Direct Circuit Board Connection

The present invention relates to electrical interconnection between separate circuit boards and particularly relates to making electrical interconnection between circuit boards of a type having the circuitry etched on a metal foil laminated on an insulating substrate or printed circuit boards as they are commonly called. Heretofore, it has been the practice in mass production of electronic devices to interconnect individual circuit boards by a flexible connector such as a multiple conductor ribbon which has the opposite ends of its conductors attached to separate circuit boards which may then be stacked by bending of the flexible ribbon with the interconnection remaining intact. However, in electronic devices where the volume of the assembled device must be maintained at a minimum, it is often cumbersome and prohibitive from a volume standpoint to stack individual circuit boards with the flexible ribbon connector extending from the sides of the stacked boards.

In addition where a flexible multiconductor ribbon connector is employed to interconnect separate circuit boards, it has been found difficult to handle the boards after connection of the ends of the connector to the individual boards, particularly where the conductors are soldered during assembly operations without breaking the soldered connections of the conductor ends and particularly during the flexing of the ribbon. In addition, the cost of the multiple conductor ribbon and the individual soldering of the ends of the conductors has proven to be time consuming and costly in mass production.

Accordingly, it has long been desired to provide a simple reliable and low cost technique or way for directly interconnecting individual circuit boards and particularly printed circuit boards in a manner which readily lends itself to mass production and provides an electrical connection of sufficient integrity to prove viable during the service life of the electronic device.

The present invention provides a way or technique for directly interconnecting individual printed circuit boards in a manner which provides physical support for the interconnection with the boards extending mutually at right angles and also provides for direct electrical interconnection of the circuit strips on the individual printed circuit boards. The primary circuit board has an elongated slot formed therein with lug portions of the substrate material extending from the sides of the slot to a closely controlled distance oppositely spaced from each other to provide tolerance control of the width of the slot. The secondary printed circuit board has an insert portion thereof formed to a size and configuration to interfit the slot with the thickness of the secondary board corresponding to the width of the slot for insertion therethrough. The primary board has a plurality of exposed conductive strips formed on the surface thereof in spaced parallel relationship and terminating at the edge of the slot. The secondary board has a correspondingly disposed plurality of spaced parallel conductive strips formed thereon. Assembly insertion of the insert portion of the secondary board into the slot on the primary board is accomplished in closely fitting relationship with the long portions of the slot giving mechanical positioning support to the assembly. The adjacent ends of the conductive strips on the individual boards are then electrically interconnected by soldering, preferably by wave soldering, which bridges the slight gap therebetween. The present circuit board connection permits direct plug-in of a secondary board into a slot in a primary board and with the assembly thereof wave soldered for electrical interconnection and thus provides a simple economical and reliable way of connecting individual circuit boards in mass production without the need for external electrical conductors.

FIG. 1 is an axonometric view of the assembled circuit boards of the secondary circuit board inserted into the slot of the primary circuit board;

FIG. 2 is a portion of a section view taken along section indicating lines 2--2 of FIG. 1; and,

FIG. 3 is a portion of a section view taken along section indicating lines 3--3 of FIG. 1.

Referring to FIGS. 1 through 3, the assembly of the present invention is indicated generally at 10 and includes a primary circuit board 12, typically a printed circuit board, which has an elongated slot 16 formed therein. The printed circuit board 12 is of the type having a substrate of insulating material formed with conductive film thereon portions thereof masked and etched away to form a desired circuit configuration (not shown). Although not illustrated, it will be understood that discrete components may be secured to the board 12 and any circuit thereon.

The opposite elongated sides of the slot 16 have extending therefrom a plurality of space projections of the substrate material denoted by reference numeral 18. The ends of the projections 18 on opposite sides of the slot 16 terminate at a closely controlled distance from each other so as to define a slot having tightly controlled tolerances on the width of thereof. This distance is denoted by the reference character "D" in FIG. 3.

The circuit board 12 has a plurality of spaced generally parallel conductive strips, denoted by reference numerals 20,22,24 in the drawings, provided on one side of the slot 16. A second plurality of spaced generally parallel strips denoted by reference numerals 26,28,30 extends on the opposite side of the slot 16 which strips are formed on the surface of the printed circuit board 12 with their ends terminating at the edges of the slot 16 intermediate the projections 18.

As shown in FIG. 2, if desired each of the strips such as strips 20,22,24,26,28,30 on the upper surface of the primary board 12 may have a counterpart strip located directly below on the undersurface of the board as denoted by reference numerals 20',22',24',26',28',30' in FIGS. 1 and 2. It will be understood however, that the counterpart strips 20',22',24',26',28',30' are not necessary for the practice of the invention.

The secondary board 14 likewise has a plurality of conductive strips disposed thereon in spaced generally parallel relationship on the insert portion of the board which is denoted by reference numeral 32 and which strips are denoted by reference numerals 34,36,38 on the front side of the board portion 32. Preferably counterpart strips denoted with corresponding primed numerals are provided on the opposite face thereof.

Referring to FIG. 2, the strips on the portion 32 of member 14 are disposed oppositely in pairs at a common station thereon such as the pair 36, 36' and are interconnected through a hole or "via" aperture 40 formed through the insulating substrate material which permits the metal conductor when plated on the board 14 to be deposited in the "via" aperture and interconnect the strips 36, 36'. It will be understood that in similar fashion strips 34 and its oppositely disposed strip 34' which is shown only in dashed outline are interconnected, as are strip 38 and its oppositely disposed strip 38' which is shown only in dashed outline.

Upon insertion of the portion 32 of secondary board 14 into the slot 16, the lug portions 18 position and maintain the boards 12, 14 in mutually perpendicular arrangement. The strips on the primary board are then interconnected with the strips respectively disposed adjacent thereto by soldering as denoted by reference numeral 42, preferably by wave soldering, which bridges the gaps therebetween and makes electrical contact with the strips on the secondary board. FIG. 2 illustrates typically the electrical connection between strip 36 and the strips 22, 22' and the electrical connection between strip 36' and the strips 28, 28'. It will be understood that strips 20',22',24' and 26',28',30' may be omitted and are not essential for the practice of the invention.

The present invention thus provides for direct plug-in connection of individual circuit boards by insertion of a portion of one sized and configured to closely interfit a slot in the other board with strips provided on each board terminating closely spaced and adjacent and which are subsequently electrically interconnected by soldering.

Although the invention has been described hereinabove with respect to the illustrated embodiments, it will be understood that the invention is capable of modification and variation and is limited only by the following claims.