Regen time vs. capacity calculation: Cryo-pumps need regeneration periodically. How often should this be done? The answer is: it depends how fast the cryo-pump surface is saturated with frozen gas. Let us say the cryo-pump has a capacity of 1000atmLiter; that is the amount of gas it can absorb before requiring regen. It is used to pump down a sputter machine which has a wafer counter. During each wafer processing, MFC1 flows at 100sccm, MFC2 flows at 50 sccm. Both flow for 60sec. A purging gas flows at 500sccm for 10sec after each wafer is processed. The machine also needs maintenance done every 1000 wafers. After the PM event the equipment needs to be pump down to 1mTorr using a rough pump followed by the cryo pump down to 10-8 torr. The chamber is about 100L. Assume the PM pump down and the processing gas described above account for all amount of gas captured by the cryo-pump. How many wafers will it take before regeneration is absolutely needed?