In the modern electronics manufacturing industry, printed circuit boards (PCB) as the basic components of electronic equipment, its quality and performance are directly related to the reliability and service life of the final product. Therefore, the PCB circuit board storage conditions are particularly important. Reasonable storage conditions can not only extend the service life of PCB, but also effectively ensure its reliability and stability in the production and use process. In this paper, we will discuss the key conditions of PCB circuit board storage, including temperature, humidity, packaging, environmental cleanliness and anti-static measures, in order to provide a useful reference for the electronics manufacturing industry.

Temperature control

PCB circuit board storage temperature is one of the key factors affecting its performance. Excessively high temperatures can lead to aging or degradation of the PCB's substrate (e.g. FR-4, CEM-3, etc.), while excessively low temperatures may make the board brittle, increasing the risk of damage during processing or use. Therefore, PCB storage temperature should be controlled within a suitable range. Generally speaking, it is recommended that storage ambient temperatures be controlled between 15°C and 30°C, with an optimal range of 20°C to 25°C. This range of temperatures is effective in slowing down the aging of the materials and avoiding embrittlement of the boards due to excessively low temperatures.

Humidity Control

Humidity is also critical to the storage of PCBs. High humidity can cause PCBs to absorb moisture, which in turn affects their dielectric properties and increases the risk of layer separation or delamination. In addition, high humidity can cause corrosion or oxidation problems, damaging sensitive components. On the contrary, a low humidity environment may lead to static electricity accumulation, also causing damage to the PCB. Therefore, the relative humidity of the storage environment should be kept between 30% and 70% RH, preferably below 50% RH. For special types of circuit boards, such as high frequency PCBs, more stringent moisture-proof seals and low humidity environments should be used as their dielectric materials are particularly sensitive to humidity.

Packaging

The way PCBs are packaged has a direct impact on their storage quality. First of all, the PCB should be in the production process after the first time using vacuum packaging, and vacuum packaging bags should be placed inside the desiccant to ensure that the packaging is tight, to avoid contact with water and air. For PCBs that are not used for a long time, it is best to brush three-proof paint on their surfaces to protect them from moisture, dust and oxidation, thus prolonging the storage life. In addition, unpacked PCBs should be used up within a specified period of time (e.g., within 3 days), and if unused, they need to be re-sealed with static bags in a vacuum to prevent static electricity and moisture damage.

Environmental cleanliness

Dust and chemical contamination may lead to poor soldering or short circuit of PCB, therefore, the storage environment should be kept clean, dust-free, and free of corrosive gases.PCB should be stored in sealed storage cabinets or cupboards, avoiding contact with acid and alkali substances. Meanwhile, direct exposure of PCB to sunlight should be avoided to prevent material aging due to UV radiation.

Anti-static measures

Static electricity is a major threat during PCB storage. Electrostatic discharge (ESD) may damage sensitive circuits and pad surfaces on PCBs, leading to performance degradation. Therefore, the storage environment should take appropriate anti-static measures, such as using conductive storage boxes or anti-static bags, to ensure that PCBs are not subject to static interference. When contacting PCBs, operators should wear protective equipment such as anti-static gloves and anti-static bracelets to minimize the generation and accumulation of static electricity.

Storage period and reprocessing

The storage time for PCBs with different surface treatment processes varies. For example, the storage period of spray tin (HASL) is generally 6 months, more than the period of time is easy to surface oxidation or tin layer failure; chemical gold plating / immersion gold (ENIG) is relatively stable, the storage period is usually up to 12 months; and immersion silver is easy to oxidize, the recommended storage period of no more than 3 months. For PCBs with slightly oxidized surfaces, solderability can be restored through cleaning or re-plating. However, if multilayer boards or critical processes are damaged, it is recommended that they be scrapped to avoid potential reliability issues arising from their use.

Conclusion

In summary, the storage conditions of PCB circuit boards involve temperature, humidity, packaging, environmental cleanliness and anti-static measures and other aspects. Reasonable storage conditions not only extend the service life of the PCB, but also ensure the stability and reliability of its performance. Therefore, when storing PCBs, it is important to strictly comply with the above conditions to ensure their long-term preservation and effective use. At the same time, with the continuous development of the electronics manufacturing industry, the requirements for PCB storage conditions will also be more stringent and refined, which requires us to continue to explore and innovate in practice to better meet the needs of the industry development.