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Setting of reflow profile of lead-free solder paste

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Update time : 2022-10-20 19:20:43
The setting of the lead-free solder paste furnace temperature curve is very important, and everyone must be careful. Only by mastering the method of how to set the furnace temperature curve of lead-free solder paste can we ensure that the lead-free solder paste is in the best state.
Attention should be paid to the temperature setting of the solder paste furnace:
The temperature setting of the paste oven temperature is related to the type of solder paste and the temperature requirements of the thermally sensitive components to be passed through the oven. That is to say, the temperature curve should make the solder paste melt without damaging the components. The temperature setting value is related to the actual PCB board. There is a gap in the temperature on the board. The set value is 260. Maybe the actual temperature of the pad on the board is only 240. It is also affected by the environment, personnel, materials, machinery, and technology. It may be set in winter and summer. The fixed value is the same, but the temperature of the pad on the board is different. Therefore, the temperature time curve measured in the furnace with a thermocouple should be used as the standard. The curve standard is generally 150-180 ℃ for 90-120 seconds. Above 220 ℃ 30 -60 seconds, within 30 seconds above 230°C.
In view of the widely used lead-free solder paste, this paper discusses the process requirements and setting methods of the lead-free solder paste reflow soldering temperature curve, and briefly explains the basic principle of solder paste reflow soldering.
Reflow soldering is the core process of SMT surface assembly. Circuit design, solder paste printing, and component assembly in SMT production are ultimately for soldering into finished PCBs. All bad will manifest after reflow. However, most of the process control in SMT production is to obtain quality results with high pass-through rate. If the reflow soldering temperature curve is not set properly, all the quality control in the previous stage will be meaningless. Therefore, setting the reflow soldering temperature correctly and optimizing the temperature profile is the top priority in the process control of all SMT production lines. In the heating zone A, the purpose is to quickly heat the PCB board to the flux activation temperature. Ramp from room temperature to around 150°C in about 45-60 seconds, the slope should be between 1 and 3. If the temperature rises too fast, it is prone to collapse, resulting in defects such as tin beads and bridging. In constant temperature zone B, the temperature rises gently from 150°C to 190°C. The time is controlled within 60 to 120 seconds based on specific product requirements, so as to give full play to the activity of the fluxing solvent and remove oxides on the soldering surface. If the time is too long, it is prone to over-activation, which affects the welding quality. In this stage, the active agent in the fluxing solvent begins to work, the rosin resin begins to soften and flow, and the active agent diffuses and infiltrates with the rosin resin on the soldering end surfaces of the PCB pads and parts, and interacts with the surface oxides on the soldering surfaces of the soldering pads and parts. React, clean the surface to be welded and remove impurities. At the same time, the rosin resin rapidly expands to form a protective film on the outer layer of the welding surface to isolate it from contact with the outside gas, and protect the welding surface from oxidation.
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