Wave Soldering Furnace And Reflow Oven
What is wave welding, reflow welding? What should be paid attention to in the related production?
The wave welding refers to the melting soldering material (lead-tin alloy), which can be formed by the electric pump or the electromagnetic pump jet into the solder wave peak of the design requirement, and can also be formed by injecting nitrogen into the solder pool, so that the printed circuit board which is pre-installed with the components can pass through the solder wave peak, thus realizing the soft soldering of the mechanical and electric connection between the welding end of the components or the pins and the pad of the printed circuit board. According to the wave peaks of different geometry used by the machine, the wave welding system can be divided into many kinds.
Wave welding process: Insert the component into the corresponding component hole → pre-coating flux → pre-baking (temperature 90-1000C, length 1-1.2m) → wave welding (220-2400C) → remove the redundant plug feet → inspection.
The reflow soldering process realizes the soldering of the mechanical and electrical connection between the welding end or the pin of the surface assembled component and the pad of the printed board by remelting the pasty solder pre-distributed on the pad of the printed board.
Wave welding has a new welding technology with the enhancement of people's consciousness of environmental protection. It used to be tin-lead alloy, but lead is heavy metal, which is very harmful to human body. So now there's a lead-free process. It uses * Sn, Ag, Cu alloy * and special flux, and the welding temperature requires higher and higher preheating temperature. It also requires a cooling zone workstation after the PCB board passes the welding zone. On the one hand, to prevent thermal shock, on the other hand, if there is an ICT, it will have an impact on detection.
Why N2 protection
With the increase of assembly density, the appearance of Fine pitch assembly technology has produced nitrogen-filled reflow soldering process and equipment, improved reflow soldering quality and yield, and has become the development direction of reflow soldering. Nitrogen reflow soldering has the following advantages:
Prevent reduction of oxidation
Increasing welding wetting force and speeding up wetting speed
The invention can reduce the production of tin balls, avoid bridging, and obtain good welding quality
It is particularly important to get the listed welding quality that the solder paste with lower active flux can be used, at the same time, the performance of the solder joint can be improved, the color change of the base material can be reduced, but the disadvantage is that the cost is obviously increased, this increased cost increases with the amount of nitrogen, when you need to achieve 1000ppm oxygen content and 50ppm oxygen content in the furnace, the demand for nitrogen is different. The present tin paste manufacturers are all committed to developing the wash-free solder paste which can be well welded in the atmosphere with high oxygen content, thus reducing the consumption of nitrogen.
For the introduction of nitrogen in the middle reflow soldering, it is necessary to carry out cost-benefit analysis, its benefits include product yield, quality improvement, rework or repair cost reduction and so on, complete analysis often reveals that the introduction of nitrogen does not increase the final cost, on the contrary, we can gain from it.
Most of the furnaces used at present are forced hot air circulation type, in which control of nitrogen consumption is not easy. The invention has several methods to reduce the consumption of nitrogen gas, reduce the opening area of the inlet and outlet of the furnace, the important point is to use a clapboard, a rolling curtain or the like to block the space of the part of the inlet and outlet which is not used, the other way is to use the principle that the hot nitrogen gas layer is lighter than the air and is not easy to mix, when designing the furnace, the heating chamber is higher than the inlet and outlet, thus forming a natural nitrogen layer in the heating chamber, reducing the compensation amount of nitrogen gas and maintaining the required purity.
Application example of instrument correlation
Diagram of oxygen content and nitrogen flow regulation
Workflow
