Thick film ceramic metalization has been utilized since the mid 1950's in projects such as high voltage klystrons
and TWT "traveling wave tubes" for RF and microwave applications. Since then the use of metalized ceramics
has expanded greatly. From simple insulators brazed into housings for the micro-electronic industry and LTCC
"low temperature co-fired ceramics" for imbedded circuits to large domes for housing intricate missile electronics.
Many types of ceramic materials can be metalized for electrical continuity or wire bonding using thin film screen
printing or sputter coating in vacuum of solder materials such as gold. These processes can only be utilized for
low temperature low vacuum application because the mechanical bond strength is not sufficient for large
expansion changes due to temperature.
Molybdenum Manganese thick film inks or pastes are used on aluminum oxide or beryllium oxide ceramics to
provide an expansion stable interface. The metal-oxide ink has a glass constituent that when fired (sintered) at
approximately 1300 degrees centigrade in a reducing or inert atmosphere, usually wet hydrogen or nitrogen the
glass phase in the oxide ceramics bond with the glass constituent in the metalizing ink forming a robust interface.
The ink is applied using various methods such as screen-printing, spraying, hand applied with a brush, using
needles such as hypodermic or even dipped. The metalization layer is 0.00035” (350 microinches) to 0.0015”
(1500 microinches thick depending on the ink formulation and application method.
The metalization layer is electrically conductive and can be plated with any electrolytic precious metal plating
chemistry such as gold, silver, copper, platinum or nickel, In most cases the metalization is plated with nickel then
it is sintered at approximately 650 degrees centigrade diffusing the nickel into the metalization creating a
protective coating and a strong bond.
Now having a nickel surface a metal component can be brazed to the ceramic using any number of braze alloys at
a variety of temperatures. CuSil or copper-silver is commonly used in single braze application. A thin preform or
paste material made from the alloy is placed between the metalized ceramic and the metal part, which is usually
kovar due to the ceramic and kovar complimentary (CTE) coefficient of thermal expansion. The assembly is then
brazed at just under 900 degrees centigrade for CuSil. Using another braze alloy material such as copper would
have a higher braze temperature or indium, which would have a much lower braze temperature. The material is
defined by the manufacturing process requirements and the application for finished product utilization.
The preceding information is an overview of the process. Pacific Advanced Components would be pleased to put
you in touch with the appropriate engineering group to best help you with your application. Please give us a
call at 916-947-2865 or email engineering@pacificadvanced.com.
| Molybdenum Manganese Thick Film Metalization on Oxide Ceramics |
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