Method of fabricating multilayer ceramic substrate

1. A method of fabricating a multilayer ceramic substrate comprising:

stacking one or a plurality of unfired ceramic greensheets on one or both sides of a previously fired ceramic substrate, thereby forming a stack, each unfired ceramic greensheet having a firing temperature substantially equal to or lower than a firing temperature of the previously fired ceramic substrate;

stacking a restricting greensheet on the unfired ceramic greensheet composing an outermost layer of the stack, the restricting greensheet having a higher firing temperature than each unfired ceramic greensheet;

firing the stack at the firing temperature of the unfired ceramic green sheets with or without pressure applied via the restricting greensheet while the stack is under restriction by the restricting greensheet, thereby integrating the stack; and

eliminating remainders of the restricting greensheet after the firing step, wherein the previously fired substrate and the unfired ceramic greensheets are made from different ceramic materials from each other.

2. The method according to claim 1 , wherein the previously fired substrate and the unfired ceramic greensheets are temporarily tacked together in the step where the unfired ceramic greensheets are stacked on the previously fired substrate.

3. The method according to claim 1 , wherein the restricting greensheet and the unfired ceramic greensheets are temporarily tacked together in the step where the restrictina greensheet is stacked on the unfired ceramic greensheets.

4. The method according to claim 1 , wherein the previously fired substrate and the unfired ceramic greensheets are made from different ceramic materials from each other, and the firing temperature of each unfired ceramic greensheet is equal to or lower than the firing temperature of the previously fired substrate.

5. The method according to claim 1 , wherein each unfired ceramic greensheet made from a low-temperature firable ceramic material which is fired at a temperature equal to or lower than 1000° C.

6. The method according to claim 1 , wherein the previously fired substrate and/or each unfired ceramic greensheet are made from a ceramic having any one of insulation characteristic, dielectric characteristic, magnetism, piezoelectric, and resistivity.

7. A method of fabricating a multilayer ceramic substrate having a cavity using the method of fabricating a multilayer ceramic substrate according to claim 1 , wherein the previously fired substrate is placed on a bottom of a portion where the cavity is to be formed, and an opening for forming the cavity is formed in the unfired ceramic greensheet which is stacked on the previously fired substrate, before or after stacking.

8. The method according to claim 1 , wherein a conductor pattern co-firable with the unfired ceramic greensheet is printed on said unfired ceramic greensheet and thereafter, said unfired ceramic greensheet is stacked on one or both sides of the previously fired ceramic substrate.

9. The method according to claim 1 , wherein the multilayer ceramic substrate has a surface and a back each one of which is dissimilar to the other.

10. The method according to claim 1 , wherein a thick film resistor is formed on the previously fired substrate and the thick film resistor is trimmed for adjustment of a resistance value, and thereafter the unfired ceramic greensheet is stacked on the previously fired substrate.

11. A method of fabricating a multilayer ceramic substrate having a stepped cavity comprising:

stacking one or a plurality of unfired ceramic greensheets on one or both sides of a previously fired ceramic substrate, thereby forming a stack, each unfired ceramic greensheet having a firing temperature substantially equal to or lower than a firing temperature of the previously fired ceramic substrate;

stacking a restricting greensheet on the unfired ceramic greensheet composing an outermost layer of the stack, the restricting greensheet having a higher firing temperature than each unfired ceramic greensheet;

firing the stack at the firing temperature of the unfired ceramic green sheets with or without pressure applied via the restricting greensheet while the stack is under restriction by the restricting greensheet, thereby integrating the stack; and

eliminating remainders of the restricting greensheet after the firing step,

wherein the previously fired substrate is placed on a bottom of a portion where the cavity is to be formed, and an opening for forming the cavity is formed in the unfired ceramic greensheet which is stacked on the previously fired substrate, before or after stacking, and

wherein every time a predetermined number of the unfired ceramic greensheets corresponding to a number of layers of one step of the stepped cavity is stacked on the previously fired substrate, the restricting greensheet are stacked on the unfired ceramic greensheet into the stack, and the stack is fired while being under restriction by the restricting greensheet, thereby fabricating a new fired substrate with one step of cavity, and thereafter, another predetermined number of the unfired ceramic greensheets corresponding to a number of layers of a subsequent step of the stepped cavity and the restricting greensheet are stacked on said new fired substrate into a stack, and the stack is fired while being under restriction by the restricting greensheet, after remainders of the restricting greensheet for fabrication of said new fired substrate has been eliminated, repeatedly so that the multilayer ceramic substrate having the stepped cavity is fabricated.