Abstract:
An intercoupling component is of the type used to couple an array of electrical connection regions disposed on a first substrate to an array of electrical connection regions disposed on a second substrate. The intercoupling component comprises: an insulative support member; a plurality of electrically conductive terminal elements; a second insulative support member; and a seal member positioned between the first insulative support member and the second insulative member to restrict fluid flow along the terminal elements.

Description:
TECHNICAL FIELD 
   This invention relates to making connections between integrated circuit array packages and circuit boards, and more particularly to intercoupling components for making such connections. 
   BACKGROUND 
   Ball grid array (BGA) packages are becoming increasingly popular because of their low profiles and high densities. With a BGA package, for example, the rounded solder balls of the BGA are generally soldered directly to corresponding surface mount pads of a printed circuit board rather than to plated thru-holes which receive pins from, for example, a pin grid array (PGA) IC package. 
   Sockets allow particular IC packages to be interchanged without permanent connection to a circuit board. More recently, sockets for use with BGA packages have been developed to allow these packages to be non-permanently connected (e.g., for testing) to a circuit board. Such sockets can be attached to circuit boards at connection points that mirror those of the BGA packages that the sockets are used with. However, problems can exist in attaching a socket to a circuit board using reflowable substances. 
   SUMMARY 
   This invention features an intercoupling component of the type used to couple an array of electrical connection regions disposed on a first substrate (e.g., a BGA package) to an array of electrical connection regions disposed on a second substrate (e.g., a printed circuit board). The intercoupling component includes a seal member which limits the flow of fluids (e.g., molten solder) into the intercoupling component. This can improve the reliability of the electrical connection provided by the intercoupling component. 
   The intercoupling component can include two sheets of insulative material which are stiffer than the seal with the seal member located between them. Alternatively, the intercoupling component can include a single sheet of insulative material which is stiffer than the seal member with the seal member located on or near a face of the insulative material. 
   An aspect of the invention features an intercoupling component is of the type used to couple an array of electrical connection regions disposed on a first substrate to an array of electrical connection regions disposed on a second substrate. The intercoupling component includes: an insulative support member having a first upper surface and an opposite first lower surface, the support member including an array of first holes extending transversely from the first upper surface to the opposite first lower surface, the array of first holes located in a pattern corresponding to the array of the electrical connection regions of the first substrate; a plurality of electrically conductive terminal elements, press-fit within the first holes and configured to electrically connect the array of connection regions of the first substrate to the array of connection regions of the second substrate; a second insulative support member having a second upper surface, an opposite second lower surface and a first stiffness characteristic, the second insulative support member including an array of second holes extending transversely from the second upper surface to the opposite second lower surface, the array of second holes receiving the plurality of electrically conductive terminal elements; and a seal member positioned between the first insulative support member and the second insulative member, the seal member having a third upper surface, an opposite third lower surface and a second stiffness characteristic less than the first stiffness characteristic, the seal member including an array of third holes extending transversely from the third upper surface to the opposite third lower surface, the array of third holes receiving the plurality of electrically conductive terminal elements and sized and shaped to restrict fluid flow along the terminal elements. 
   Another aspect features a method of manufacturing an intercoupling component of the type used to couple an array of electrical connection regions disposed on a first substrate to an array of electrical connection regions disposed on a second substrate. The method includes: providing an array of first holes extending through a first insulative support member, the array of first holes located in a pattern corresponding to the array of the electrical connection regions of the first substrate; providing an array of second holes extending through a second insulative support member having a first stiffness characteristic, the array of second holes located in a pattern corresponding to the array of the electrical connection regions of the first substrate; providing an array of third holes extending through a seal member, the seal member having a second stiffness characteristic less than the first stiffness characteristic; positioning electrically conductive terminal elements within the first holes, the electrically conductive terminal elements configured to electrically connect the array of connection regions of the first substrate to the array of connection regions of the second substrate; and inserting the terminal elements through the third holes and the second holes such that the seal member is positioned between the first insulative support member and the second insulative member with the array of third holes sized and shaped to restrict fluid flow along the terminal elements. 
   Embodiments of these aspects of the invention may include one or more of the following features. In some embodiments, each terminal element includes solder preattached to an end of the terminal element. The solder can include a solder ball adapted to be reflowed to connect the terminal element to a corresponding one of the array of connection regions disposed on the second substrate. 
   In some embodiments, the seal member is formed of an insulative material and or can include a polyimide film. In some embodiments, the seal member is thermally-stable at temperatures below 400 degrees Centigrade and/or is substantially non-porous. 
   In some embodiments, the seal member includes a plurality of seals. Each seal can have third holes corresponding to a subset of the first holes. Similarly, each of the plurality of seals can have an annular shape. 
   In some embodiments, the first holes are sized to allow an end of the terminal elements to be press-fit into the first insulative support member. The first holes can have a diameter of less than about 0.020 inch (0.508 millimeters) and/or can be located with a pitch of between about 0.019 inch (0.500 millimeters) and 0.050 inch (1.27 millimeters). The second holes can have a first diameter that is greater than or equal to a second diameter of the third holes. 
   In some embodiments, the first insulative support member includes a first epoxy impregnated laminate with a first thickness and the second insulative support member includes a second epoxy impregnated laminate with a second thickness. The first thickness can be more than the second thickness. The first thickness can be between about 0.025 inch (0.635 mm) and 0.100 inch (2.54 mm) (e.g., 0.062 inch (1.57 millimeters)). The second thickness can be between about 0.005 inch (0.127 mm) and 0.025 inch (0.635 mm) (e.g., 0.015 inch (0.380 mm)). 
   In some embodiments, providing the second holes comprises machining the third holes to have a first diameter that is equal to or less than a second diameter of the second holes. For example, machining the third holes can include machining the third holes to have a first diameter of less than about 0.020 inch (0.508 mm). 
   In some embodiments, providing the array of third holes comprises drilling holes extending through a polyimide film (e.g., polyimide film that has a third thickness that is between about 0.004 inch (0.102 mm) and 0.006 inch (0.152 mm). Inserting the terminal elements through the third holes can include engaging sides of the terminal elements with portions of the seal member defining the third holes. 
   The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is an exploded perspective view of intercoupling component of the type used to couple a printed circuit board to a BGA package. 
       FIG. 2  is a side view of the intercoupling component of  FIG. 1 . 
       FIG. 2A  is an expanded side view of a portion of the intercoupling component of  FIG. 2 . 
       FIG. 3  is a cross-sectional view of a socket terminal extending through a portion of the intercoupling component of  FIGS. 1 and 2 . 
       FIG. 4  is a plan view of a seal member. 
       FIG. 5  is a plan view of another seal member. 
       FIG. 6  is a plan view of still another seal member supported by a secondary support member. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 2 , a BGA socket converter assembly  10  for intercoupling a BGA package  12  to a printed circuit board  14  is shown. BGA socket converter assembly  10 , serving as an intercoupling component, includes an electrically insulative member  16  for supporting converter socket terminals  18 , each of which is press-fit within a corresponding one of an array of holes  20  in the insulative member. 
   The array of holes  20  are provided in a pattern corresponding to a footprint of rounded solder balls of BGA package  12  as well as a footprint of surface mount pads  24  of printed circuit board  14 . Other embodiments include electrical connection regions other than surface mount pads on substrates other than printed circuit boards (e.g., flexible circuits or test boards). Insulative member  16  with converter socket terminals  18  is press-fit into a guide box  26  having sidewalls  28  along which the peripheral edges of BGA package  12  are guided so that solder balls of the BGA package are aligned over converter socket terminals  18 . Insulative member  16  and guide box  26  may be formed as a one-piece, integral unit. 
   As shown in  FIG. 1 , BGA socket converter assembly  10  also includes a hold-down cover  30  for securing the BGA package  12  into the socket converter assembly. Cover  30  includes a pair of opposite walls  31  having tab members  33  which engage recessed portions  37  along the underside of the insulative member  16 . Hold-down cover  30  includes a threaded thru-hole  34  which threadingly receives a heat sink  32  to provide a thermal path for dissipating heat from the IC device generated within BGA package  12 . Heat sink  32  is inserted and backed-in from the bottom of the cover  30  and includes a lip  49  which engages a flat counter-bored surface (not shown) on the bottom surface of the cover to ensure that the heat sink will contact the surface of the BGA package. A slot  36  formed in the heat sink facilitates threading the heat sink within the cover, for example, with a screwdriver or coin. Other latching mechanisms (e.g., clips or catches) may also be used to secure BGA packages within the socket converter assembly. It is also appreciated that other heat sink arrangements, including those with increased surface area (e.g. heat sinks with finned arrangements), may be substituted for the lower profile version shown in  FIG. 1 . In some applications, a heat sink may not be required with only the cover providing the downward compressing force to the BGA package. 
   Referring to  FIGS. 2 ,  2 A, and  3 , the insulative member  16  includes a primary support member  40  and a seal  42 . The seal  42  includes a secondary support member  44  and a seal member  46 . The support members  40 ,  44  and seal member  46  have matching holes  20 A,  20 B,  20 C located in a pattern that corresponds to the footprint of surface mount pads  24  of printed circuit board  14 . The holes  20 A in the primary support member extend from its upper surface  41  through the primary support member to its lower surface  43 . Similarly, the holes  20 B in the secondary support member  44  extend from its upper surface  45  to its lower surface  47  and the holes  20 C in the seal member  46  extend from its upper surface  49  to its lower surface  51 . The terms “upper” and “lower” are used here and throughout this document for descriptive purposes rather than to imply any absolute relative orientation. 
   The primary support member  40  and the seal  42  can be spaced apart as shown. In other embodiments, the seal  42  abuts the primary support member  40 . The relative location of the primary support member  40  and the seal  42  is maintained by the converter socket terminals  18 . 
   The primary support member  40  is made of a material that is substantially non-conductive to electricity (e.g. having resistivity greater than about 200K Mohms), has high-temperature resistance, is stable, and is inert. Appropriate materials include, for example, commercially available glass epoxy laminates. The thickness of the primary support member  40  is selected based on the required support and the characteristics of the material used to construct the primary support member  40 . A related factor is that it is desirable to limit the space requirements of the overall intercoupling component, and, thus, the thickness of the primary support member  40 . 
   Both the secondary support member  44  and the seal member  46  are also made of materials that are substantially nonconductive to electricity. The seal member  46  is configured to restrict fluid flow (e.g. the flow of molten solder) upwards along the socket terminals  18 . The secondary support member  44  supports the seal member  46  and provides a level surface through which the solder balls  50  of the socket terminals extend. The seal member  46  is made of a material (e.g. a polyimide film) that has a stiffness characteristic less than the stiffness characteristic of the material (e.g. FR4) of the secondary support member  44  (i.e. the seal member is more flexible than the secondary support member  44 ). It is also preferable that the secondary support member  44  be visually distinct from solder. 
   The aligned holes  20 A,  20 B,  20 C receive the converter socket terminals  18  which extend through both the primary support member  40  and the seal  42 . The holes  20 C are sized with a diameter that is slightly smaller than the diameter of the matching portion of the socket terminal  18 . Thus, when a socket terminal  18  is inserted into a hole  20 C, the seal member  46  flexes and the hole  20 C expands slightly such that the seal member engages the sides of the socket terminal. 
   The seal  42  restricts fluid flow along the converter socket terminals  18  which extend through both the primary support member  40  and the seal  42 . For example, molten solder can have a tendency to “wick” along outer surfaces of the converter socket terminals  18  when the solder balls  50  are heated to attach the socket terminal assembly  10  to the printed circuit board  14 . When this occurs, flow of the solder into and/or through the primary support member  40  can result in a loss of electrical contact between individual socket terminals  18  and the underlying surface mount pads  24 . By restricting fluid flow along the converter socket terminals  18 , the seal  42  helps limit such “wicking” and, thus, maintain the desired electrical contact between the converter socket terminals  18  and the underlying surface mount pads  24 . As the seal member can come in contact with molten solder, it is desirable that the seal member be thermally-stable at temperatures below 400 degrees Centigrade. 
   Now referring to  FIG. 4 , in the exemplary embodiment, the seal member  46  is made of a single sheet of polyimide defining the 484 (22×22) array of holes  20 C. By limiting “wicking” of solder along the socket terminals  18 , the seal member  46  allows the holes  20 A,  20 B through the support members  40 ,  44  to be sized to compensate for positional and machining tolerances in the location and sizing of both the holes  20 A,  20 B and the socket terminals  18 . This is thought to reduce the physical stresses on the insulative member  16  (particularly the support members  40 ,  44 ) that occur as the socket terminals are inserted through the holes  20 . 
   Now referring to  FIG. 5 , in alternate embodiments, the seal member  46  has multiple sections  46 A that together define the 22 by 22 array of holes  20 C and cover the face of the secondary support member (not shown). Now referring to  FIG. 6 , in still further embodiments, the seal member has multiple annular sections  46 B each of which is located such that a hole  20 C extending through the annular section is approximately aligned with one of the holes  20 B extending through the secondary support member  44 . These alternate embodiments of the seal member  46  further reduce the cumulative physical stresses on the insulative member  16  that occur as the socket terminals  18  are inserted through the holes  20  because the multiple sections  46 A,  46 B of seal member only contact subsets of the socket terminals. 
   Although the insulative member  16  and its seal member  46  are shown being used in conjunction with socket terminals with attached solder balls, the insulative member  16  and its seal member  46  are also useful with other assemblies that are attached using reflowable materials (e.g. socket terminals with thru-hole pins, socket terminals attached using solder paste initially placed on the printed circuit board, or socket terminals with solder bumps). 
   Referring again to  FIG. 3 , each socket terminal assembly includes a female socket  48  positioned within one of the array of holes  20  of insulative member  16 . Female socket  48  includes a solder ball  50  pre-attached (e.g., by soldering) to its bottom end  52  to provide an identical mating condition to surface mount pads  24  as would have been the case had BGA package  12  been connected directly to the printed circuit board  14 . Solder balls  50  are eventually soldered to corresponding surface mount pads  24  of circuit board  14 . Positioned within the interior of female socket  48  is a contact spring (not shown) press-fit within the interior and upper end of the female socket. 
   In one exemplary insulative member  16 , both the primary support member  40  in the secondary support member  44  are made of a black glass epoxy U.L. rated 94V-0 commercially available as FR4. The seal member  46  is made of a polyimide film commercially available as Kapton. The black glass epoxy of the support members is visually distinct from solder. This is thought to aid in the detection of any solder which passes through the seal member  46 . 
   The seal member more flexible than the support members to allow the seal member to conform to the sides of the socket terminal assemblies  18 . Both of the support members  40 ,  44  and the seal member  46  have square faces with sides approximately 0.906 inch (23.00 millimeters) in length. The primary support member  40  is approximately 0.062 inch (1.575 millimeters) thick, the secondary support member  44  is approximately 0.020 inch (0.508 millimeter) thick, and the seal member  46  is approximately 0.005 inch (0.13 millimeter) thick. A 22 by 22 array of holes  20 C is machined in each of the support members  40 ,  44  and the seal member with a pitch of approximately 0.0394 inch (1 millimeter). In this context, pitch is the distance between the centers of adjacent holes. The holes  20 A,  20 B, and  20 C have diameters of approximately 0.0335 inch (0.851 millimeter), 0.019 inch (0.483 millimeter), and 020 inch (0.508 millimeter), respectively. 
   In one embodiment, the parts of the intercoupling component  16  are manufactured separately and then assembled. An array of holes  20 A is provided extending through the primary support member  40 , an array of holes  20 B is provided extending through the secondary support member  44 , and an array of holes  20 C is provided extending through the seal member  46 . As described above, the arrays of holes  20 A,  20 B, and  20 C are located in patterns corresponding to the footprint of the surface mount pads  24  of printed circuit board  14  and the stiffness characteristic of the seal member  46  is less than the stiffness characteristic of the secondary support member  44 . Electrically conductive elements (e.g. socket terminals  18 ) configured to electrically connect the array of surface mount pads  24  on the printed circuit board  14  to the array of connection regions of the BGA package  12  are positioned within the holes  20 A. The electrically conductive elements are inserted through the holes  20 B and  20 C such that the seal member  46  is positioned between the primary support member  40  and the secondary support member  44 . The holes  20 C in the seal member  46  are sized and shaped to restrict fluid flow along the terminal elements. 
   Providing the holes  20 B can include machining (e.g., drilling, stamping, water drilling) the holes  20 B to have a first diameter that is equal to or less than a second diameter of the holes  20 C. For example, in one embodiment, holes  20 B and holes  20 C were drilled in the secondary support member  44  and in the seal member  46 , respectively. 
   After the holes  20 A,  20 B,  20 C are machined in the support and seal members, the socket terminals are inserted through the holes  20 A,  20 B,  20 C such that sides of the socket terminals engage with portions of the seal member. 
   A number of embodiments of the invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, although the exemplary seal  46  is configured as a single sheet whose dimensions approximate the dimensions of the support members, other seals are configured as multiple rectangular sheets or multiple annuli. Similarly, although the illustrative embodiments have 22×22 arrays of holes to receive socket terminals, other numbers and/or configurations of holes and socket terminals could be used in other embodiments. Similarly, in other embodiments, intercoupling components are configured to couple a printed circuit board to a second printed circuit board. Accordingly, other embodiments are within the scope of the following claims.