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Difference Between Reflow Soldering and Wave Soldering

Soldering is a crucial procedure that involves melting solder to join electronic components to printed circuit boards (PCBs). It forms permanent electromechanical bonds. The most common technologies used for PCB manufacturing and Assembly are wave soldering and reflow soldering. This blog will show how wave soldering differs from reflow soldering.
 
Reflow soldering is used in SMT technology during PCB assembly, while wave soldering is used in THT during PCB assembly. Regardless of which technology, FC as China’s excellent PCB manufacturer can provide you with the technology and services!
 
Before we get into the discussion, watch the following video that will give you a better understanding of the difference between reflow and wave soldering

Wave Soldering

Wave soldering is a solder paste application method. Solder paste is applied to the surface of a printed circuit board (PCB) using the wave effect. The wave at high pressure and temperature spreads solder paste across PCB surfaces. The temperature range of the wave soldering iron varies from 200°C to 600°C based on the used metal. It’s an efficient, easy method for connecting copper wires that can be used for many purposes. An induction coil or torch can be used as the heat source for wave soldering. Special tools, like high-voltage transformers and capacitors, are needed for wave soldering.
 
The components are positioned on the board, and then a wave of hot solder flows over them in the wave soldering process. A wave soldering machine is used to accomplish the task. The temperature is not as carefully regulated during this process. It is less effective than reflow soldering.

Principle of Wave Soldering

Wave soldering combines heat and vibration to combine several materials. Vibratory and electromagnetic solders are the two types of wave solders.
 
When the solder comes into contact with both surfaces, an electromagnetic iron employs an electromagnetic field to create heat that melts the solder together. A vibratory iron creates a joint by oscillating back and forth at a high frequency.

Advantages and Disadvantages of Wave Soldering

Wave soldering offers a variety of advantages for electronics manufacturing, especially when it comes to through-hole component assembly. However, it also has some limitations and drawbacks. FC chooses which technique to use based on the characteristics of the product.
Advantages of Wave Soldering
Disadvantages of Wave Soldering
  1. It is far less expensive than other soldering techniques.
  2. The process was both quick and tedious.
  3. Easy and quick setup.
  4. Mostly employed in high-volume production of units.
  5. It is possible to utilize lead-free solder.
  1. It uses a significant quantity of flux.
  2. It uses a significant quantity of solder
  3. It needs a significant quantity of nitrogen.
  4. It uses more electricity
  5. Soldering requires cleaning.
  6. Rework should be increased after soldering to guarantee strong solder junctions.

Wave soldering Process

At FC, the different processes of wave soldering consist of four steps. They are spraying of flux, Pre-heating, wave soldering, and cooling.

Step One: Fluxing

The first process of wave soldering is fluxing. In this process, flux is applied over the PCB. The flux eliminates the oxidation layer on the board’s surface and avoids developing new oxidation layers.
 
Fluxes come in various types. It includes rosin-based, water-soluble, and no-clean fluxes. Flux is used in the appropriate quantity so that it does not degrade the quality of the PCB. The excess use of flux can degrade the quality, and less flux use can increase the risk of loose joints.
 
It is of two types. They are spray, and foam wave fluxing. Spray Flux is applied to the board’s underside. After that, we eliminate the extra flux using a compressed air jet.
 
Foam flux is the flux added to a tank into which a plastic cylinder with holes has been submerged. The plastic cylinder is covered by a metal chimney, pumping air. This causes the flux to increase. The flux is applied across the surface of this flux foam as a PCB passes over it.

Step Two: Pre-Heating

Wave soldering technologies involve higher temperatures for PCBs. This high temperature may cause a thermal shock to PCBs and their electronic components, causing the board or individual components to fail.
 
PCBs go through a preheating process that causes their temperature to rise gradually to prevent failure. Heaters that generate hot air are used to pre-heat PCBs. The PCBs are heated by the heaters and then directed toward the wave soldering equipment. The PCBs are occasionally preheated using infrared heaters. The PCB is heated effectively, avoiding hot or cold areas.
 
Preheating not only stops thermal shocks but also turns on the flux. The flux subsequently removes the oxidation layer, leaving a clean surface ready for soldering.

Step Three: Wave Soldering

Melted solder is applied to the PCB to form long-lasting connections between the parts. The exposed metal pads are covered by the solder wave, which is usually made of a solder alloy. Solder connections are formed through the processes of wetting and solidification.
 
Regulating the solder wave’s temperature and contact time is essential to achieving regular and dependable solder junctions. Variables including solder wave height, conveyor speed, and solder alloy composition are also essential to maximize soldering parameters.

Step Four: Cooling

The last process includes cooling, which is essential for wave soldering. The solder joints are quickly solidified during the cooling cycle, stabilizing the assembly and avoiding faults. Several cooling techniques, including water quenching and forced air cooling, can be used, depending on the particular needs of the assembly and production environment. Maintaining the strength of the solder junctions and preventing heat stress on components require controlled cooling. In addition to reducing the possibility of faults like solder fractures, proper cooling raises the soldered assembly’s overall reliability.
Reflow soldering is a method of joining two metal pieces by applying pressure and heat. Unlike wave soldering, the result is a strong bond that will not break with regular use.
 
Smaller-scale reflow soldering is carried out. Heat guns are a cheap way to apply solder paste to your components and the board, but we should use caution while handling them because they may get very hot. Make sure your heat gun is at the right temperature before we begin, as solder can become toxic if overheated. For a Pb-Free (Sn/Ag) solder, the reflow temperature range is 240–250 degrees Celsius.

Advantages and Disadvantages of reflow Soldering

Reflow soldering offers a variety of advantages that make it ideal for soldering surface mount components in the electronics industry. However, reflow soldering has some drawbacks that should be considered when selecting a soldering method.
Advantages of reflow Soldering
Disadvantages of reflow Soldering
  1. It is simple to monitor and control reflow soldering.
  2. Less solder paste is used because it only needs to be applied where soldering is required.
  3. In a single operation, reflow soldering proves to be highly efficient for many SMT kinds.
  4. The operator might limit soldering to avoid bridging.
  5. Unlike other soldering techniques, reflow soldering is pure.
  6. Due to the components not being submerged in hot solder, reflow soldering has relatively less thermal shock.
  1. The reflow soldering profile must meet the exact specifications for solder paste and heat thresholds.
  2. Lead-free solder does not alter the fundamentals of reflow soldering; rather, it narrows the thermal process window.
  3. Solder faults in reflow soldering occur due to incorrect printing parameters.
 
At FC‘s reflow soldering has different processes, including pre-heating, thermal soak, reflow soldering, and cooling.
 
Before going into detail about the reflow soldering process, watch the related video below to help you understand it better.

Step One: Pre-Heating

The preheating procedure is crucial to the production of PCBs. It serves two main functions for reflow soldering:
The PCB assembly can effortlessly attain the required temperature to guarantee thermal profiling.
Any volatile solvents in the solder are forced out and assisted in their expulsion by preheating. The quality of your soldering can decrease if you don’t perform this correctly.

Step Two: Thermal Soak

The type of solder flux included in the solder paste can affect the soldering process. The solder needs to heat up considerably to activate this flux. Soldering will not be successful if the flux is not activated by the solder.

Step Three: Reflow Soldering

The goal of reaching the maximum temperature is to facilitate the appropriate melting and reflow of the solder paste. A temperature that is too high can destroy a board or even harm its components, while one that is too low might completely prevent this operation. Controlling the temperature is essential to the operation in every way.
 
BGAs that are not soldered correctly may have unequal ball-to-ball contacts and a greater likelihood of unraveling during reflow soldering. Manufacturers concentrated on creating more effective reflow soldering procedures as a result of this accessibility.

Step Four: Cooling

The temperature curve will begin to decline as soon as the temperature hits the top. The solder paste and components are permanently bonded to their contact pads after it cools.

Difference Between Wave and Reflow Soldering

From the above introduction, I believe you have a certain understanding of reflow and wave soldering. A summary of wave and reflow soldering is given below:
Wave Soldering
Reflow Soldering
It involves molten solder forming a solder wave.
It involves the use of high-temperature hot air to create reflow and melt solder.
Wave soldering is not a highly preferred method for surface mounting.
It is the preferred method for surface mounting.
It is faster and cheaper.
Reflow Soldering is more expensive.
This process takes less time.
This process takes more time.
It is less reliable than reflow soldering.
It is more reliable than wave soldering.
It produces large PCBs.
It produces less PCB.
It is mainly used for soldering through-hole components.
It is mainly used for soldering surface-mounted components.
It is a complex technique.
It is a relatively uncomplicated technique.
FC has 22 years of experience in soldering printed circuit boards, and we help you manufacture your products with the best products. We have strong production capabilities for wave soldering and reflow soldering. In addition, we have a large production facility that can perform any soldering technique in bulk. We offer a one-stop shop that can save you time and resources! Therefore, FC is your most trusted partner!
 
If you need to solder printed circuit boards, contact us immediately. We look forward to hearing from you!

Conclusion

Wave and reflow soldering provides complimentary benefits when it comes to PCB assembly. Wave works well for big boards, double-sided soldering, and through-hole insertion, whereas reflow is best for SMT components with precise pitches. It is more complicated in certain aspects. Careful observation is required for board temperature and time spent in the solder wave.

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