In recent years, as the requirements for the quality of welding products have become higher and higher, and the country’s requirements for environmental protection have also become higher and higher, lead-free welding has been widely used and inert nitrogen welding has been popular in improving the quality of products. Favor. Although it takes a certain amount of money to purchase a nitrogen atmosphere, it is much lower than the environmental protection requirements and the repair cost due to welding defects. For this reason, the role of inert nitrogen atmosphere in SMT welding has attracted more and more attention, and will gradually be accepted and widely used by people. However, the cost of using nitrogen depends to a large extent on the flow rate, the number of operating hours, the structure of the reflow furnace and the production process, and the choice of nitrogen source is more important.

1. There are two main sources of nitrogen: liquid canned nitrogen (cryogenic air separation), nitrogen generator is used to generate nitrogen ( extract nitrogen directly from the total air, non-cryogenic air separation ) .
　Liquid canned nitrogen ( one ton of liquid nitrogen is equivalent to 799m3 of nitrogen under normal temperature and pressure , and the general loss is 5%) :
　Gaseous nitrogen is produced by large-scale nitrogen production equipment, and then subjected to ultra-high pressure and ultra-low temperature treatment ( usually: 500Mpa , 1800C) to convert it into liquid nitrogen. We use gaseous nitrogen ( that is, input nitrogen into the equipment ) . Therefore, there must be a gasification process before using liquid nitrogen, which is achieved through a vaporizer: decompression and temperature rise. In general, the temperature of nitrogen can reach normal temperature after vaporization. Liquid nitrogen storage tanks need to be purchased or leased separately, which requires a large investment and high operating costs.

2. There are two types of nitrogen generators: membrane separation nitrogen generator, PSA nitrogen generator:
　membrane separation nitrogen generator: the purity of the nitrogen produced can reach 99.9 % or the oxygen content < = 1000ppm , the advantage is: fast startup 2~3 Qualified nitrogen can be produced in minutes, which can be started and stopped at any time, the system is stable and reliable, the nitrogen purity fluctuates little, the maintenance amount is small, and the maintenance is simple;

Disadvantages: high investment and maintenance costs, and high energy consumption when entering the air.
　

    PSA制氮机：采用碳分子筛(Carbor  Molecule Sieve)为吸附剂，利用变压吸附(Pressure Swing Adsorbtion)工艺,直接生产出氮气纯度为99.99％或氧含量<＝100ppm)的氮气充入设备。

優點: 可24小時連續運轉產出純度穩定的氮氣 , 無須專人看顧

3、现场制氮机在SMT行业中的实际使用案例
　制氮机系统在SMT行业中的实际应用：
　选用现场PSA制氮机首先要考虑的是用气量和氮气纯度：
　l、单位时间的耗气量(通常以每小时多少立方米计算)：不同品牌、不同型号的炉子耗气量不同，输入PCB的尺寸不同耗气量也不同，链条转动的速度不同耗气量也不一样，所以确切的耗气量要以现场实验为依据，富士康集团每台炉子的氮气使用量为 20m3/h
　2、氮气的纯度(多少个九，或氧含量的ppm值)；先确定炉子中的氮气纯度，再确定制氮机出口纯度。氧化反应的充要条件是氧分子的存在，同样条件下氧含量越高，氧化反应越激烈；反之氧含量越低，氧化反应越微弱。当然氮气纯度越高越好，但应考虑投资成本与产品的不良率和返工量的平衡。目前大多数的电子厂商都选择：99.99％或氧含量l00ppm，也有选择：99.9％或氧含量1000ppm，少数选择：99.999％或氧含量10ppm。所以确切的纯度应根据产品的档次、允许的不良率、公司政策、产品对浸润性的要求等因素决定。确定了炉子中的氮气纯度后，再确定制氮机出口纯度；通常制氮机不与SMT生产线一起放在车间里，而是放在屋顶，或车间外，通过管道输入炉子，之间有很多个连接口，很有可能造成氮气纯度下降，所以制氮机的出口纯度也要有余額。富士康集团使用的纯度为99.99%制氮机，出口氧含量<＝100ppm。
　下面以一套纯度为99.99%，产气量为20m3/Hr 的氮气发生机用于一条SMT生产线，作出简要经济性分析与比较如下：
　1、液氮使用成本
　市场上的液氮约为1200元/吨，一吨液氮可气化成纯度为99.99%，780m3的气态氮，所以购买1m3的氮气价格是1.4元。如果加上液氮储罐的租金、汽化器的购置费、每年人工的费用等，使用1m3氮气的成本接近1.6元。
　2、PSA制氮机的使用成本
　现场PSA制氮机的使用成本主要是电能的消耗，电能的消耗主要来自以下几个方面：
　空压机：空压机的额定功率为22kw（已考虑余量）,因为在系统选型时就考虑到空压机的卸载和适当的压缩空气余量，所以空压机的实际消耗功率约为额定功率的80%左右，即为：17.6kw左右。电费按0.6元计算，一年的平均运行时间为8000小时，每年电费总计为17.6×8000×0.6=84480元。
　冷冻干燥机：冷冻干燥机的额定功率为1kw.。冷干机的电费总计为 1×8000×0.6=4800元。
　制氮机：制氮机的原料是压缩空气，而制氮机本身基本不耗电，其主要是仪表用电，额定功率大约为0.4kw。
　每年电费总计0.4×8000×0.6=1920元。
　人工费：因设备无须专人职守，所以该套制气设备在计算运行成本时,可忽略不计。
　设备折旧费：设备投资按Calculated at 200,000 yuan, the annual depreciation is 20,000 yuan.
　The cost per cubic meter of nitrogen is (8.5+0.48+0.2+2)÷(20×8000)=0.7 yuan 　 The
　annual price difference between the two nitrogen methods is