Method for forming sealed co-fired glass ceramic structures

A method for forming a co-fired glass ceramic structure comprising at least one metallized green sheet of a first crystallizable glass in a thermally decomposable binder having a pattern of conductive paste comprising conductive metal, a second crystallizable glass and a thermally decomposable binder, said pattern comprising at least one via, the method comprising the steps of:

• firing said green sheet according to the following firing cycle steps:
• a. preheating said green sheet to a first temperature in a furnace with a neutral or reducing ambient so as to effect pyrolysis of said thermally decomposable binders, wherein said first temperature is insufficient to coalesce said first crystallizable glass or said conductive paste;
• b. introducing a steam ambient into said furnace and then heating said green sheet in said furnace at said first temperature to burn off said pyrolyzed binders;
• c. replacing said steam ambient with a neutral or reducing ambient and raising the temperature to a second temperature to effect densification and crystallization of said first and second glasses;
• d. maintaining said second temperature for a predetermined time to effect sealing of said at least one via wherein for a first portion of said predetermined time, the ambient in said furnace is a neutral or reducing ambient and for a second portion of said predetermined time, the neutral or reducing ambient is replaced with a steam ambient;
• and
• e. cooling said structure.

A method for forming a co-fired glass ceramic structure comprising a plurality of stacked and laminated metallized green sheets of a first crystallizable glass in a thermally decomposable binder, at least one of the metallized green sheets having a pattern of conductive paste comprising conductive metal, a second crystallizable glass and a thermally decomposable binder, said pattern comprising at least one via, and at least one of the metallized green sheets having a pattern of conductive paste comprising conductive metal, a thermally decomposable binder and no crystallizable glass, the method comprising the steps of:

• firing said green sheets according to the following firing cycle steps:
• a. preheating said green sheets to a first temperature in a furnace with a neutral or reducing ambient so as to effect pyrolysis of said thermally decomposable binders, wherein said first temperature is insufficient to coalesce said first crystallizable glass or said conductive paste;
• b. introducing a steam ambient into said furnace and then heating said green sheets in said furnace at said first temperature to burn off said pyrolyzed binders;
• c. replacing said steam ambient with a neutral of reducing ambient and raising the temperature to a second temperature to effect densification and crystallization of said first and second glasses;
• d. maintaining said second temperature for a predetermined time to effect sealing of said at least one via wherein for a first portion of said predetermined time, the ambient in said furnace is a neutral or reducing ambient and for a second portion of said predetermined time, the neutral or reducing ambient is replaced with a steam ambient;
• and
• e. cooling said structure.