FAQ
What is Hermetic Seal?
- Hermetic seal means forming a leak tight seal by means of brazing/soldering alloy. Typically the sealing process is
performed in a furnace under atmospheres such as hydrogen, air, or in a vacuum.
What is the most popular brazing materials for hermetic Seals?
- CuSiL (Silver and copper) is the most popular.
What is the most popular ceramic material for Hermetic Seals?
- Al2O3 (Aluminum Oxide) 96% purity and up.
What is the bonding strength of Hermetic Seal?
- Strength can be up to 4000 PSI.
What are popular glasses for Glass-to-Metal seals?
- AlKaLi Barium (Corning 9010) for compression seal.
- AlKaLi Borosilicate (Corning 7056) for matched seal.
What is Ceramic Metallization?
- A coating process using a metallic layer on ceramic to receive conductivity and is suitable for brazing or soldering to
other components.
What kind of Ceramic Metallization does Complete Hermetics specialize in?
- High temperature MoLy Manganese (Mo/Mg). 500-1500 " thickness.
Do I need Nickel Plating after Ceramic Metallization?
- In general, Nickel plating of 100-200"is needed for better wettability and Mo/Mg protection. Electrolytic Nickel, QQ-N-290 or Electroless Nickel Plating is commonly used.
What is Brazing?
- Brazing is known as the ‘joining of two pieces of metal by fusing layer of brass or spelter between the adjoining surfaces.
The process basically involves a braze melting and flowing between the two pieces of material. This is commonly referred
to as ‘wetting’ and is absolutely critical - particularly when brazing ceramics. Today there are many materials that can be
fused to produce joints between materials - those that melt above ~450°C are classed, brazes, materials melting below
~450°C are called solders.
What is Wetting?
- If a braze alloy is melted between two ceramics, a poor joint is likely to result, because of poor wetting. Wetting is measured
in terms of the contact angle between the braze and substrate after melting. For good wetting, the contact angle (?) is less
than 90°; for poor wetting, the angle is greater than 90°.
What are Methods to Increase Wettability?
- In addition to a controlled atmosphere utilizing Nitrogen or Argon and vacuum environment, two methods are generally used
to increase wetting. The first method is to apply something to the surface of the ceramic in order for the braze to wet; common
surface treatments are metallization, metal coating, metal hydride treatment. The second method is to apply something to the braze to induce wetting.
What are Brazing Alloys?
- Brazing alloys are the alloys utilized for brazing. Currently, high temperature (appox. 1200°C) brazing of SiC and low temperature (420°C) active brazes, capable of joining ceramics in air versus a controlled atmosphere, are the most prospective alloys in the market.
What is High Temperature Active Metal Brazing?
- High-Temperature Active Metal Brazing process involves coating the ceramic with reactive or refractory metal (W, Ta, Cr, Mo)
then brazing using high temperature braze alloys, such as palladium or platinum based systems. Although, high temperature
alloys are not readily available commercially and the majority of active brazes are developed for moderate temperature use,
high temperature braze alloys have the potential for higher strength, oxidation resistance, and ductility at a larger range
of temperatures.
What is Reactive Air Brazing (RAB)?
- RAB is a novel brazing process that reactively modifies one or both ceramic surfaces with an oxide compound dissolved
in a molten noble metal alloy such that the newly formed surface is readily wetted by the remaining liquid filler material.
This technique forms a predominantly metallic joint directly in air without need of vacuum chamber/ inert cover gas or the
use of surface reactive fluxes.