How to Solder - A Complete Beginner's Guide to PCB Soldering

Understanding how to PCB soldering your circuit board properly can be an exciting thing for PCB enthusiasts.  Whether you are a beginner or an experienced PCB hobbyist, there are some problems you are likely to encounter. Knowing to solve them is what this article tries to share with you. For the most experienced people, this should be a refresher and shed more information on market trends.

 

Other aspects like the soldering technology to employ is another factor we will discuss. Looking at the various available options, we will suggest superior technology that perfectly integrates with today's technology.  Let’s get started.

1、Introduction to PCB Soldering Technology

Learning how to solder while incorporating proper soldering techniques is an important skill, especially for PCB manufacturers. Soldering is a useful and practical technique ideal for affixing two or more surfaces together. This article concerns how to go about PCB soldering and how you can safely sell it regardless of the scenario. 

 

an engineer soldering a PCB.jpg

2、PCB Soldering Type

There are plenty of solder types in the market, and finding the best one can end up being a challenging experience. If you are in the market for the best kind of PCB soldering, make sure that you choose one that fits your needs. Of all the types of PCB soldering, reflow soldering is the common one. 

 

2.1 Introduction to reflow soldering 

Reflow soldering uses a solder paste to temporarily attach either one or hundreds of components/parts to their respective contact pads, followed by their assembly's subjection to controlled heat. 

 

2.1.1  Process of reflow soldering

The first stage of reflow soldering is applying the solder paste and the components on the bare PCB. After that, a pick-and-place machine accurately picks and places all the details on the board’s required parts. After that, the board goes through some preheat to bring the board to the required temperature. 

 

After preheating the board, a thermal soak follows. The purpose here is to ensure that areas that were not adequately heated come to the required temperature. After this, the reflow process follows. The purpose of the reflow process is to create the required or necessary solder joints and remove volatiles. Cooling is the last step. Proper cooling prevents thermal shock and excess intermetallic formation to parts of the board. 

 

2.1.2 Introduction to the recirculation zone 

Recirculation involves the process or act of something circulating again or making something to occur or spread also. During PCB soldering, it's essential to ensure the air filtration system’s recirculation to reduce reducing odors and chemical fumes in a soldering environment. Here, are four things to note about PCB soldering:

 

•  Warm-up – just as the name suggests, this stage involves warming up the soldering gun or iron. The soldering iron must come up to the right temperature to ensure effective performance. 

•  Soaking – soaking involves removing oxidized substitutes on the surface of a PCB to make perfect solder joints. These joints stand in between PCB pads and component pins. 

•  Backflow – backflow takes place solder begins flowing in the wrong direction during the soldering process. Severe backflow can lead to board failure.

•  Cooldown - when it comes to cooling down of a PCB after soldering, patience is essential. Waiting for twenty to thirty minutes will ensure that your board(s) components stick to their intended place. 

 

2.1.3 Adapt to temperature and curve 

When undertaking PCB soldering, you need to ensure that you do so under the recommended temperature. When soldering SMD components, 315C is sufficient to solder the joints properly without overheating the entire piece. 

 

2.2 Wave soldering 

Wave soldering is more of a large-scale soldering process, and This process involves the soldering of electronic components to a PCB to create an electronic assembly. It consists of molten solder waves as a means of attaching molten solder to a PCB. 

 

2.2.1  Introduction to wave soldering

As mentioned, wave soldering is more of a bulk soldering process that finds much use in PCBs’ manufacture. The process involves passing a PCB over a pan that contains molten solder whereby some pump produces upwelling solder resembling a standing wave. Ideal temperatures are ideal during wave soldering. Wave to such may lead to cracks and loss of conductivity on the board. Additionally, insufficient preheating and bad weather can make the board susceptible to some stress. 

 

2.2.2  Wave soldering process 

Wave soldering involves five essential steps. The first step consists in melting the solder, followed by cleaning the components. After that, the placement of the PCB components follows. After placing the PCB, the application of solder follows. Finally, there's the cleaning of the board. 

 

2.2.3 Adapt to temperature and curve 

During wave soldering, the typical temperature range should be 240-250°C. Of importance to note is that the tin-lead reflow temperature range tends to be a little bit critical, and minor temperature deviations of components and equipment do not create soldering problems as such. 

 

2.3 Manual welding 

Manual welding isn't an easy skill, as you may imagine. It demands top-notch skills and talent. When it comes to the manufacture of a PCB, sometimes the use of manual welding. Manual welding is a little bit cheaper compared to robotic or computerized welding. However, manual welding is highly susceptible to errors. 

 

the process of wave soldering a PCB.jpg

3、Indispensable Flux

3.1 The function of flux

In soldering of PCBs, flux does serve a threefold purpose. First, it rids off oxidized metal from PCBs surfaces. It also seals out any air to prevent further oxidation. Lastly, it facilitates amalgamation to improve the wetting characteristics of liquid solder. 

 

3.2 Types of flux

There are several types of flux, as briefly highlighted below: 

•  Rosin flux – this is a combination of solvent and rosin and ideally suited for easy-to-clean surfaces. 

•  Organic acid flux – this type of flux consists of four main components: activators, chemicals, disrupting, and dissolving metal oxides. The role of organic acid flux is to aid the entire soldering process. 

•  Inorganic acid flux – inorganic flux contains the same components playing the same role as organic fluxes. However, they find heavy usage in some brazing and high-temperature applications. 

 

the application of flux on a PCB.jpg

4、The Choice of Solder in PCB Soldering

Without a doubt, the type of solder that you choose to use on your PCB will impact its functionality. If you choose a substandard solder, it may fail to hold all the components together.

 

4.1 What is soldering

Soldering is a process of joining two or more components together using a melting solder. In a PCB, soldering is attaching components on a circuit board. Solder is an alloy of metal made of lead and tin that's melted using a hot iron. 

 

4.2 Types of solder

There are several types of solder, as briefly highlighted below:

 

  • Lead alloy solder – this type of solder jump-started the electronics revolution. Lead alloy solder is a mixture of 60% tin and 40% lead. It also goes by the name soft solder based on a high concentration of tin. 

  • Lead-free solder – this one began taking off immediately after the EU started to restrict the use of lead in consumer goods. These types of solders have a higher melting point compared to conventional ones.

  • Silver alloy solder – these came into the scene as alternatives to lead-containing solders. Ordinary silver alloy solders contain 3% to 5% of silver.

 

4.3 How to choose a suitable solder 

Choosing the best solder for an electronics project can be a daunting task. It can be confusing for beginners and seasoned veterans alike. But all is not lost. You need to ensure that the lead you choose is water-soluble and rosin-based for the best solder. You also need to factor in matters to do with costs, welding type, the welding material, and the welding temperature. While lead-free solders are environmentally friendly, they lack a good reputation based on technical matters to do with the soldering process. 

 

4.3.1 What type of solder do I need?

As mentioned earlier, there are several types of solder. Based on the project that you have, you may go for one best suited for it. But when it comes to electronics (especially PCBA), lead-free rosin core solder is the best. Rosin-based solder has a composition of tin and copper alloy. 

 

4.3.2 Lead or no lead?

For decades, leaded solder has been an electronics manufacturer's go-to product. The most significant driving factor for using leaded solder is that it heats faster at lower temperatures than lead-free solder. Therefore, it poses a less thermal threat to the fundamental component. 

 

4.3.3 What size solder do I need?

The size of the solder depends on the project at hand. However, for basic/everyday electronics work, you may need a solder wire of approximately 0.711mm to 1.63mm in diameter. For a majority of electronic books, the best solder ranges from 0.4 – 1.0mm in diameter. 

 

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5、Tools Needed for PCB Soldering

Before you undertake the process of soldering, you need some tools and equipment. Without the right tools, then you may end up jeopardizing the entire project. The following are essential tools necessary for PCB soldering:

 

•  Soldering iron – without a soldering iron, you can't do much of soldering. But again, the soldering doesn't need to be expensive. You can get the best ones for as little as 69.12 Chinese Yuan ($10), especially if you are a beginner. 

 

•  Soldering Stations – a soldering station is also essential during soldering. A soldering station is a multipurpose power soldering equipment designed to solder electronic components. It finds heavy usage in electronics and electrical engineering. 

 

•  Soldering iron tip – soldering iron tips are mainly made of copper and used to transfer heat to the board. Unless manufactured by a single company, soldering iron tips are not typically interchangeable. There are mainly two basic types of soldering iron tips. They include conical tip soldering irons and chisel tip soldering irons. 

 

•  Brass or traditional sponge – brass or a conventional sponge is another tool that you'll need when undertaking PCB soldering. Either brass or a conventional sponge is necessary when you want to clean the soldering iron tip. It also prevents instances of oxidation at the end.

 

•  Soldering iron stand – during the process of soldering, you'll notice that the soldering iron gets hot. When such happens, you'll have to place it in a very safe way in between the soldering. For this reason, a soldering iron stand is essential. Fortunately, such frames do not cost a lot and worth having one. 

 

•  Core – core is another essential thing that you'll require when it comes to printed circuit board soldering. It's highly advisable that when purchasing solder, ensure that you do not go for the acid core. The reason for this is because it can damage the components in your circuit. 

 

•  Solder Sucker – last but not least, you'll need a solder sucker during your PCB soldering process. For instance, if you apply much solder on the board, you may have to remove excess solder. Without a solder sucker to suck the excess solder, then the whole project may fail. A solder sucker is a hand-held mechanical device that sucks up excess hot solder by pressing a button.

 

a top view of PCB soldering tools.jpg

6、PCB Soldering Temperature

Do you have somåe trouble getting your solder to melt? If this is the case, then it means that you need to turn up the heat a little bit. But again, if you are burning your components, then you have to reduce the heat or temperature. The recommended PCB soldering temperature is between 350 degrees Celsius and 400 degrees Celsius. That is equal to åßto 660 to 750 Fahrenheit. 

 

6.1 The rigid PCB soldering temperature

Rigid printed circuit boards are those boards that cannot bend or flex. The recommended PCB soldering temperature is 150 degrees Celsius. The reason for such is to ensure that delamination doesn't occur in the event of thermal shocks or humid conditions. 

 

6.2 The flexible PCB soldering temperature 

Just as the name suggests, flexible PCBs are those boards that can easily flex or bend. However, unlike rigid PCBs, flexible PCBs require less soldering temperature. Here, the recommended soldering temperature is 105 degrees Celsius. 

 

a top view of several soldered rigid PCBs.jpg

7、PCB Soldering Steps

With some knowledge regarding what PCB soldering is, various types of PCB soldering, and the right tools for the job, now let's shift attention to PCB soldering steps. 

 

Step 1: Warm up the iron.

Before you can begin, your soldering iron needs to be hot. If not, it can't heat and melt the solder. Warm up the iron and let it rest for a while until it reaches the full heat. 

 

Ensure you heat the soldering iron.jpg

 

Step 2: Prepare a little space.

The key to effective soldering is to begin on a clean surface. Prepare a little working space and ensure that it's clean from dust and other debris. Make sure that your room has got only all the tools that you require. 

 

Ensure you have appropriate working space.jpg

 

Step 3: Thoroughly coat the solder tip on the solder

Now, you have to coat the tip with solder thoroughly. Make sure that you cover the entire information by using a lot of solder material. However, you need to be prepared to handle excess solder that drips. 

 

Coat your solder gun tip with the solder.jpg

 

Step 4: Clean the solder tips

After coating the solder tip, you need to clean it. You can clean the solder tips using a wet sponge. Cleaning the solder tip gets rid of excess flux residue. You need to clean the information immediately so that the flux doesn't solidify in the end. If it hardens, it becomes challenging to get rid of it later. 

 

Step 5: Soldering the PCB

Now, begin soldering the printed circuit board. Connect all the parts by fusing them with solder. Depending on your project, you may choose to use selective soldering, wave soldering, or solder reflow. 

 

you can then now solder your PCB.jpg

 

Step 6: Surface treatment

The surface treatment is the application of a substance on the surface of a material to make it better in some way. In PCBs, manufacturers apply a solder mask to make boards to be resistant to corrosion or wear. Surface treatment follows after you complete soldering the PCB. 

 

Step 7: Component placement

If you are dealing with a simple circuit, you'll likely be soldering one or just two components at once. However, if you work with a complicated board, you may have to start with small pieces first as you scale up to the larger ones. Start by selecting small pieces and placing them on where they belong on the board. Ensure that the leads bend at a 45-degree angle on the bottom of the board. 

 

 Be careful on how you place your components on the PCB board.jpg

 

Step 8: Heating

If you want to ensure that you heat the joint properly, you need to hold the iron so that the tip touches both the component lead and the board. The reason for this is because if the information gets in contact with one of these components, then it won't stick. Again, ensure that overheating doesn't take place. If you notice some bubbles in an area, get rid of heat immediately. Give it time to cool before proceeding with heating it over again. 

 

Step 9: Apply solder to the joint

After you complete heating particular joints, then you should be ready to begin soldering. Start the process by touching the tip of the solder pad and the lead. If you have heated this space as required, the solder should flow freely with the flux bubbling.

 

Make sure to add solder around this joint until it gets entirely coated. As the joints relaxed, make sure that you don't touch or move the board. If you move the board around, the finish will appear grainy and dull. 

 

Ensure that you apply correctly solder to all joints.jpg

 

Step 10: Check the joints and clean up.

The moment all the joints are cold, do a short inspection. If the solder is appealing, then trim the leads. You do this using cutters. Once you are through, clean up the extra flux from the board to leave you with a clean and appealing finished product. 

 

A complete soldered board ready for use.jpg

8、Skills of PCB Soldering Technology

When it comes to printed circuit board soldering technology, some skills and knowledge are of high importance here. The following are eight essential skills of PCB soldering technology:

 

8.1 Monitoring heat dissipation during assembly

The trend towards higher power densities means that there needs to be greater attention paid in heat transfer. Therefore, designers need to get rid of heat to ensure that a circuit's components stay below the required temperature limits. During PCB assembly, the ability to effectively monitor heat dissipation is an essential skill that designers must possess. 

 

8.2 Keep the soldering iron tip clean.

The tip of your soldering iron is a critical component that will impact the performance of the equipment. If the information isn't clean, then expect a poor understanding of the soldering iron. Expect scenarios such as low heat transfer and other soldering problems. 

 

8.3 The sequence of welding parts

Welding sequence involves affixing or just welding components of a device or structure in a particular order. When it comes to PCB soldering, the line of soldering all the parts to come up with a finished product is also an important skill. Designers must know what comes first and what comes last.

 

8.4 Removal of solder residue

Solder residue is a flux that's leftover on the PCB after the process of soldering is complete. You need to get rid of solder residue as it may bring about low voltage insulation short. Mastering the art of effectively removing flux/residue from a PCB is also an essential skill for designers. 

 

8.5 Soldering SMT resistors and capacitors

Soldering surface mount technology (SMT) resistors and capacitors isn't an easy process as such. Many designers find this process quite challenging for them. However, the ability to correctly solder SMT resistors and capacitors differentiate the best and average PCB designers. 

 

8.6 Check continuity and sensor output.

The moment a circuit device malfunctions, then testing for continuity and sensor output is a must. If the current doesn't flow properly, then it means that there's a problem. Again the ability to do such tests with ease is a vital PCB soldering technology skill. 

 

8.7 Removal of flux/rosin residues

When soldering, you may end up with excess flux or rosin residue. Unfortunately, many designers find it hard, removing flux and rosin residues. You may use pure alcohol to get rid of stubborn residue. Mastering the art of perfectly-getting rid of excess flux is essential. 

 

8.8 Prevent flexible PCB welding from bending

To prevent flex-PCB welding from turning, you need to place a thick stiffener very close to accelerometer solder joints. Again, this is a critical PCB soldering technology. 

 

an engineer working on a PCB.jpg

9、Common PCB Soldering Defects and Solutions

The following are seven of the most common soldering defects and their answers: 

 

9.1 Insufficient hole filling

Insufficient hole filling occurs when there's no enough solder to holes drilled initially into the board. The perfect solution for such is to ensure that the pads’ size and the diameter of the pins match.

 

9.2 Gaps in solder joints

Several reasons cause gaps or skips in solder joints. The use of the wrong wave height between the board and the soldering wave is a significant cause. Also, placing variable pad sizes during the design stage is another cause. To prevent such, designers must be aware of the thickness of their boards. The ideal pad to gap ration should be 0.5mm or below. 

 

9.3 Solder ball phenomenon

This scenario occurs during the soldering process. It takes place if the solder attaches to the PCB. If the preheating temperature isn't suitable or the PCB was wet during production and storage, solder balls may occur. Solutions to solder balls include proper storage of the PCB, baking the PCB, and applying it evenly. 

 

9.4 Discoloration of solder mask

This one happens when manufacturers use flux at high temperatures. Also, if cure cycles change, discoloration may occur. Furthermore, altered and mixed batches is also another reason for such. Perfect solutions for this include avoiding mixing batches and sticking with a single supplier. Also, cure cycles need to be standard. 

 

9.5 Poor penetration

On a printed circuit board, low penetration results from the application of inadequate flux. Also, it happens if there was some inadequate preheating. The solutions to low penetration are simple. The solder and the preheating must be adequate. 

 

9.6 Module uplift phenomenon

Also known as tombstoning, this is a phenomenon characterized by lifted components off from the pad. If solder on one place doesn't complete wetting or some unequal thickness, module uplift may occur. If you want to avoid such, the residence must be allowed to complete its wetting process. 

 

9.7 Branding

Lastly, there's branding. Again this is a PCB soldering defect mainly caused by the use of inferior materials or inexperienced personnel. You'll need to brand your PCBs to distinguish them from those of the competitor. To achieve perfect branding, ensure that you use the best materials and experienced staff. 

 

effects of solder balling.jpg

10、Common Problems in Soldering

1. Interfered joints 

Interfered joints is that joint subjected to some movements during solder solidification. If you look closely, you'll notice that the joint appears somewhat crystalline, frosted, or rough. 

 

2. Cold joint/overheat joint. 

These occur if the soldering iron tends to be lower than the optimal temperature. It may also happen if the duration of heating the joint was significantly short. Solder joints do have a messy, dull, and pockmarked look. 

 

3. Excessive solder

Too much solder on a board tends to create bubble-like solder balls at the solder joint. Appearing like an abnormal growth on a PCB, excess solder may, in the long run, affect the functionality of the entire board. Such is true when the solder begins to melt under high-temperate conditions. 

 

4. Insufficient wetting (on pads, pins and surface mount)

The lack of wetting of the solder joints is another problem during soldering. A badly wetted joint brings about poor connections to the board. Such ends up impairing the performance of the entire circuit. 

 

5. Solder hunger

During soldering, insufficient soldering may take place. Solder hunger is identifiable by a situation where designers use little solder. Solder hunger amounts to poor electrical contact between the parts of a circuit.

 

6. Untrimmed leads

Based on their length, these are leads that run a high risk of coming into contact with the rest of the charges. Such may end up creating some unwanted short circuits. Before soldering, all the tips require trimming to their required lengths. 

 

A close pic showing the effects of overheating on a PCB.jpg

11、Cold Solder Joint Problem

Here are more frozen joint issues you need to pay attention to:

 

1. What is a cold solder joint

A cold solder joint is a rigid, rough, and uneven joint, especially on a PCB. A cold solder joint is highly susceptible to failure and cracking. 

 

2. Causes of cold solder joints

The leading cause of cold solder joints is when the solder doesn't melt correctly or entirely. If such happens, then expect a cold solder joint on your board.

 

3. Repair of cold solder joints

The process of repairing cold solder joints isn't as complicated as such. All you have to do is re-heat the joint using a hot iron until the solder gets to flow. 

 

4. How to prevent cold solder joints

We need to avoid such errors in the future to prevent such a mistake from occurring in the future, and it's better to ensure that you properly preheat the soldering iron. Also, ensure that the soldering iron operates the appropriate power.  

 

PCB solder joint repair.jpg

12、Safety Issues of Soldering

Safety is paramount during PCB soldering. After all, you do not want to work with people injured or cause bodily harm. The following are essential safety soldering issues:

 

12.1. Pay attention to a high temperature – high temperature during soldering can harm the board and yourself. You need to ensure that you regulate the temperature to acceptable levels. 

 

12.2. Sufficient light – without enough light, you may be able to solder components on the board’s wrong part. Ensure that you have enough light while soldering. 

 

12.3. Fume from welding – of course, there will be an emission of fumes during welding. Fumes can be hazardous to your health. While welding, ensure that you wear a protective mask on your face.

 

12.4. Safety equipment and protection – while soldering, you need to ensure your equipment’s safety and security before and after use. Store the equipment in a safe place far away from children. Remove anything that you don't need and put it in a safe place. 

 

PCB soldering technician adhering to safety measures.jpg

13、Summary

Achieving the perfect PCB soldering appears to be a challenge to many. However, that's not a challenge to us at WellPCB. We've served and continue to help hundreds of thousands of clients in need of reliable PCB soldering. Should you need assistance or further knowledge on PCB soldering, feel free to contact us. We are highly reliable, efficient, and dependable PCB soldering experts.

 

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