Why some PCB solder service life is short? They are occured bad welding phenomenon after a period of time led the electric device bad.Today, let’s analyze the main reasons.
PCB poor welding analysis:
- PCB surface pad or SMT be oxidated lead to poor solder.
- PCB has dusty or oily materials on the surface.
- The soldering flux activity isn’t enough to completely remove the oxidizing material of the PCB weld plate or the SMD welding position.
- The temperature of the reflow welding area is too low, the speed is too fast, and the tin is not melted.
- The wetting performance of the solder paste is not enough to make the tin solution not fully infiltrated on the welding surface and the components pins, resulting in poor welding.
- If there part of solder is not full, there may be a solder paste not mixing fully and tin power not fully fusion before use.
- Insufficient solder paste in solder joint.
- In the reflow soldering, the preheating time is too long or the preheating temperature is too high, which causes soldering flux failure in the solder paste.
- Used double peak process,the active ingredient in the flux has been completely decomposed for the first time when it passes through the tin. When the second wave peaks are applied, the flux can not remove the oxidation and infiltration.
- There is no solder flux in partial of the welding surface, lead can not soldering.
- Welding surface is unequal or other cause led solder area no tin.
- The circuit board is wrong direction in wave welding, there are more dense rows of solder joint and the tin wave is perpendicular to the direction of tin lead poor welding.
How to solve these problems?
Solution for poor welding
- Check the appearance of PCB product before operation, whether dirty oxidation and so on.
- Check the concentration of solder paste is beneficial to soldering.
- In generally, PCB does not need to be heated. If solder is bad, it can be heated with 35~50 ℃ in oven. And then put it on the machine and add the paste.
- Control the temperature of PCB welding at 55-80 ℃ and ensure sufficient preheating time。
- Use of flux with correct way.
- Strictly control the storage time and environmental conditions of the storage process, and strictly operate the production process
- Use the solvent to clean up the sundries, and if it is silicone oil, a special cleaning solvent is needed to wash it.
- Increase the temperature of the tin furnace and lengthen the solder time to reflow the excess tin to the tin furnace.
- Increasing the preheating temperature, can reduce the wetting heat required by the substrate, increase the flux effect.
- Change the proportion of flux, slightly reduce the proportion of flux. The high proportion is easy lead to short as thick tin,the low proportion easy lead to tin bridge and tin tip as thin tin.