Flammability of microelectronic components, particularly those using molding compounds as encapsulants, is a safety concern that can be mitigated by the use of appropriate materials. In most common plastic encapsulants, Flame Retardant capability is acquired through the use of bromine-based aromatic compounds. These brominated flame retardants (BFRs) are preferred because of their low cost and effectiveness, especially in their ability of to ensure compliancy with industrial flammability standards. Thus, the flame retardants with aromatically bonded bromine have the highest market share, primarily because they tend to be resistant to breakdown over time or temperature. When the epoxy encapsulants are exposed to heat or open flames, the epoxy compounds break down and in the process release free radicals such as OH and H in the form of flammable gases. BFRs work by chemically interfering with the gas phase of the combustion process. However, bromine containing compounds have also been found to form dioxins during the combustion process, and these active dioxins are considered to be carcinogens by the Environmental Protection Agency (EPA). Therefore, a strong trend is emerging for selecting bromine replacement materials that is focused primarily on environmental, health, and reliability concerns.
Phosphorous based flame retardants (PFRs) have been considered as alternate replacement materials to BFRs. Phosphorous based flame retardants impede the combustion process through multiple reaction steps. These PFRs are primarily divided into organic and inorganic compounds. Organic phosphorous based flame retardants currently used in electronic applications consist of phosphates, phosphonates, phosphinates, and phosphine oxides. However, the addition of organic phosphorous into molding compounds tends to increase the water absorbing property of the plastic encapsulants, increasing the probability of popcorning and moisture related failure mechanisms.
Inorganic phosphorous compounds have been used, including red phosphorous, to overcome the drawbacks of the organic compounds. Red phosphorous has been used and has exhibited a very high flame retarding capability. However, consistent concerns about long-term stability of red phosphorous-based fire retardants with moisture have limited their extensive use in microelectronic applications. When red phosphorus reacts with water an electrolyte is produced. Improvements in formulating and processing the red phosphorus-based compounds have not eliminated this problem. Using red phosphorus as an alternative to bromine compounds for flame retardancy is just one approach and not all epoxy manufacturers use it, therefore this issue does not apply uniformly across the industry.
