Design Considerations for Emergency and Standby Power Supplies Supporting Wafer Fab Operations
Alan Gillespie
(FM Global)
Even with well-engineered and reliable electrical power supplies, power outages can and do occur. This could be the result of external electrical faults, internal electrical faults or loss of external power generation at one of more power stations. Loss of power has the potential to affect life safety systems, critical control systems, critical support services as well many fab tools. There is also the potential for spoilage for any work in process (WIP). This hazard is generally acknowledged by the semiconductor industry with most Fabs installing uninterruptable power supplies (UPS) and emergency power generation systems. The design of UPS and emergency power generation systems require careful consideration to ensure that all critical systems are included and that the supplies will last long enough to supply these critical loads until normal power supplies are reinstated. Normally UPS and emergency power systems are in standby and rarely get used. It is critical that the design of these systems allows them to be realistically tested on a periodic basis. Large Fabs can have power demands in the 100’s of MW’s. Providing 100% UPS and emergency power generation is generally not practical. However, the design case needs to consider the potential consequences of not providing emergency power generation for all loads. There is the potential for product spoilage and significant interruption to production operations. This paper will discuss the design considerations associated with UPS systems and emergency power generation to minimise the impact of a power outage to fab operations and to ensure a reliable emergency supply is available for life safety systems, critical support services and fab tools.