Soldering is a process that joins two or more metal components by melting and applying a filler metal—known as solder—that solidifies to form a permanent electrical and mechanical connection. In electronics, it’s primarily used to mount components onto printed circuit boards (PCBs).

Because today’s devices are smaller, faster, and more complex, soldering must be:

• Accurate to avoid bridging or cold joints
• Clean to prevent oxidation or contamination
• Repeatable across high-volume production lines

This is where controlled atmospheres, like nitrogen-rich environments, come into play.

In PCB assembly, three primary soldering methods are employed, each suited to specific applications and component types: Reflow soldering, wave soldering, and selective soldering.​

Reflow soldering

This method is predominantly used for surface-mount components. A solder paste—comprising flux and powdered solder—is applied to designated pads. Components are then positioned, and the assembly is heated in a reflow oven, melting the paste to establish robust joints.​

• Ideal for: High-density or miniature components​
• Advantages: Precise temperature control
• Common applications: Consumer electronics, telecommunications, and medical devices​

Wave soldering

Traditionally favored for through-hole components, wave soldering involves passing the PCB over a continuous wave of molten solder. The solder wave contacts the board's underside, forming joints in a single pass.​

• Ideal for: Large batches and simpler board designs​
• Advantages: Rapid processing for suitable layouts​
• Common applications: Automotive, lighting, and industrial assemblies​

Selective soldering

For assemblies that combine both surface-mount and through-hole components—or when certain areas must avoid heat exposure—selective soldering offers a targeted solution. This technique uses a localized solder fountain or robotic soldering tip to apply solder precisely to specific joints without affecting neighboring components.​

• Ideal for: Mixed-technology boards and heat-sensitive components
• Advantages: Minimizes thermal stress and allows for precise solder application​
• Common applications: Automotive electronics, medical devices, and aerospace assemblies

While soldering can technically be performed in ambient air, many manufacturers use nitrogen-enriched atmospheres—especially in reflow ovens and wave soldering machines—to improve soldering quality and consistency.

Benefits of nitrogen in soldering include:

• Reduced oxidation on component leads and pads
• Better wetting, leading to stronger, more reliable joints
• Less bridging and fewer soldering defects
• Improved flow and surface tension control
• Reduced dross formation in wave soldering baths

Maintaining consistent gas purity is especially important in high-reliability sectors such as automotive, aerospace, and medical electronics.

Selecting the appropriate soldering method is crucial and depends on various factors such as product design, component types, and production setup. Here's a comprehensive comparison of the three primary soldering techniques: Reflow soldering, wave soldering, and selective soldering.​

Reflow soldering is predominantly utilized for surface-mount components, offering precise temperature control, making it ideal for high-density assemblies. It's commonly employed in manufacturing consumer electronics, telecommunications devices, and medical equipment.​

Wave soldering is suited for through-hole components and is efficient for large batches of simpler board designs. This method is often applied in the production of LED drivers, automotive electronics, and various industrial assemblies.​

Selective soldering provides a targeted approach, beneficial for mixed-technology boards where both SMD and through-hole components are present. It minimizes thermal stress on sensitive components and is commonly used in automotive electronics, medical devices, and aerospace assemblies.​

In many manufacturing environments, a combination of these soldering methods is employed to accommodate diverse product lines and complex assembly requirements. Understanding the distinct advantages and applications of each technique ensures optimal soldering results tailored to specific production needs.