Electronic components moving along a conveyor belt

PCB assembly & soldering

for the electronic manufacturing services market

This article will briefly touch upon related information pertaining to PCB assembly. We'll first introduce the EMS market, and then define a PCB while connecting its importance. You'll also find information about the soldering process and why N₂ is essential.

To better understand the importance of printed circuit board (PCB) manufacturing in the growing electronic manufacturing services (EMS) market, we've also created a series of articles. They go into detail on the following topics related to PCB assembly.

● The basics of PCB assembly & soldering

● The electronic manufacturing services market

● Why nitrogen (N₂) is essential for PCB assembly

● N₂ vs air (oxygen) in PCB assembly

● On-site N₂ generation cost and sustainability benefits for PCB assembly

Read on to learn more.

Electronic manufacturing services (EMS) market

Simply put, the EMS market comprises companies that produce components for original equipment manufacturers (OEMs). These OEMs include computer, electronics, aerospace and defense, medical and healthcare, automotive, semiconductor manufacturing, robotics, agriculture, and power and energy production companies.

One area of huge demand for EMS suppliers is the electric vehicle (EV) industry. When an OEM, like an automotive manufacturer, uses an EMS company, it can focus on the overall assembly and development of the car. The OEM also makes sure all parts fit perfectly.

Of course, PCBs play a huge role in the EMS market. EVs, in particular, depend on advanced PCBs to function, as well as in related equipment – like charging stations. You can read more about the EMS market in our related WIKI.

What is a PCB?

A printed circuit board or PCB is made of insulating material, such as fiberglass or plastic. In addition, it contains conductive pathways. Before use, the board is stenciled and cut to size. Solder paste is then added to mount components before soldering occurs.

Commonly, parts were secured with through-hole technology (THT), but now surface mount technology (SMT) is becoming the norm. During soldering, N₂ is used due to its inert nature and low levels of oxides. This, among other benefits, is discussed in our related article.

Read more about PCB assembly and soldering

Someone uses a tablet to create a printed circuit board design

Soldering processes for printed circuit board manufacturing

There are three methods commonly used for soldering. These are wave, reflow, and selective soldering. When discussing PCB assembly, wave and reflow are the types that are usually carried out. The right process will depend on whether THT or SMT is used. Wave soldering is mostly used for THT, while reflow is best for SMT.

When comparing wave to reflow soldering, it's important to understand that reflow involves a hardening process in an oven around 250 C. This is because the solder needs to be set after it's applied. With wave soldering, the board is passed over a solder bath to secure the metal components.

It’s worth mentioning that selective soldering can also be applied to a PCB with THT. This is because its method is similar to wave soldering. That said, it's less economical and quick than wave soldering. Selective soldering is more precise and allows for better wetting. It essentially provides the benefits of hand soldering through an automated process and is needed for THT PCBs.

With the above information, it's worth pointing out that SMT is becoming the preferred type due to its advantages. These include the capability to design more compact PCBs with shorter circuits. The latter allows for faster connections. We cover the differences between THT and SMT further in here.

Nitrogen is essential for the PCB assembly process

N₂ is preferred for PCB assembly due to its low oxide and wetting properties. The latter, ensures a smoother solder flow and stronger bonds with the PCB pads and component leads. With this, you’ll want to make sure to match the right flow to the soldering type. N₂ also produces less dross.

N₂ reduces oxide formation

Oxide is an oxygen compound that prevents or impedes wetting the solder on the PCB. It can also cause corrosion. While oxide can't be completely avoided, N₂ reduces its impact. Surface oxides must be removed with fluxes before the soldering process.

Lower surface tension means the solder flows better

To ensure the solder flows exactly where it's needed, it's good to have a desired surface tension. This is better facilitated with N₂ than air (and the oxygen it contains). N₂ allows for better wetting of SMD pads and improved penetration of plated-through and metallized holes in the PCBs during THT assembly. Better flow also means less rework is needed.

N₂ results in less dross

Dross is an oxide layer that forms on liquid solder, especially in the machines. This typically occurs where large quantities of liquid tin are present. For example, on the wave and on the selective solder. Dross looks like slag but is nothing more than oxidized tin. The less dross produced, the less maintenance is required.

Why on-site N₂ generation

There are two main ways to receive N_2: you can either use on-site generation or use a delivery service. With a nitrogen generator, you'll always have readily available gas whenever needed. In addition, it reduces carbon emissions because no transport is required.

While there are upfront costs involved with a nitrogen generator system including buying the air compressor, the generator itself, air treatment equipment (dryers and filters), and air and N₂ storage, it usually pays for itself. There are also all-in-one N₂skids that contain everything you need to get started.

When investing in an air compressor for PCB assembly, it is possible to use oil-injected equipment. This is because the right air treatment equipment can improve air quality to a level that’s sufficient for small to medium sized PCB companies. For soldering, you’ll also want to look for a generator with Pressure Swing Adsorption (PSA) technology, that can deliver the correct purity (up to very high purity), adapted to your process.

Learn more about on-site nitrogen generation

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