Wave Soldering vs. Reflow Soldering

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Sep 13, 2021|Technological Advancements and Materials

There is evidence that soldering has been a part of human cultures and metalworking for over 5,000 years. Despite its history, the world of soldering today is as innovative and technically fascinating as ever.

There are several heating methods in soldering and just as many complicated overlaps and differences. But wave soldering and reflow soldering stand out and draw the most attention. What is the difference between reflow and wave soldering? We discuss everything you need to know and weigh the pros and cons of both methods in this article.

What Is Wave Soldering?

Wave soldering is a bulk process of soldering various electrical components to printed circuit boards (PCB) to produce an electronic assembly. The circuit boards cross a pan of solder, which a specialized pump agitates into a wave, contacting the components and soldering them in place.

The name “wave soldering” derives from the radiating shape of the molten solder as it coats the exposed circuit boards in repeating waveforms. Wave soldering is a central process in manufacturing computer parts and any high-precision instruments used in certain industries like healthcare and telecommunications. The liquid used in wave soldering is dissolved tin and lead.

The Wave Soldering Process

Four primary steps make up the conventional wave soldering process.

1. Spraying the Flux

Flux is a chemical compound that aids in the process of keeping the soldering surface clean. Solder flux helps ensure a tight bond in the solder and a long-lasting metalworking product. It also protects the circuit boards from oxidizing or overheating.

2. Preheating Stage

In the first stage involving the circuit boards, the PCBs pass through a heating chamber to reach ideal temperatures and activate the flux.

3. Wave Soldering

At the correct temperature, the solder paste begins to melt into its liquid form. The circuit boards travel across pans of solder, washing over them in a wave, creating a tight bond.

4. Cooling Stage

Immediately after the solder binds, its internal temperature drops. Production allows the boards to cool to room temperature before completion.

Wave Soldering Application Field

Wave soldering has several applications. The most common use is in SMT or surface mount technology. THT, or through-hole technology, and DIP, or dual-in-line packaging, are also widely used.

What Is Reflow Soldering?

Reflow soldering requires that components be temporarily attached to their circuit board with solder paste, a molten substance that combines solder and flux. Then, the assembled board passes through a “thermal soak” in which a reflow soldering oven melts the solder.

In many production lines, reflow soldering has replaced wave soldering. However, both methods are still popular and widespread. Reflow soldering has fewer steps involved, and the process is generally easier to automate with pick-and-place robots.

The Reflow Soldering Process

Reflow soldering has two main elements: pre-assembling the circuit boards and applying solder paste, then the soldering process proper. Below we’ll cover the basic steps.

1. Preheat Stage

Once the pick-and-place machines apply solder paste to the components, the boards are loaded on a track that slowly raises their core temperature. This step burns off solvents in the flux and ensures the components reach temperature gradually.

2. Thermal Soak

At the appropriate temperature, the flux activates and prepares the circuit board for soldering.

3. Reflow Soldering

Peak temperatures controlled by the reflow oven melt the solder paste within a narrow range of acceptable heats. Too hot, and the boards and mounts may warp. Too cool, and the solder paste won’t melt properly. It is a delicate balance.

4. Cooling Stage

As with wave soldering, the oven releases the soldered circuit board, and workers allow the unit to cool to room temperature.

Reflow Soldering Application Field

Reflow soldering is most commonly used in THT assemblies, though SMT, or surface mount assemblies. A PIP, or pin in paste, method usually helps in the application of THT.

Wave Soldering vs. Reflow Soldering

From a distance, wave soldering and reflow soldering may seem to have many shared attributes. They are different in actuality. It’s important to know which method you are going to use if purchasing direct from assemblers.

Wave soldering has a flux spraying step, while reflow incorporates flux into solder paste. This setup means that reflow soldering requires a precise oven to activate the flux without overheating the components.

Soldering Reliability

Overall, the soldering reliability of both application methods depends on the people controlling the oven systems and solder pans, among dozens of other variables. Even expert metalworkers can make mistakes. However, the frequency of poor production quality does not appear to fall one way or the other.

Selection Standard

Reflow soldering has its best uses as well as wave soldering. Generally, professionals apply reflow soldering with SMT assembly and wave soldering for other assemblies like THT or DIP. Of course, most circuit boards contain components from both assemblies. Consequently, reflow and wave processes often work in tandem.

Designing for Wave Soldering vs. Reflow Soldering

As stated above, wave and reflow soldering are preferred for distinct types of assembly. These preferences determine which decisions designers make in their assemblies and constructions.

Wave Soldering Design Considerations

Wave soldering is ideal for large-scale production. The wave soldering format can churn out completed PCBs at a much faster rate than reflow.

Designing surface mount and through-hole assemblies is less and less a matter for wave soldering. As components grow smaller, reflow soldering took up the #1 position. Wave soldering is still the best method for large power devices, and anytime SMD isn’t in production.

Reflow Soldering Design Considerations

Reflow soldering is in vogue right now because it allows designers to process both plated through-hole and SMT components. More precise robots can manipulate the solder paste on components with stencils. Consequently, designers opt for reflow soldering in the majority of cases.

Conclusion

Wave soldering vs. reflow soldering has a long history, with reflow techniques taking a prominent role in PCB production today. However, the field of PCB design is constantly changing, and the advantages of wave soldering are sure to find widespread use again.

We hope this article has been informative and given you a little backstory on the world of soldering. Determining which process is best for your production is never straightforward, but the information above should give a little guidance.