Wave soldering

Nitrogen and the advances in wave soldering

June 30, 2021

The mass production of printed circuit boards (PCBs) took off in the 1950s with a process known as wave soldering. In wave soldering, the underside of the PCB is sprayed with flux and then heated before being passed over a wave of solder. This solders the components to the PCB. Though it is best suited for through-hole assembly, it is also used in surface-mount technology (SMT).

Partial gas treatment and tunnel systems

While soldering quality is dependent on temperature and the process, wave soldering is characterized by issues such as defect formation (such as pin hole and blow hole solder joints), high flux, solder and electricity consumption and reworking and extra cleaning needs. To mitigate defects and inefficiencies, wave soldering is done in an inert environment such as that with nitrogen presence.
When wave soldering is performed in a nitrogen environment, either of two approaches can be employed: partial gas treatment or tunnel system. In partial gas treatment, only the solder wave is under a blanket of nitrogen. In the tunnel system, all stages of the process are performed in a nitrogen environment. The following are the stages of wave soldering:

  • Fluxing: Flux (a chemical agent that removes oxides) is sprayed on the underside of the PCB to ensure a clean surface on which soldering can effectively take place. It has the effect of removing the oxides from the surface of the board and the pins. It also allows for better heat transmission.
  • Heating: The board is passed through a heat source to activate the flux.
  • Soldering: The PCB is passed over a tank of liquid solder in which a wave is formed, bonding the components to the board.
  • Cooling: After the soldering stage, the board is cooled to room temperature.
  • Cleaning: In the final stage, the flux residues are cleaned out, and the board is washed with solvents.
Both partial gas treatment and tunnel system significantly reduce dross build-up. However, as the tunnel system of wave soldering operates in a nitrogen environment in all stages, it is more effective than the partial gas system and produces less dross, reducing the need for its removal and replacement with solder, leading to lower solder consumption and costs. But there’s more to nitrogen that just reducing dross.

Effects of nitrogen on soldering

Being an inert gas, nitrogen reduces oxidation by displacing oxygen, which allows for appropriate spreading behavior at lower temperatures. It also reduces defect formation, owing to imperfections not being introduced in the process, material or surface. It improves flow properties and wettability (bonding between the solder and PCB/component). The use of nitrogen also reduces the quantity and intensity of flux required, which leads to further cost savings. More importantly, it leads to high-quality solder joints that require less heat and flux.

The industry preference for nitrogen use in soldering is heavily influenced by the improved process window, as performing the production process in nitrogen compared to air reduces issues such as defect formation. But the cost benefits are important as well, as the savings offset the nitrogen expenses. Therefore, on-site nitrogen generation in particular makes a better case for cost and resource savings.

On-site nitrogen for quality soldering

An on-site nitrogen generator not only gives you control over air purity for soldering purposes (which is critical in ensuring appropriate solder spreading behavior at lower temperatures) but also reduces your operating costs (as compared to third-party supply) and ensures you have a constant flow of nitrogen gas when downtime can interrupt production. Generating nitrogen on your own with an on-site nitrogen generator allows safer handling and ensures a lower carbon footprint. Additionally, on-site nitrogen generators, such as those from Pneumatech, are easy to integrate into existing systems.

Pneumatech designs and manufactures both standard and engineered on-site gas generator products. Explore Pneumatech’s full range of nitrogen generators. Or get in touch with us right away. 

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