Mechanically flexible cold plates for low power components
An assembled circuit board has a topology that defines positions, dimensions and power dissipation of components mounted to the circuit board, including a high power component and one or more low power components. A cold plate makes thermal contact to the high power component through a thermal interface material. A thermally conductive sheet overlays the circuit board and is formed to match the topology of the low power component or components. The sheet has a first portion that makes thermal contact with the cold plate and a second portion that overlays the low power component or components. The cold plate removes heat directly from the high power component and indirectly through the thermally conductive sheet from the low power component or components. The thermally conductive sheet conforms to the topology of the low power components either by preforming or by flexibility.
1. A method comprising:
obtaining a topology of an assembled circuit board, wherein the topology defines dimensions and locations of components on the circuit board, wherein the components include a high power component and one or more low power components;
attaching a cold plate in thermal contact with the high power component via a thermal interface material (TIM), wherein the cold plate and the TIM match the topology of the high power component in a first region; and
forming a thermally conductive sheet, wherein the sheet comprises a first portion that is thermally connected to the cold plate in the region of the high power component and a second portion that matches the topology of the one or more low power components, wherein the first portion of the thermally conductive sheet is attached to the cold plate by spring fingers around a periphery of the cold plate.
2. The method of claim 1 wherein forming the thermally conductive sheet includes plastically preforming the sheet to fit the topology within a tolerance of 1.0 millimeter (mm).
3. The method of claim 1 wherein the thermally conductive sheet is flexible, so that it can deflect to match the topology by about 0.5 mm for an applied force of up to 3 pounds per linear inch, for a separation of one inch between the perimeters of different components.
4. The method of claim 1 wherein forming the thermally conductive sheet includes forming the sheet to have a thermal conductivity not less than 40 Watts per meter Kelvin between the first portion and the second portion.
5. The method of claim 1 further comprising: assembling the thermally conductive sheet to the circuit board with the first portion of the sheet making thermal contact with the cold plate that overlays the high power component and with the second portion of the sheet overlaying the one or more low power components, wherein the sheet contacts the low power component or components of the circuit board via a separable thermal interface material, and the sheet conducts heat from the low power component or components to the cold plate.
6. The method of claim 5 further comprising: removing the thermally conductive sheet and the cold plate from the circuit board as a unit.
7. The method of claim 1 further comprising: making thermal contact between a plurality of cold plates and a plurality of first portions of the thermally conductive sheet, wherein the overall structure comprising cold plates and sheet allows for vertical displacement between the designed positions of the various cold plates, in order to adjust to tolerances in the assembled heights of the cold plates above the circuit board, wherein the assembly can absorb about 0.5 mm of height variation between a pair of cold plates for an applied force of up to 3 pounds per linear inch, given a separation of one inch between the perimeters of the different cold plates.
8. The method of claim 7 , wherein the vertical displacement between cold plates is enabled by flexing of the thermally conductive sheet.
9. The method of claim 7 , wherein the vertical displacement between cold plates is enabled by flexing or slippage of the thermal contact between the first portions of the sheet and the cold plates.
10. An apparatus comprising:
an assembled circuit board, which has a topology that defines positions and dimensions of components mounted to the circuit board;
a high-power component mounted to the circuit board;
a cold plate that makes thermal contact with the high power component through a first thermal interface material (TIM);
one or more low-power components mounted to the circuit board;
a thermally conductive sheet that is formed to match the topology and that overlays the circuit board, wherein the sheet comprises a first portion that makes thermal contact with the cold plate and a second portion that overlays the low power component or components, wherein the first portion is movably attached to the cold plate via spring fingers that surround a periphery of the cold plate.
11. The apparatus of claim 10 wherein forming the thermally conductive sheet includes plastically preforming the sheet to fit the topology within a tolerance of 1.0 mm.
12. The apparatus of claim 11 wherein the high power component protrudes from the circuit board to a first height and the low power component protrudes from the circuit board to a second height that is different from the first height.
13. The apparatus of claim 10 wherein forming the thermally conductive sheet includes forming the sheet to have a thermal conductivity not less than 40 Watts per meter Kelvin between the first portion and the second portion.
14. The apparatus of claim 10 further comprising a separable thermal interface material disposed between the sheet and the low power components mounted to the circuit board.
15. The apparatus of claim 10 further comprising coolant piping connected in fluid communication with the cold plate, wherein the thermally conductive sheet is attached to the coolant piping by a tab.