The temperature of the lead-free reflow soldering furnace is much higher than that of the lead-free reflow soldering. The furnace temperature parameter setting in the four basic temperature zones of lead-free reflow soldering is also different from that of the lead-free reflow soldering furnace. Anhui Guangshengde shares how to set the temperature parameters of the lead-free reflow soldering furnace.

Features of automatic lead-free reflow oven

The lead-free reflow soldering process is a process of reflow soldering temperature change. It generally changes through four temperature zones: heating zone, constant temperature zone, soldering zone and cooling zone. The temperature of lead-free reflow soldering is generally higher than that of leaded reflow soldering. It should be more than 20 degrees higher (of course, low temperature solder paste is not included, here refers to the commonly used lead-free solder paste). When the traditional tin/lead alloy is reflowed, the eutectic temperature is 179℃ ~ 183℃, the peak temperature of the pins on the small components reaches 240℃, and the temperature on the large components is about 210℃, the large/small components The temperature difference is nearly 30°C. 

This difference will not affect the life of the components. When using lead-free solder paste, the melting point temperature of the lead-free solder paste is higher than the eutectic temperature of tin/lead. This makes the pin temperature of the large component to be padded higher than 230 ℃ to ensure the melting temperature, while the peak temperature of the small component pin should be kept at about 240 ℃, and the temperature difference between the large and small components is less than 10 ℃. This is another main feature of lead-free reflow soldering.

Large ten-temperature zone lead-free reflow soldering furnace

1. Preheating zone: the temperature ranges from room temperature to 150°C, the temperature rise rate is controlled at about 2°C/s, and the time in this temperature zone is 60 to 150s.

2. Uniform temperature zone: the temperature is from 150°C to 200°C, and the temperature rises slowly and steadily. The temperature rise rate is less than 1°C/s, and the time in this area is controlled within 60~120s (Note: This area must be heated slowly, otherwise it will easily lead to poor welding ).

3. Recirculation zone: the temperature is from 217℃～Tmax～217℃, and the whole interval time is controlled at 60～90s.

4. If there is BGA, the highest temperature: keep within 240 to 260 degrees for about 40 seconds.

5. Cooling zone: The temperature ranges from Tmax to 180°C, and the maximum temperature drop rate cannot exceed 4°C/s.

6. The temperature rise from room temperature 25℃ to 250℃ should not exceed 6 minutes.

7. The reflow soldering curve is only a recommended value, and the client needs to adjust accordingly according to the actual production situation.

8. The reflow time is 30~90s as the target. For some single boards with large heat capacity that cannot meet the time requirements, the reflow time can be relaxed to 120s.

Precautions for temperature parameter setting of lead-free reflow soldering furnace:

1. Increase the preheating temperature: During lead-free reflow soldering, the preheating temperature of the reflow oven should be higher than the preheating temperature of tin/lead alloy reflow. It is usually about 30°C higher, at 170°C-190°C (traditional preheating temperature is generally 140°C-160°C). The purpose of increasing the temperature of the preheating zone is to reduce the peak temperature and reduce the temperature difference between components.

2. Extend the preheating time: Prolong the preheating time properly. Too fast preheating will cause thermal shock on the one hand, which is not conducive to reducing the temperature difference between the components and the components that form the peak reflow temperature. Therefore, properly extend the preheating time to make the temperature of the welded components rise to the predetermined preheating temperature smoothly.

3. Adjust the consistency of the temperature curve: When testing and adjusting the temperature curve, although the temperature curve of each test point has a certain degree of dispersion and cannot be completely consistent, it must be carefully adjusted to make the temperature curve of each test point as consistent as possible.

4. Extend the trapezoidal temperature curve in the reflow zone: Extend the trapezoidal temperature curve in the reflow zone. While controlling the maximum reflow temperature, increase the width of the temperature curve of the reflow zone, extend the peak time of components with small heat capacity, so that components with large and small heat capacities can reach the required reflow temperature, and avoid overheating of small components.