This invention relates to thick film conductors employing nickel oxide.
Thick film conductors are well known in the art and are acquiring increasing importance in view of trends in the electronic industry towards smaller and smaller circuits. In the past, thick film conductors have been produced wherein the circuit was of a noble metal. By noble metal is meant gold, silver, palladium, platinum mixtures thereof and alloys thereof. More recently, considerable efforts have been expended in attempting to produce thick film conductors employing base metals such as copper, nickel, and cobalt. Examples of such efforts are described, for example, in:
U.S. Pat. No. 4,070,517 to Kazmierowicz; and
U.S. Pat. No. 4,070,518 to Kazmierowicz; and
U.S. Pat. No. 4,072,771 to Grier; and
U.S. Pat. No. 4,079,156 to Youtsey et al; and
U.S. Pat. No. 4,082,898 to Miller et al; and
U.S. Pat. No. 4,122,232 to Kuo; and
U.S. Pat. No. 4,140,817 to Brown; and
U.S. Pat. No. 4,158,716 to Miller et al; and
U.S. Pat. No. 4,172,919 to Mitchell.
Unfortunately, the prior art suffers from a number of disadvantages. The use of nickel is burdensome because nickel powder tends to oxidize on storage. The oxidation of nickel powder on storage gives the nickel powder an oxide coating which means that the powder is in reality a composition of nickel metal and nickel oxide of varying proportions depending upon the degree of oxidation.
Another severe problem of the prior art is the necessity of employing an inert atmosphere such as that of nitrogen or a reducing atmosphere such as that of hydrogen. Nitrogen atmospheres and the special belt furnaces necessary to employ a nitrogen atmosphere are expensive. Hydrogen atmospheres, in addition to being expensive, are potentially explosive and also require special furnaces for their utilization.
It is therefore an object of the present invention to provide an improved thick film conductor paste substantially free of one or more of the disadvantages of prior pastes.
An additional object of the present invention is to provide a process and a thick film conductor paste that can be fired in air.
Another object of the present invention is to provide an improved thick film conductor paste which does not employ a noble metal.
Yet another object of the present invention is to provide an improved thick film conductor paste which does not require the presence of nickel metal but will tolerate the presence of nickel metal.
Yet another object of the present invention is to provide a thick film conductor paste that has a long shelf life.
Still another object of the present invention is to provide an improved method for making a thick film conductor.
Still another object of the present invention is to provide an improved thick film conductor.