This invention relates generally to mounting devices for electronic circuit boards or cards, and more particularly to an improved card mount and thermal transfer assembly.
Because of the density of electronic circuitry and the amount of electrical power handled on some electronic circuit cards, a considerable amount of heat is generated that must be carried away from the card to prevent thermal damage to electronic components. In some well ventilated applications this can be accomplished by simple convection air currents. In some, the addition of blowers can be used to augment the natural air flow.
Other applications that require less readily ventilated packaging of circuit cards, such as in an aircraft or spacecraft, have used mechanical refrigeration systems, one example of which is provided by U.S. Pat. No. 3,776,305 to C. E. Simmons.
The removal of heat from electronic circuit cards by thermal transfer to heat sink means such as a mounting frame has been utilized in the apparatus disclosed in U.S. Pat. No. 3,550,681 to P. G. Stier, et al. In that apparatus a T-shaped bar is adapted to be held in heat transfer contact with a frame by frame mounted spring clips and has a lost motion connection with one edge of a circuit card that permits heat transfer from the card and limited positioning thereof for effecting mating with a connector.
While the foregoing expedients have been satisfactory for some applications they are not suitable for certain other special situations, particularly in the case of mounting of electronic circuit cards in small, high powered underwater devices such as towed sonar instruments or apparatus. Those apparatus are necessarily characterized by severe space, weight, and power limitations in that the size and weight of the vehicle are important factors in determining the speeds and depths of tow, and also whether the apparatus can be easily handled and steamed from a tow craft. In addition, the use of refrigeration systems, coolant circulating pumps, and the like, are prone to produce acoustic and electronic signatures that are detrimental to the operation of sonar systems. Another factor is that of accessibility of the cards for inspection or replacement, in view of the usually tubular configuration of the apparatus hull or housing, a portion of which must be removed for access to the cards.