Surface preparation of ceramic substrates for metallization

In a process for metallizing a surface of a ceramic substrate which includes adhesion promoting the surface with an alkali metal composition containing one or more alkali metal compounds and subsequently depositing metal on the adhesion promoted surface, the improvement which comprises:

• providing said alkali metal compound(s) in the form of a multiplicity of discrete solid pellets, each pellet having a mass between 150 mg and 200 mg;
• contacting the ceramic surface with a quantity of said alkali metal composition which when molten will spread across and uniformly wet the ceramic surface;
• heating the alkali metal composition and the substrate for a time period between 5 to 20 minutes at a temperature between about 450.degree. C. and about 700.degree. C. to melt the pellets in situ on the ceramic surface, the melting pellets spreading out and uniformly wetting the ceramic surface, said time and temperature being sufficient to adhesion promote the ceramic surface and render it receptive to subsequent adherent metal deposition,
• and in a later step plating an adherent metal layer on the treated ceramic surface or selected parts thereof.

A process for producing a printed circuit on a surface of a ceramic substrate comprising:

• (a) contacting the ceramic surface with an alkali metal composition comprised of an alkali metal compound in the form of a multiplicity of discrete solid shapes sized 25 mg to about 500 mg, each shape having a preselected mass, said shapes being present in a quantity which when molten will spread across and uniformly wet the ceramic surface;
• (b) heating the alkali metal composition and the substrate for a time period and at or above a temperature at which the alkali metal composition becomes molten in situ on the ceramic surface, spreading out and uniformly wetting the ceramic surface, and which is sufficient to adhesion promote the ceramic surface and render it receptive to subsequent adherent metal deposition
• (c) treating the ceramic surface to activate it for electroless metal deposition;
• (d) depositing metal onto the activated surface;
• (e) removing portions of the deposited metal to produce a metal printed circuit conductor pattern adhering to the surface of the ceramic substrate.

The process for producing a metallized conductor pattern on a surface of a ceramic substrate having a surface roughness less than about 0.7 micrometers, the process comprising:

• contacting the surface with an alkali metal composition comprised of one or more alkali metal compounds in the form of a multiplicity of discrete solid shapessized 25 mg to about 500 mg, said shapes being present in a quantity which when molten will spread across and uniformly wet the ceramic surface;
• heating the alkali metal composition and the substrate for a time period and at or above a temperature at which the alkali metal composition becomes molten in situ on the ceramic surface, spreading out and uniformly wetting the ceramic surface, and which is sufficient to adhesion promote the ceramic surface and render it receptive to subsequent adherent metal deposition;
• rinsing said surface with an aqueous solution;
• neutralizing said ceramic surface with an acid;
• repeating said rinsing step;
• contacting said ceramic surface with an activator solution providing stannous tin ions and precious metal ions, to activate said surface for electroless metal deposition;
• and
• contacting said activated surface or selected parts thereof with a metal depositing solution for a time period sufficient to form a metal layer thereon.