The role of adding nitrogen to the reflow oven Advantages and disadvantages of nitrogen reflow soldering

What is the role of nitrogen in the reflow oven? The main effect 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, it is not easy to produce compounds with metals, and it can also isolate oxygen and metals in the air. Contact at high temperatures accelerates the oxidation reaction.

Firstly, the principle of using nitrogen to improve the solderability of SMT is based on the fact that the surface tension of the solder in a nitrogen environment will be less than that of exposure to the atmosphere, so that the fluidity and wettability of the solder are improved.

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

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

First、The advantages of reflow soldering and nitrogen:

1、Reduce boiler oxidation; 2. Improve welding ability; 3. Enhance solderability; 4. Reduce voiding rate. Because the oxidation of the solder paste or solder pad is reduced, the fluidity of the solder becomes better.

Second、Disadvantages of reflow soldering and nitrogen:

1、The cost of reflow soldering and nitrogen is relatively high; 2, increase the probability of tombstone production; 3, enhance the capillary phenomenon (wick effect).

Third、What kind of circuit boards or parts are suitable for nitrogen reflow?

1、The board with OSP surface treatment and double-sided reflow is suitable for nitrogen

2、It can be used when the part or circuit board does not eat tin well. Such as increasing the wettability of QFN to eat tin

3、Large package and high density BGA

Nitrogen is often referred to as an inert gas. It is used in certain inert atmospheres for metal treatment and in bulbs to prevent arcing, but it is not chemically inert. It is an essential element in the life of plants and animals, and is a component of many useful compounds. Nitrogen combines with many metals to form hard nitrides, which can be used as wear-resistant metals. A small amount of nitrogen in steel will inhibit grain growth at high temperatures and will also increase the strength of certain steels. It can also be used to produce hard surfaces on steel. Nitrogen can be used to make ammonia, nitric acid, nitrate, cyanide, etc.; in the manufacture of explosives; filling high-temperature thermometers, incandescent bulbs; forming inert materials to preserve materials, used in drying boxes or glove bags. Liquid nitrogen during food freezing; used as a coolant in the laboratory.