Nitrogen reflow soldering is the process of filling the reflow chamber with nitrogen gas in order to block the entry of air into the reflow oven to prevent oxidation of the component feet during reflow soldering. The use of nitrogen reflow is mainly to enhance the quality of soldering, so that the soldering occurs in an environment with very low oxygen content (100 PPM) or less, which can avoid the problem of oxidation of components. Therefore the main issue of nitrogen reflow soldering 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, the nitrogen reflow process and equipment have been produced, which has improved the soldering quality and yield of reflow soldering and has become the development direction of reflow soldering. Guangshengde to talk about nitrogen reflow soldering has the following advantages.
(1) Prevention and reduction of oxidation.
(2) improve the soldering wetting force and speed up the wetting speed.
(3) reduce the generation of tin balls, to avoid bridging, to get a better quality of welding.
But its disadvantage is the obvious increase in cost, this increase in cost with the amount of nitrogen, when you need to reach 1000ppm oxygen content in the furnace with 50ppm oxygen content, the general nitrogen content test is by supporting the online type oxygen content analyzer, oxygen content test principle is by the oxygen content analyzer first connected through the nitrogen reflow soldering collection point, and then collect the gas, after the oxygen content analyzer test The oxygen content value is analyzed to derive the nitrogen content purity range. Nitrogen reflow soldering gas collection points have at least one, high-end nitrogen reflow soldering gas collection points have more than three, welding product requirements are different on the demand for nitrogen is a world of difference.
For the introduction of nitrogen in reflow soldering, it is necessary to conduct a cost-benefit analysis, its benefits include product yield, quality improvement, rework or maintenance costs reduction, etc. A complete and unbiased analysis will often reveal that the introduction of nitrogen does not increase the final cost, on the contrary, we can benefit from it, the current common liquid nitrogen, there are nitrogen machines, nitrogen selection is also more flexible.
How much PPM of oxygen is appropriate in a nitrogen furnace?
The relevant literature argues that below 1000PPM infiltration will be very good, 1000-2000PPM is the most commonly used, but the actual use of most of the process using 99.99% that is 100PPM nitrogen, and even 99.999% that is 10PPM, and some customers even in the use of 98% of the nitrogen that is 20,000PPM. another statement OSP process, double-sided welding, with PTH should be below 500PPM, while the increase in the number of standing monuments is caused by poor printing accuracy.
Most of the furnaces used today are of the forced hot air circulation type, and it is not an easy task to control the consumption of nitrogen in such furnaces. There are several ways to reduce the amount of nitrogen consumption: one is to reduce the opening area of the import and export of the furnace, it is important to use partitions, curtains or similar devices to block the part of the import and export of space that is not used, another is to use the principle that the hot nitrogen layer is lighter than air and less likely to mix, when designing the furnace to make the heating chamber than the import and export are high, so that the heating chamber to form a natural nitrogen layer, which reduces the amount of nitrogen compensation and reduces the amount of nitrogen and makes it easier to mix. This reduces the amount of nitrogen compensation and maintains the required purity.
Post time: Aug-23-2022