Nitrogen reflow is to fill the reflow furnace with nitrogen in order to prevent the air from entering the reflow furnace and prevent the element element in reflow welding from oxidizing. The use of nitrogen reflow welding is mainly to enhance the quality of welding, so that welding occurs in an environment with very little oxygen content (100PPM) or less, which can avoid the oxidation problem of components. Therefore, the main problem of nitrogen reflow welding is to ensure that the oxygen content is as low as possible.



With the increase of assembly density and the emergence of Fine pitch assembly technology, nitrogen filled reflow welding process and equipment are produced, and the quality and yield of reflow welding are improved, which has become the development direction of reflow welding. Nitrogen reflow has the following advantages: (1) Prevent the reduction of oxidation (2) improve the welding wetting force, accelerate the wetting speed (3) reduce the generation of tin balls, avoid bridging, get better welding quality Get better welding quality is particularly important, you can use less active flux solder paste, but also improve the performance of the solder joint, reduce the discoloration of the substrate, but its disadvantage is that the cost increases significantly, This increased cost increases with the amount of nitrogen. When you need to reach 1000ppm oxygen content and 50ppm oxygen content in the furnace, the general nitrogen content test is carried out by the supporting online oxygen content analyzer. The oxygen content test principle is that the oxygen content analyzer is first connected to the collection point of nitrogen reflow welding, and then the gas is collected. The oxygen content and purity range of nitrogen are obtained by the oxygen content analyzer. There is at least one nitrogen reflow gas collection point, and there are more than three high-end nitrogen reflow gas collection points. The requirements of welding products are different and the demand for nitrogen is very different. Today's solder paste manufacturers are working on developing no-wash solder pastes that perform well in high oxygen atmospheres, thus reducing nitrogen consumption.

For the introduction of nitrogen in reflow welding, we must carry out a cost-benefit analysis, its benefits include product yield, quality improvement, rework or maintenance cost reduction, etc., complete and accurate analysis often reveals that the introduction of nitrogen does not increase the final cost, on the contrary, we can benefit from it, currently common liquid nitrogen, as well as nitrogen machine, nitrogen selection is more flexible.



How much oxygen content in the nitrogen furnace is appropriate in PPM?

Checked the relevant literature below 1000PPM infiltration will be very good, said 1000-2000PPM is the most commonly used, but in the actual use of most of the use of 99.99%, or 100PPM of nitrogen, and even 99.999%, or 10PPM, and some customers actually in the use of 98% of nitrogen, or 20000PPM. Another argument is that the OSP process, double-sided welding, should be below 500PPM when there is PTH, and that the increase of the monument is caused by the low printing accuracy.

Most of the furnaces currently in use are forced hot air circulation type, and it is not easy to control nitrogen consumption in such furnaces. There are several ways to reduce the consumption of nitrogen and reduce the opening area of the furnace inlet and outlet. It is important to use a partition, curtain or similar device to block the unused space of the inlet and outlet. Another way is to use the principle that the hot nitrogen layer is lighter than the air and not easy to mix, so that the heating chamber is higher than the inlet and outlet. In this way, a natural nitrogen layer is formed in the heating chamber, reducing the compensation amount of nitrogen and maintaining the required purity. Double reflow welding both sides

Through hole reflow welding: Through hole reflow welding, sometimes called sort element reflow welding, is on the rise. It can remove the wave soldering link and become a process link in PCB mixed assembly technology. One of the biggest advantages is that through hole inserts can be used to obtain better mechanical joint strength while taking advantage of the surface mount manufacturing process. For the larger size of the PCB board, the flatness can not make all the pins of the surface mount components can contact the pad, and at the same time, even if the pin and the pad can contact, the mechanical strength provided by it is often not large enough, and it is easy to be detached in the use of the product and become the point of failure. Although through hole reflow can provide repayment benefits, there are several disadvantages in practical applications. The amount of solder paste is large, which increases the degree of contamination to the machine due to the flux swing cooling, and requires an effective flux residue removal device. Another point is that many connectors are not designed to withstand reflow temperatures, and early stoves based on direct infrared heating are no longer suitable, which lack the efficient heat transfer efficiency to handle common surface mount components and through-hole connectors with complex geometric appearance on the same PCB. Only the large capacity of the forced convection furnace with high heat transfer, it is possible to realize the through hole reflux, and has been proved by practice, the remaining problem is how to ensure that the solder paste in the through hole and the element foot have a proper reflow temperature curve. With the improvement of process and components, through-hole reflow welding will be applied more and more.