Function of adding nitrogen to reflow furnace? Advantages and disadvantages of nitrogen reflow welding?

Function of adding nitrogen to reflow furnace?

The main function of adding nitrogen to SMT reflow furnace is to reduce the oxidation of welding surface and improve the wettability of welding. Because nitrogen is an inert gas, it is not easy to produce compounds with metals. It can also isolate the oxygen in the air from contacting with metals at high temperature and accelerate the production of oxidation reaction.

Firstly, the principle that using nitrogen can improve the weldability of SMT is based on the fact that the surface tension of solder in nitrogen environment will be less than that exposed to atmospheric environment, so that the fluidity and wettability of solder can be improved.

Secondly, nitrogen reduces the solubility of oxygen in the original air and substances that can pollute the welding surface, which greatly reduces the oxidation during high-temperature soldering, especially in the improvement of the second side reflow quality.

Nitrogen is not a panacea for PCB oxidation. If the surface of parts or circuit boards has been seriously oxidized, nitrogen cannot bring them back to life, and nitrogen can only remedy slight oxidation (remedy, not solution)

Advantages of reflow welding plus nitrogen:

Reduce furnace oxidation

Improve welding ability

Enhance solderability

Reduce void rate. Because the oxidation of solder paste or pad is reduced, the fluidity of solder becomes better.

Disadvantages of adding nitrogen for reflow welding:

Burn money

Increase the probability of tombstone generation

Enhanced capillarity (wick effect)

What kind of circuit board or part is suitable for nitrogen reflow?

The board with OSP surface treatment and double-sided back welding is suitable for nitrogen

Parts or circuit boards can be used when tin eating effect is not good. For example, increase the wettability of QFN to eat tin

Large package and high density BGA