Explanation and solution to the problem of virtual soldering and false soldering in reflow soldering

The problems of virtual soldering and false soldering in reflow soldering not only pose significant quality risks to products, but also have a negative impact on customers, seriously affecting the company's image and reducing production efficiency while increasing production costs. JEENOCE provides the following methods and measures to prevent false soldering and false soldering in reflow soldering.

1、 Explanation of virtual soldering and false soldering issues in reflow soldering

1. What is virtual soldering:

Virtual soldering refers to a situation where there is only a small amount of solder sticking at the solder joint, and occasionally there is an open circuit phenomenon, that is, poor contact between the component and the solder pad, greatly reducing the reliability of the PCB multi-layer board.

2. What is false welding:

False soldering is similar to virtual soldering, where the circuit works normally in the initial stage and gradually opens in the later stage.

3. The hazards of virtual soldering and false soldering in reflow soldering

Due to the existence of false soldering and false soldering in reflow soldering, the reliability of PCB multilayer boards and overall products is greatly reduced, causing unnecessary maintenance in the production process, increasing production costs, reducing production efficiency, and posing significant quality and safety hazards to products that have already left the factory, increasing after-sales maintenance costs.

2、 Reasons for false soldering and false soldering in reflow soldering

1. Solder pads and component pins oxidized

It is easy to cause solder paste to be in a liquefied state during reflow soldering, which cannot fully infiltrate the solder pad and lead to solder crawling, resulting in virtual soldering.

2. Shaotin

During the solder paste printing process, due to factors such as the small opening of the steel mesh or the low pressure of the scraper, there is insufficient solder, resulting in insufficient solder paste to fully solder the components during soldering

3. Temperature too high or too low

If the temperature is too high, not only will the solder flow, but it will also accelerate the surface oxidation rate and may also cause virtual soldering.

4. Low melting point of solder paste

Low temperature solder paste has a relatively low melting point, and the thermal expansion coefficient of component pins and fixed component boards is different due to different materials. Over time, with changes in the working temperature of the component, virtual soldering will occur under the force of thermal expansion and contraction.

5. Quality issues with solder paste

Poor quality solder paste, easy oxidation of solder paste, and loss of flux can directly affect the soldering performance of solder paste, leading to false soldering/false soldering.

3、 Solution to virtual soldering and false soldering in reflow soldering

1. Moisture proof storage of components:

If the components are left in the air for too long, it can cause them to absorb moisture and oxidize, resulting in insufficient removal of oxides during the welding process, leading to virtual soldering and false soldering defects. Therefore, PCBA processing plants will be equipped with ovens, which can bake components with moisture during the welding process and replace oxidized components.

2. Choose well-known brand solder paste:

The virtual soldering and false soldering defects that occur during the PCBA welding process are closely related to the quality of the solder paste.

3. Adjusting printing parameters:

The problems of virtual soldering and false soldering are mostly caused by insufficient tin. During the printing process, the pressure of the scraper needs to be adjusted, and a suitable steel mesh should be selected. The mesh opening should not be too small to avoid situations where there is too little tin.

4. Adjust the reflow soldering temperature curve:

When carrying out reflow welding sequence, it is necessary to control the welding time well. If the preheating time is not enough, the flux cannot be fully activated, and the surface oxide at the welding site cannot be removed. If the time in the welding area is too long or too short, it can cause virtual welding and false welding.

5. Choose the appropriate testing equipment:

Choose AOI detection equipment or X-ray detection equipment. When the X-ray detection equipment can detect the difference in radiation intensity that penetrates the object, it can detect the parts of the circuit board with virtual soldering, circuit board voids, and circuit board fractures, detect the welding quality, and reduce the flow of defective products caused by virtual soldering and false soldering.