In the process of PCB design and production, have you ever encountered the issue of poor solderability? For engineers, when a PCB suffers from poor solderability, it often necessitates re-soldering or even remanufacturing, leading to significant inconvenience. So, what causes poor solderability in PCBs, and how can we prevent it? Typically, the primary reason for poor solderability is that certain areas of the circuit’s surface are not properly coated with solder. Such PCBs exhibit the symptoms illustrated in the following figure:

1. PCB boards that suffer from poor solderability are a common issue in manufacturing. There are several reasons contributing to this problem, which can be summarized as follows:

2. Grease, impurities, and other debris can adhere to the surface of the PCB. Additionally, grinding particles left during the substrate manufacturing process or residual silicone oil can also hinder proper soldering.

3. If any of the above issues are detected during inspection, solvents can be used to clean the debris. However, silicone oil requires a special cleaning solvent for effective removal.

4. Another factor leading to poor solderability is prolonged storage time or exposure to humid environments during manufacturing, which can cause oxidation on the tin surface and dullness on the copper surface of the PCB.

5. In such cases, simply using flux may no longer be effective, and technicians may need to perform re-soldering to improve solderability.

6. Insufficient temperature or inadequate soldering time during the PCB assembly process, as well as improper use of flux, can also result in poor solderability.

7. Typically, the soldering temperature should be 55 to 80 degrees Celsius higher than the melting point of the solder. Inadequate preheating time can contribute to poor solderability.

8. The distribution of flux on the circuit surface is influenced by its specific gravity. Checking this can help eliminate the possibility of using incorrect flux due to mislabeling or poor storage conditions.

9. The quality of solder material and the cleanliness of terminals directly impact the final soldering result. Impurities in the solder or dirty terminals can lead to poor solderability.

10. Regularly inspecting solder purity and ensuring terminal cleanliness during soldering are crucial steps to prevent soldering issues. Non-compliant solder should be replaced with standard solder.

11. Apart from poor solderability, another related issue is tin stripping, which mainly affects tin-lead-plated substrates. Tin stripping exhibits symptoms similar to poor solderability but is more severe as solder adhered to the tin road tends to pull back into the tin furnace during detachment.

12. In cases of tin stripping, simply re-soldering may not resolve the issue, necessitating the return of the PCB to the factory for repair.