Microwave monolithic integrated circuit assembly with multi-orientation pyrolytic graphite heat-dissipating assembly

A microwave monolithic integrated circuit assembly, comprising:

• a microwave monolithic integrated circuit lying in an MMIC circuit plane and having a first region of relatively high heat production and a second region of relatively low heat production;
• and
• a heat-dissipating assembly in thermal contact with the microwave monolithic integrated circuit, the heat-dissipating assembly having a core comprising at least two pieces of pyrolytic graphite embedded within a casing and bonded to an interior wall of the casing, the at least two pieces of pyrolytic graphite comprising
• a first piece of pyrolytic graphite underlying the first region of relatively high heat production and having a high-thermal-conductivity x-direction of the first piece lying substantially perpendicular to the MMIC circuit plane,
• a second piece of pyrolytic graphite underlying the second region of relatively low heat production and having a high-thermal-conductivity x-direction of the second piece lying substantially parallel to the MMIC circuit plane.

A method for fabricating a microwave monolithic integrated circuit assembly, comprising the steps of:

• furnishing a microwave monolithic integrated circuit lying in an MMIC circuit plane and having a first region of relatively high heat production and a second region of relatively low heat production;
• fabricating a heat-dissipating assembly which has a relatively large dimension lying in a heat-dissipating-assembly plane and a relatively small dimension lying perpendicular to the heat-dissipating-assembly plane, the heat-dissipating assembly having a core comprising at least two pieces of pyrolytic graphite embedded within a casing and bonded to an interior wall of the casing, the at least two pieces of pyrolytic graphite comprising
• a first piece of pyrolytic graphite having a high-thermal-conductivity x-direction of the first piece lying substantially perpendicular to the heat-dissipating-assembly plane, and
• a second piece of pyrolytic graphite, having a high-thermal-conductivity x-direction of the second piece lying substantially parallel to the heat-dissipating-assembly plane;
• and
• assembling the microwave monolithic integrated circuit to the heat-dissipating assembly with the MMIC circuit plane parallel to the heat-dissipating-assembly plane and with the first piece of pyrolytic graphite underlying the first region of relatively high heat production and the second piece of pyrolytic graphite underlying the second region of relatively low heat production.