The Multi-Board Module (MBM) scheme has been conceived to provide a cost-effective way to combine digital electronic circuits into dense, lightweight packages, within which high-speed signals can be transmitted readily along three-dimensional conductive paths with minimal lengths. As the title suggests, the MBM scheme involves stacking of circuit boards in modules. Unlike in other circuit-packaging schemes, neither cables nor traditional electrical connectors are used to make the electrical connections among circuit boards in a module. Inasmuch as connectors and cables typically occupy a large fraction of the volume and constitute a large fraction of the mass of a package, the MBM scheme offers the potential for significant reductions in size and weight.
As shown in the figure, the connections between two adjacent circuit boards are made via gold-plated beryllium/copper contact springs. Each contact spring is soldered to printed wiring at a via hole on one of the boards. During assembly, each spring is pushed into contact with the printed wiring at a via hole at the corresponding location on the adjacent board. Inserts made of silicone rubber can be used to reinforce the contact springs.
In addition to eliminating the cost, weight, and bulk of cables and traditional electrical connectors, this contact scheme affords several advantages:
- The contacts are self-aligning and structurally reliable.
- Maintenance, repair, and testing are possible because circuit boards can readily be removed from stacks.
- To facilitate testing, one can turn off selected contacts by inserting insulating tabs; alternatively or in addition, one can insert thin conductive pads at selected contacts to gain access for probing.
- Unlike in conventional edge connection and in other three-dimensional-connection schemes, contacts can be located almost anywhere on the circuit boards; this makes it possible to reduce signal-path lengths and thereby accommodate higher-speed signals.
In applying the MBM concept, designers might have to contend with limits on the sizes of modules and with guidelines regarding the numbers and placements of contacts and structural supports. High circuit densities could give rise to a need for thermal straps for additional heat sinking. Under some circumstances, it could be necessary to design against a tendency for contacts to open when the circuit boards are subjected to strong vibrations.
This work was done by John D. Baker and Alberto Montalvo of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the category.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to
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This Brief includes a Technical Support Package (TSP).
Packaging Electronic Circuits in Multi-Board Modules.
(reference NPO19972) is currently available for download from the TSP library.
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