RoHS, which stands for Restriction of Hazardous Substances, is a certification that ensures electrical and electronic products comply with specific restrictions on the use of certain hazardous substances. The goal of RoHS is to protect human health and the environment by reducing the presence of harmful materials in electronic devices.

The RoHS directive was originally introduced by the European Union (EU) in 2002 and has since been adopted by many countries around the world. The directive restricts the use of six hazardous substances in electrical and electronic equipment (EEE). These substances are:

1. Lead (Pb): Lead is commonly found in solder used in electronic components and can be harmful to human health, especially in high concentrations.
2. Mercury (Hg): Mercury is often present in batteries, lamps, and switches. It is toxic and can have detrimental effects on the environment and human health.
3. Cadmium (Cd): Cadmium is primarily used in batteries and can be found in some electronic components. It poses risks to human health and the environment.
4. Hexavalent Chromium (Cr6+): This form of chromium is used in various industrial processes and can be found in coatings and finishes of electronic devices. It is known to be carcinogenic.
5. Polybrominated Biphenyls (PBB): PBBs are flame retardants used in plastics and can be found in circuit boards, cables, and connectors. They are harmful to human health and the environment.
6. Polybrominated Diphenyl Ethers (PBDE): PBDEs are also flame retardants commonly used in plastics and can be found in similar electronic components. They are known to persist in the environment and have toxic effects.

To obtain RoHS certification, manufacturers must ensure their products meet the restrictions set by the directive. This involves testing and verifying that the levels of the restricted substances in their products are below the permitted limits. Manufacturers are also required to maintain records and documentation to demonstrate compliance.

RoHS compliance is typically indicated by affixing a "CE" marking on the product, which stands for Conformité Européene. This marking indicates that the product meets the requirements of applicable EU directives, including RoHS.

RoHS certification is important for manufacturers, as it allows them to market their products in countries and regions that have adopted the directive. It also reassures consumers that the products they purchase are free from hazardous substances, thereby promoting environmental sustainability and human health protection.