A system and method for depositing an elec­trical insulator over a substrate are disclosed. The system (20) includes first, second, and third chambers (24, 26, 28), the second chamber (26) being a deposition chamber for depositing the in­sulator over the substrate. A plurality of gas gates (34, 36) communicate the second chamber with the first chamber, and the second chamber with the third chamber in series relation. An endless con­veyor (40, 42, 44) in each of the chambers trans­ports the substrate through the chambers in suc­cession. A plurality of absolute pressure control pumps (56, 58, 60) maintain unidirectional gas flow from the first and third chambers into the second chamber to maintain a desired degree of isolation, which may be expressed as a concentra­tion ratio of the gas constituents between the chambers.