How to set the reflow soldering temperature

The most important factor in setting the reflow soldering temperature is still based on the characteristics of the solder paste, and each type of solder paste is given a parameter value. In addition to the temperature parameter values for reflow soldering, we also need to consider environmental factors. The reflow soldering temperature setting also depends on other reasons. JEENOCE will share it below.

Factors to consider when setting reflow soldering temperature: 1. The material and thickness of the PCB board, whether there are many layers, and the size of the dimensions, which must be considered during the production process.

2. The density of the surface mounted components, the size of the components, and the presence or absence of special components such as BGA and CSP.

3. There are significant differences between hot air stoves and infrared stoves in their use. Infrared stoves mainly rely on radiation conduction, with the advantages of high thermal efficiency, large temperature changes, and easy control of temperature curves. When double-sided soldering, the upper and lower temperatures of the PCB are easy to control. The disadvantage is that the temperature is not uniform enough. The colors and sizes on the same PCB vary greatly, resulting in significant temperature differences. In order for the temperature of the surrounding components to reach the welding temperature, it is necessary to increase the welding temperature, which can easily affect the quality of welding.

4. The hot air stove is mainly used for convective conduction. Its advantages lie in its ability to receive uniform heating and relatively good welding quality. The disadvantage is that the temperature difference on the PCB and the temperature of the welding furnace are not easy to control. At present, in the production process, some improvement measures are taken for the convection mode of the hot air stove, such as small convection mode, independent adjustment of air volume for each temperature zone, and refrigeration methods below the stove. This can ensure that the temperature in the upper, lower, and length directions of the stove increases, thus meeting the requirements of the process curve.

5. The temperature of the environment also has a certain impact on the furnace temperature. For reflow soldering furnaces with short heating and narrow furnace body width, the temperature of the furnace is greatly affected by the environment. Therefore, in the production process, it is necessary to avoid convection air at the outlet of the reflow soldering furnace.

The correct setting of reflux temperature should be based on the following points:

A. 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.

B. In addition, settings are 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.

C. 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.

D. 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.

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

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

Several parameters simultaneously affect the shape of the curve, with the most critical being the conveyor belt speed and the temperature setting for 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.

In short, when setting the reflow soldering temperature, the most important thing to consider is the characteristics of the solder paste and the type of routine reflow soldering belongs to. These other factors are all reference items.