According to what setting is the temperature curve for lead-free reflow soldering

The appearance of lead-free reflow solder joints is rough, with many pores, a large wetting angle, and no crescent shape, which is significantly different from lead-based solder joints. If measured by the original lead based inspection standards, it can even be considered unqualified, because lead-free solder has poor wettability. But for general requirements of civil electronic products, these do not affect the quality of use. JEENOCE would like to share how to set the temperature curve for lead-free reflow soldering.

1. Set according to the size of the exhaust air volume. Generally, reflow soldering furnaces have specific requirements for exhaust air volume, but the actual exhaust air volume may vary due to various reasons. When determining the temperature curve of a product, the exhaust air volume should be considered and measured regularly.

In addition, settings should be made based on the specific condition of the equipment, such as the length of the heating zone, the material of the heating source, the structure of the reflow soldering furnace, and the heat conduction mode.

3. Set according to the temperature curve of the solder paste used. Solder pastes with different metal contents have different temperature curves, and the specific reflow soldering temperature curve should be set according to the temperature curve provided by the solder paste supplier.

4. Determine the set temperature for each temperature zone based on the actual position of the temperature sensor. If the temperature sensor is located inside the heating element, the set temperature is about 30 ℃ higher than the actual temperature.

5. Set according to the density and size of surface assembly board components, as well as the presence or absence of special components such as BGA and CSP.

6. Set according to the material, thickness, multi-layer board, and size of the PCB board.

Several parameters of lead-free reflow soldering simultaneously affect the shape of the curve, with the most critical being the conveyor belt speed and the temperature setting in each zone. The speed determines the duration of exposure of the board to the temperature set in each zone, and increasing the duration allows more time for the circuit assembly to approach the temperature setting in that zone. The total processing time is determined by the total duration spent in each zone. The setting of the solder paste reflux temperature curve is best based on the data provided by the solder paste supplier, while grasping the principle of internal temperature stress changes in the components, that is, the heating temperature rise rate is less than 3 ℃ per second and the cooling temperature drop rate is less than 5 ℃. If the size and weight of PCB assembly are very similar, the same temperature curve can be used. The temperature setting of each zone affects the temperature rise rate of the PCB, and high temperatures create a significant temperature difference between the PCB and the zone. Increasing the set temperature of the zone allows the machine board to reach the given temperature faster.