Reflow soldering is primarily used in surface-mount technology (SMT), notably in fine pitch ball grade array (BGA) components. For this purpose, solder paste, which contains flux suspended with solder, is used. With the help of a stencil, the paste is applied to the contact pads on the printed circuit board (PCB), and the components are then placed with a pick-and-place machine.
The board then goes to a reflow oven, where the paste melts and flows into place, binding the components to the board. In the case of a double-sided board, the board is flipped, and the process is repeated. Reflow soldering takes place in a reflow soldering oven.
Stages in reflow soldering
Pre-heat: The board is exposed to heat to raise its temperature to that required. The process gets rid of any solvents present that will otherwise affect the soldering quality.
Thermal soak: The flux contained in the solder paste is activated. It also ensures even heat distribution.
Reflow soldering: Here the reflow oven temperature is increased to induce the melting of the solder paste. The plate is maintained at that temperature to ensure wetting occurs between the PCB and components.
Cooling: The board is cooled at a relatively fast rate to ensure that the soldered joints are mechanically sound.
Use of nitrogen in reflow soldering
The quality of reflow soldering depends on many aspects of the soldering process, including the quality of the components, PCB and solder paste, the machine (reflow soldering oven) and the reflow profile. But soldering defects such as head-in-pillow (HIP) defects are largely caused by wettability issues (issues in the bonding of the solder to the component and substrate) arising from excess oxidation. A nitrogen reflow environment is preferred, as it prevents/slows down oxidation, improves wettability, thus reducing defects significantly, and improves the quality of the solder joints.
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 low 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.