In recent years, with the increasing demand for the quality of welding products and the increasingly stringent national environmental protection requirements, lead-free welding has become widely popular. Inert nitrogen welding has been favored for its ability to improve product quality. Although the purchase of nitrogen atmosphere requires a certain amount of investment, it is much lower than the cost of environmental protection and rework due to welding defects. Therefore, the role of inert nitrogen atmosphere in SMT welding is increasingly valued and will gradually be accepted and widely used. However, the cost of using nitrogen depends largely on the flow rate, operating hours, reflow oven structure, and production process, and the choice of nitrogen source is even more important.

        In recent years, with the increasing demand for higher quality welding products and stricter national environmental protection requirements, lead-free welding has become widespread. Inert nitrogen welding has gained popularity for its ability to improve product quality. Although purchasing a nitrogen atmosphere requires a certain investment, it is significantly cheaper than the costs associated with environmental protection requirements and rework due to welding defects. Therefore, inert nitrogen atmospheres areSMTwelding is receiving increasing attention and will gradually be accepted and widely used. However, the cost of using nitrogen depends largely on the flow rate, operating hours, reflow oven structure, and production process; the choice of nitrogen source is even more critical.

1Nitrogen sources are mainly of two types: liquid nitrogen (cryogenic air separation) and nitrogen generated by nitrogen generators.(Directly extracting nitrogen from the atmosphere, non-cryogenic air separation.)。
　Liquid nitrogen(One ton of liquid nitrogen is equivalent to nitrogen gas at standard temperature and pressure799m3The general loss is5%：
　Gaseous nitrogen is produced using large-scale nitrogen generation equipment, and then processed at ultra-high pressure and ultra-low temperature(Typically:500Mpa，1800Cto convert it into liquid nitrogen. We use(It is to input nitrogen gas into the equipment.)is gaseous nitrogen. Therefore, before using liquid nitrogen, a gasification process is required, which is achieved through a vaporizer: decompression and heating. Generally, the temperature of the nitrogen gas after vaporization can reach room temperature. Liquid nitrogen tanks need to be purchased or leased separately, which requires significant investment and high operating costs.

2Nitrogen generators come in two types: membrane separation nitrogen generators andPSAnitrogen generators:
　Membrane separation nitrogen generators: The purity of the nitrogen produced can reach99.9% or oxygen content<＝1000ppmAdvantages: Quick start-up2~3minutes to produce qualified nitrogen, can be started and stopped at any time, the system is stable and reliable, the nitrogen purity fluctuation is small, the maintenance is small, and the maintenance is simple;

Disadvantages:High investment and maintenance costs, high energy consumption of air intake.
　

    PSANitrogen generator: Using carbon molecular sieve(Carbor  Molecule Sieve)as the adsorbent, using pressure swing adsorption(Pressure Swing Adsorbtion)technology,Directly produces nitrogen with a purity of99.99% or oxygen content<＝100ppmnitrogen gas is filled into the equipment.

Advantages: Can operate continuously for 24 hours to produce nitrogen with stable purity, no need for special personnel to monitor.

3On-site nitrogen generators inSMTindustry application cases
　Nitrogen generator systems inSMTindustry applications:
　When selecting an on-sitePSAnitrogen generator, the first considerations are gas consumption and nitrogen purity:
　lGas consumption per unit time(Usually calculated in cubic meters per hour)Different brands and models of ovens have different gas consumption rates. InputPCBsize will also affect gas consumption, as will the speed of the chain. Therefore, the exact gas consumption should be determined through on-site experiments. Foxconn Group's nitrogen consumption per oven is 20m3/h
　2Nitrogen purity(Number of nines, or oxygen contentppmvalue); First determine the nitrogen purity in the oven, then determine the outlet purity of the nitrogen generator. The necessary and sufficient condition for oxidation is the presence of oxygen molecules. Under the same conditions, the higher the oxygen content, the more intense the oxidation reaction; conversely, the lower the oxygen content, the weaker the oxidation reaction. Of course, the higher the nitrogen purity the better, but the investment cost should be balanced with the product defect rate and rework amount. Currently, most electronics manufacturers choose:99.99% or oxygen contentl00ppmSome also choose:99.9% or oxygen content1000ppmA small number choose:99.999% or oxygen content10ppm. Therefore, the exact purity should be determined based on the product grade, allowable defect rate, company policies, and the product's wetting requirements. After determining the nitrogen purity in the oven, the outlet purity of the nitrogen generator is then determined; usually, the nitrogen generator is notSMTplaced in the workshop with the production line, but on the roof or outside the workshop, and the gas is input to the oven through pipelines. There are many connection points, which may cause a decrease in nitrogen purity, so the outlet purity of the nitrogen generator should also have a margin. Foxconn Group uses a purity of99.99%nitrogen generator, outlet oxygen content<＝100ppm。
　Below is a brief economic analysis and comparison of a set of nitrogen generators with a purity of99.99%and a gas production of20m3/Hrused on oneSMTproduction line:
　1Liquid nitrogen usage cost
　Liquid nitrogen on the market is approximately1200Yuan/per ton. One ton of liquid nitrogen can be gasified into gaseous nitrogen with a purity of99.99%，780m3的气态氮，所以购买1m3The price of nitrogen gas is1.4Yuan. If we add the rental of liquid nitrogen tanks, the purchase cost of the vaporizer, the annual labor costs, etc., the cost of using1m3nitrogen is close to1.6Yuan.
　2、PSAThe cost of using a nitrogen generator
　On-sitePSAThe main cost of using an on-site nitrogen generator is the consumption of electricity, which mainly comes from the following aspects:
　Air compressor: The rated power of the air compressor is22kw(Including margin),Because the system selection considers the unloading of the air compressor and an appropriate amount of compressed air margin, the actual power consumption of the air compressor is about80%of the rated power, which is:17.6kw左右。电费按0.6Yuan, the average annual operating time is8000hours, and the total annual electricity cost is17.6 × 8000 × 0.6 = 84480Yuan.
　Refrigerated dryer: The rated power of the refrigerated dryer is1kw.. The total electricity cost of the refrigerated dryer is 1 × 8000 × 0.6 = 4800Yuan.
　Nitrogen generator: The raw material of the nitrogen generator is compressed air, and the nitrogen generator itself basically does not consume electricity. It mainly uses instrument electricity, and the rated power is approximately0.4kw。
　Total annual electricity cost0.4 × 8000 × 0.6 = 1920Yuan.
　Labor costs: Because the equipment does not require dedicated personnel, when calculating the operating cost of this gas generation equipment,can be ignored.
　Equipment depreciation: Equipment investment is calculated at20ten thousand yuan, with annual depreciation of2ten thousand yuan.
　The cost per cubic meter of nitrogen is(8.5 + 0.48 + 0.2 + 2) ÷ (20 × 8000) = 0.7Yuan
　The annual price difference between the two nitrogen usage methods is