What is the effect of adding nitrogen to the reflow oven?
The main function of adding nitrogen (N2) to the SMT reflow furnace is to reduce the oxidation of the welding surface and improve the wettability of the welding, because nitrogen is a kind of inert gas, and it is not easy to produce compounds with metals. It can also isolate oxygen and metals in the air. Contact at high temperature accelerates the oxidation reaction.
Firstly, the principle that using nitrogen can improve the solderability of SMT is based on the fact that the surface tension of the solder in the nitrogen environment will be less than that exposed to the atmospheric environment, so that the fluidity and wettability of the solder will be improved.
Secondly, nitrogen reduces the solubility of oxygen in the air and substances that can contaminate the soldering surface, greatly reducing the oxidation of high-temperature soldering, especially in improving the quality of the second-side reflow soldering.
Nitrogen is not a panacea for PCB oxidation. If the surface of a part or circuit board has been severely oxidized, nitrogen cannot bring it back to life, and nitrogen can only have a remedial effect on slight oxidation (it is a remedy, not a solution).
Advantages of reflow soldering with nitrogen:
Reduce furnace oxidation
Improve welding ability
Enhance solderability
Reduce voids. Because the oxidation of the solder paste or pad is reduced, the fluidity of the solder becomes better.
Disadvantages of reflow soldering with nitrogen:
burn money
Increased chance of tombstones spawning
Enhanced capillarity (wicking effect)
What kind of boards or parts are suitable for nitrogen reflow?
The board with OSP surface treatment double-sided reflow is suitable for using nitrogen gas
It can be used when parts or circuit boards have poor tin effect. For example, increase the wettability of QFN tin
Large package and high density BGA
