In the process of PCBA processing, experienced operators are required to control the furnace temperature curve of reflow soldering to ensure the quality of soldering and the quality and reliability of the final product. Then, I will introduce to you several temperature zones and furnace temperature setting skills of reflow soldering furnace.
The reflow oven has several temperature zones and furnace temperature setting skills
The reflow oven has 4 zones, which are divided into preheating zone, constant temperature zone, tin melting zone and cooling zone. Most solder pastes can be operated in these temperature zones. In order to deepen the understanding of the ideal temperature curve, the The temperature, residence time and the changes of solder paste in each area are introduced as follows:
Preheating zone: The purpose is to heat the PCB board to achieve the preheating effect so that it can be fused with the solder paste. However, at this time, it is necessary to control the heating rate and control it within a suitable range to avoid thermal shock and damage to the circuit board and components. The heating slope of the preheating zone should be less than 3°C/sec, and the set temperature should be between room temperature and 130°C. The residence time is calculated as follows: set the ambient temperature to 25°C, if the heating rate is calculated at 3°C/sec, then (150-25)/3 is 42s; if the temperature rise rate is calculated at 1.5°C/s, then (150-25) / 1.5 is 85s. Usually, the time is adjusted according to the size difference of the components, and it is best to control the heating rate below 2°C/s.
Constant temperature zone: The main purpose is to stabilize the temperature of the components on the PCB circuit board and minimize the temperature difference. We hope that in this area, the temperature of the large and small components can be balanced as much as possible, and the flux in the solder paste can be fully volatilized. It is worth noting that in this interval, the components on the circuit board should have the same temperature to ensure that there will be no poor soldering and other phenomena when they enter the reflow section. The set temperature of the constant temperature zone is 130℃~160℃, and the constant temperature time is 60~120s.
Reflow Zone: This zone has the highest temperature, allowing the temperature of the component to rise to the peak temperature. In reflow soldering, the soldering peak temperature varies depending on the solder paste used. Generally, we recommend adding 20~40 °C to the melting point temperature of the solder paste. The peak temperature is 210°C~230°C, and the time should not be too long to prevent adverse effects on the PCB board. The heating rate in the reflow zone is controlled at 2.5-3°C/s, and the peak temperature should generally be reached within 25s-30s. There is a trick here that the tin melting temperature is above 183 °C, and the melting time can be divided into two, one is 60~90s above 183 °C, the other is 20~60s above 200 °C, and the peak temperature is 210 ℃~230℃.
Cooling zone: In this zone, the lead and tin powder in the solder paste has melted and fully wetted the surface to be connected. It should be cooled as fast as possible, which will help to obtain bright solder joints and have a good shape. Rough solder joints will be produced. The cooling rate of the cooling section is generally 3~4°C/s to 75°C, and the cooling slope is less than 4°C/s.
