How To Set The Reflow Soldering Temperature

The most important thing to set the reflow soldering temperature is to set it according to the characteristics of the solder paste. Each solder paste has a parameter value. In addition to the temperature parameter value of reflow soldering, we also need to consider environmental factors, and the setting of reflow soldering temperature also depends on other reasons, SYS Technology will share below.

Factors to consider when setting reflow soldering temperature.

1. The material and thickness of the PCB board, whether there are many layers of boards, and the size of the board are all factors that must be considered in the production process.

2. The density of the components mounted on the surface, the size of the components, and whether there are special components such as BGA and CSP.

3. There is a big difference between the hot blast furnace and the infrared furnace in the process of use. The infrared furnace is mainly for radiation conduction. The advantages are that the thermal efficiency is relatively high, the temperature change is relatively large, the temperature curve is relatively easy to control, and the PCB is soldered on both sides. The upper and lower temperatures are easy to control. The disadvantage is that the temperature is not uniform enough. The color and size are different during the same PCB, and the temperature is very different. In order for the temperature of the surrounding components to reach the welding temperature, the welding temperature must be increased, which will easily affect the quality of the welding.

4. The hot blast stove is mainly convection conduction. Its advantage is that it can be heated evenly and the quality of welding is better. The disadvantage is that the temperature difference between the top and bottom of the PCB and the temperature of the soldering furnace are not easy to control. At present, in the production process, some improvement measures will be taken for the convection mode of the hot blast stove, such as small convection mode, independent adjustment of air volume for each temperature zone, and cooling means under the furnace, which can ensure that the furnace is up and down. And the temperature in the direction of the length increases, so that the requirements of the process curve can be met.

5. The temperature of the environment also has a certain influence on the furnace temperature. For the reflow furnace with short heating and narrow furnace body width, the temperature of the furnace is greatly affected by the environment, so the reflow furnace should be avoided during the production process outlet convection wind.

The correct setting of the reflow temperature depends on the following points:

A.Set according to the size of the exhaust air volume. Generally, reflow ovens have specific requirements for the exhaust air volume, but the actual exhaust air volume sometimes changes 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, set according to the specific conditions of the equipment, such as the length of the heating zone, the material of the heating source, the structure of the reflow oven, and the heat conduction method.

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

D. Determine the set temperature of each temperature zone according to the actual position of the temperature sensor. If the position of the temperature sensor is inside the heating element, the set temperature is about 30°C higher than the actual temperature.

E.Set according to the density of surface mount board components, the size of components, and whether there are special components such as BGA and CSP.

F.Set according to the material, thickness, multi-layer board or not, and size of the PCB board.

Several parameters simultaneously affect the shape of the curve, the most critical of which are the conveyor speed and the temperature settings for each zone. The tape speed determines the duration of exposure of the board to the temperature set for each zone, increasing the duration allows more time for the circuit assembly to approach the temperature set for that zone. The sum of the durations spent in each zone determines the total processing time.

It is best to set the solder paste reflow temperature curve according to the data provided by the solder paste supplier, and at the same time grasp the principle of temperature stress change inside the component, that is, the heating temperature rise rate is less than 3°C per second and the cooling temperature drop rate is less than 5°C. The same temperature profile can be used for PCB assemblies if the size and weight are very similar. The temperature setting of each zone affects the temperature rise rate of the PCB, and high temperature produces a large temperature difference between the temperature of the PCB and the zone. Increasing the set temperature of a zone allows the plate to reach a given temperature more quickly.

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

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