How to Solve Common Wave Soldering Defects

Wave Soldering Defects

The wave soldering process is the primary process that causes defects in PCBA components. It causes a defect rate of up to 50% in the entire PCBA assembly process. Wave soldering is best suited for through-hole components (components with leads inserted into drilled holes in the circuit board).

The following are some common problems and their solutions during the wave soldering process:

Incomplete Solder

Incomplete soldering occurs when the solder fails to adhere properly to the soldering points during the soldering process of electronic components. This can lead to weak solder joints or intermittent contact issues. Soldering defects may be caused by various factors, such as inadequate soldering temperature, insufficient flux, inadequate soldering time, dirty soldering surfaces, etc. To prevent the issue of poor soldering, you can implement the following measures:

• Ensure that the soldering temperature is appropriate to allow the solder to fully melt and effectively wet the soldering surface.
• Use an appropriate amount of flux to enhance the adhesion of the solder to the soldering surface.
• Control the soldering time to ensure that the soldering is fully completed but not too short.
• Clean the soldering surface before soldering to ensure that the soldering point is clean and free of contamination.
• Regularly check the soldering quality, detect, and promptly repair issues such as weak welds.

Void

Outgassing issues are a common challenge in wave and hand soldering. Porosity refers to the gas holes that appear in welded joints. The formation of pores may be related to the presence of oxides, grease, or impurities on the solder surface, or it may be caused by gas release during the soldering process. These pores may appear as tiny holes or larger cavities on the surface of the joint.

In through-holes, the correct copper plating thickness is critical, with a minimum of 25µm of copper thickness on the surface of the hole wall. At the same time, ensure that the soldering surface is clean and free of any oxides, grease, or impurities. Adjust soldering parameters, such as increasing soldering temperature and solder flow, to reduce gas generation and accumulation. Through these measures, porosity problems can be effectively reduced, and soldering quality and reliability can be improved.

Excess Solder

Common soldering beginners often believe that more solder is better, but excessive solder can lead to the component terminals and pins being engulfed in solder or the formation of bubbles in the middle of the solder joints, which are typically round and convex in shape.. Possible causes include excessive protruding lead length, insufficient flux, excessive solder drag, and improper nozzle stripping motion.

Excess solder can usually be removed using the tip of a hot iron. In extreme cases, a solder extractor or solder wick can also be helpful.

Solder Flag

The solder joint tip refers to the abnormal shape of the solder joint that appears during the soldering process, exhibiting a sharp or protruding form. After trimming, the solder joint tip needs to conform to the overall component foot and extend beyond the PCB by no more than 2mm.

The main causes of solder tip tinning issues include the soldering iron tip leaving the solder joint in the wrong direction, the soldering iron moving too slowly from the solder joint, poor solder quality, excessive impurities in the solder, and soldering at a temperature that is too low. The consequences of tipping include poor appearance and the potential to cause bridging. In high-voltage circuits, tip discharge may also occur.

To prevent the issue of solder joint sharpening, it is essential to focus on controlling the angle, speed, and temperature during the soldering process, choosing high-quality solder, and ensuring the proper functioning of the soldering equipment. Through proper soldering operations and quality control, the occurrence of solder joint sharpening can be effectively minimized, leading to improved soldering quality and reliability.

Cold  Solder

It is called solder disorder. The surface of the solder joints exhibits irregular marks and unevenness. Cold soldering is the same as virtual soldering. It is difficult to fully disclose during the production process. Users often need to use it for a period of time, which could range from days to months or even years. This will not only have extremely negative effects but also lead to extremely serious consequences. Due to the low strength of cold soldering, the conductivity is not good.

● The chain vibrates and is affected by external forces during cooling, causing the solder to become disordered.

● If the soldering temperature is too low or the chain speed is too fast, the viscosity of the molten solder will be too high, resulting in a wrinkled surface of the solder joint.

● To repair a cold solder joint, simply reheat the joint with a hot soldering iron until the solder flows.

Solder Joints Bridged or Shorted

Solder joint bridging is a common defect in wave soldering. The component pins are too close together, or the wave is unstable. The possible reasons are as follows: the soldering temperature is set too low, the soldering time is too short, and the soldering temperature drops after the soldering is completed. The time passes too quickly, and the amount of flux sprayed is too minimal.

In this case, it is necessary to check the waveform and confirm whether the soldering coordinates are correct. This can be improved by increasing the soldering temperature or preheating temperature, extending the soldering time, prolonging the cooling time, and increasing the amount of flux sprayed.