In many customer cases of our company, the standard setting of lead-free reflow soldering temperature has always been a concern of everyone. The lead-free reflow soldering process is an important soldering process in current surface mount technology. It has been widely used in many industries including mobile phones, computers, automotive electronics, PCB boards, communications, LED lighting and so on. Next, I will introduce how to set the furnace temperature of lead-free reflow soldering!

1. Set according to the amount of exhaust air. Reflow soldering furnaces generally have special requirements for the amount of exhaust gas, but for various reasons, the actual amount of exhaust gas sometimes changes. When determining the temperature profile of the product, the exhaust volume should be considered and measured regularly.

2. In addition, according to the specific conditions of the equipment, such as the length of the heating zone, the material of the heat source, the structure and heat conduction method of the reflow furnace.

3. Lead-free reflow soldering is set according to the temperature curve of the solder paste used. Solder pastes with different metal contents have different temperature profiles. The reflow temperature curve of the specific product should be set according to the temperature curve provided by the solder paste supplier.

4. Determine the set temperature of each temperature zone according to the actual position of the temperature sensor. If the temperature sensor is located in the heating body, the set temperature is about 30 ° C higher than the actual temperature.

5. It is based on the density, size and surface assembly of special devices such as BGA and CSP.

6. According to the printed circuit board material, thickness, multilayer board and size settings.

Pay attention to the adjustment of lead-free reflow soldering curve

1. Increase the preheating temperature

The preheating temperature of lead-free reflow soldering furnace should be higher than that of tin-lead alloy reflow soldering. The purpose of raising the preheating temperature to 170 ℃ -190 ℃ (traditional preheating temperature is generally 140 ℃ -160 ℃) is to reduce the temperature difference between the peak temperature and the component.

2. Extend the warm-up time

If the preheating time is prolonged properly, preheating too fast will cause thermal shock, which is not conducive to reducing the temperature difference between the part and the shirt, forming a peak temperature for reflow soldering. Therefore, the preheating time should be properly extended to make the temperature of the weldment rise steadily to the preset preheating temperature.

3. Expansion of trapezoidal temperature curve in the reflow zone of lead-free reflow soldering

Extend the trapezoidal temperature curve in the reflow zone. At the same time, the maximum reflow temperature is controlled, the width of the temperature curve in the reflow zone is increased, and the peak time of the small heat capacity components is extended, so that the large and small heat capacity components reach the required reflow temperature to avoid overheating of small components.

4. 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, it cannot be completely consistent, but it should be carefully adjusted so that the temperature curve of each test point tends to be as consistent as possible.

Standard temperature curve setting of lead-free reflow soldering:

1. The flux preheating temperature and time before lead-free reflow soldering are basically the same.

2. Use more than two reflow heating areas as soldering areas. The first heating zone of the soldering zone is used for rapid temperature rise, so that the surface temperature of the printed circuit board reaches 10-20 ° C above the temperature of lead-free molten tin. The second heating zone of the welding zone is used to maintain the melting temperature of the previous heating zone and increase the melting time. From the temperature curve, there is a temperature platform in the welding zone.