Glass to Metal Seals

Introduction

Glass to metal seals are vacuum tight assemblies, in which metallic wires, tubes, eyelets or flanges are firmly bound in a glass material. These are normally used as insulated feed-throughs for electrical connections in hermetically sealed devices and UHV systems as well as mounts for electrodes, filaments etc. The materials chosen have the properties of wettability by glass, matched temperature coefficients of expansion and low outgassing rates even at elevated temperatures making them suitable for application in ultra high vacuum systems. This technology has been developed for various types of glass to metal seals- like flat bead seals, circular bead seals, eyelet type seals, tubular seals, wafer base seals and glass to metal feedthroughs for high pressure applications. All these types of seals are being produced in B.A.R.C. and are being used in several in-house applications in the Department of Atomic Energy and its research centres.

Technology being offered

Technology for the fabrication of flat bead seals and Circular Bead Seals with the desired configuration of pins is being offered at present. Along with this, the design of mounting jigs and other fixtures will also be given.

Specifically, (a) flat bead seals with five pins in one line configuration in a glass bead of approximate dimensions 23 mm x 6 mm x 4 mm. This type of seal is presently being used as a mount for the electron emitting filament and a shield plate in the mass spectrometer. (b) circular bead seals with a diameter of 17 mm and all the eight pins which are arranged in a configuration suitable for mounting the three filaments of a thermal ionization mass spectrometer.

Although technology being transferred covers only these two specific types of seals, the recipient party of this technology will be able to produce seals with any desired pin configuration as required by the customer/user after designing and making of necessary jigs and fixtures.

Applications

As electrical feed throughs and as insulating mounts for hot filaments, electrodes etc. in instrumentation, vacuum gauges, electronic devices and high / ultra high vacuum systems.

Raw Materials Required

Special glass tubes of required sizes, Glass powder, pins of iron-nickel cobalt alloy (Kovar or Fernico etc.), LPG, Oxygen and cleaning chemicals.

Infrastructure Required

Controlled atmosphere furnace, annealing furnace, fabrication facilities for making jigs and fixtures, wafer base sealing machine, facility for working on glass (cutting, polishing, blowing etc.), provision for acid cleaning and disposal of cleaning fluids in a well ventilated room of about 12' x 12' area.

Manpower

For a production capacity of approximately 1000 flat bead seals per month two glass technicians are required. Alternatively, these technicians can make about 500 circular bead seals (with straight pins in a desired pin configuration) per month.

For further information please contact

Head,
Technology Transfer & Collaboration Division,
Bhabha Atomic Research Centre,
Trombay, Mumbai - 400 085
Tel : 091-022-25505337/25593897
Fax : 091-022-25505151
E-mail : headttcd@barc.gov.in