Reflow Soldering (Inert Gas / Nitrogen)  [ Return towards  Applications  ]

The use of nitrogen for inert soldering in the assembly of PCBs continues to increase globally for both wave and reflow soldering operations. More and more, assemblers are recognizing that inert soldering not only improves joint quality and yield but also reduces sensitivity to process variables and fluctuations ('process window widening'). 

There is little doubt that nitrogen "improves" the wave soldering process. However, applying it in reflow equipment is often debatable. But one thing is clear, the advantages or necessity of nitrogen in reflow depends on the process. That is, nitrogen will always improve the process but the benefit value analysis will differ. Therefore, pre-evaluating and testing is important.

Benefits of N2 in a Reflow Soldering Process

• Flexibility – wider "process window";
• Use Of low solids;
• Reduced cleaning – residues not polymerized or eliminated;
• Reduced automatic testing false fails;
• BGA voiding;
• Reduced defects / increased yield;
• Increased joint reliability; and
• Aesthetic / shiny joints.

  Proven Conditions that Brings About Benefits of N2

• Integrated components assembly (BGA, CSP, COB, etc);
• Fine-pitch non-reworkable components;
• Expensive assemblies;
• Multi-pass assemblies;
• Higher temperature processes;
• OSP / Bare copper boards;
• Low volume / Prototype; and
• Lead-Free

Reflow Soldering of Pin-Through-Hole Components 

The use of Pin-Through-Hole (PTH) connectors and power-related components are necessary for the wave soldering process. Although wave soldering is a cost-effective method, it poses problems such as real estate and flexibility limits, on the printed circuit boards. Large I/O components are also restricted from the substrate side that is in contact with the wave.   To address these problems, assemblers can adopt other methods such as selective soldering or reflow soldering of through-hole (ROT) components, also known as pin-in-paste soldering or intrusive reflow. The latter provides board flexibility – large I/O components or connectors can be placed on both sides of the board. This eliminates the need for additional soldering equipment. Capital cost and overhead costs such as floor space, power, maintenance, etc. that are associated with wave soldering and selective soldering are eliminated.

Recent reports have reported that the joints formed under ROT are reliable. Nevertheless, the implementation of such process represents a challenge and every process parameters must be optimized to ensure a high-yield process. The use of nitrogen atmosphere, for example, has proven extremely useful in ROT. Nitrogen increases the wetting force and speed I- a critical parameter in the formation of ROT solder joint. Additionally, nitrogen produces smoother and shinier solder fillets with a stronger grain microstructure. Nitrogen intrusive reflow produces robust and consistent joint while lowering soldering defects.