Glass Seal

Background

Glass to metal (GTM) sealing uses a vitreous glass, devitrifying glass or glass composite to form a hermetic seal. GTM seals can be formed using paste, preforms or dry frit powder.

Optical windows often use a sealing glass for hermeticity and dielectric properties. For some window caps, the window itself can be directly fused to the flange. The process requires heating the window glass beyond the softening point to the working range of the glass. The glass will flow to touch, wet and seal to the flange. Using a fixture, the result is a flat and smooth window cap assembly.

Matched vs. Compression Seals

For electrical feedthroughs, there are two types of seals. For a “matched seal”, the pin closely matches the glass and housing in terms of Coefficient of Thermal Expansion (CTE). A standard combination of materials for a matched seal is Kovar pin, Corning 7052 glass, and Kovar housing. This mitigates residual thermal stress that forms upon solidification and cooling of the assembly.

A “compression seal” uses a housing with relatively large CTE (Alloy 52 pin, Corning 9013 glass, SST housing). Upon cooling, the glass will be placed under radial compression. Compression seals are used in situations that require high mechanical strength. Historically, they are the predominant design for military feedthroughs.

Custom Glass Frit Formulation

Besides these routine matched and compression glass to metal seals, STC Material Solutions services challenging seals using alternatives to commercial sealing glass products. For the product line of opto-electronic window or lens assemblies, we use sapphire, optical spinel, diamond, optical filter glass and others in various metal flanges. STC Material Solutions uses commercially available sealing glasses or those from our stock. We formulate and produce specialty glasses for various seal applications that may be different from the routine matched and compression sealed assemblies. Please refer to our Sealing Glass List under Corporate Literature. The Sealing Glass List contains glasses STC Material Solutions formulated from scratch or modified from commercially available options.

STC Material Solutions has its capability of sealing metal and glass together regardless if it is for an electrical feedthrough or opto-electronic window application. If there is a lack of materials to choose from, we may formulate per your need. For the specialty glass matter, STC Material Solutions is unique. We might be the only company or one of very few who can formulate or are interested in formulating a sealing glass per a specific need.

Examples of Work

Some example applications where we have innovated glass science solutions include:

• Glass sealing silica and silica.
• Glass sealing optical fiber and fiber mount.
• Glass coating over Cu, Al, SST, etc.
• Glass sealing at low temperature to prevent heat exposure damage on other components.
• Application temperature higher than sealing temperature. Solution based on nucleation and crystallization kinetics of devitrifying glass formula.
• Glass coating on Al suitable to withstand sudden heat exposure without cracking or crazing.
• Glass coating OD and ID of a tube of virtually all metals and alloys.

STC Material Solutions is also a source for dielectric coatings over metals or alloys. If your substrate needs to have a vitreous coating over a ceramic, STC Material Solutions can provide a glazing service. Again, we may be able take care of both the selection of the glazing material and the glazing process. Many of the sealing materials can be applied as a coating as well but we may be able to formulate one for the specific need.

Please contact STC Material Solutions using 1-714-546-8522 or info@ijresearch.com.

Please click for a PDF copy of the brochures, Glass to Metal Seal.

Electrical feed through or micro-electronic package: