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How to use nitrogen in the welding process?

2019-05-05 15:54 admin
Nitrogen is extremely suitable as a shielding gas, mainly because of its high cohesive energy. Chemical reactions occur only under high temperature and high pressure (> 500C, >100 bar) or energy addition. At present, a nitrogen gas is produced. Useful ways. Nitrogen in the air accounts for about 78%. It is an inexhaustible and economical protective gas. On-site nitrogen generators, on-site nitrogen production equipment, make it easy to use nitrogen and low cost!

     Nitrogen is used in reflow soldering before the inert gas is applied to the wave soldering process. Part of the reason is that in the reflow soldering of surface-bonded ceramic hybrid circuits, the hybrid IC industry has long used nitrogen. When other companies saw the benefits of mixed IC manufacturing, they applied this principle to PCB soldering. In this type of welding, nitrogen also replaces the oxygen in the system. Nitrogen can be introduced into each zone, not only in the recirculation zone, but also in the process of cooling. Most reflow systems are now ready for the application of nitrogen; some systems can be easily upgraded to use gas injection.

The use of nitrogen in reflow soldering has the following advantages:

‧Wetting of terminals and pads is faster

‧ less weldability change

‧ Improved flux residue and appearance of solder joint surface

‧Quick cooling without copper oxidation

     Nitrogen is used as a shielding gas. The main function in welding is to eliminate oxygen during welding, increase weldability and prevent reoxidation. Reliable soldering, in addition to the selection of suitable solder, generally requires the matching of flux. The flux is mainly to remove the oxide of the soldering part of the SMA component before soldering and prevent the reoxidation of the soldering part, and form excellent soldering conditions and improve solderability. . Tests have shown that the addition of formic acid under nitrogen protection can play the above role. The ring nitrogen wave peak welding machine with tunnel welding groove structure is mainly a tunnel welding processing tank. The upper cover is composed of several pieces of openable glass to ensure that oxygen cannot enter the processing tank. When nitrogen is introduced into the weld, and the different specific gravity of the shielding gas and air are utilized, the nitrogen will automatically drive the air out of the weld zone. During the welding process, the PCB board is continuously introduced into the oxygen injection zone, so nitrogen is continuously injected into the weld zone to allow oxygen to be continuously discharged to the outlet. Nitrogen plus formic acid technology is generally applied to tunnel reflow soldering furnaces with infrared convection mixing. The inlet and outlet are generally designed to be open, and there are multiple curtains inside, which have good sealing and can preheat the components. Drying, reflow soldering cooling is done in the tunnel. In this mixed atmosphere, the solder paste used does not need to contain an activator, and no residue remains on the PCB after soldering. Reducing oxidation, reducing solder ball formation, and eliminating bridging are extremely beneficial for soldering fine pitch devices. It saves cleaning equipment and protects the global environment. The additional cost of nitrogen is easily recovered from the cost savings from cost reductions and the labor savings required.

    Wave soldering and reflow soldering under nitrogen protection will become the mainstream of surface assembly technology. The combination of ring nitrogen wave peak welder and formic acid technology, combined with the extremely low activity of the ring nitrogen reflow soldering machine and formic acid, can be removed. Cleaning process. In today's rapidly evolving SMT soldering technology, the main problem encountered is how to break the oxide and obtain a pure surface of the substrate for a reliable connection. Typically, flux is used to remove oxides, wet the surface being soldered, reduce the surface tension of the solder, and prevent reoxidation. At the same time, however, the flux will leave residue after soldering, which will adversely affect the PCB components. Therefore, the circuit board must be thoroughly cleaned, and the size of the SMD is small, and the gap at the non-welding portion is also getting smaller and smaller, and thorough cleaning is impossible, and more importantly, environmental protection. CFC has a destructive effect on the atmospheric ozone layer, and the CFC as the main cleaning agent must be disabled. An effective solution to the above problem is to use no-clean technology in the field of electronic assembly. The addition of a small amount and a quantitative amount of formic acid HCOOH to nitrogen has proven to be an effective no-clean technique, without any cleaning after soldering, without any side effects or any concerns about residues.