Technique for damping electronic module printed wiring board

#The invention relates generally to a system for damping vibration energy in a printed circuit board by utilizing a high hysteresis elastomer in a remotely positioned damping laminate.

#Shock and vibration environments have dictated the use of techniques designed to protect electronic component parts which are exposed to those environments. One such technique which has been used on printed circuit boards comprises a laminate of a thin layer of high hysteresis elastomer between the circuit board and a second structural sheet member which may be made of the same or of a different material as the circuit board. This laminate acts to dampen vibration in the printed circuit board by absorption of much of the input energy by the elastomer. This energy is dissipated in the form of heat generated by shear stresses in the elastomer. Because of this energy conversion the vibration oscillation of the laminate is damped and, thus, the duration and amplitude of vibration are reduced. The high hysteresis elastomer may also be used as a bonding agent for the laminate.

#There are at least two problems inherent in the above described prior art vibration control systems: First, one side of the printed circuit board is inaccessible after assembly. This makes testing and trouble finding more difficult. Second, assuming that a fault is located, it is very difficult to replace the faulty component due to the aforemetioned inaccessibility.

#These and other aspects of the invention will be better understood by inspection of the drawings, here summarized:

#FIG. 1 illustrates in cross section a typical embodiment of the invention utilizing two laminated damping elements.

#FIG. 2 shows an external view of the module of the embodiment of FIG. 1.

#Referring to FIG. 1, it will be seen that printed circuit board 2 is positioned between and parallel to laminated damping elements 4 and 6. Damping element 6 is spaced sufficiently from printed circuit board 2 to allow clearance for electronic components 8, 10 mounted on printed circuit board 2. Of course, it is also possible to mount additional electronic components (not shown) on the opposite side of printed circuit board 2 by displacing damping element 4 sufficiently from printed circuit board 2.

#Damping element 6 is connected to printed circuit board 2 by means of post members 12, 12'. Damping element 4 is connected to printed circuit board 2 by means of post members 14, 14'. The lengths of posts 12, 12', 14, 14' may be varied to accommodate different maximum heights of electronic components, such as 8, 10. Posts 12, 12', 14 and 14' are fastened at their extremities to damping elements 4 or 6 and to printed circuit board 2. A semiflexible epoxy or other suitable bonding agent may be used to obtain the structural connections. Alternately, mechanical fastening techniques may be utilized to provide the necessary connections.

#Damping elements 4 and 6 may be similar or identical in structure. As shown in FIG. 1, damping elements 4 and 6 are identical and each comprise two outer layers or skins 16, 16' which may be made of thin aluminum or other suitable material. Aluminum skins 16, 16' may be from 0.008 to 0.016 inches thick but the invention is not limited to this dimensional range. Skins 16, 16' are bonded together by high hysteresis bonding agent 18 which may be a polyurethane material, but other suitable materials will be apparent to one skilled in the art. High hysteresis bonding agent 18 may be from 0.005 to 0.008 inches thick but the invention is not limited to this dimensional range.