Abstract:
Disclosed is an area array connector adapted to connect contact pads on one generally planar circuit element to corresponding contact pads on another generally planar circuit element. The connector has an insulative contact mounting sheet having a plurality of contact mounting apertures therein. A plurality of electrically conducting contacts are mounted in the contact mounting apertures, each contact having contact pad engaging legs resiliently projecting away from opposite faces of the contact mounting sheet. Two insulative contact securing sheets are provided, one laminated to each face of the contact mounting sheet, each contact securing sheet having apertures therein to accommodate the resiliently projecting legs of the contacts.

Description:
This invention relates to area array connectors which are adapted to connect the contact pads on one generally planar circuit element, such as a printed wiring board, to corresponding contact pads on another generally planar circuit element. 
     SUMMARY OF THE INVENTION 
     In many electronic applications, compactness of the equipment, both overall and in detail, is an important goal. One manner of achieving this is to stack printed wiring boards, or printed circuit boards, one upon another, and electrically connecting them together face-to-face instead of in a more space consuming arrangement of daughter printed circuit boards being connected together through current paths routed through a motherboard. 
     In order to make use of such a compact arrangement, it is necessary that the face-to-face connection be assuredly made both electrically and mechanically, and area array connectors are needed to connect corresponding contact pads on adjacent printed circuit boards. 
     BACKGROUND OF THE INVENTION 
     In accordance with the invention, an area array connector is provided which is made up of the required number of electrically conductive connector elements or contacts carried in a three-layer laminated insulative housing. The contacts project from either side of the housing and are positioned to engage contact pads on printed circuit boards in a stack, the connector being interleaved between adjacent printed circuit boards. 
     More specifically, in accordance with the invention, there is provided an area array connector adapted to connect the contact pads on one generally planar circuit element, such as a printed wiring board, to the corresponding contact pads on another generally planar circuit element or printed circuit board. The connector includes an insulative contact mounting sheet having a plurality of contact mounting apertures in it. A plurality of electrically conducting contacts are mounted in the contact mounting apertures; each contact has contact pad engaging legs resiliently projecting away from opposite faces of the contact mounting sheet. Two insulative contact securing sheets are provided; one laminated to each face of the contact mounting sheet. Each contact securing sheet has apertures in it to accommodate the resiliently projecting legs of said contacts. 
     In a preferred embodiment of the invention, each of the electrically conducting contacts has a base leg adapted and proportioned to fit in and engage the contact mounting apertures of the contact mounting sheet and two pad engaging legs which are cantilevered resiliently outwardly from the base leg in opposite directions. In accordance with one preferred embodiment, it is preferred that the pad engaging legs of the contacts have a shorter linear extent than the base legs of the contacts. In such embodiment, in order to assure that the contacts are securely held in position, it is preferred that the contact mounting apertures are each greater in linear extent than the corresponding apertures of the contact securing sheets. In accordance with another embodiment, it is preferred that the pad engaging legs of the contacts have substantially the same length as the base legs of the contacts. In this embodiment, it is preferred that the thickness or width of at least part of the base legs be greater than the thickness or width of the pad engaging legs. It is further preferred in all embodiments that the contact mounting apertures are each greater in area than the corresponding apertures in the contact securing sheets. 
     In accordance with the invention, it is preferred that the contacts are aligned with one another in a staggered pattern, or alternately that the contacts are aligned with one another in a rectangular array, in which the spacing between adjacent contact projecting leg ends is less than the length of a projecting contact leg, and further in which the contacts are skewed with respect to the alignment of the rectangular array to accommodate the length of the projecting contact leg. 
     In accordance with another aspect of the invention, an assembly of a plurality of generally planar circuit elements is provided. The circuit elements have contact pads on at least one surface thereof, and are stacked one upon another, with area array connectors being interleaved between adjacent circuit elements. The area array connectors are made up of an insulative contact mounting sheet which has a plurality of contact mounting apertures therein, a plurality of electrically conducting contacts mounted in the contact mounting apertures, each contact having contact pad engaging legs resiliently projecting away from opposite faces of the contact mounting sheet, and two insulative contact securing sheets, one laminated to each face of the contact mounting sheet. Each contact securing sheet has apertures therein to accommodate the resiliently projecting legs of the contacts. Framing means are provided for holding the assembly together and for establishing pressure contact between the contact pads and corresponding contact pad engaging legs. It is preferred to have spacer means mounted in the sheets to establish and maintain a uniform thickness of the connector. 
     In accordance with still another aspect of the invention, there is provided a method for making an area array connector adapted to connect contact pads on one generally planar circuit element to corresponding contact pads on another generally planar circuit element that includes providing an insulative generally planar contact mounting sheet, selecting positions on the contact mounting sheet at which contacts are desired to be mounted, and laser machining contact-accommodating apertures in the contact mounting sheet at said selected positions thereon. Contacts of conducting material are formed, each contact having a mounting leg for fitting into and engaging the contact-accommodating apertures, and further having contact pad engaging legs resiliently projecting away from opposite faces of the contact mounting sheets. The contacts are mounted in the contact-accommodating apertures. Two insulative contact securing sheets are provided having apertures laser machined therein which are registerable with the projecting legs of contacts mounted in the contact mounting sheet. One of the apertured contact securing sheets is adhesively laminated to each face of the contact mounting sheet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the area array connector of the invention; 
     FIG. 2 is an enlarged perspective view of a corner of the area array connector of FIG. 1; 
     FIG. 3 is a still further enlarged view of a portion of the connector of FIG. 1; 
     FIG. 4 is a perspective view of an assembly of printed circuit boards and area array connectors of the invention; 
     FIG. 5 is an exploded view of the assembly of FIG. 4; 
     FIG. 6 is a cross-sectional view, partly in elevation, of one embodiment of the connector of the invention showing in enlarged scale a contact mounted in the insulative housing formed of three insulative sheets; 
     FIG. 7 is a cross-sectional view, partly in elevation, similar to FIG. 6, of another embodiment of the invention on the same scale as FIG. 6; 
     FIG. 8 is a perspective view of a single contact of the invention; 
     FIG. 9 is an exploded view in perspective of the connector of FIG. 1; 
     FIG. 10 is an enlarged view of a portion of the contact mounting sheet forming the middle layer of the laminated connector of FIG. 9; 
     FIG. 11 is a perspective view of a connector showing the contacts in rectangular array, but with the individual contacts skewed in accordance with the invention; 
     FIG. 12 is a perspective view of a connector showing the contacts arranged in staggered or triangular array; and 
     FIG. 13 is another perspective view of a single contact of the invention drawn to the same scale as FIGS.  11  and  12 . 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In FIG. 1 there is shown a connector of the invention designated generally as  10 . It is made up of three generally planar sheets, the center sheet being a contact mounting sheet  1 , and the contact securing sheets  12  and  13  laminated to the sheet  11  on either face thereof. An array of contacts  14  is arranged on the connector as is indicated very diagrammatically in FIG. 1, but which is shown on a larger scale in succeeding figures. The sheets  11 ,  12  and  13  are all made of insulative materials, such as plastics (for example, phenolic, Teflon or Duroid (polytetrafluoroethylenes), diallyl phthalate (DAP)) or ceramics (for example, aluminum oxide or beryllium oxide), and the sheets need not be all formed of the same material. 
     The laminated sheets  11 ,  12  and  13  are adhesively secured to one another by a suitable adhesive, such as epoxy or acrylic adhesives. 
     Attention is now directed to FIGS. 2 and 3, which show on different scales contacts protruding through apertures in contact securing sheet  13 . The contacts are designated  14 , and it can be seen that they are made up of a contact leg  16 , which projects into the aperture  15 , and integral with it a contact head  17 , which also projects through the aperture  15 . The contact head  17  is at the cantilevered end of the contact leg  16 , as will appear in greater detail below. 
     The laminated connector  10  has holes  18  in it positioned to pass framing bolts or studs (not shown) for building up an assembly of printed circuit boards and array connectors and for aligning of the area array connectors with the printed circuit boards that are interleaved with them. 
     FIGS. 4 and 5 show an assembly designated generally  20 . It is formed of printed circuit boards designated as  21   a ,  21   b  and  21   c . The circuit boards are of the kind having electric contact pads on at least one surface thereof. Interleaved between the printed circuit boards are area array connectors  10 . The assembly is held together by means of framing members  22   a  and  22   b . Bolts or other fastening means (not shown) pass through holes  18  in the framing members, the printed circuit boards, and the area array connectors. 
     The parts of the assembly of FIG. 4 just discussed are shown in exploded form in FIG. 5 with the same reference characters being used. The before-mentioned contact pads on the printed circuit boards are designated  23  in FIG.  5 . The contacts  14  on the connectors  10  are positioned to align with the contact pads  23 . 
     FIG. 6 is a sectional view partly in elevation transversely through the connector  10  at the location of a contact  14 . From this figure, it can be seen that the contact mounting sheet  11  has a slot  24  in it, which is generally aligned with slots or apertures  15 , but which is longer or greater in linear dimension than the apertures  15  in the contact securing sheets  13  and  12 . FIG. 6 also shows that the contact  14  is generally E-shaped, having a base leg  25  centrally located in the E-shape. Base leg  25  terminates in an enlarged aperture engaging portion  26  integrally formed therewith. The contact  14  has two contact pad engaging legs  16  resiliently cantilevered or projecting away from the base leg. The contact pad engaging legs  16  terminate in contacting heads  17 . The legs and heads taken together are proportioned so that the contact legs resiliently project outwardly from the contact securing sheets, as well as the contact mounting sheet, yet can be resiliently moved back into the laminate upon engaging a contact pad on an adjacent printed circuit board with the contacting head almost flush with the surface of the contact securing sheet. 
     FIG. 7 is similar to FIG. 6, but illustrates another preferred embodiment of the connector of the invention. Corresponding parts in these two figures are given the same reference characters. In FIG. 7, the slot  24  in contact mounting sheet  11  is substantially the same length as apertures  15 . Slot  24  is, however, wider than apertures  15 , and the surfaces of contact securing sheets  12  and  13  thus capture the enlarged portion  26  of base leg  25 . 
     FIG. 8 shows a contact drawn in isolation with its parts marked with the same reference characters as those used in FIGS. 6 and 7. The contact  14  may be formed of a material having good electrical conducting properties and good resiliency or spring properties, such as beryllium copper, and the actual points of contact with the contact pads of a printed circuit board may be plated with gold or other materials for establishing good electrical contact. 
     FIG. 9 shows the connector  10  of FIG. 1 in exploded form, with all but one of the contacts  14  installed, and with the apertures  24  and  15  in the sheets shown. Also seen in FIG. 9 are spacer means  29  which fit into holes  30  in the sheets to help establish a uniform thickness to the laminate when it is formed. Spacer means  29  are preferably longer than the combined thickness of the three sheets so that they, and not the sheets, establish the spacing between circuit boards. 
     FIG. 10 shows a contact mounting sheet  11  having slots  24  in it. Contacts  14  are shown mounted in the slots or apertures in sheet  11 . It can be seen that the legs  16  terminating in heads  17  project outwardly from the face of the contact mounting sheet  11 . It can also be seen that aperture  24  in sheet  11  is contoured in profile to accommodate the enlarged end portion  26  of leg  25 . 
     FIG. 11 shows a portion of a connector  10  in which the contact heads  17  of the several connectors  14  are arranged in a rectangular grid. The spacing of the grid is such that it is smaller than the linear length of a contact, and for this reason, in accordance with the invention, the contacts are skewed with respect to the rectangular layout so that they do not interfere with the tightly arranged rectangular array. 
     FIG. 12 shows an arrangement of contacts  14  which is preferred to that of FIG.  11 . In this arrangement, the contact heads  17  are in a staggered or triangular pattern. This makes for ease of manufacture. 
     FIG. 13 shows a contact  14  drawn to the same scale as the contacts in FIGS. 11 and 12. 
     In accordance with the method aspect of the invention, it is preferred that the apertured sheets  11 ,  12  and  13  not be molded, as is conventional, but rather that the sheets be cut from larger stock and the apertures machined in them by numerically controlled laser or equivalent techniques. This is advantageous because the area array connectors are most often needed in relatively small numbers for a given design, and conventional tooling would be excessively costly. In addition, this manufacturing method provides very great flexibility in the choice of number, size, shape, and positioning of the apertures, thus facilitating custom design of small production lots.