solder cannot resist external forces. If exposed to harsh environments, the components may come off quite easily. 

Length of shelf life

Extend the shelf-life of lead solder flux used by the manufacturer. However, that’s not the case with lead-free soldering. Due to exposure to oxygen in lead-free soldering, the change may not hold for long. Pure lead consists of lower aging mechanisms. Its shelf life is 2x longer when you compare it to lead soldering. 

(Lead-free soldering components on a printed circuit board)

5. The Performance Difference Between a Lead-free solder VS. Lead Solder

Melting Point Difference

Performance-wise, lead, and lead-free solder works slightly differently. The first difference is the difference in the melting point. Lead-free solder demands some of the highest iron temperatures. Because of the high melting points, you should be ready to wait for longer dwell times. 

As briefly mentioned before, the melting point of the traditional lead solder is around 183°C. On the other hand, that of lead-free solder is 217°C. Since the melting point of lead-free solder is high, it comes with a few consequences. For instance, the rising temperature later leads to the oxidization of the solder. The soldering temperatures may also affect electrolytic capacitors. 

Wettability 

The difference in wettability is another differentiating factor too. When it comes to PCBs, wetting is how properly the molten solder paste bonds with PCB components. Improperly wetted solder looks gray and dull. Wetting tends to be slower when you use lead-free solder and tends to be dull appearance-wise. But traditional lead solder joints tend to be shiny and clean. Insufficient wettability is dangerous on the joints of a PCB. It makes the joints perform poorly and high reject ratios of circuit boards. 

Different applicable temperature

Lastly, different applicable temperature is another performance difference between the two. Lead-free solder demands high soldering iron temperatures. The same isn’t true when it comes to lead solder. Even the remelting temperatures for lead-free solder needs to be slightly higher, unlike those of lead solder. 

(A close picture of lead-free solder and a soldering gun)

6. The Physical Difference Between Lead-free solder VS. Lead Solder

There are a few physical differences to note between lead solder and lead-free solder. Arguably, the most significant difference between the two is the raw materials. In the production of the two, manufacturers use flux. When there’s the addition of the lead solder paste, we call it lead change. But upon adding the lead-free solder paste, it goes by the name lead-free flux. 

The next physical differentiating aspect is the difference in use. Mostly, lead solder finds much use in hobbyists’ projects. These projects don’t fall under strict RoHS guidelines. But on the other hand, lead-free soldering applies to serious projects that must satisfy RoHS directives. 

Lead-free solder joints tend to be gray, dull, and rough in appearance. But if you examine leaded solder joints, most of them tend to be shiny and clean. They exhibit a polished look and a softer look. Also, in terms of density, lead solder tends to be slightly heavier than lead-free solder. Leaded solder is 8.5g/m2, while lead-free solder is 3.5g/m2. 

(Lead-free solders on an isolated white background)

7. Lead-free solder vs. Lead solder– Defects caused by lead-free solder

Lead-free soldering, especially by use of RoHS compliant directives, isn’t a new concept as such. Hundreds of thousands of circuit board assemblers use it during board assembly. However, a few notable defects come with lead-free soldering. These defects often involving thick, multilayer PCB.

Tin Whiskers

At this point, we’ll attempt to examine the significant defects that lead-free solder causes. The first defect that lead-free solder causes are Tin Whiskers. Tin whiskers are thin and conductive needle-lie or filament structures protruding from the surface of a PCB. These surfaces consist of tin as the final surface finish. 

Unfortunately, tin whiskers constitute a significant defect caused by lead solder. Tin whiskers bring about instances of short circuits on a circuit board. If you want to avoid such, then you need some experience with a soldering iron. You need a good experience when working with lead-free solder. You’ll need experience, practice, and knowledge when soldering. 

Growth of metal dendrites

Besides the growth of tin whiskers, another problem caused by the lead solder is the growth of metal dendrites. The development of metal dendrites is another problem known for affecting the functionality of aboard. A dendrite is a dendritic-shaped metal oxide deposit or a piece of metal that you’ll find at the surface of PCB insulation. 

Metal dendrites feature several different growing procedures that come from tin whisker. The metal dendrites come out due to ionic electromigration and are also dangerous to a circuit board. According to PCB assemblers, they also bring about instances of short circuits. These short circuits may then affect a board’s functionality. 

Generate CAF

Thirdly, lead-free solder tends to generate CAF (Conductive Anode Filament). Conductive Anode Filament also occurs due to instances of an electrochemical reaction. Like the previous two, Conductive Anodic Filament is another big problem that results in PCBs’ failure. 

Even though lead-free soldering tends to be ideal compared to leaded soldering, it comes with its disadvantages. As you can see, Conductive Anode Filament is one such problem. If manufacturers don’t repair this problem early enough, it may end up being costly on their end. 

Tin defect

Last, we have the tin pest or tin defect as another problem that lead-free solder may cause. Many electronic manufacturers seem to struggle in this area a lot. The occurrence of tin pests/defects is not something desirable as such. 

Tin pests do come about during spontaneous polymorphism phase change. Suppose the temperature happens to be lower than 13 degrees Celsius. There will be some notable changes. It will change from white tin with a density of 7.30g/cm3 to grey with a thickness of 5.77g/cm3

Theoretically, tin pests or defects are threatening. Many circuit makers do their best to ensure that they avoid instances of tin pests. While it may lead to reliability risk, they seldom occur since most of the time; there’s a mixture of impurities in the tin.

All the above are possible defects that may amount when using lead-solder. Of importance to note is that those are not all. Others include instances of copper contamination, copper erosion. The fillet lifting. Some make a report of shrinkage void and lower fluidity, with others reporting tighter operating parameters. 

As you can see, the defects that lead-free solder can cause are quite many. However, eliminating or minimizing such weaknesses isn’t a challenging process as such. As long as manufacturers stick to modern soldering technologies, they can avoid such. 

(Defects of lead-free soldering)

8. Lead-free solder vs. Lead solder– How should we choose the best lead soldering solution?

So, how do you go about choosing the type of solder to use? Should you go for laded or lead-free solder? For the longest time possible, solder based while using lead seemed a universal exercise. Nobody attempted questioning it. However, things began changing since the information comes with damaging effects on individuals’ health. 

Lead can cause liver failure and kidney damage. It’s even worse for pregnant mothers who may ingest it. Since many saw the damaging effects of charge. A movement began towards the adoption of lead-free solder. Lead-free solder doesn’t contain lead. Large commercial electronics makers emphasize the use of information. 

Today, if you happen to be keen enough, you’ll notice that lead-free solder applicable in almost all electronic devices even though some argue that it’s slightly harder to work with (such as its high melting points). Nevertheless, we will overcome the difficulties bit by bit. 

But all that we can say right now is that the choice of lead depends on your project. Are you a hobbyist who wants to learn something about soldering? Perhaps you are not a commercial circuit manufacturer. If that’s the case, then you’ll find leaded solder ideal. It’s cheap, and you won’t be going against RoHS directives since they aren’t commercial. 

But are you are a high-quality manufacturer who wants to sell your products? If so, then you may want to resort to lead-free solder. Lead-free solder is environmentally friendly and non-hazardous to human health. They also bring out some of the best circuit board soldering results. If quality is paramount for you, then go for lead-free solder. 

(Repairing a circuit board using a lead-free solder)

Summary

So there you have it; a comprehensive guide you should know between lead-free solder and lead solder. Depending on your project, you may have to choose between lead solder and lead-free solder. Make sure to stay away from leaded solder as you may run into trouble with authorities. Soldering with lead-free solder brings out the best possible results. 

Do you have any further questions that need urgent solutions? When you find suitable, give us a call for your entire lead or lead-free soldering needs. We are more than happy to be of assistance to you. With us, rest assured of high-quality information or lead-free PCB solutions. We have a team of supportive and highly responsive attendants. At all times, they are ready to assist you with all your queries and concerns. 

Hommer Zhao
Hi, I am Hommer, the founder of WellPCB. So far, we have more than 4,000 customers worldwide. If you have any questions, you can feel free to contact me. I really appreciate any help you can provide.

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