Soldering under nitrogen? Why we have had the best experience with this process
Three Benefits of Nitrogen in Soldering for EMS Manufacturing
As an EMS manufacturer, our core expertise lies in SMD assembly. We use different soldering methods for both SMD and THT assembly. To achieve better and more reliable results, we solder under nitrogen. In just a few minutes of reading, you’ll learn about the three ways nitrogen affects the soldering process and the final result.
Why do we solder under nitrogen in EMS manufacturing?
Before we answer this question, let’s first clarify what nitrogen actually is. Because part of the answer lies right there. Nitrogen is used as a shielding gas during soldering. This shielding gas displaces oxygen, thereby reducing oxidation. Rust is the most well-known form of oxidation caused by oxygen. Incidentally, the air we breathe consists of about 78 percent nitrogen, about 21 percent oxygen, and about one percent other gases. In EMS manufacturing, we use nitrogen during soldering to achieve good soldering results more easily and reliably. The shielding gas displaces oxygen during the soldering process. The result: the liquid solder, as well as the metal surfaces of the components and the contact areas of the printed circuit boards, oxidize significantly less.
We use nitrogen for these soldering processes:
Reflow soldering is a process used to solder SMD components. In this process, solder paste mixed with flux is applied to the pads on the printed circuit board prior to component placement. By applying heat in a convection oven, the entire assembly is heated according to a predetermined temperature-time profile to the melting temperature of the solder paste, causing it to melt and the solder joints to form during the subsequent cooling process.
We use the wave soldering process to solder THT-assembled components. In our two wave soldering machines (ERSA for lead-free solder and ERSA for leaded solder), the flux is first applied automatically, the assembled component is preheated, and then it is fed into the actual soldering process. During this process, the assembly is transported with its underside facing the solder wave, where the future solder joints are wetted with the liquid solder. The solder joints then form during the subsequent cooling process.
Soldering under nitrogen: Three Advantages of Nitrogen in Soldering for EMS Manufacturing
1. Nitrogen reduces oxide formation
Oxides are oxygen compounds that can prevent or hinder solder wetting on the printed circuit board. Nitrogen reduces the formation of such oxides during the soldering process, but cannot prevent it entirely. Therefore, existing surface oxides must still be removed with flux.
A flux is a clear liquid that we apply to the areas to be soldered. This flux breaks down the oxide layer. In the process, the flux leaves behind residues as it evaporates in the solder wave. The less flux we have to use, the fewer residues we have on the soldered assembly. Fewer residues also form at the solder joint itself. This offers advantages for subsequent inspection and testing procedures. During ICT testing, test probes are guided to defined contact points on the assembly. Residues or oxide layers can impair electrical contact. Clean and well-wetted contact surfaces therefore support reliable test results.
2. The Solder Wets the Surfaces More Effectively
To ensure that the solder reaches exactly the intended areas, the surfaces must be easily wettable. Fewer oxide layers form in a nitrogen atmosphere. This allows the solder to better wet pads, component leads, and metallized holes. As a result, we achieve better wetting of SMD pads and more reliable solder penetration in through-holes and metallized holes during THT assembly.
The more stable soldering process can also reduce the need for rework. The closer the component pins are spaced on an assembly, the greater the risk of solder bridges. Nitrogen can help make the process more controllable. However, the assembly design, the temperature profile, and the selection of solder and flux remain critical factors.
3. Nitrogen creates less dross
Slag is a layer of oxide that forms on liquid solder, primarily inside machines. This occurs especially where large quantities of liquid solder come into contact with oxygen, such as on the solder wave or in the area of a selective soldering nozzle. Dross is an oxide layer that forms on liquid solder, particularly where larger quantities of solder come into contact with oxygen for example, on the solder wave or around a selective soldering nozzle. Dross resembles slag, but it consists of oxidized solder and is therefore waste. The less dross that forms, the lower the solder loss and maintenance effort.
„Nitrogen is not a miracle cure. If you don't have a good grasp of your soldering process, nitrogen alone won't help you achieve better results. But it does make it easier to achieve good soldering results. In other words, nitrogen makes an already established process even more reliable."
Kristin Teichmann
Head of Production
A+B Electronic
Our conclusion: Nitrogen Supports Reliable Soldering Results and Makes Typical Problems Easier to Control
When we compare the costs across the entire manufacturing process—that is, the cost of purchasing nitrogen and the savings achieved through its use—we realize an economic advantage. Less oxidation, better wetting, less dross, and reduced rework and maintenance requirements make the soldering process more reliable. This ultimately allows us to offer better terms to our partners as well.
Here at A+B Electronic, we have more than 50 years of experience in SMD assembly. We implement your wishes precisely and can guarantee fast processing and delivery thanks to our own parts warehouse on site. We will be happy to discuss your order with you directly. Or you can write us a few words about the project you have in mind - and we will call you back.
