How to set the temperature of reflow welder?

It is 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 furnace and the heat conduction mode.

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

1. It is 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 furnace and the heat conduction mode.

2. Set according to the temperature curve of solder paste. Solder pastes with different metal contents have different temperature curves. The reflow temperature curve of specific products shall be set according to the temperature curve provided by the solder paste supplier.

3. Set according to the size of exhaust air volume. Generally, reflow soldering furnace has specific requirements for 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 shall be considered and measured regularly.

4. The setting temperature of each temperature zone is determined according to the actual position of the temperature sensor. If the temperature sensor is located inside the heating body, the setting temperature is about 30 ℃ higher than the actual temperature.

5. It is set according to the material, thickness, multilayer board and size of PCB.

6. It shall be set according to the density of components on the surface assembly board, the size of components and special components such as BGA and CSP.

For hot air reflow soldering, the solder paste in the welding process needs to go through the following processes, namely, the volatilization of solvent, the removal of oxide on the surface of weldment by flux, the melting, re flow and the cooling and solidification of solder paste. In terms of its temperature curve, we can divide it into preheating area, insulation area, reflow area and cooling area. Jeenoce will briefly introduce these areas of its temperature curve below.

As far as the preheating zone is concerned, its main purpose is to preheat the PCB and components to achieve balance. At the same time, it can also remove the moisture and solvent in the solder paste, so as to prevent the collapse of the solder paste and the splashing of solder everywhere. The temperature rise rate should also be strictly controlled within an appropriate range. Generally, we specify that the large temperature rise rate is 4 ℃, the rise rate is set to 1 ~ 3 ℃, and the standard low level of ECS is 3 ℃.

The insulation area for reflow soldering generally refers to the area where the temperature rises from 120 ° C to 160 ° C. The main purpose is to make the temperature of various components of PCB tend to be uniform, minimize the temperature difference, and ensure that the solder can be completely messed up before reaching the reflow temperature. At the end of the insulation area, the oxides on its pads, solder balls and component pins should also be removed, and the temperature of the whole circuit board will reach a balanced level at this time.

For the reflow area, the temperature in this area will reach high, and the temperature of its welding value will vary with the solder paste. Generally, it will be 20 ~ 40 ℃ higher than the melting point of the solder paste. At this time, the solder in the solder paste has begun to melt and show a flowing state. Sometimes we can also divide the reflow of reflow soldering into two areas, namely melting area and reflow area. An ideal temperature curve should be that the end area exceeding the melting point of solder has a small coverage area, and its left and right sides are symmetrical to each other. Generally, the time when the temperature exceeds 200 ℃ is 30 ~ 40 seconds.

Rapid cooling after reflow soldering helps to obtain a bright solder joint with full shape and low contact angle. Slow cooling will easily lead to more decomposition of pad into tin, resulting in some gray and impetuous solder joints, and even lead to poor tin adhesion and weak bonding force of solder joints. Generally speaking, the cooling rate in the cooling area is within - 4 ℃ and the cooling temperature is 75 ℃, In general, it is also necessary to use a cooling fan for forced cooling.