Cold soldering and false soldering in PCBA processing will seriously affect the quality of product use, so PCBA processing needs to reduce false soldering and false soldering to a minimum. The following introduces the causes and solutions of cold soldering and false soldering in PCBA processing.
What is a cold solder joint? A cold solder joint refers to the presence of an isolation layer between the solder and the pin, that is, poor contact between the component and the pad. They are not completely in contact, which is generally invisible to the naked eye, but its electrical characteristics are not conductive or poorly conductive, affecting the circuit characteristics.
What is a false solder joint? A false solder joint is similar to a cold solder joint. It is a phenomenon in which the circuit works normally at the beginning and gradually becomes open in the later stage.
1. What are the causes of cold soldering/false soldering?
1. Oxidation of solder pads and component pins
During reflow soldering, the solder paste cannot fully wet the solder pads in a liquefied state, and tin creeps, resulting in cold soldering.
2. Insufficient tin
During the solder paste printing process, due to the small opening of the steel mesh or the small pressure of the scraper, there is insufficient tin, so that during welding, the amount of solder paste is insufficient and the components cannot be fully soldered.
3. Too high or too low temperature
If the temperature is too high, not only will the solder flow, but also the surface oxidation rate will be increased, which may also cause cold soldering.
4. Low melting point of solder paste
Low-temperature solder paste has a relatively low melting point, and the component pins and the board materials of the fixed components are different, and their thermal expansion coefficients are different. Over time, with the change of the working temperature of the components, under the action of thermal expansion and contraction, cold soldering will occur.
5. Solder paste quality issues
Poor solder paste quality, easy oxidation of solder paste, loss of flux, will directly affect the solder paste's welding performance, leading to false solder joints/fake solder joints.
2. Solutions to Solve False Solder/Fake Solder
1. Moisture-proof storage of components:
PCBA processing plants are equipped with ovens, which can bake components with moisture during welding and replace oxidized components.
2. Choose solder paste from well-known brands:
The defects of false solder and fake solder appearing during PCBA welding are closely related to the quality of solder paste.
3. Adjust printing parameters:
During the printing process, adjust the pressure of the scraper, select a suitable steel mesh, and the steel mesh mouth should not be too small to avoid too little tin.
4. Adjust the reflow soldering temperature curve:
During the reflow soldering process, it is necessary to control the welding time. If the time in the preheating zone is not enough, the flux cannot be fully activated and the surface oxides at the welding point cannot be removed. If the time in the welding zone is too long or too short, it will cause false solder and fake solder.
5. Choose suitable testing equipment:
Select AOI testing equipment or X-ray testing equipment to detect welding quality and reduce the outflow of defective products of false solder and fake solder.
The above is an introduction to "Causes and solutions for PCBA processing of false solder joints and false solder joints". I hope it will be helpful to everyone!