Magnesium zinc titanate powder with a barium boron lithium silicate flux and a multilayer ceramic COG capacitor made therefrom
AssigneeMRA Laboratories, Inc.
InventorsGaleb H. Maher, Samir G. Maher
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Abstract
In a start powder mixture of magnesium zinc titanate and a barium lithium boro-silicate flux, it is discovered that the addition of lithium to the flux enables the manufacture of multilayer ceramic capacitors using the powder mixture, that perform to the COG standard including an accelerated life test. This addition of lithium also makes possible the sintering to maturity of COG multilayer capacitors at temperatures as low as 950° C., which in turn allows the use of silver-palladium alloy buried electrodes of high silver and low palladium content which in turn lead to higher capacitor Q and lower manufacturing costs.
Claims18
A dielectric ceramic powder mixture consisting essentially of agglomerates, each of said agglomerates comprising a homogenous group of two kinds of powder particles having been mildly calcined and superficially co-reacted to bind said group of powder particles together to form said each agglomerates, said two kinds of powder particles in said each agglomerates being comprised, respectively, of from 87 to 98 weight percent of a magnesium zinc titanate powder, and from 2 to 13 weight percent of a powdered barium lithium boro-silicate sintering flux.
A method for making a dielectric ceramic powder mixture comprising:
- a) combining from 87 to 98 weight percent of a magnesium zinc titanate and from 2 to 13 weight percent of a powdered barium lithium boro-silicate sintering flux;
- b) mixing said combined powders to form a homogenous powder mixture;
- and
- c) mildly calcining said homogeneous mixture at from 600° C. to 750° C. to obtain a powder comprised of agglomerates of said homogeneous powder mixture wherein each of said agglomerates has essentially the same composition of magnesium zinc titanate and barium lithium boro-silicate as in said combined powders.
A method for making a multilayer ceramic capacitor comprising:
- a) making a slurry by milling in an organic vehicle a dielectric ceramic powder mixture consisting essentially of agglomerates, each of said agglomerates comprising a homogenous group of two kinds of powder particles having been mildly calcined and superficially co-reacted to bind said group of powder particles together to form said each agglomerates, said two kinds of powder particles in said each agglomerates being comprised, respectively, of from 87 to 98 weight percent of a magnesium zinc titanate powder, and from 2 to 13 weight percent of a powdered barium lithium boro-silicate sintering flux;
- b) forming layers of said slurry and drying the layers and depositing a first patterned film of palladium silver alloy on one of said dried layers;
- c) forming a stack by stacking at least a second green ceramic layer over said first patterned alloy film stacking, depositing a second patterned alloy film over said second green ceramic layer, and forming at least a third green ceramic layer over said second patterned film;
- d) sintering said stack at a temperature within the range of 950° C. to 1120° C. to form a dense mature ceramic body;
- e) applying a silver paste to the ends of said body to which an edge of said first and second alloy patterns may extend;
- and
- f) heating said stack to cure said silver paste and form terminations contacting each of said first and second alloy layers.
A multilayer ceramic capacitor comprising a dense mature ceramic body and at least one sheet electrode buried in said body, said at least one electrode extending to one body end, said body having been co-fired with said buried electrode;
- said body being comprised of from 87 to 98 weight percent of a magnesium zinc titanate and from 2 to 13 weight percent of a powdered barium lithium boro-silicate sintering flux.
Dependencies are inferred from the claim text.