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In the PCBA processing and production process of PCBA manufacturer, the reflow soldering of SMT technical equipment is one of the important PCBA processing links. The reflow soldering furnace of SMT technical equipment has high process difficulty. The reflow soldering furnace of SMT technical equipment is a group soldering process. All electronic components on PCB circuit board are welded at one time through overall PCBA heating, In this PCBA processing process, experienced SMT technical operators are required to control the furnace temperature curve of reflow welding to ensure the welding quality of components on PCB circuit board and the quality and reliability of final products.
SMT technology equipment reflow soldering furnace has four zones. The standard is divided into preheating zone, constant temperature zone, tin melting zone and cooling zone. Most solder pastes can carry out PCB circuit board placement in these temperature zones. In order to strengthen everyone's understanding of the standard temperature curve of PCB Factory, PCBA processing and SMT technology equipment reflow soldering furnace, the temperatures of each zone of SMT technology equipment reflow soldering furnace are The change of residence time and solder paste in each area is detailed as follows:
1. Preheating zone: it is used to heat PCB circuit board to achieve preheating effect, so that it can be fused with solder paste; However, at this time, the heating rate should be controlled within an appropriate range to avoid thermal shock and damage to circuit boards and components. The heating slope of the preheating zone shall be less than 3 degree Celsius / sec, and the set temperature shall be room temperature ~ 130 degree Celsius. The residence time is calculated as follows: if the ambient temperature is 25 degree Celsius, if the heating rate is 3 degree Celsius / sec, then (150-25) / 3 is 42s; if the heating rate is 1.5 degree Celsius / s, then (150-25) / 1.5 is 85s. Generally, it is best to adjust the time according to the difference of element size to control the heating rate below 2 degree Celsius / s.
2. Constant temperature zone: the purpose is to stabilize the temperature of the components on the PCB circuit board and minimize the temperature difference. We hope that the temperature of large and small components can be balanced as much as possible in this area, and the flux in the solder paste can be fully volatilized. However, it should be noted that in this area, the components on the PCB circuit board should have the same temperature to ensure that there will be no poor welding when entering the reflow section. The set temperature of the constant temperature zone is 130 degree Celsius ~ 160 degree Celsius, The constant temperature time is 60 ~ 120s.
3. Reflow zone: the temperature in this zone is the highest, which makes the temperature of components on PCB circuit board rise to the peak temperature. The peak temperature of reflow soldering in SMT technology equipment depends on the solder paste used. It is generally recommended to use the melting point temperature of solder paste temperature plus 20 ~ 40 degree Celsius. The peak temperature is 210 degree Celsius ~ 230 degree Celsius, and the time should not be too long to prevent adverse effects on PCBA; The temperature rise rate of the reflux zone shall be controlled at 2.5-3 degree Celsius / s, and the peak temperature shall generally reach within 25s-30s. One skill here is that the tin melting temperature is above 183 degree Celsius, and the tin melting time can be divided into two, one is 60-90s above 183 degree Celsius, the other is 20-60s above 200 degree Celsius, and the peak temperature is 210 degree Celsius ~ 230 degree Celsius.
4. Cooling zone: the SMT technical equipment in this section has melted and fully wetted the lead tin powder in the solder paste on the surface of the connected PCBA. The PCBA shall be cooled as quickly as possible, which will help to obtain bright solder joints and good appearance quality, and will not produce rough solder joints on the PCBA, The cooling rate of SMT equipment solder paste machine in the cooling section is generally 3 ~ 4 degree Celsius / s, cooling to 75 degree Celsius, and the cooling slope is less than 4 degree Celsius / s.
