Electronic assembly and casing therefor
A secure control unit is provided with a completely sealed casing ( 22 ) of which at least one wall ( 24 ) forms a heat sink. The circuit board provided in the casing ( 22 ) is designed such that all of the heat generating components ( 16 - 20 ) which require cooling are located on the lower side of the circuit board ( 10 ) and in thermal connection with the heat sink wall ( 24 ). Components which do not generate excessive heat are located on the upper side of the circuit board ( 10 ). Raised conductive blocks ( 32 - 36 ) couple thermally the components ( 16 - 20 ) to the wall ( 24 ). With this arrangement it is not necessary to provide cooling internally of the casing ( 22 ) and it is possible nevertheless to use high powered components of the type which are found in modern computers. The casing remains secure and thus suitable for high security applications.
1. An electronic assembly including a casing with walls providing an internal chamber, at least one circuit board located in the chamber and provided with a plurality of electronic components connected thereto, the circuit board including:
a. a front side facing the internal chamber,
b. a rear side facing a bottom thermally conductive wall of the casing,
c. a first set of heat generating components which require cooling during operation, the first set being located on the rear side of the circuit board, and
d. a second set of components which generate insufficient heat to require cooling, at least some of the second set of components being located on the front side of the circuit board,
wherein there is provided at least one resilient biasing element for biasing each of the heat generating components of the first set against the bottom wall of the casing, each biasing element connecting the circuit board to the bottom wall.
2. An assembly according to claim 1 , wherein there is provided at least one coupling element for coupling the heat generating component or components to said wall.
3. An assembly according to claim 2 , wherein the coupling element or elements include a conductive block between said wall and the or each component, and wherein the block or each block is a part of the wall or a separate component fixed to the wall.
4. An assembly according to claim 2 , wherein the or each coupling element is made of a metal or metal alloy, and/or wherein there is provided one coupling element per heat generating component of the circuit board.
5. An assembly according to claim 2 , wherein there is provided a heat transfer agent between the or each heat generating component and its respective coupling element.
6. An assembly according to claim 5 , wherein the transfer agent includes a thermal grease or a thermal pad.
7. An assembly according to claim 1 , wherein the casing is substantially completely or completely closed or sealed.
8. An assembly according to claim 1 , wherein said wall to which the heat generating components are thermally coupled are provided with cooling fins on external sides thereof.
9. An assembly according to claim 8 , including a fan for promoting air flow through the cooling fins.
10. An assembly according to claim 1 , wherein there is provided at least one spring located to push the or each component against said wall or associated the coupling element.
11. An assembly according to claim 10 , wherein the or at least one of the biasing elements includes a sprung loaded screw, bolt pin or rivet.
12. An assembly according to claim 1 , wherein the or each biasing element is located proximate an associated heat conducting element.
13. An assembly according to claim 12 , wherein the or each biasing element is located no more than around 15 mm from its associated component.