Soldering under nitrogen? Why we have had the best experience with this process
3 Effects of nitrogen on the soldering process in EMS production
As an EMS manufacturer, our core competence covers SMD assembly. We use different soldering processes for this and for THT assembly. To achieve better results, we solder under nitrogen. In just a few minutes of reading time, you can find out what three effects this has on EMS production, among other things.
Why do we solder under nitrogen in EMS production?
Before we answer this question, let's first clarify what nitrogen actually is. Because that's part of the answer. Nitrogen is a shielding gas. This shielding gas displaces oxygen and prevents oxidation. Rust is the best known oxidation caused by oxygen. Incidentally, the air we breathe consists of approx. 78 percent nitrogen, with the remainder made up of 21 percent oxygen and 1 percent various gases. In EMS production, we use nitrogen for soldering in order to achieve good soldering results more easily. The shielding gas displaces the oxygen in the soldering process. The effect: the liquid solder and the tin surfaces of the components and contact surfaces of the PCBs oxidize significantly less.
We use nitrogen for these soldering processes:
Reflow soldering is a process for soldering SMD components. Solder paste with flux is applied to the pads of the circuit board before assembly. By supplying thermal energy in the approx. 6m long convection oven, the entire assembly is heated above the melting temperature of the solder paste according to a predetermined temperature-time curve, causing it to melt and the solder joints to form as a result of the subsequent cooling process.
We use the wave soldering process (also known as wave soldering) for soldering THT-equipped assemblies. In our two wave soldering systems (ERSA for lead-free solder and ERSA for leaded solder), the flux is first applied automatically, the assembled module is preheated and then fed to the actual soldering process. Here, the assembly is transported with its underside over the solder wave where the subsequent solder joints are wetted with the liquid tin and the solder joints are formed by the subsequent cooling process.
Soldering under nitrogen: 3 direct effects on the soldering process and final result
1. nitrogen reduces oxide formation
Oxide is an oxygen compound that prevents or impedes coating with solder on the PCB. Nitrogen reduces this process, but it cannot be completely prevented. Therefore, the surface oxides must be removed with fluxes before the soldering process.
A flux is a clear liquid that we apply to the areas to be soldered. This flux breaks up the oxide layer. When the flux evaporates, it leaves residues in the solder wave. The less flux we have to use, the less residue we have on the soldered assembly. There is also less residue at the solder joint itself. This has advantages for subsequent inspection and test procedures. In the ICT test, needles are moved to the solder joints. If such a needle hits one of the unwanted oxide layers, it does not make contact. We can avoid this contact problem by using nitrogen.
2. Lower surface tension - the solder flows better
In order for the solder to flow exactly where we need it, we have to reduce the surface tension accordingly. This process works better under nitrogen than under oxygen. This means that with nitrogen we achieve better coating of SMD pads and better access to the plated-through and metallized holes in the PCBs during THT assembly.
In addition, the improved flow behavior of the solder reduces rework. The closer together the pins of the components are on the assembly, the greater the risk of the solder forming a bridge. The more liquid the tin is, the less surface tension we have, the less the tin tends to bridge. This means less time for reworking and therefore lower costs.
3. Nitrogen creates less dross
Dross is an oxide layer that forms on the liquid solder, especially in the machines. This occurs particularly where large quantities of liquid tin are present. For example, on the solder wave and on the selective solder wave. Dross looks like slag, but is nothing more than oxidized tin and therefore waste. The less dross is produced, the less maintenance is required. Every maintenance means a machine out of operation. The use of nitrogen therefore means less machine downtime, saving us time and money.
„Nitrogen is not a miracle cure. If you can't solder, you won't be able to do it any better with nitrogen. 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 increases good soldering results and makes typical problems manageable
If you compare the costs of the entire production process - purchasing nitrogen and the savings made by using nitrogen - we save costs. Ultimately, we can also offer our partners better conditions.
At A+B Electronic, we have almost 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.
Do you need a company that offers more than just assembly?
Then find out more about us here – or contact us directly without obligation. Then we talk about future projects and how we can grow together.
