Talking about SMT reflow soldering technology Briefly
SMT reflow soldering , also known as return soldering, is a soldering method that does not require any additional solder during the soldering process by remelting the pre-placed solder to form solder joints.
Compared with wave soldering, it has the following advantages:
1, Quantitative distribution of solder paste, high precision, less heat generation of solder, less agitation and less usage;
2, Suitable for all kinds of high precision and high requirements components;
3, There are few soldering defects in the mountingprocessing, and the bad solder joint rate is below10ppm.
Second, reflow welding method:
1,Infrared reflow oven
80% of the energy in the heat is emitted in the form of electromagnetic waves – infrared rays. The wavelength is between 0.7~0.8um and 1mm of visible light, 0.72~1.5um for near infrared; 1.5~5.6um for mid-infrared; 5.6~1000um for far infrared, and microwave is above on far infrared.
The mechanism of temperature rise: When the vibration frequency of the infrared wavelength coincides with the vibration frequency between the molecules of the irradiated object, resonance occurs, and the intense vibration of the molecule means the temperature rise of the object. The wavelength is 1~8um.
The fourth zone has the highest temperature setting, which can cause the temperature of the weld zone to rise rapidly and improve the wetting force. Advantages: rapid water gasification of flux and organic acid and halide to improve wetting ability; infrared heating radiation wavelength is similar to absorption wavelength, so substrate heating is fast, temperature difference is small; temperature curve control is convenient, elasticity is good; infrared heater High efficiency and low cost.
Disadvantages: poor penetration, shadow effect – uneven heat.
Countermeasure: A hot air circulation is added to the reflow.
2, Infrared hot air reflow soldering.
The speed of convective heat transfer depends on the wind speed, but excessive wind speed will cause component displacement and promote oxidation of the solder joint. The wind speed is controlled at 1.0~1.8m/s. There are two forms of hot air generation: axial fan generation (easy to form laminar flow, which causes the temperature to be unclear) and tangential fan (the fan is installed outside the heater to create a panel vortex to make the first temperature zone available to control precisely).
Adjustment of basic structure and temperature curve:
1,Heater: tube heater, plate heater aluminum plate or stainless steel plate;
2,Transfer system: heat-resistant PTFE fiberglass cloth;
3,Smooth operation and good thermal conductivity;
4,Suitable for small hot plate stainless steel mesh, suitable for double-sided PCB.
The above is the industry knowledge provided by FASTPCBA Electronics, I hope it’s helpful you!
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