Abstract:
The present invention provides a carrier that provides improved retention to the individual contact elements resulting in LGA interposer connectors with improved manufacturability, reliability and more uniform mechanical and electrical performance. In one embodiment, the carrier, which includes upper and lower sections of dielectric material with an adhesive layer in between, includes a plurality of openings, each of which may contain an individual contact element. During assembly of the connector, once the contact elements are inserted, the adhesive layer is reflowed, thereby allowing the carrier to capture the location of the contact elements both with respect to each other as well as to the carrier. Alternately, the carrier may be implemented in a fashion that, while not including an adhesive layer to be reflowed, still provides improved retention of the individual contact elements. These embodiments may by easier to assemble, and less expensive to manufacture, especially in high volumes. Description of the processes to assemble the carrier and overall connector are also disclosed.

Description:
RELATED PATENT APPLICATIONS 
     This application is related to copending U.S. patent application Ser. No. 09/457,776, filed Dec. 9, 1999 and copending U.S. patent application Ser. No. 09/866,434, filed May 29, 2001, both of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electrical connectors for interconnecting at least two electrical circuit members such as printed circuit boards, circuit modules, or the like and, more particularly, to connectors of this type, which may be used in information handling system (computer) or telecommunications environments. 
     BACKGROUND OF THE INVENTION 
     The current trend in design for connectors utilized in high speed electronic systems is to provide both high density and highly reliable connections between various circuit devices, which form important parts of those systems. The system may be a computer, a telecommunications network device, a handheld “personal digital assistant”, medical equipment, or any other electronic equipment. High reliability for such connections is essential due to potential end product failure, should vital misconnections of these devices occur. Further, to assure effective repair, upgrade, and/or replacement of various components of the system (i.e., connectors, cards, chips, boards, modules, etc.), it is also highly desirable that such connections be separable and reconnectable in the field within the final product. Such a capability is also desirable during the manufacturing process for such products in order to facilitate testing, for example. 
     A land grid array (LGA) is an example of such a connection in which the two primarily parallel circuit elements to be connected each has a plurality of contact points, arranged in a linear or two-dimensional array. An array of interconnection elements, known as an interposer, is placed between the two arrays to be connected, and provides the electrical connection between the contact points or pads. 
     LGA interposers described in the prior art are implemented in many different ways. Of interest in this patent application are those interposers that include an insulative carrier with an array of primarily circular openings, each of which may contain a single contact element. The contact elements extend vertically both above and below the carrier. The retention of the contact elements provided by the carrier is minimal. Examples of these interposers are described in U.S. Pat. Nos. 4,922,376, 5,163,834, 5,473,510, 5,949,029 and 5,599,193, and in connectors bearing the trademark, “Cin::apse” from Cinch Connectors, a division on Labinal Components and Systems, Inc., and the trademark, “Fuzz Button” from Tecknit USA. 
     At first viewing some of the elements of U.S. Pat. No. 5,599,193 appear similar to those of various embodiments of the invention, but further study shows significant differences are present. The embodiment in FIGS. 1 and 2 describes an LGA connector with non-conductive elastomeric elements formed at the same time as the elastomeric carrier for the elements through a process such as molding. The elastomeric elements are selectively plated on their outer surface to create a plurality of conductive elements. Unfortunately, since the elastomeric elements are integrally formed with the carrier, it would be extremely difficult to repair a conductive element that has been damaged. Therefore the entire connector must be scrapped. Furthermore, since the carrier is composed of elastomer, its coefficient of thermal expansion (CTE) is substantially different than the surrounding structures. 
     The embodiment in FIGS. 4 and 5 of U.S. Pat. No. 5,599,193 describes an LGA connector with a rigid carrier that has openings with a shape complementary to the externally conductive elastomeric elements. While such an embodiment provides retention of the conductive elements, it would be difficult to implement such a structure with the low profile necessary to meet today&#39;s stringent mechanical and electrical requirements. 
     The individual cavities in the carriers for most of these connectors are cylindrical in shape and provide a minimal amount of retention of individual contact elements. Unfortunately, this makes the assembly and the proper engagement of the connector more difficult, since the individual contact elements may tend to fall out or shift vertically. Although a missing contact element will always result in an open circuit, an element shifted vertically may lead to problems maintaining uniform electrical and mechanical properties, thereby significantly reducing the reliability of the interconnection. 
     It is believed that a carrier that provides improved retention of the individual contact elements will result in LGA interposer connectors with improved manufacturability, reliability and more uniform mechanical and electrical performance, constituting a significant advancement in the art. 
     It is, therefore, an object of the invention to enhance the electrical connector art. 
     It is another object of the invention to provide a carrier for land grid array connectors with improved contact element retention. 
     It is an additional object of the invention to provide a carrier for land grid array connectors that results in a connector with improved manufacturability. 
     It is an additional object of the invention to provide a low profile carrier and land grid array connector combination. 
     It is an additional object of the invention to provide a carrier and land grid array connector combination that is reworkable if a contact member is damaged. 
     It is a still further object of the invention to provide a carrier for land grid array connectors that results in a connector with uniform electrical and mechanical performance. 
     SUMMARY OF THE INVENTION 
     The present invention provides a carrier that provides improved retention to the individual contact elements resulting in LGA interposer connectors with improved manufacturability, reliability and more uniform mechanical and electrical performance. In one embodiment, the carrier, which includes upper and lower sections of dielectric material with an adhesive layer in between, includes a plurality of openings, each of which may contain an individual contact element. During assembly of the connector, once the contact elements are inserted, the adhesive layer is reflowed, thereby allowing the carrier to capture the location of the contact elements both with respect to each other as well as to the carrier. Alternately, the carrier may be implemented in a fashion that, while not including an adhesive layer to be reflowed, still provides improved retention of the individual contact elements. These embodiments may by easier to assemble, and less expensive to manufacture, especially in high volumes. Description of the processes to assemble the carrier and overall connector are also disclosed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when taken in conjunction with the detailed description thereof and in which: 
     FIG. 1 a  is a partial perspective view of an electrical connector in accordance with the prior art; 
     FIG. 1 b  is a side view, in section and on an enlarged scale, of a prior art connector shown in FIG. 1 a , the connector being located between and in alignment with a pair of circuit members for eventually providing interconnection therebetween; 
     FIG. 2 a  is a partial perspective view of an electrical connector in accordance with one embodiment of the present invention; 
     FIG. 2 b  is a side view, in section and on an enlarged scale, of the connector shown in FIG. 2 a ; 
     FIG. 3 a  is a side view of a carrier for an electrical connector in accordance with a second embodiment of the present invention; 
     FIG. 3 b  is a top view, and on an enlarged scale, of the carrier shown in FIG. 3 a ; 
     FIG. 4 a  is a side view of a carrier for an electrical connector in accordance with a third embodiment of the invention; 
     FIG. 4 b  is a top view, and on an enlarged scale, of a carrier shown in FIG. 4 a ; and 
     FIG. 4 c  is a top view, and on an enlarged scale, of another example of a carrier for an electrical connector in accordance with the embodiment shown in FIGS. 4 a  and  4   b . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Generally speaking, the present invention is a carrier that provides improved retention to the individual contact elements of LGA interposer connectors. Improved manufacturability, reliability and more uniform mechanical and electrical performance are achieved with this invention. 
     Referring first to FIGS. 1 a  and  1   b , there are shown perspective and side views, respectively, of a connector  10  of the prior art for electrically interconnecting a pair of electrical circuit members  24  and  34 . Examples of circuit members suitable for interconnection by connector  10  include printed circuit boards, circuit modules, etc. The term “printed circuit board” is meant to include but not be limited to a multilayered circuit structure including one or more conductive (i.e. signal, power and/or ground) layers therein. Such printed circuit boards, also known as printed wiring boards, are well known in the art and further description is not believed necessary. The term “circuit module” is meant to include a substrate or like member having various electrical components (e.g., semiconductor chips, conductive circuitry, conductive pins, etc.), which may form part thereof. Such modules are also well known in the art and further description is not believed necessary. 
     Connector  10  includes a common, electrically insulative carrier member  12  having a plurality of internal apertures or openings  14 . The openings  14  are typically cylindrical in shape. Resilient contact members  16  are located so as to substantially occupy a respective opening  14  in carrier member  12 . 
     Each opposing end  18  and  20  of each contact member  16  is designed for electrically contacting respective circuit members. As stated, these circuit members may be printed circuit boards  34  having flat conductive pads (e.g., copper terminals)  28  located on an upper surface thereof. These circuit members may also comprise a circuit module  24  including a substrate  26  having a plurality of semiconductor elements  32  thereon and corresponding thin, flat, copper conductive pads  28  located on a bottom, external surface. The conductive pads  28  are, understandably, electrically coupled to corresponding circuitry, which forms part of the respective electrical circuit members. These pads  28  may provide signal, power or ground connections, depending on the operational requirements of the respective circuit member. 
     Connector  10  is designed for being positioned between opposing circuit members  24  and  34 , and for being aligned therewith. Such alignment may be possible by placement of the carrier member  12 , which may also include alignment openings  22 . 
     Each resilient contact member  16  is thus compressed during engagement to form the appropriate interconnection between corresponding pairs of conductive pads  28 . 
     As discussed hereinabove, openings  14  in carrier member  12 , typically cylindrical in shape, provide a minimal amount of retention of individual resilient contact members  16 . Unfortunately, this makes the assembly and the proper engagement of the connector more difficult, since the individual contact elements may tend to fall out or shift vertically. Although a missing contact element will always result in an open circuit, a shifted element may lead to problems maintaining uniform electrical and mechanical properties, thereby significantly reducing the reliability of the interconnections. 
     Referring now to FIGS. 2 a  and  2   b , there is shown perspective and side views, respectively, of a connector  40  of the present invention for electrically interconnecting a pair of electrical circuit members  24  and  34 . Examples of suitable circuit members include printed circuit boards, circuit modules, etc. 
     Connector  40  includes a common, electrically insulative carrier member  42  having a plurality of internal openings  50 . In contrast to the prior art carrier member  12  (FIG. 1 a ), electrically insulative carrier member  42  consists of an upper section  44 , upper spacers  52 , a lower section  46 , and lower spacers  54 , with an adhesive layer  48  between the upper and lower sections  44 ,  46 . In one example of this embodiment, the openings  50  are cylindrical in shape. Each resilient contact member  16  is located so as to substantially occupy an opening  50  in carrier member  42 . 
     Although resilient contact members  16  may be of the type as shown in the prior art, they are preferably of a construction and composition as that taught in copending U.S. patent application Ser. No 09/457,776. 
     In one example of the invention, each resilient contact member  16  may possess a diameter of about 0.026 inch and a corresponding length (dimension LL in FIG. 2 a ) of about 0.040 inch. Openings  50  have a diameter of 0.028 inch, just a few thousandths of an inch larger than the contact members. The center-to-center distance is 0.050 inch, but could be reduced to about 0.040 inch if required. 
     In this embodiment, upper section  44  and lower section  46  are made of epoxy-glass-based materials typically used in printed circuit board fabrication (e.g., FR4). These materials are preferred because their coefficient of thermal expansion (CTE) substantially matches the CTE of the surrounding structures, and because of their relatively low cost. Each section  44  and  46  is 0.007 inch thick. Layer  48  consists of a 0.002-inch layer of pressure sensitive adhesive (PSA). One company that manufactures appropriate adhesive layers is Minnesota Mining and Manufacturing Company (3M). Layer  48  may consist of other materials including prepreg. 
     Once an appropriate combination of pressure and temperature is applied to connector  40  during assembly, the adhesive layer  48  of PSA reflows and attaches conductive members  16  to carrier member  42 , thereby capturing contact members  16  and uniformly maintaining their location/position relative to each other as well as to carrier member  42 . It should be noted that FIGS. 2 a  and  2   b  show connector  40  prior to the reflow of adhesive layer  48 . 
     While a carrier  40  with single layers for the upper section  44 , upper spacers  52 , lower section  46 , lower spacers  54 , and adhesive layer  48  between the upper and lower sections  44 ,  46  has been chosen for purposes of disclosure, it should be obvious that the principles taught by the instant invention can also be applied to structures having multiple layers for one or more the elements listed above. For example, for certain applications it may be desirable to split upper section  44  and lower section  46  in half and include an additional adhesive layer between each of the two halves, thereby increasing the amount of adhesive for retention of conductive members  16 . 
     Upper spacers  52  and lower spacers  54  are also made of epoxy-glass-based materials typically used in printed circuit board fabrication ge.g., FR4). These materials are preferred because their CTE substantially matches the CTE of the surrounding structures, and because of their relatively low cost. Each spacer  52  and  54  is 0.0055 inch thick. The overall thickness of carrier member  42  (including the upper and lower sections, the upper and lower spacers, and the adhesive layer) is 0.027 inch. The function of spacers  52  and  54  is to limit the maximum amount that contact members  16  may be compressed, which is from 0.040 to 0.027 inch in this particular case. 
     The inclusion of adhesive layer  48  in electrically insulative carrier member  42  helps to alleviate deficiencies of the prior art carrier, those being to ensure that contact members  16  do not fall out during assembly or engagement, and more commonly, to ensure that all individual contact members maintain uniform electrical and mechanical properties, thereby significantly improving the reliability of the interconnections. 
     As with the prior art, each opposing end  18  and  20  of resilient contact member  16  is designed for electrically contacting respective circuit members. These circuit members may be printed circuit boards  34  having flat conductive pads (e.g., copper terminals)  28  located in an upper surface thereof. These circuit members may also comprise a circuit module  24  including a substrate  26  having a plurality of semiconductor elements  32  thereon and corresponding flat conductive pads (e.g., thin copper elements)  28  located on a bottom, external surface. The conductive pads  28  are, understandably, electrically coupled to corresponding circuitry, which forms part of the respective electrical circuit members. These pads  28  may provide signal, power or ground connections, depending on the operational requirements of the respective circuit member. It is preferred that conductive pads  28  be plated with a layer of metal (e.g., gold) to ensure reliable interconnection to connector  40 . 
     Connector  40  is positioned between opposing circuit members  24  and  34 , and is aligned therewith. Such alignment may be possible by placement of the carrier member  42 , which also includes alignment openings  56 . 
     Alignment of the circuit members  24  and  34  relative to interim connector  40  may be provided utilizing a pair of protruding pins  30  which extend from one of the circuit members (e.g., module  24 ), these pins being aligned with and positioned within corresponding openings  56  within carrier member  42  and openings  36  (shown hidden) within the other circuit member  34 . It should be understood that other means of alignment are readily possible, including the provision of pins extending from opposing surfaces of carrier member  42  for inversion within corresponding openings within the respective circuit members. To adjust for tolerancing, one of the openings  56  within connector  40  may be of an elongated configuration, forming a slot, for example. 
     Each resilient contact member  16  is thus compressed during engagement to form the appropriate interconnection between corresponding pairs of conductive pads  28 . 
     Carrier member  42  may be constructed in many different ways. A preferred method is to start by removing the protective sheet from one side of an adhesive layer and to laminate to either the upper or lower section of FR4. In one case a temperature of 185 degrees F. and a pressure of 20 pounds per square inch (PSI) were used. Once this operation is complete, remove the protective sheet from the other side of an adhesive layer/FR4 laminate and laminate it to the other section of FR4. A computer numerically controlled (CNC) drilling machine can then be used to create the upper and lower spacers, to drill openings and alignment holes and/or slots as required, and to define the overall outer edges of the carrier member. 
     Another method to construct carrier member  42  is to start by removing the protective sheet from one side of an adhesive layer and to laminate to either the upper or lower section of FR4. This time, however, the FR4 layer is thinner and used to create only the upper and lower sections, not the upper and lower spacers. Once this operation is complete, remove the protective sheet from the other side of an adhesive layer/FR4 laminate and laminate it to another thinner section of FR4. Upper and lower spacer layers can be created separately and then laminated to the FR4/adhesive/FR4 composite, preferably after the CNC drilling operations described above are completed. 
     A method for constructing the overall connector  40  is to start with a fixture that will hold the bottom surface of the carrier member a distance equivalent to the distance that the conductive members should protrude below the carrier member. Once the carrier is aligned to the fixture, conductive members are inserted in the openings and held in place by means such as a vacuum. A proper combination of temperature and force can then be applied to the assembly to allow the adhesive layer to reflow and to attach the conductive members to the carrier member, thereby capturing contact members and uniformly maintaining their location/position relative to each other as well as to the carrier member. 
     Referring now to FIGS. 3 a  and  3   b , there are shown side and top views, respectively, of an electrically insulative carrier member  62  to be used as part of a connector in accordance with an alternate embodiment of the invention. A pair of electrical circuit members  24  and  34  can be electrically interconnected. 
     The primary purpose for using carrier member  62  over prior art carriers is the same as for carrier member  42  (FIG. 2 b ): to better retain the conductive members  16  during both assembly and actual operation. 
     The cross section of electrically insulative carrier member  62  is similar to that of carrier member  42  of the previous embodiment with the primary difference being that adhesive layer  48  (FIG. 2 b ) is replaced by retention layer  64 . In one example, retention layer  64  is made of Mylar (a trademark of E. I. DuPont deNemours &amp; Co., Wilmington, Del.) and is 0.002-inch thick. For the elements and materials common to both this example and that shown in FIG. 2 b , the dimensions and materials of said elements are unchanged. For example, the thickness of upper section  44  in one case is still 0.007 inch and preferably of an epoxy-glass-based material such as FR4 for the reasons previously mentioned. Since the thickness of retention layer  64  is the same thickness ac that of adhesive layer  48  (0.002 inch), the overall thickness of carrier member  62  is still 0.027 inch, the same as that: of carrier member  42 . 
     Retention layer  64  has a plurality of smaller openings  66  formed by a plurality of retention segments  68  that are created by the removal of a portion of retention layer  64  and the segmentation of the remaining material within a larger opening  70  in carrier member  62 . In one example each larger opening  70  contains four retention segments  68  that form primarily circular smaller opening  66 . The specific dimensions of each of the elements of this invention can be varied to produce the desired amount of retention force on conductive members  16  (not shown in this figure). 
     Carrier member  62  provides a tradeoff of performance versus ease-of-manufacturability compared to carrier member  42  (FIG. 2 b ). While carrier member  62  provides improved retention of conductive members  16  compared to the prior art, it would probably not be as high as the retention of reflowed adhesive layer  48  of carrier member  42 . On the other hand, carrier member  62  does not require the application of heat and pressure during the assembly process. 
     Referring now to FIGS. 4 a  and  4   b , there are shown side and top views, respectively, of an electrically insulative carrier member  82  to be used a part of a connector in accordance with another embodiment of the invention. The cross section and dimensions of electrically insulative carrier member  82  are similar to other inventive carrier members described hereinabove, and particularly that of carrier member  62  (FIGS. 3 a  and  3   b ), with the primary difference being that the previous multilayered structures are replaced by a single, unified structure. The benefits of this approach are for ease of Manufacture, and for ultimately lower cost, especially in high-volume production. 
     Carrier member  82  has a plurality of smaller openings  84  formed by a plurality of retention segments  86  within larger openings  88 . In one example, each larger opening  88  contains three retention segments  86  that form smaller opening  84 . The specific dimensions of each of the elements of this invention can again be varied to produce the desired amount of retention force on conductive members  16  (not shown in this figure). 
     In one example, carrier member  82  is formed by molding a plastic material such as a liquid crystal polymer (LCP). Suitable examples of LCP are Vectra (a trademark of Hoechst Celanese Corporation) and Ryton (a trademark of Philips Petroleum Company). 
     Referring now to FIG. 4 c , there is shown a top view, and on an enlarged scale, of another example of an electrically insulative carrier member  92  for an electrical connector in accordance with the embodiment shown in FIGS.  4   a  and  4   b . 
     Carrier member  92  has a plurality of smaller openings  94  formed by a plurality of retention segments  96  within larger openings  98 . In one example, each larger opening  98  contains three retention segments  86  that form smaller opening  94 . The specific dimensions of each of the elements of this invention can again be varied to produce the desired amount of retention force on conductive members  16  (not shown in this figure). 
     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, this invention is not considered limited to the examples chosen to purposes of this disclosure, and covers all changes and modifications which does not constitute departures from the true spirit and scope of this invention. 
     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.