NOVELTY - A low temperature co-fired ceramic (LTCC) structure is formed by forming first and second LTCC structures each comprising a first side including cavities and a second side, subjecting the LTCC structures to pressure, arranging the structures, and subjecting the structures to a third pressure to join the first LTCC structure to the second LTCC structure.    USE - For forming an LTCC structure used to form electronic devices, e.g. ceramic capacitors, multi-layered ceramic integrated circuits (MCIC), multichip modules, integrated circuit packaging, high temperature sensors, fuel cells, and fuel cell reformer systems.    ADVANTAGE - The inventive method increases the flatness of portions of LTCC structures. It forms structures having cavity in each opposing faces that produces cavity floors with a flatness variation of less than 1 mil/inch.    DETAILED DESCRIPTION - Formation of a low temperature co-fired ceramic structure having an open cavity on each of first and second opposing sides comprises forming a first LTCC structure comprising a first side including cavities (18, 20, 22) and a second side, subjecting the first LTCC structure to a first pressure, forming a second LTCC structure comprising a first side having cavities (38, 40) and a second side, subjecting the second LTCC structure to a second pressure, arranging the first LTCC structure and the second LTCC structure so that the first LTCC structure second side faces the second LTCC structure second side, and subjecting the first and second LTCC structures to a third pressure to join the first LTCC structure to the second LTCC structure. An INDEPENDENT CLAIM is also included for an LTCC structure comprising a first side having a cavity having a floor and a second side opposite the first side having a cavity having a floor, where the first side cavity floor is formed to have a flatness of less than or equal to1 mil/inch.    DESCRIPTION OF DRAWING(S) - The figure is a side elevational view of an LTCC structure formed by laminating the third stack.    Cavities (18, 20, 22, 38, 40)