The temperature setting of each temperature zone of reflow oven with 8 temperature zones is set according to the action principle of the temperature zones (preheating zone, constant temperature zone, reflow soldering zone and cooling zone) of reflow soldering. In fact, no matter with 8, 10 or even 12 temperature zones should follow this basic principle. Of course, we need to adjust it according to the actual situation of our production site, such as RTS or RSS profile? Different products are produced with different raw materials (PCB substrate material, thickness, material, mounting type, etc.), with different solder paste. the temperature settings is different.
The function of preheating area is to make solder paste through preheating first to improve its activity, so as to avoid bad products caused by sharp temperature rise during solder dipping. The temperature of preheating zone should be controlled from room temperature to 150 ℃, the rate of temperature rise should be controlled at about 2 ℃ / s, and the heating time of preheating zone should be controlled at 60 to 150 s.
The function of the constant temperature zone is to keep the temperature of the components in the reflow oven stable gradually, so that the components in the oven have enough time in the constant temperature zone to reduce the temperature difference. The temperature of different size components tends to be the same, and the flux in solder paste is fully volatilized. The temperature in the constant temperature zone shall be kept from 150 ℃ ~ 200 ℃, and the temperature shall be kept rising steadily and slowly. The heating rate shall be less than 1 ℃ / s, and the heating time shall be controlled within 60 ~ 120s. In particular, the constant temperature zone shall be heated slowly, otherwise it is easy to cause quality problems in product welding.
When the PCB enters the reflow soldering area, the temperature in the oven rises rapidly, which makes the solder paste melt, and the liquid solder forms solder joints to the components. The temperature in the reflow soldering zone is set higher, which makes the temperature in the furnace rise to the peak temperature rapidly. The peak temperature is generally determined by the melting point temperature of solder paste, the heat-resistant temperature of PCB and components. The temperature of reflow welding zone is 217 ℃ ~ Tmax ~ 217 ℃, and the whole zone is kept in 60 ~ 90s. If there’s BGA, the peak temperature should be set within 240 to 260 degrees and held for about 40 seconds. In addition, it should be noted that the reflow welding time should not be too long in the reflow area, so as to avoid damage to the furnace, or cause the PCB to be scorched or the component function to be poor.
The function of cooling zone is to let the temperature drop and make the solder joint solidify. The speed of cooling rate will affect the strength of solder joint. If the cooling rate is too slow, the eutectic metal compounds and large grains will be produced at the welding point, which will result in low strength of the welding point. The temperature in this area is from Tmax to 180 ℃, and the cooling temperature can be set to be 75 ℃, and the rate of temperature drop should not exceed 4 ℃ / s.
The following points need to be paid attention to when setting the temperature of each temperature zone of reflow oven with 8 temperature zone:
1. The time for the temperature inside the furnace to rise from room temperature to 250 ℃ shall not be more than 6 minutes.
2. There is a temperature difference between the actual temperature in the reflow furnace and the temperature set in the system. The temperature profile proposed in this paper is only for reference, and it needs to be adjusted according to the temperature profile provided by the solder paste factory and the actual situation of its own products.