1. Field of the Invention
The present invention relates to circuit card assemblies and more particularly, to a structure of a circuit card assembly that can be used in harsh dynamic and thermal environments.
2. Background of the Invention
In an effort to modularize the assembly of electronic devices, electronic components are frequently assembled together on a single circuit card assembly. A circuit card assembly often contains one or more complete circuits for performing selected functions. Circuit card assemblies are typically handled as a single part of a larger circuit or device at assembly time, thereby increasing production speed and simplifying the overall assembly process of the larger circuit or device.
FIGS. 1A and 1B illustrate a prior art circuit card assembly, in which FIG. 1A is a top view of an exemplary circuit card assembly 10 and FIG. 1B is a cross-sectional view thereof. As shown in these Figures, electronic components 11 can be bonded either on an upper surface or both of the upper surface and a lower surface of a printed wiring board (PWB) substrate 12. In the case that electronic components 11 are bonded to both surfaces of PWB substrate 12, vias 14 that penetrate through substrate 12 may be further provided for providing an electrical connection between the upper and lower surfaces of substrate 12. Circuit card assembly 10 further comprises a connector 13 that includes a plurality of pins (not shown) for electrically connecting circuit card assembly 10 with other electrical circuits (not shown) during an assembly process.
As more electronic components are included on a circuit card assembly, its failure rate increases when it is subjected to harsh environments, such as harsh dynamic or thermal environments. One reason for the higher failure rate is that electronic components 11 are exposed without protection, resulting in damage caused by heat or moisture in the environment. Another reason is that electronic components 11 are not properly supported so that components 11 can be shaken loose from the circuit card assembly.
To alleviate this failure rate problem, circuit card assemblies have been “bulked up” with heavy stiffening materials to increase their rigidity. Stiffening can be accomplished by attaching either stiffening ribs or plate structures to the surface of PWB 12 or by providing additional layers of substrate material. In addition, circuit card assemblies are often mounted in aluminum housings that surround the assemblies to control electromagnetic interference (EMI). As a by-product, these housings provide rigidity to the circuit card assembly. These stiffening methods (intentional or otherwise), however, significantly increase the size and weight of the circuit card assembly, thereby making such assemblies difficult to work with especially in compact-size electronic devices.
Accordingly, there is a need to develop a new circuit card assembly structure that can effectively protect the electronic components mounted thereon without largely increasing the weight and volume of the overall circuit card assembly.