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Understand the repair and reflow soldering of SMT equipment
PCBA Tech
Understand the repair and reflow soldering of SMT equipment

Understand the repair and reflow soldering of SMT equipment

2021-11-07
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Author:Downs

The repair of PCBA equipment is very important to equipment suppliers and equipment users. Suppliers generally focus on the diagnosis of equipment failures, and then replace the smallest accessory unit they can provide. The user focuses on the timely repair of the equipment to ensure non-stop, and then purchase the smallest accessory unit. Often the smallest unit accessories provided by suppliers are very expensive, such as circuit control boards, motor drives, etc., ranging from a few thousand dollars to tens of thousands of dollars. The average user will not spend a lot of money to reserve these expensive accessories. However, once a component is broken, it usually takes a long time to buy from a supplier, ranging from two weeks to one month, which causes the problem of long-distance quenching of thirst. Therefore, it is not enough for the equipment user to rely on the supplier, and he will pay a high price. He should provide maintenance personnel for his equipment and encourage them to repair the broken parts by themselves. For example, as mentioned in the following table, there is a problem with a servo motor controller, the entire high-speed machine cannot be moved, and the entire production line cannot be produced. It costs 5,000 US dollars to find a supplier immediately, and it is out of stock, and it takes at least two weeks; and after repairs The personnel inspection found that only the power output module (GTR) in the controller was broken and the GTR was available in the local market. Therefore, it only took about one day and less than US$100 to solve the problem. The time benefit can be imagined.

pcb board

The quality of equipment maintenance personnel is very important, and they should have knowledge of mechatronics, automatic control, and computers. SMT equipment is a highly automated control equipment, and the technology used is more advanced in the world, so another quality of maintenance personnel is to accept new knowledge and technology quickly. Equipment maintenance personnel should have basic tools: multimeters, oscilloscopes, IC data or can instantly access relevant data on the Internet. Generally, don’t expect the random device to have circuit schematic diagrams of various control boards and driver boards. You can only rely on your own analysis and draw part of the circuit. Figure to analyze the control circuit to find out the problem.

Detailed introduction of reflow soldering

Reflow soldering, also known as "reflow soldering" or "reflow soldering machine" or "reflow oven" (ReflowOven), it provides a heating environment, Shenzhen SMT patch processing makes the solder paste melted by heat to allow surface PCB mounting A device in which components and PCB pads are reliably combined with solder paste alloys. According to the development of technology, it is divided into: gas phase reflow soldering, infrared reflow soldering, far infrared reflow soldering, infrared heating air reflow soldering and full hot air reflow soldering. In addition, according to the special needs of soldering, a nitrogen-filled reflow oven is included. At present, the most popular and practical ones are far infrared reflow soldering, infrared heating air reflow soldering and full hot air reflow soldering.

1. The first generation-hot plate reflow soldering furnace;

2, the second generation-infrared reflow soldering furnace:

80% of the thermal energy is in the form of electromagnetic waves-infrared rays are emitted outwards. The wavelength of Shiyan SMT patch processing is between 0.7-0.8um and 1mm, the upper limit of visible light, 0.72-1.5um is near-infrared; 1.5-5.6um is mid-infrared; 5.6~1000um is far-infrared, and microwave is between far-infrared superior.

The mechanism of heating up: When the vibration frequency of the infrared wavelength is consistent with the vibration frequency between the molecules of the irradiated object, resonance will occur. The intense vibration of the molecules processed by the Xixiang SMT patch means that the object is heating up. Wavelength is 1-8um

The fourth zone has the highest temperature setting, which can cause the temperature of the welding zone to rise quickly and increase the weeping force. Advantages: the flux, organic acids and halides are quickly hydrated to improve the wetting ability; the radiation wavelength of infrared heating is similar to the absorption wavelength, Xixiang SMT chip processing, so the substrate heats up quickly and the temperature difference is small; the temperature curve control is convenient, Good flexibility; infrared heaters have high efficiency and low cost.

Disadvantages: poor penetration, shadow effect-uneven heat.

Countermeasure: Added hot air circulation in reflow welding.

3, the third generation-infrared hot air reflow welding.

The speed of convective heat transfer depends on the wind speed, but excessive wind speed will cause the PCB components to shift and promote the oxidation of the solder joints. The wind speed of Xixiang SMT patch processing is controlled at 1.0-1.8m/s. There are two forms of hot air generation: axial fan generation (it is easy to form laminar flow, and its movement causes unclear boundaries between temperatures) and tangential fan (the fan is installed outside the heater to generate eddy currents on the PCB panel so that each temperature zone can be Precise control).