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Lead-free era makes whether need nitrogen in reflow a hot topic . As the lead-free solder flow resistance, wettability is not as good as lead solder, especially when the circuit board pad processed with OSP (organic protective film bare copper), the pad is easily oxidized, often caused problems that solder wetting angle is too largely exposed and copper pad phenomenon.
Although a number of electronics manufacturers for operating costs consideration is not temporarily using nitrogen, but with the continuous improvement of the quality requirements of lead-free soldering, the use of nitrogen will become more and more common. So a better choice is although actual production is not necessarily using nitrogen, but the equipment is best left a nitrogen interface, in order to ensure the flexibility of nitrogen production .
• The use of nitrogen reflow
In order to improve the quality of solder joints, sometimes we need to use the nitrogen reflow. Nitrogen is an inert protective gas, it can protect circuit board pad from oxidizing in the welding, It plays a significant improving effect to improve the weldability of lead-free solder.
With the improvement of the packing density and fine pitch (Fine pitch) assembly technologies ,the nitrogen reflow process and equipment improve the quality and yield of the reflow soldering. Nitrogen reflow has become the development direction. Nitrogen reflow has the following advantages:
(1) to prevent oxidation
(2) improve the welding wetting rate
(3) reduce the generation of the solder balls, to avoid bridging to obtain good welding quality
Get better welding quality is particularly important and can use a lower-activity flux paste, but also can improve the performance of the joints, to reduce the discoloration of the substrate, but its disadvantage is the significant cost increase,cost increases with the amount of nitrogen, when you need furnace 1000ppm oxygen content of 50 ppm oxygen content, the demand for nitrogen is a world of difference. Paste manufacturers are committed to the development that can be carried out in the higher oxygen content of the atmosphere a good solder no-clean solder paste, so that you can reduce the consumption of nitrogen.
Introduction of nitrogen reflow, cost-benefit analysis must be carried out, its proceeds include product yield, improve quality, reduce rework or repair fees, etc., complete and correct analysis often reveals that the introduction of nitrogen did not increase the final cost, On the contrary, we have been able to benefit from it.
Currently most of the oven are forced hot air circulation.It is not easy to control nitrogen consumption. There are several ways to reduce the consumption of nitrogen and the furnace imcome and out opening area, a very important point is to use the separator, shutter or similar device to separate that part, and the other ways is the use the theory that hot nitrogen layer is lighter than air and difficult the mixed ,when design of the furnace so that the heating chamber are higher than the import and export natural nitrogen layer. the heating chamber, reduces the amount of compensation of nitrogen and maintenance in purity requirements.
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