Does your printed circuit board (PCB) project always work? Do you find it frustrating when your PCB is not working just because of short-circuiting, maybe? But what causes this short circuit? Too much solder, maybe. But, don't worry; even expert engineers encounter problems during the soldering process.
So, if you are looking for solutions to the various problems caused by soldering, we got you covered. In this article, we will tell you all about PCB welding or soldering. We will mention how to do it properly and what common problems occur during or after the process. And then, we will discuss how to prevent or reduce these PCB welding problems.
1、Methods of PCB welding
Welding is the method to place one or more electronic components on PCB using a solder. Hence, PCB welding is also called PCB soldering. The solder melts and fixes the electronic components at their places. The melting point of solder metal is smaller than that of components and the PCB.
Therefore, the welding process has a vast number of applications. It can be utilized in plumbing, repairing home electronics, electronics, and electrical projects, etc. The working and performance of your electronic circuit greatly depend upon on ideal PCB welding. First of all, you need to be an expert to develop the entire PCB circuit. And if you are inexperienced, you need to know about welding hacks. Welding hacks are good methods of soldering.
In the next sections, different methods of PCB welding have been described. Read them carefully and get started. You will need a printed circuit board, soldering iron, soldering lead, and flux. Figure 1 shows a soldering iron welding a printed circuit board.
Methods of welding are of two types: hard welding and soft welding. Furthermore, hard welding also gets divided into two more categories of brazing and silver welding.
This category of welding or soldering involves connection of two components of metals by a solid solder, which spreads into the gaps of the elements that are visible because of high temperature. The gaps filler metal holds high temperatures, which may be over 840◦F. So, this was the basic concept behind hard soldering. Now, we will tell you about brazing and silver welding.
1.2.2 Silver Welding
It is a spotless method helpful for manufacturing small elements, built-up tools, and doing irregular maintenance. You will need to buy a silver alloy, and that will act as a gap filler metal. However, silver soldering is not recommended for gap filling. We will suggest you to use a different flux to get accurate results from silver welding.
1.2.3 Braze Welding
In Braze welding, two components are connected by creating liquid metallic gap filler. This filler will follow the vessel and run through the joints. Then, it will cool down to provide solid union to the electronic components. Atomic magnetism and diffusion are the processes responsible for this solid union. You will see that this type of welding makes a very strong connection. Brass metal is mostly used for gap filling. Figure 2 illustrates the close view of hard brazing copper element.
1.2.4 Soft Welding
Soft welding is the technique used for placing very tiny compound parts having low melting points. The compounds parts would have been cracked during the welding process. Can you guess why? It is because welding is done at high temperatures. Thus, in this case, you will need to get a tin-alloy for the gap filling metal. The melting point of the gap filler metal should not be smaller than 752◦F. If you are looking for a heat source recommendation, we will suggest you buy a gas torch.
Don't worry if you are not familiar with some welding terms like soldering flux, iron, etc. In the next chapter, we will explain these terms in detail. Further, we will also give you some tips for the welding process.
2、Tools and Tips for Welding
Some of you will already be familiar with all the tools required for soldering the PCB. However, beginners in the field of electronics often suffer because they start working without first getting the necessary information. Knowing everything beforehand is the key to reduce the various welding problems.
In this chapter, we will tell you all about the required tools and tips for PCB soldering. Thus, as a beginner, you will be able to solder your electronics components even in the first attempt successfully.
Soldering iron is the basic tool required for the welding or soldering process. It acts as a heat source for the soft solder. You can use it to solder electronic components manually. It melts the soldering wire so that it can run into the gaps among two connections. For the majority of electronics projects, soldering guns having power capacity from 15W to 30W are best.
Moreover, if you want to weld heavy cable and elements, you should buy an iron with higher power capacity. Mostly, 40W power capacity or higher will suffice the purpose. Figure 3 demonstrates a soldering iron and its stand. Figure 4 shows a soldering gun. You can easily observe the difference in their shapes. The gun will always have higher wattages and will need an electric current to pass through them.
Figure 3 A soldering iron placed on its stand
Figure 4 A soldering gun ready to solder electronic components
You will also need to buy a soldering paste or cream for perfect welding. This soldering cream will have solder flux in it. The soldering paste is used to attach the legs of integrated circuits (ICs) to the connection points on a PCB. The legs are the leads of your ICs or chip packages.
The included solder flux is a chemical purifying agent. It is beneficial for the welding process as it has three primary functions. First, it removes rust from the electronic elements that are to be soldered. Second, it keeps the air out and thus removes extra rust. And third, it advances the soaking capability of the fluid solder. Figure 5 illustrates the soldering paste.
Figure 5The soldering paste
2.1.3 Soldering Wire and Wire Stripper
Lastly, you will undoubtedly need a soldering wire and its stripper. Soldering wire is the metal wire that will act as the soft solder. It has a low melting point and acts as a gap filler for the joints on the PCB. In other words, it is simply a "solder." You would encounter tin and lead soldering wires for electronic projects. Figure 6 shows a reel of soldering wire and figure 7 demonstrates its stripper.
Figure 6 Reel of Soldering Wire
Figure 7 A wire stripper
Here, we will discuss a few tips which will help you in avoiding many welding problems. First of all, you should use heat sinks. They are necessary for attaching wires of sensitive electric components like integrated circuits and transistors.
Secondly, try your best to keep the soldering iron tip neat and clean. A neat iron tip will ensure better heat conduction, and it will result in an improved joint. You can use a damped sponge to clean the tip. Thirdly, make sure that the soldered joints are correct. Because in complex circuits, there is a chance that some of the soldered connections are not there. So, checking after soldering each electronic component will save the frustration at the end. You need to confirm that joints are there.
Fourthly, you should first solder the small electronic components. Small components include diodes, resistors, jumper wires, and similar items. And, large components are like transistors and capacitors. This tip will make components assembling on PCB easier for you. Further, you should also solder the sensitive electronics components at the end. It will help in avoiding any damages to them while you are soldering other components. Sensitive components include MOSFETs, CMOS, ICs, microcontrollers, etc.
In the end, this is a health tip: make sure to work in a room with sufficient ventilation. You should avoid the smoke generated from the soft solder. This smoke is toxic, and plenty of ventilation will make sure that it doesn’t build up in your room. Figure 8 illustrates the smoke that forms during the soldering process.
Figure 8The smoke that forms during the soldering process
3、Common Problems of Welding
Some welding problems can occur when you are modeling a printed circuit board. These problems can increase your costs and decrease manufacturing yields. Worst of all, your product will encounter delays in going from the drawing board to the user. And, these problems mostly result from faults in the manufacturing or design process of your projects. Luckily, there are solutions present to avoid these problems.
In this chapter, we will discuss the common soldering problems, and in the next chapter, we will discuss their solutions.
The following are the six common problems caused by soldering by hand:
1.Disturbed Joint: A disturbed joint results from solder movement as it was solidifying. The joint may have a crystalline, rough, or frosted surface. It is also sometimes called a "cold joint." The next point defines what a cold joint is. The figure below shows a disturbed joint.
2.Cold Joint: You will cause a "cold joint" if you didn't let the solder melt completely. An uneven or rough surface often categorizes the joint. The solder connection will be poor, and the breaks may grow in it with time. The figure below illustrates a cold joint.
3.Overheated Joint: You will encounter an overheated joint if the solder has not run well. And, fixing this joint gets difficult because of remains of the burnt flux. The figure shown below illustrates an overheated joint.
4.Insufficient Wetting: In this case, the solder nicely wets the leads but doesn’t form a mature connection with the pad. This problem can be caused if you don’t provide heat to the pin and the pad. The figure shown below demonstrates insufficient wetting.
5.Starved Solder: You will cause a starved solder joint if you don't use enough solder. It will result in a weak joint and may cause stress breaks and damage with time. The figure shown below demonstrates starved solder joint.
6.Too much solder: You should not put too much solder at a joint as this also causes a problem. There is a chance that neither the pad nor the pin gets wetted. Make sure that you give the solder joint a concave surface as shown in the figure below.
Well, if you are wondering that welding problems are only caused by working manually, you are wrong. Even PCB manufacturers, using machines, can cause soldering problems that should be tackled. The following are the four common problems caused by manufacturers:
1.Solder Bridge: In a solder bridge, two solder joints make an unexpected connection. This connection can result in short circuits in your circuit. The figure shown below demonstrates a solder bridge.
2.Lifted Components: During the wave soldering process performed by the manufacturers, electronics components can raise off the surface of your PCB. The figure shown below illustrates lifted components.
3.Lifted Pads: When manufacturers try to de-solder components, their pads can get lifted from the surface of your PCB. The figure shown below demonstrates lifted pads.
4.Solder Ball: In solder balling, a small piece of solder gets stuck to your PCB. It happens during the wave soldering process. The figure shown below shows a solder ball.
4、Techniques to Reduce Welding Problems
In this chapter, we will explain in detail how you can quickly repair all the previously-mentioned soldering problems.
Repair Disturbed Joint: You can re-heat it and give it time to cool down without interruption.
Repair Cold Joint: Here again, you can re-heat it until the solder starts to flow.
Repair Overheated Joint: Clean your PCB using a toothbrush or a little isopropyl alcohol. It will eliminate the burnt flux.
Repair Insufficient Wetting: You need to simply put hot iron’s tip at the end of the joint until the solder starts to flow. This liquid solder will then cover the pad.
Repair Starved Solder: You should add more solder after re-heating the joint.
Repair Too Much Solder: Excess solder can be pulled off with a hot iron tip, solder wick or a solder-sucker.
Repair Solder Bridge: Excess solder can be pulled off with a hot iron tip, solder wick or a solder-sucker.
Prevent Lifted Components: The manufacturers should use a strong PCB during the wave soldering process. The PCB should not bend if the elements are staying flat.
Repair Lifted Pad: You can connect the lead to a still-in-place copper trace by soldering.
Prevent Solder Ball: Again, it can be repaired by reheating it. For prevention, the manufacturers should not set too high temperatures in the wave soldering machine.
In this article, we have explained everything that you need to know about PCB welding. Our main aim was to tell you about the methods and techniques to reduce welding problems. But before jumping to it directly, we have also mentioned the required background information. Moreover, we have also included the tips that will help you in avoiding these problems in the first place.
If you still have any questions, you can contact us at [email protected].Our team of experts and engineers will be more than happy to help you out.