Sulfur-free paper is used to prevent PCB oxidation, during which there is a silver precipitation process, hence PCB is also known as silver-plated board. The silver plating process has become one of the important methods for the surface treatment of printed circuit boards. However, silver has a strong affinity for sulfur. When encountering hydrogen sulfide gas or sulfide ions, it is easy to produce silver salts (Ag2S) that are difficult to dissolve in the air.
Due to the rapid deposition rate of silver, a low-density silver precipitate layer forms, making it easy for copper beneath the silver layer to come into contact with air. This necessitates increasingly thicker silver coatings to achieve antioxidant properties. This means thicker silver layers must be deposited on sulfur-free paper during production, which can increase costs and the likelihood of solderability issues, such as micro-gaps and poor焊接 quality. Sulfur-free gloves must be worn when handling silver plates. During observation and transfer, the silver plates should be separated from other objects using sulfur-free paper. At the end of the specified 8-hour period, the silver plates should be separated from the packaging bags using sulfur-free paper. When removing the packaged silver plates from the silver coating line.

In summary, the intention of using sulfur-free paper is as follows:
Sulfur-free paper itself contains no sulfur and does not react with the appearance of the PCB silver layer.
Sulfur-free paper can act as an insulator, preventing silver layers beneath the copper layer from reacting with oxygen in the air.
Wholesale硫酸纸 advises on sulfur-free paper storage precautions:
Stored in a warehouse with gentle cool air, protected from direct sunlight, away from fire sources and water. Be mindful of high temperatures, moisture, and prevent contact with liquids (especially acids and alkalis). The main material of PCB is copper. The copper layer is very simple. Oxygen in the air is the oxidizing agent. This reaction produces deep brown cuprous oxide.
Above, we've explained the usage intention and storage factors of sulfur-free paper; we hope it's helpful to all.