Process for producing a ceramic multilayer substrate

DETAILED DESCRIPTION To produce a ceramic multilayer substrate, unfired, green ceramic foils are used.
The green ceramic foils are made of ceramic particles, an inorganic binder and an organic binder.
Suitable materials for these components are listed, for example, in U.
S.
Pat.
No.
5,085,720.
The green ceramic foils have a flexible structure and can be easily worked.
Thus, for example, the punching of holes for plated contactings (vias) is easily possible during this phase of the substrate production.
After the ceramic foils have been provided with the necessary plated contacting holes, they are filled with a conductive paste during a printing operation.
After that, in a further printing operation, the printed circuit traces are imprinted on the ceramic foils.
During printing, a conductive paste is used as a printing carrier which contains no highly volatile solvent.
The conductivity of the paste is produced by a great number of small metal particles, e.
g.
silver particles having a particle size of 0.
5 .
mu.
m-10 .
mu.
m.
As a printing carrier, the conductive paste contains a wax made of organic compounds that is solid to kneadable below a temperature range of approximately 40.
degree.
C.
to 70.
degree.
C.
, and above this temperature range changes, without decomposing, into the highly liquid state.
Particularly well suited for a preferred embodiment according to the present invention are conductive pastes consisting of a wax which changes into the liquified state at approximately 60.
degree.
C.
to 70.
degree.
C.
During the production of the printed circuit traces and the plated contactings on the green ceramic foils, the conductive paste is heated to a temperature of more than 70.
degree.
C.
, so that the paste becomes printable and exhibits the rheological properties necessary for the printing operation.
Such pastes are commercially available at present for other purposes, for example, under the description ENVIROTHERM pastes.
Since the printed paste contains no highly volatile solvent, no solvent diffuses into the green ceramic foils during the printing process either