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SMT reflow soldering machine four temperature zones detailed explanation

  • Time:2020-03-26
  • Visits:249

SMT reflow soldering machine four temperature zones detailed explanation


In the SMT reflow soldering machine process, we often divide them into four stages: preheating, constant temperature, SMT reflow soldering machine, and cooling. Each stage has its own important significance. The editor will discuss with you the operation mode and specific functions of the four temperature zones of SMT reflow soldering machine.


1. The role of SMT reflow soldering machine preheating zone

Preheating is a heating behavior carried out to activate the solder paste and avoid rapid high-temperature heating during tin immersion, which may cause component defects. It is to heat the PCB at room temperature as soon as possible to achieve the second specific goal, but the heating rate should be controlled within an appropriate range. If it is too fast, it may cause thermal shock and damage to the circuit board and components; If it is too slow, the solvent evaporation is not sufficient, which affects the welding quality. Due to the fast heating speed, there is a large temperature difference in the later stage of SMA in the temperature range. To prevent damage to components caused by thermal shock, the maximum speed is generally set at 4 ℃/s. However, the usual rate of increase is set at 1-3 ℃/s. The typical heating rate is 2 ℃/s.


2. The role of SMT reflow soldering machine insulation zone

The main purpose of the insulation stage is to stabilize the temperature of various components in the SMT reflow soldering machine furnace and minimize the temperature difference as much as possible. Give enough time in this area to catch up with the temperature of larger components and ensure that the flux in the solder paste is fully evaporated. At the end of the insulation section, oxides on the solder pads, solder balls, and component pins are removed by the action of the flux, and the temperature of the entire circuit board reaches equilibrium. It should be noted that all components on the SMA should have the same temperature at the end of this section, otherwise entering the reflux section will result in various poor soldering phenomena due to uneven temperatures in each part.


3. The role of SMT reflow soldering machine in the SMT reflow soldering machine area

The temperature of the heater is set to the highest in this area, causing the temperature of the components to quickly rise to the peak temperature. The peak welding temperature in the reflow section varies depending on the type of solder paste used, and it is generally recommended to add 20-40 ℃ to the melting point temperature of the solder paste. For 63Sn/37Pb solder paste with a melting point of 183 ℃ and Sn62/Pb36/Ag2 solder paste with a melting point of 179 ℃, the peak temperature is generally between 210-230 ℃, and the reflow time should not be too long to prevent adverse effects on SMA. The ideal temperature curve is the minimum area covered by the "tip zone" that exceeds the melting point of the solder. In the SMT reflow soldering machine area, special attention should be paid to the reflow time not being too long to prevent damage to the SMT reflow soldering machine furnace, which may also have adverse effects on the performance of electronic components or cause circuit boards to be burnt.


4. The role of the SMT reflow soldering machine cooling zone

At this stage, the temperature is cooled below the solid-phase temperature to solidify the solder joint. The cooling rate will have an impact on the strength of the solder joint. The lead tin powder in the solder paste in this section has melted and fully wetted the connected surface. Cooling should be carried out as quickly as possible, which will help to obtain bright solder joints with good appearance and low contact angle. If the cooling rate is too slow, it will lead to the production of excessive eutectic metal compounds and the formation of large grain structures at the welding points, resulting in a decrease in the strength of the welding points. The cooling rate in the cooling zone is generally around 4 ℃/S, and it can be cooled to 75 ℃.


Briefly introduced the operation mode and specific functions of the four temperature zones of SMT reflow soldering machine from the above four aspects, hoping to be helpful to everyone.