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What is Wave Soldering?

wave soldering

Table of Contents

What is Wave Soldering?

The Wave Soldering Process is used to mass solder electronic components to PCBs. The process involves using a wave of molten solder; thus, it has the name “Wave Soldering.”

Wave soldering is a widely used soldering technique in electronics manufacturing for large-scale soldering of circuit boards. It involves using a wave soldering machine to solder electronic components onto a PCB. 

The primary working principles of wave soldering are as follows:

  1. The PCB with electronic components goes over an electromagnetic field of molten solder.
  2. This solder wave wets the PCB’s exposed metal pads, forming a robust and permanent link between the components and the circuit board.
  3. As the PCB moves over the wave, the solder binds to the metal pads by capillary action, resulting in solder connections.
  4. Residual solder is removed with air blades or another way to verify that no flux remains on the board.
  5. The PCB is cooled, solidifying the solder joints and completing the soldering process.

The desired temperature is required during wave soldering. If you fail to control the temperature, it can lead to cracks, resulting in conductivity loss. Also, insufficient heating can lead to cavities and poor conductivity and board strength. 

Wave soldering is chosen due to its efficiency, allowing it to solder several connections simultaneously. It ensures consistency and reliability in electronic assemblies. It is widely utilized in mass manufacturing electronic goods such as computers, televisions, and automobiles.

Key Components and Equipment

components of wave soldering

Wave soldering is a way to solder components onto a PCB. It’s often used for through-hole parts. Equipment for wave soldering includes a solder wave machine, fluxing system, preheating stage, conveyor system, and cooling zone.

Solder Wave Machine

The solder wave machine is the main part. It has a tank of hot solder made of tin and lead. A pump makes a wave of solder flow over the bottom of the PCB, joining the parts.

Fluxing System

Flux is put on the PCB before it meets the solder wave. Flux removes any rust and helps solder stick well. Usually, a sprayer or foam applicator spreads the flux evenly.

Preheating Stage

Before the PCB meets the solder, it goes through a preheating stage. This warms up the PCB and parts to activate the flux. It also lessens shock when they touch the hot solder.

Conveyor System

A conveyor moves the PCB through the soldering stages. It keeps the process steady so each part gets soldered correctly.

Cooling Zone

After the PCB goes through the solder, it enters a cooling zone. Fans or other cooling tools help the soldered joints cool quickly. This stops them from getting too hot and makes sure they harden well.

Step-by-Step Wave Soldering Process

Solder Preparation

It is the initial step in the wave soldering process. It is an essential requirement to melt the solder. In the wave soldering process, there is a tank or solder pot with the solder. Thus, to melt the solder, heat the solder pot. 

Ensure you maintain a solder at an appropriate temperature in the solder pot of the wave soldering machine. The wave soldering has a temperature range from 245 to 270 degrees C. It depends on the metal type. The greater temperature will enhance the efficiency of the joints. 

Component Cleaning

For optimal soldering results, ensure your solder is clean and impurities-free. The presence of oxide layers on the components should be removed. This is carried out using the method called fluxing. The fluxing method called corrosive and non-corrosive fluxing is famous for this. 

PCB Positioned

After carrying out the above process, place the PCB in the melted solder. Metal clasps of equipment held the board. This will ensure the proper positioning and placement of the circuit board to place the components after applying the solder it.

Soldering

After that, molten solder is applied, which is then allowed to settle down firmly. Manufacturers provide a suitable time for this step that allows the solder to settle into the joint. The process is carried out such that there are no bumps. 

Cooling systems, such as fans or water sprays, rapidly cool the PCBs after soldering.

Excess Solder Removal

After passing through the solder wave, excess solder may remain on the PCB. Use air knives, hot gas, or other methods to remove excess solder and achieve clean solder joints.

Inspection

Inspect the solder joints visually or using automated inspection equipment. Ensure solder joints are correctly formed, defects-free, and meet quality standards.

Advanatges and Disadvanatges of Wave Soldering

wave soldering process

Advantages

Wave soldering has various advantages, including:

  • It can process the volume boards in a short time period.
  • It can solder PCB at high speed, which ultimately reduces the costs.
  • It supports lead-free solders. 
  • It ensures consistent soldering results across multiple PCB assemblies. 
  • It is suitable for through-hole components.
  • It automates the soldering process, reducing the need for manual labor. 

 

Disadvantages

  • Wave soldering couldn’t be used for heat-sensitive components. For example, surface mount components may require alternative soldering methods.
  • It produces a high amount of thermal stress, which may cause damage to the components. 
  • It may require additional cleaning steps of flux residues, adding cost and complexity. 
  • The equipment requires the initial setup and periodic maintenance to ensure the optimal performance.

Wave Soldering vs Reflow Soldering

Let’s see how wave soldering differs from reflow soldering below:

 

Aspect

Wave Soldering

Reflow Soldering

Process

Soldering components using a continuous wave of molten solder.

Soldering components by melting solder paste through controlled heating.

Component Compatibility

Suitable for through-hole components.

Suitable for surface-mount components and some through-hole components.

Temperature Control

Uses a single, high-temperature solder wave.

Utilizes precise temperature profiles to melt solder paste without overheating components.

Soldering Precision

Less precise, with solder applied to the entire board.

Offers higher precision, allowing targeted application of solder to specific areas.

Flux Application

Flux is typically applied before soldering.

Flux is often included in solder paste and applied during component placement.

Environmental Impact

It generates more waste and requires proper disposal of solder and flux residues.

Produces less waste and typically requires less flux, reducing environmental impact.

Setup and Maintenance

Requires setup and maintenance of wave soldering machine and solder pot.

Requires setup and maintenance of reflow oven and stencil printing equipment.

Cost

Initial equipment costs can be higher but may be more cost-effective for high-volume production.

Initial equipment costs can be lower, but operational costs may vary based on production volume.

Wave Soldering for SMD Components

Wave soldering, normally utilized for through-hole components, has several limitations when soldering surface mount device (SMD) components. This is due to the flat surfaces of the SMD components and their proximity to the PCB. Wave soldering for SMD components requires additional processes and special equipment.

One frequent method is to use a selective soldering machine with a mini-wave nozzle. This nozzle allows precision solder application to specific locations where SMD components are installed, avoiding contact with the wider solder wave. Another technique is to add solder paste to the SMD pads before reflow soldering. The PCB is heated during this operation to melt the solder and connect the components.

Conclusion

Wave Soldering is a technology for producing large volumes of circuit boards. It can be used in various materials and substrates, including glass, silver, gold, ceramic, and more. 

The primary principle of wave soldering to join various materials effectively is heat and vibration. The joints are created with the help of vibratory iron that oscillates back and forth. Meanwhile, the solder melts when it comes into contact with electromagnetic iron that generates heat. 

FAQs

What is wave soldering?

Wave soldering is a technique used to make electronics where electronic parts are sold onto a printed circuit board (PCB). 

Here’s how it works: the PCB is moved over a molten solder wave, which melts and creates solder connections between the parts and the board.

What types of components are suitable for wave soldering?

Through-hole components like capacitors, resistors, diodes, and connectors are soldered with the help of wave soldering. These components have the leads present to pass through holes in the PCB. This allows them to come in contact with solder waves. 

Can wave soldering be used for lead-free soldering?

Yes, wave soldering can be used for lead-free soldering. For this, it should use solder alloys that follow the regulations such as RoHS (Restriction of Hazardous Substances). 

Lead-free soldering requires higher temperatures. It also involves different flux formulations compared to traditional soldering methods.

What are some common defects in wave soldering?

The most common defects in wave soldering include solder bridges, where the solder forms unnecessary connections between adjacent pads and solder balls, cold solder joints, which are insufficient or incomplete soldering, and inadequate wetting. 

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About Michael

Michael is the general manager of ELEPCB, a leading PCB design and manufacturing company based in China. He has over 10 years of experience in the PCB industry, and has been involved in various projects.

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