Board to board interconnect structure
BACKGROUND 
     The present invention relates to interconnect structures for electrically connecting vertically arranged circuit boards. 
     Examples of prior art structures are shown in U.S. Pat. Nos. 4,283,755; 3,591,834; 3,489,954; 3,459,998 and 3,418,533. 
     Conventionally, in order for one board to &#34;talk&#34; to an adjacent overlying or underlying board, signal lines are run from the chips of the first board to the edge of the board, conductors are then provided from the edge of the first board to the edge of the second board, and signal lines then connect the conductors along the edge of the second board to the chips of the second board. 
     While the prior art evidences some progress in improving upon this circuitous route for board to board signal lines, none of the prior art structures discloses an interconnect structure which suitably solves the board to board interconnect problem, especially for boards carrying many chips. Moreover, in the past, the &#34;well space&#34; directly underlying each of the chips, and generally bounded by its pin arrangement, has been ignored as an interconnect region, wasting valuable circuit board space. 
     SUMMARY 
     The present invention therefore comprises a board to board interconnect structure which can be installed directly between the well spaces of chips mounted on vertically arranged multilayer circuit boards. The interconnect structure includes mating housing members which support and position electrical contacts projecting from the opposed boards. Each pair of opposed contacts is frictionally, but removeably, joined together at one end and has opposite ends frictionally secured to plated through apertures of the adjacent boards. The plated through apertures are selectively connected to the circuit layers of the boards. The coupled contact structure as supported by the mating housing members, thus, provides direct board to board vertical signal lines between the adjacent boards. Moreover, such an interconnect assembly can be installed between the well spaces of the chips of the opposed circuit boards, greatly reducing conductor congestion along the input/output edge region of the circuit board. 
     It is therefore an object of the present invention to provide an improved board to board interconnect structure. 
     It is a further object of the invention to provide an interconnect structure which can be installed between the well spaces of chips mounted on adjacent boards. 
     It is a further object to provide an interconnect structure for adjacent boards which is comprised of mating housing members secured to the boards and carrying contacts which frictionally engage one another when the housing members are assembled to provide direct vertical signal lines between the boards. 
     Yet another object is to provide a board to board interconnect structure which reduces conductor congestion along the input/output edge region of the circuit board. 
     Still another object is to provide an interconnect structure which reduces board to board signal path length to speed up the operation of the circuitry. 
     These and other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional elevational view of the present invention showing the oppositely mounted chips 16 and 76. 
     FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1 and showing the bottom of chip 16. 
     FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 1 and showing a portion of the top of board 5. 
     FIG. 4 is an enlarged cross-sectional elevational view of a portion of FIG. 1. 
     FIG. 5 is a plan view of the first housing member 30. 
     FIG. 6 is an elevational view taken along line 6--6 of FIG. 5. 
     FIG. 7 is an elevational view taken along line 7--7 of FIG. 5. 
     FIG. 8 is an elevational view of pin 38a. 
     FIG. 9 is an elevational view of pin 46a. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The circuit board interconnect assembly of the present invention is indicated by the numeral 1 in FIG. 1. The assembly 1 interconnects a first circuit board 5 to a second circuit board 65. 
     First circuit board 5 is a multilayer circuit board having circuit layers 7, 8 and 9. The board 5 supports a plurality of integrated circuit chips. A representative chip 16 is shown in FIG. 1 supported by the board 5 at an interior region 11. As shown in FIG. 2, chip 16 has a plurality of pins 17 disposed in a pin array 18 about a well space 19. The pins 17 are frictionally received at their lower ends 18 into the plated through sockets 12 which are disposed in a socket array 13 corresponding to pin array 18. See FIG. 3. The sockets 12 are selectively connected to the internal circuit layers 7, 8 and 9 of circuit board 5 in the conventional manner. With further reference to FIG. 3, circuit board 5 has a well space 21 which corresponds directly to the well space 19 of chip 16. A plurality of electrically conductive apertures 23 are formed through circuit board 5 within the well space 21. The apertures 23 are selectively connected to the circuit layers 7, 8 and 9, and are disposed in an aperture array 25. The apertures 23 are utilized to electrically connect the circuit layers 7, 8, 9 (and chips 16) of board 5 to the interconnect assembly 1 as will now be described. 
     With particular reference to FIG. 4, the assembly 1 is comprised of a first housing member 30 and a second housing member 90. The housing members 30 and 90 are identical, and therefore, only housing member 30 will be described in detail. Housing member 30 is best shown in FIGS. 5-7. Member 30 is a solid plastic block type structure having an array 31 of through-formed apertures 32, 34. Apertures 32 comprise socket apertures while apertures 34 comprise pin apertures. Each of the socket apertures 32 has a deep recess 33, and each of the pin apertures 34 has a shallower, but broader, recess 35. The aperture array 31 of member 30 corresponds directly to the aperture array 25 of circuit board 5 shown in FIG. 3. Each of the apertures 32 or 34 of the array 31 has a correspondingly positioned aperture 23 of the array 25. Note that there are twenty-six apertures in array 31, thirteen socket apertures 32 and thirteen pin apertures 34. Member 30 also includes a rectangular alignment projection 36 and a rectangular alignment cavity 37. The projection 36 and cavity 37 initially assist in aligning member 30 with member 90 during assembly as will later be more fully described. 
     Member 30 is secured to the underside of circuit board 5 by socket contacts 38a. See FIG. 4. As shown in FIG. 8 each of the socket contacts 38a has a socket end 40a and a pin end 42a opposite thereto. One of the socket contacts 38a is installed in each of the socket apertures 32, with the socket end 40a of each contact 38a being slideably received within the recess 33 of the aperture 32, and the pin end 42a being frictionally received within an aperture 23 of aperture array 25 of board 5. Each of the remaining thirteen apertures of the aperture array 31 has a flex contact 46a installed therein. With reference to FIG. 9, each flex contact 46a has a c-section 48a formed at one end and a pair of spring legs 50a, 52a disposed from the other end. A flex contact 46a is frictionally secured into each of the apertures 23 of array 25 which corresponds to a pin aperture 34 of array 31 by means of its c-section 48a which deflects inwardly somewhat upon insertion into the aperture 23. See FIG. 4. The oppositely disposed spring legs 50a, 52a of each of the contacts 46a extends through the corresponding pin aperture 34 of housing member 30. 
     Having described the manner in which the first housing member 30 is physically secured to circuit board 5 and electrically connected to the circuit layers 7, 8 and 9 by means of the contacts 38a, 46a, the manner in which the second housing member 90 is installed upon second circuit board 65 can easily be appreciated. Second circuit board 65 is a multilayer board like board 5 having circuit layers 67, 68, 69. A chip 76 is secured by pins 77 to the board 65. See FIG. 1. The pins 77 are selectively connected to the internal circuit layers 67, 68, 69 of board 65 in the coventional manner. Chip 76 is identical to the chip 16 in FIG. 2 and includes a well space 79 identical to well space 19 of chip 16. Circuit board 65 includes a well space 81 which corresponds directly to well space 79 and includes a array of conductive apertures 83 identical to the array 25 of board 5. Second housing member 90 is identical to member 30. Member 90 has an aperture array directly corresponding to the array of apertures 83 of board 65 and identical to the array 31 of member 30. The array is comprised of socket apertures 92 and pin apertures 94. See FIG. 4. Each of the socket apertures 92 has a deep recess 93, and each of the pin apertures 94 has a shallower, but wider, recess 95. Member 90 also includes an alignment projection 94 and an alignment cavity 96. 
     A socket contact 38b, identical to 38a, and having a socket end 40b and a pin end 42b, is installed in each of the thirteen socket apertures 92 to secure housing member 90 to circuit board 65. Flex contacts 46b, identical to contacts 46a, are frictionally engaged to apertures 83 of board 65 by their c-sections 48b and have their oppositely disposed spring legs 50b, 52b projecting through the thirteen pin apertures 94 of member 90. 
     With reference to FIG. 4, the assembly of housing member 30 to member 90 will now be described. As the members 30 and 90 are moved towards one and other the projection 36 of member 30 must be aligned with cavity 96 of member 90, and projection 94 of member 90 must be aligned with cavity 37 of member 30. Once this initial alignment is achieved, the thirteen pairs of spring legs 50a, 52a of each of the pin contacts 46a of member 30 will align with the corresponding socket ends 400b of the thirteen socket contacts 38b of member 90. Simultaneously, the thirteen pairs of spring legs 50b, 52b of the pin contacts 46b of member 90 will align with the corresponding socket ends 40a of the socket contacts 38a of member 30. The member 30 and 90 are then assembled together with projections 36, 94 being slideably received within the respective cavities 96, 37, and each of the spring legs 50a, 52a and 50b, 52b being deflected inwardly and frictionally received within the respective socket ends 40b, 40a. Note that in the assembly position the recesses 35, 95 of the respective pin apertures 34, 94 accommodate the terminal portions of the respective socket ends 40b, 40a of the socket pins 38b, 38a. 
     Having described the basic structure of the interface assembly 1, the manner in which it operates can now be appreciated. Each of the boards 5 and 65 carry a plurality of chips 16, 76 which are connected by pins 17, 77, respectively, to the internal circuit layers 7, 8, 9 and 67, 68, 69 of the boards 5, 65. An interconnect assembly 1 is secured between the respective well spaces 21 and 81 of each pair of oppositely mounted chips 16 and 76. Each interconnect assembly 1 provides twenty-six direct board-to-board electrical interconnections between board 5 and board 65. Hence the assemblies 1 directly interconnect the chips 16 of board 5 with the chips 76 of board 65 through the respective circuit layers 7, 8, 9 and 67, 68, 69 and the coupled contacts 38a, 46b and 38b, 46a. 
     By utilizing the direct board-to-board interconnect assembly 1 of the present invention, the signal paths between the chips 16 and chips 76 are considerably shortened, increasing the speed of operation. In addition the number of board to board input/output terminals which must be provided along the edge of the circuit board is reduced. In fact, the invention has the effect of merging together each pair of adjacent boards in a vertically arranged stack of boards so that each pair of adjacent boards appears as a single circuit board to the remainder of the system. Circuit density is therefore increased while the design of the interconnect circuitry is simplified. 
     As an additional advantage, the members 30, 90 when assembled together serve as spacers for the boards 30, 90 providing a definite air space between the boards 5,65. By holding the air space to a definite distance, the forced air cooling of the boards can be closely controlled. 
     Having described the preferred embodiment of the present invention, many modifications and variations thereof would be obvious to one skilled in that art. The invention is, therefore, intended to be limited only by the scope of the appended claims.