Structure and Method for Interconnecting Printed Circuit Boards

This invention pertains to a structure and method for interconnecting a plurality of stacked printed circuit boards.

In order to reduce the costs in the manufacture of television (TV) instruments, it is necessary to automate factory assembly lines. A major effort in this area is the development of an Advanced Instrument Line (AIL) for automating the assembly of modular TV components. The AIL system comprises several automatic-assembly work stations where one or more modular components are accurately located for assembly and subjected to a mechanized assembly operation.

One cost effective approach used in the automatic assembly of TV instruments in an AIL is to assemble parts in layers in a stack to form a compact unit or module. This approach can be utilized to satisfy the modular demands of a varied product mix for future TV instruments. The effectiveness of the approach is largely dependent on successful design treatment of the wired interconnections between printed circuit (PC) boards. Typically, the PC boards have spaced contact areas at the edges thereof and are interconnected by various connectors which are relatively costly. For example, U.S. Pat. Nos. 4,245,876 and 4,028,794, both issued to Ritchie et al., disclose a laminated connector and method for making same comprising a plurality of identical elongated metal contacts, each of which is a resilient spring, spaced along a continuous web of insulative material which serves to locate the contacts in desired positions and provides an insulation back or cover for the contacts. The present invention provides a structure and method for automatically interconnecting a layered assembly of printed circuit boards which is fast and accurate, and eliminates the expense and unreliability of conventional connectors.

The present invention comprises a structure and method for interconnecting a plurality of stacked printed circuit boards, each board having a plurality of spaced contact areas at an edge thereof, wherein a multiconductor cable has a plurality of insulation-stripped window regions therein at predetermined intervals. The cable is continuous through a plurality of the window regions which are positioned, respectively, adjacent the edges of the printed circuit boards so that, at each window region, each stripped wire is aligned with a different contact area. The stripped wires are soldered in bulk to their respective contact areas.

FIG. 1 is a perspective view of an embodiment of the present invention.

FIG. 2 is a partial perspective view of a portion of a second embodiment of the present invention.

FIG. 3 is a perspective view of parts of the embodiment shown in FIG. 1 during an intitial assembly step in the present method.

FIG. 4 is a diagrammatic elevation view of an embodiment of a system for performing the method of assembly according to an aspect of the present invention.

FIG. 1 of the drawings shows a structure 10 in which a plurality of stacked printed circuit (PC) boards 12 are interconnected. The PC boards 12 are disposed parallel to each other in a spaced stack-like arrangement and held together by spacers 14 connected to the four corners thereof to form a layered assembly. Each PC board 12 has a plurality of spaced contact areas 16 at an edge 18 thereof. The contact areas 16 may comprise copper etched edge pad terminals that are pre-tinned. FIG. 2 shows a portion of a second embodiment wherein each of the contact areas 16 has a V-shaped groove 20 notched therein. The grooves 20 help to prevent lateral movement of stripped wires positioned therein during a subsequent soldering step, as is described below.

A continuous insulated multiconductor cable 22 electrically interconnects the PC boards 12, as shown in FIG. 1. As is shown in FIG. 3, which shows the embodiment of FIG. 1 during an initial assembly step, the multiconductor cable 22 has a plurality of insulation-stripped window regions 24 therein at predetermined intervals. The cable 22 is continuous through a plurality of these window regions 24, and has a plurality of bare conducting wires 26 juxtaposed in a substantially parallel relationship at each window region 24. Preferably, the multiconductor cable 22 comprises a flat cable, and the insulation is stripped therefrom across the complete width of the cable 22 at the window regions 24.

The window regions 24 in the cable 22 are positioned, respectively, adjacent the edges 18 of the PC boards 12 so that, at each window region 24, each stripped wire 26 is aligned with a different contact area 16. Preferably, the stripped wires 26 are bent around the edges 18 so as to have a U-shaped profile which facilitates their making contact with the respective contact areas 16, as shown in FIG. 1. The interconnection is completed by having the wires 26 soldered to their respective contact areas.

FIG. 4 shows a system 28 for performing the present method of interconnecting the PC boards 12 in the layered assembly. The insulation is first removed from the cable 22 at predetermined intervals to form the insulation-stripped window regions 24. The intervals are determined by the spacing between the PC boards 12. Preferably, toward this end, the system 28 includes equipment which feeds the flat cable 22 from a spool 30 through an automatic wire stripper 32, as shown in FIG. 4. Although the insulation can be removed by any technique, ideally, this step is accomplished by a commercial wire stripper. Such a wire stripper is available as Model 46A from Carpenter Manufacturing Company, Manlius, N.Y.

The layered assembly of PC boards 12 is transported to a work station, disposed beneath a series of U-shaped applicators 34, by a conveyor belt 36 which moves in a direction, shown by arrow A in FIG. 4, orthogonal to the planar surfaces of the PC boards 12. The cable 22, after stripping, continues to feed to a location above the contact areas 16 of the PC boards 12 by moving in the direction of arrow A so that the window regions 24 in the cable 22 are positioned, respectively, adjacent the edges 18 of the PC boards 12. At each window region 24, each stripped wire 26 is aligned with a different contact area 16, as shown in greater detail in FIG. 3.

The stripped wires 26 are then formed around the edges 18 of the respectively adjacent PC boards 12 so that each wire 26 touches its adjacent contact area 16. In the present embodiment, this forming step is performed by placing the U-shaped applicators 34 against the stripped wires 26 opposite each of the edges 18 and pressing the open U-shaped portions of the applicators 34 over the edges 18, whereby the wires 26 are forcibly bent around the edges 18 to form U-shaped profiles. The forming step can be done to each board 12 one at a time in sequence, as shown in FIG. 4, or can be performed simultaneously with respect to all PC boards 12 in a given assembly.

The conveyor belt 36 next transports the layered assembly of PC boards 12 to a station where a shearing device 38 cuts the cable 22. The present interconnect method is completed by soldering the wires 26 to their respective contact areas 16 at another station (not shown) along the conveyor belt 36. The soldering step may be performed by passing the layered assembly of PC boards 12 through a reflow solder position where the pre-tinned contact areas 16 are heated by infrared radiation. Alternatively, the soldering step may be performed by wave soldering. Preferably, the soldering step is performed simultaneously with respect to all PC boards 12 in a given assembly. Such a bulk soldering operation has been shown to provide successful results.

The essence of the present technique is the use of the multiconductor cable 22 which is formed to act as its own connector, and the fact that no other mechanical connector is needed to make contact between the layered assembly of PC boards 12. A standard mechanical connector may still be used in conjunction with this technique to make electrical connection to other PC boards or equipment. The economic benefits of the present concept are that it lends itself to a quick bulk soldering operation, and no costly connectors are required.