Heat dissipation assembly

1. An assembly for dissipating heat in an electronic circuit, the assembly comprising:

an alloy heat spreader having a high thermal conductivity for drawing heat from the electronic circuit, the heat spreader being a plate having mounts for connecting the heat spreader to the electronic circuit;

a ceramic substrate bonded to the heat spreader on a first side of the substrate, the substrate having a ground plane embedded in the substrate, the heat spreader extending over a portion of the substrate and the ground plane, at least a portion of the substrate extending above the heat spreader, the heat spreader being removably connected to the substrate via fasteners for replacing the electronic circuit and the heat spreader with a replacement electronic circuit and a replacement heat spreader, the substrate having a lower thermal conductivity than a thermal conductivity of the heat spreader;

a heat slug having a high thermal conductivity and being bonded to the heat spreader via electrically conductive connector material on a first side of the heat slug and adjacent to the substrate, the heat slug having a uniform cross-sectional shape; and

an alloy backplate having a high thermal conductivity and being connected to the substrate on a second side of the substrate opposite the first side of the substrate and bonded to the heat slug on a second side of the heat slug opposite the first side of the heat slug via electrically conductive connector material, the heat spreader, the substrate, and the backplate forming a layered stack of materials with a highly thermally conductive path for cooling the electronic circuit, the heat slug having a lower material strength than material strengths of the heat spreader, the substrate, and the backplate, wherein the heat spreader, the substrate, and the backplate have coefficients of thermal expansion differing by less than 3 parts-per-million per degree Celsius from each other and differing by at least 3 parts-per-million per degree Celsius from a coefficient of thermal expansion of the heat slug, the connector material bonding the heat slug to the heat spreader and the connector material bonding the backplate to the heat slug being reversibly compressible so as to form a constant, thermally conductive connection between the heat slug and the heat spreader and between the backplate and the heat slug.

2. The assembly of claim 1 , wherein the substrate includes a cavity having a first opening and a second opening on opposite sides of the substrate, and the heat slug is disposed in the cavity and connected to the heat spreader near the first opening and connected to the backplate near the second opening.

3. The assembly of claim 1 , wherein the heat spreader is formed of a single piece of material.

4. The assembly of claim 1 , wherein the heat spreader is shaped to have continuous radio frequency grounding.

5. The assembly of claim 1 , wherein the substrate is configured to be connected to the electronic circuit via a low inductance wire.

6. The assembly of claim 1 , wherein the connector material bonding the heat slug to the heat spreader and the connector material bonding the backplate to the heat slug are epoxy.

7. The assembly of claim 1 , wherein the connector material bonding the heat slug to the heat spreader and the connector material bonding the backplate to the heat slug are solder.

8. The assembly of claim 1 , wherein the heat slug and the substrate are made of a preformed material so that stresses induced when the layered stack is at a minimum temperature and stresses induced when the layered stack is at a maximum temperature are of equal magnitude, so that maximum induced stress is minimized.

9. The assembly of claim 1 , wherein the backplate includes a planar surface, and the substrate and the heat slug are connected to the backplate via the planar surface.