What You Need To Know About PCB Soldering Process

The PCB soldering process can look difficulty to inexperienced technicians. However, it is one of the easiest and the most enjoyable job for experienced technicians and engineers. It involves fixing a component by dissolving a solder and running it on the two contacts that You want to join.


Firstly you can view PCB Assembly Process here then you can know the soldering process in PCB Assembly Procedure more clearly.


It is commonly used when mounting components on the PCB even though it can also be applied in plumbing and other electrical projects. In electronics, the performance of any circuit depends on the effectiveness of the soldering process.


Thus, it is necessary that You solder your components faultlessly if You want Your circuit to perform the job it is designed to do.

1、What is Soldering on PCBs?

Soldering on PCBs results in populating the board with components. The tip of the iron is used to heat the solder and allow it to flow around Your components.


The solder sticks at the tip to help transfer the heat and raise the temperature of the metallic part of the components to the solder's melting point. This allows the component to stick to the PCB.So firstly you need to assure the quality of your PCB is ready for the following processes.


1.1 The Use of Soldering

Soldering is widely used in electronics. It is used to join components in circuits and to make electrical contacts. Typically, soldering entails the use of alloys with a melting point that that is lower than 450°C.


When it is used to join components, it allows them to perform a specific task as envisaged by the engineer.  The components come with terminals that must be connected to circuits using solder through the soldering process.  


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Figure 1: WELLPCB finished soldering product

2、Types of Soldering Process

 2.1  Reflow Soldering

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Figure 2  WELLPCB Reflow Equipment


It is where a mixture of flux and powdered solder is used to attach several electrical components to contact pads. The assembly is then subjected to heat which then melts the solder and connects the joint permanently.


The assembly is then passed through a reflow oven. Reflow soldering is commonly used to attach components to circuit boards.


It may also be used to fill holes with the solder or to insert component leads in through-hole boards. It reduces the cost of assembly to a great extent.


Typically, the main objective reflow is to melt the solder and the adjoining surfaces without damaging the electrical components.


2.1.1 The Process

A conventional reflow soldering process has several stages. Each of the stages has a distinct thermal profile. Surface Mounted Technology is the most used technology because it allows the components to be placed directly on the board using solder paste which serves as a glue.


The board is then baked by raising it to temperatures that are over 2000C so that the solder is properly melted. During this process, care must be taken because too much or too little heat may ruin the project.


The board is then sent through a series of chambers (zones) where it is treated.  


2.1.2 Reflow zones

1. Preheating – it is a lengthy stage and allows for pre-heating of the circuit by raising the temperature slowly so that the heat is distributed uniformly. This stage could last for several minutes because the temperature must be raised by 3-50 F/ second.


2. Thermal Soak – it is the second stage where the board is passed in the second chamber for the thermal soak. It ensures that heat is evenly distributed and activates the chemicals in the paste which stops it from turning or forming microbeads.  


3. Reflow SMT-oven – it is where the reflow soldering process happens by having the circuit board heated to a maximum temperature so that the solder is melted and bonded to the circuit board.


Convection method is preferred and is the most commonly used method. Timing is important since the solder must melt but it should not vaporize.


4. Cooling – the chamber allows the board to cool down to a temperature of about 860 F. It is a rapid process that makes the solder to form a superior bond by degenerating into a crystalline structure.


5. Washing – It is the last stage of the process which is often ignored by manufacturers but it is essential since it removes the grit and chemical residue that remains on the board.


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Figure 3  Soldering Process


2.1.3 Temperature and Curvature

It is referred to the bending of the board, which results from the fact that the board consists of different layers and so when subjected to heat and cooling, it must bend.


The board is made of multilayers and copper which cools slower than the substrate. Notice that industrial reflow machines allow the PCBs to go through either wave or bath solder under controlled cooling to minimize the effect of warping.


It allows one to adjust the temperature so as to meet certain parameters and allow for even heating that minimizes thermal shock when it is bathed. The controlled cooling is also important since it allows stresses to even out. Notice that stresses can cause failure in the board.


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Figure 4 Soldering Wires


2.2  Wave Soldering

It is a process that happens through a giant oven with designated components. It allows the components to be attached to the board fast. The process is efficient compared to soldering the components manually. Also, the machine can handle both surface mount and through hole processes.


2.3  Manual Soldering


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Figure 5 Manual Soldering Workshop


It is one of the oldest technology that was used to fit components onto PCBs. The process required that the surface is heated to melt the solder.


It used to be a useful technique, but advancement in technology has unveiled more efficient methods such as selective soldering which has made this old technique to fall by the wayside.


However, the soldering process is still being used by start-ups as long as they have relevant skills and a good soldering iron.


However, manual soldering is essential for particularly meticulous or very small components which can not be used in mass production or in areas where high-quality standards are required, it entails using Your hands to solder the individual components on the PCB.

3、Precautions and Tips Need To Pay Attention To

We have said that soldering is a process that entails fusing together metals through melting. In the process, a filler metal with a low melting point is used to join the metals being fused.


Soldering can suitably be used in electronics to make a connection which is an essential part in PCB Assembly.


However, the process could be dangerous and necessitates that precautionary measures be taken before any solder work is done. Here are the basic tips You should consider when soldering to ensure that You remain safe.  


•   Don't touch the soldering iron tip- this appears like common sense but the truth of the matter is that most inexperienced technicians injure themselves by touching the tip of the soldering iron heated to about 400 degrees.




Figure​ 6  Soldering Process


•   Don't touch the mains flex with the tip of soldering iron- heatproof flex provides an additional protection so it should not be touched with a soldering tip.  


•   Don't put the soldering iron on the table- ensures that the soldering iron is returned to its stand during and after use.


•   Solder Your PCBs in areas that are adequately ventilated. The reason is that the fumes released when the solder melts can make You uncomfortable and so it is recommended that You move Your head away from the project to avoid the fumes.


Ensure that there is plenty of air circulating in the area You have designated as Your working place.


•   Cleaning Your hands- It is important to remember that a solder is loaded with lead which is poisonous so it is necessary that You thoroughly wash Your hands after handling the solder.

4、Other Things You Need To Know About Soldering Process

The soldering process is critical in our day to day lives because it enables engineers to fabricate the equipment that makes our lives easy. However, the process is hazardous and produces fumes that can cause numerous health issues. However, take note of these facts:


•    Using fume extraction equipment is necessary since it helps to protect one from harmful fumes.


•    Using lead-free solder may sound like a good solution for most people. However, it is important to remember that they produce more than 250 percent particles.


•    Prolonged contact with air that is loaded with particles can cause permanent damage to Your lungs so care must be taken including wearing protective gears when working in soldering stations.


•    There are plenty of wheelable suction devices on the market which can be used in soldering stations to suck air and minimize the risks You may be exposed to.


 4.1 The Function of Flux

 Flux is a purifying agent whose job is to reduce or eliminate the elements of rust on contacts that are being soldered. Flux eliminates air in areas being soldered and makes it difficult for oxidation to take place.


Normally, engineers use Rosin –core solder in electronics which comes with solder that helps the molten solder to flow.


Also, flux helps the solder to melt and aids the molten solder to work properly. Flux can be dispensed using a needle or if it is in a pen form, it requires a little bit of pressure.


The flux helps to remove the wetting bridges especially in cases where two or more leads are to be conjoined.




Figure 7 Solder Paste


4.2 Standard of Solder Point and Solder Pad

A well-designed solder pad should afford a strong joint and minimize solder bridging. These are two critical goals in soldering which will always have conflicting dimensions needs.


Therefore, it is necessary that You consider solder pads dimension tolerance, placement, and production tolerance when choosing the dimension of Your solder pads.


The limitation of the soldering process is also critical because boards that are designed for reflow techniques have narrower pads compared to those designed for wave soldering which must have wider pads.


Notice that the standards have been calculated and can easily be accessed in programs at IPC.


Now that You have learned how to solder components on Your PCB, but there are some problems You will meet during the process, so what You need to do is to find a suitable and reliable manufacturer to help You.


As a professional manufacturer, we providing both SMT and Through-hole We use the latest PCB assembly equipment and vend products that meet the stringent quality assurance standards.


All our products are ISO, and UL certified and are ready to meet Your today's demand for PCBs. You can place Your order for quality and standard PCBs from us.  


All You need to do is to place Your order with details and specifications. We are committed to supplying You quality PCBs that meet Your needs.

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