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Wave Soldering: What Is It and How It Works?

Are you new to PCB design? Do you still rely on a producer for assembling and fabrication? Then, you may be new to the term—wave soldering.

Well, it’s a fast way to fabricate your PCB in a shorter time. So, it’s the perfect go-to if you want to set up your board in a matter of seconds.

So, as you imagined, this method is quite efficient. It’s even more reliable than soldering by hand. Plus, the system involved handles two types of PCB soldering design. Hence, they are surface mount and through-hole.

That’s why we’ll be talking about wave soldering in this article. Plus, we’ll give you an extensive guide. So, it’s good news if you’re new to wave soldering.

Are you ready? Then, let’s begin!

Wave Soldering

1. What Is Wave Soldering?

Before going deep into the definition, let’s look at the various types.

They are five major types of wave soldering:

1. Manual

2. Drag

3. Selective

4. Dip

5. Wave

Manual soldering isn’t found in every production space nowadays. Although some engineers still actively use this method. And it’s because it requires highly experienced labor. But, there’s a limit to the number of boards created by these experts.

Drag and Dip came into existence many years ago. At that time, they got introduced as more affordable alternatives. But today, they have become outdated. Hence, newer and more affordable wave systems have come into play.

So, now to the definition. What exactly is wave soldering?

It’s straightforward. Wave soldering is a PCB production process that consists of bulk soldering. So, it involves a PCB passing over a pan of molten solder. By doing so, the pump creates an upwelling of solder that resembles a standing wave.

So, components get soldered to the board. And it happens when the circuit board connects with the wave.

In the last stage of the wave soldering process, something happens. The components become glued to the PCB surface via placement equipment. Then, it runs through the molten solder wave.

Also, wave soldering is ideal for soldering through-hole components. Nowadays, surface mount PCBs have replaced through-hole PCBs. But this applies mainly to small-scale electronics. In such cases, engineers use reflow soldering applications. Nonetheless, surface mount PCBs aren’t suitable for large-scale devices. That’s why simple through-hole PCBs outshines.

2. Wave Soldering Process/ What Are the Five Steps of Soldering?

Wave Soldering Process

Wave soldering is an in-line process that treats a PCB with flux. Afterward, it preheats and immerses the PCB in liquid solder.

Thus, you should know that there are various available solder machines. And they all vary in their processing. However, the devices have similar principles and components. For instance, a primary part used is a conveyor. Hence, this conveyor moves a PCB via various zones.

But that’s not all.

There are four other necessary components found in every solder machine.

1. There’s a flux sprayer.

2. It has a preheating pad.

3. The device has a pump that creates the actual wave.

4. It has a pan solder.

Also, the solder is a combination of metals. Hence, the leaded solder has various chemical mixture. There’s 0.5% antimony, 49.5% lead, and 50% tin.

So, here is the step-by-step process of wave soldering:

Step 1: Melting the Solder

Melting the solder is the first step. Hence, it’s the most key process amongst others. Thus, the wave soldering machine has a tank containing solder. To kickstart this process, you must heat the solder. By doing so, you’ll be melting it to the purest form. Afterward, you must ensure to meet the right temperature. That way, the process will be more consistent. And this makes the wave soldering process smoother.

Step 2: Dusting the Components

This step is another very essential one. Before soldering components, you should clean through. So, while cleaning, check to confirm if there are any oxide layers. If there’s any, you need to clean them. Plus, it would help if you stopped them from forming oxide layers. Experienced engineers know the process as fluxing. Furthermore, there are two major types of fluxing.

Step 3: PCB Placement

After carrying the above steps, next is to consider the PCB placement. That’s when you place your PCB in the melted solder.

But that’s not all.

The PCB gets support from the metal clasps of the solder machine. By doing so, the board maintains the placement and firm positioning of the PCB.

Step 4: Solder Application

Now, you’ve correctly placed the PCB. You need to consider the solder application. So, you’ve to make sure the solder settles within the joints entirely. Plus, it would help if you did everything to avoid bumps from forming.

Step 5: Cleaning

In wave soldering, cleaning is the last stage to consider. Nevertheless, it’s still as essential as the first step. By cleaning, you’d have to dust the flux residues. So, you can clean and wash the circuit boards with solvents and deionized water.

3. Wave Soldering Machine

A wave soldering machine comprises of a heated solder tank. And it gets maintained at a specific temperature for the soldering procedure.

But that’s not all.

A solder wave is usually inside the tank. And the PCBs pass over the board’s underside. So, it’s at that point that the board connects with the solder wave.

Also, you must tread with caution when adjusting the wave’s height. By doing so, you’d be keeping the wave from flowing over the board’s anterior side. It’s at this point the solder gets to the required places.

Also, the PCB holds up tight in a segment on the conveyor thanks to the metal fingers. The metal fingers can withstand various temperatures. And the reason is its material is titanium in nature. Plus, it doesn’t get affected by the solder.

Preparation with a Solder Wave Machine

For an electronics PCB to be successful with a solder wave machine, it needs something. The PCB requires perfect design and production.

So, here are two standard precaution methods of solder wave machines.

Solid Resist Layer: This precaution method is the standard practice used for designing PCBs nowadays. This method includes a layer of varnish material to the PCB. But the solder hardly adheres to the PCB. So, only the areas that require soldering are left open. Plus, most of the solder resist comes in green color.

Pad Spacing: This second precaution method is also essential. It helps to ensure that there’s enough spacing between pads that require soldering. And it’s because it’s detrimental for the pads to be too close. Plus, bridging may occur if two pads are too close. As a result, it would lead to a short circuit.

4. Wave Soldering vs. Reflow Soldering

A lot of people find it difficult to identify something. And it’s differentiating between wave and reflow soldering. The reason is that many engineers don’t know their differences. Also, that’s why we chose to illustrate their differences here clearly:

4.1 Soldering Process

Wave soldering process usually contains flux spraying. But, reflow soldering doesn’t entail flux spraying.

4.2 Soldering Reliability

Defects in soldering are inevitable. So, it’s tough to determine which soldering technology is more reliable with fewer defects. However, wne could deduce a conclusion using loads of experimental data. After all, the situation varies each time. So, in conclusion, there’s no headway comparing the reliability of wave soldering with reflow soldering.

Instead, it’s best to get expert assemblers that comply with the production policies. That way, you’ll save yourself from unforeseen defects.

4.3 Selection Standard

Typically, reflow soldering is ideal for surface mount technology. And wave soldering is perfect for DIP or through-hole technology. However, it hardly happens that a PCB only contains THT or SMT components. What usually happens is that fabricators use SMT devices can withstand higher temperatures than THT devices.

5. Selective vs. Wave Soldering

If you deal with PCBs, you should be familiar with selective and wave soldering. After all, they are standard PCB soldering methods.

But, each method comes with its merits and demerits. Afterward, that’s what separates them. So, here are things you should know about them before you make a decision:

What Makes Wave Soldering Unique?

It’s a process that occurs in a protective gas atmosphere. And this happens because nitrogen is present. Plus, nitrogen helps to avoid solder defects to no small extent.

The wave soldering method is quite useful for volume production. But it has some drawbacks. First off, its operating costs are high. Also, it consumes a high amount of flux. And it consumes a lot of electricity.

What Makes Selective Soldering Different from Wave Soldering?

It’s a method that is useful for soldering PCBs. And it’s a type of wave soldering. Plus, this method applies specifically to PCBs assembled with through-hole parts.

So, it’s not a surprise that this method is gaining popularity these days. After all, double-sided PCBs are a thing now. And they permit lighter and smaller products.

One of the benefits you’ll get from this method is the reliability of the solder joints. Also, it permits putting different parameters for each part. Plus, the process doesn’t need an expensive aperture wave solder part.

Selective soldering has some snags as well. First, you may experience processing errors. And it’s because it has a host of parameters. Plus, the procedure is time-consuming. And it’s because each circuit board needs a unique program.

In summary, both methods are ideal. But, selective soldering works best for a simple board that allows consideration of some parameters.

Also, wave soldering is best for boards with large surface mount parts and through-hole components. Plus, it’s the best option for mass production.

Selective Wave Soldering Guidelines

Before you use the selective wave soldering method, it’s crucial to follow some rules.

You can carry out this process in three stages. Firstly, you have to sort out the parts that need soldering. Then, you can apply liquid flux to the various elements.

Secondly, you have to preheat the board. Thirdly, you can solder specific components with the fountain of solder.

6. Dip Wave Soldering

Dip wave soldering is an automatic process. And it’s quite useful for the mass production of electronic products. After all, the method offers product quality and efficiency.

With that said, the method begins with a PCB board. But the board must have gone through some processes like printing, curing, etc. Afterward, the PCB will move forward alongside the conveyor belt (located at the machine’s inlet end).

After this, the board will pass through a spray tank. At this stage, the PCB will get a thin layer of flux on its underlying surface and pins. Then, the board plate will move down to the preheating zone.

In this zone, the flux will lose its solvent. Then, the active agent and resin present in the flux decompose and activates. During this process, you need to thoroughly preheat the board and parts.

As the board continues to move forward, the bottom will experience its first molten solder wave. This wave helps to print the welding flux on the PCB. Then, the second molten solder wave will hit the bottom of the PCB.

This smooth wave helps to divide the connecting bridge between the welding end and pin. Also, it gets rid of welding defects.

7. What Are the Factors to Consider for Wave Soldering?

Here are a few factors to consider for wave soldering.

They are as follows:

7.1 What Is a Wave Solder Pallet?

A wave solder pallet is an insulating material. And it helps to streamline the assembly process of circuits. Plus, it takes out the need for manual labor and human resources.

7.2 Wave Soldering Temperature

When it comes to wave soldering, the temperature should be between 180 to 2250C.

7.3 Lead-Free Wave Soldering

Before you convert to lead-free soldering, it’s crucial to consider a few things. First off, you should consider the wave solder pot. After all, it’s specifically for lead-free soldering. Plus, it contains lightweight titanium hardware and higher-grade stainless steel parts.

What if you’re dealing with Sn-Ag-Cu alloys?

In this case, you have to either get a new solder pot. Or you opt for a new wave solder machine. And it’s because Sn-Ag-Cu alloys react aggressively with the materials in most older wave solder machines.

Can I work with an existing wave solder equipment?

If you insist on working with old wave solder equipment, you should know one thing. It needs more maintenance compared to newer equipment.

7.4 Wave Soldering Defects

No doubt, there’s a higher level of accuracy with wave soldering compared to manual welding.

Plus, the process has a lower error rate. But, it’s crucial to control the welding content and position. Otherwise, you may easily experience the following defects:

1. Lost film

You may experience a loss of film if the curing temperature is extreme (too high or low). Or the quality of your adhesive is poor.

2. A deformed PCB

This defect is common amongst large PCBs. And it’s because the PCBs have an uneven layout due to unbalanced components.

3. Dirty board surface

A dirty PCB surface often occurs when there’s extreme preheating temperature or high reliable content of flux.

4. Cold solder

A cold solder happens when the welding temperature is extreme. Or there’s the oxidation of the pins or pads. It could also occur when the conveyor belt’s mechanical vibration disturbs the solder joints as it’s cooling.

5. Flux residues

You may experience flux residues for a ton of reasons. It may happen due to the wrong peak circuit board shopping, various things might get you confused.  Whether you are going for a single-sided PCB, a double-sided PCB, or any other type of PCB, You can contact time. Or if the flux doesn’t work well.

6. Solder ball

If your substrate construction is low, you may have a solder ball. It can also result when the PCB is wet during storage or there’s high ambient humidity.

7. Short circuit or Solder joint bridge

A short circuit may be due to a low solder resist activity. It may also happen if your PCB design has a very narrow pad spacing.

8. Tombstones

Tombstones occur when you use parts with different requirements for temperature or solder type.

9. Inadequate hole fill

This defect may happen if the solder resists flowing into the holes has poor quality. Or if the solder viscosity is low due to extreme PCB preheating.

10. Low Wetting

This defect occurs when a solder doesn’t spread well on a pad. When this happens, you won’t get a good solder. And this directly affects the reliability of the solder joint.

In Conclusion

There you have it—a comprehensive breakdown of wave soldering. So, it’s up to you to cherry-pick which wave soldering process is best for you. While you’re at it, it’s essential to consider factors like the board components (surface mount or through-hole). You should also factor in the type of production you plan to execute.

As mentioned above, other factors are its defects, wave soldering temperature, wave solder pallets, and lead-free wave soldering.


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Hommer Zhao
Hi, I am Hommer Zhao, the founder of WellPCB. So far, we have more than 4,000 customers worldwide. If you have any questions, you can feel free to contact me! Your happiness as a customer is my priority!