Abstract:
A chip socket with one or more seals protecting the contact members. The seals are formed in a multi-step molding process. In a first step, an insulative housing is formed with grooves in the surface. In the second step, a seal material is molded into the grooves with a portion extending above the surface of the insulative housing. In use, surfaces of the chip socket are pressed against a semiconductor chip or a circuit board. When pressed together, the components of the connector system form seals that protect contact members from environmental conditions. The seals allow reliable electrical connections to be made with reduced force per contact. Greater flexibility in designing the contact members is therefore provided contact members having a low spring force and a relatively large deflection range, thereby accommodating a less stringent coplanarity requirement for the chip and circuit board.

Description:
[0001]     This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 60/639,047, entitled “Environmentally Sealed Chip Socket,” filed on Dec. 23, 2004, which is herein incorporated by reference in its entirety. 
     
    
     BACKGROUND OF INVENTION  
       [0002]     1. Field of Invention  
         [0003]     This invention relates generally to electrical connectors and more specifically to chip sockets.  
         [0004]     2. Discussion of Related Art  
         [0005]     Electrical connectors are used in many portions of electronic systems. Electrical connectors allow the system to be easily manufactured from subassemblies. The connectors interconnect the subassemblies without the need for soldering or other forms of permanent or semi-permanent attachment that can be expensive or time consuming to manufacture.  
         [0006]     Connectors also allow the subassemblies to be easily disassembled. This feature makes the electronic system easier to repair, maintain or upgrade.  
         [0007]     Electrical connectors are often installed on printed circuit boards. The connectors may be used to join conducting traces on one printed circuit board to the conducting traces on another printed circuit board. Such connectors are sometimes referred to as Level III connectors.  
         [0008]     Connectors are also used to attach components, such as integrated circuit chips in packaged or unpackaged form, to printed circuit boards. Connectors used for this purpose are sometimes referred to as chip sockets or Level II connectors. Connectors are used to connect other types of components at other “levels” of the system.  
         [0009]     Regardless of the specific application of the connector, it is desirable that the connector form a reliable electrical connection over the useful life of the product in which it may be installed.  
         [0010]     It would be desirable to provide an improved electrical connector and would be particularly desirable to provide an improved electrical connector suitable for use as a chip socket.  
       SUMMARY OF INVENTION  
       [0011]     In one aspect, the invention relates to an electrical connector having a housing and a plurality of conductive contact elements having a first portion and a second portion, with the first portion disposed in the housing and the second portion exposed in a surface of the housing. The connector includes a seal having a first portion and a second portion, with the first portion positioned in the housing and the second portion exposed in a surface of the housing. The seal outlines an area and the second portion of at least one of the plurality of conductive contact elements is positioned within this area.  
         [0012]     In another aspect, the invention relates to an electrical connector comprising a housing and a plurality of conductive contact elements having a first portion and a second portion. The first portion is disposed in the housing and the second portion exposed in a surface of the housing. The connector includes a plurality of compliant structures, each having a first portion and a second portion, with the first portion positioned in the housing and the second portion exposed in the surface. Each of the compliant structures outlines an area of the surface and the second portion of at least one of the plurality of conductive contact elements is positioned within the area.  
         [0013]     In a further aspect, the invention relates to a method of manufacturing an electrical connector. The method involves providing a plurality of conductive members; forming a housing of a first type material with a plurality of locations adapted to receive a conduction member of the plurality of conductive members, the housing having a surface with at least a portion of each of the conductive members exposed through the surface; and affixing a compliant member to the housing to encircle at least one of the locations, with a portion of the compliant member extending above the surface.  
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0014]     The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For purposes of clarity, not every component may be labeled in every drawing. In the drawings:  
         [0015]      FIG. 1  is a sketch of a connector system according to the invention;  
         [0016]      FIG. 2  is a side view of the connector system of  FIG. 1 ;  
         [0017]      FIG. 3  is an enlarged cross-sectional view of a portion of the connector system of  FIG. 1 ; and  
         [0018]      FIG. 4  is a cross sectional view of an alternative embodiment of a connector system according to the invention. 
     
    
     DETAILED DESCRIPTION  
       [0019]     This invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, is meant to encompass the items listed thereafter and equivalents thereof as well as additional items.  
         [0020]     The invention is here illustrated by a connector system  100  as shown in  FIG. 1 . In this example, the connector system includes a chip socket  110  designed to provide a separable electrical connection between a chip  120  and a substrate, such as a circuit board  130 .  
         [0021]      FIG. 1  illustrates a relatively small semiconductor chip  120  having a small number of pads that require connection to circuit board  130 . Such a configuration is shown for simplicity of illustration. The invention may be particularly useful in connection with a relatively large chip, such as a computer processor chip, which may have over one hundred I/O pads for which connections are made to a circuit board  130 .  
         [0022]     In use, a force F is applied to chip  120 . The force presses chip  120  into chip socket  110 . The force F also presses chip socket  110  against circuit board  130 . Force F may be generated by a retaining structure (not shown) attached to circuit board  130 . Such retaining structures are conventionally used with chip sockets and include levers, latches, camming surfaces or other structures that may hold chip socket  110  and chip  120  against circuit board  130 . However, any suitable retaining structure may be used to generate the force F.  
         [0023]     Chip socket  110  includes a housing  150 . In the described embodiment, housing  150  is an insulative material. In one embodiment, housing  150  is formed from a therma-plastic material so that it may be readily molded into a desired shape. Materials conventionally used to form the housing of electrical connectors, whether now known or hereafter developed, may be used to form housing  150 . Examples of suitable materials are LCP and nylon.  
         [0024]     Compliant members  114  extend from a surface  112  of chip socket  110 . For simplicity, only one of the compliant members  114  is numbered. The compliant members may be identical. Compliant member  114  may be formed from any suitable compliant conductive material. Materials traditionally used for electrical contacts in electrical connectors may be used. In the embodiments shown herein, springy metals are used. Examples of suitable materials are copper alloys and phosphor bronze. Compliant member  114  may have a protective coating over all or a portion of its surface. The coating may be formed from a relatively inert metal that resists oxidation, such as gold, nickel or tin.  
         [0025]     When chip  120  is pressed against chip socket  110 , compliant members  114  press against conductive structures on chip  120 . In this way, an electrical connection may be formed between conductors and chip  120  and the conductors within chip socket  110 . Similar compliant members (See, e.g.,  314 ,  FIG. 3 ) extend from an opposing surface of the chip socket  110  and are electrically connected to compliant members  114 . The compliant members extend from the opposing surface of housing  150  are positioned to engage conducting pads  134  on the surface of circuit board  130 . Force F presses the compliant members  314  against pads  134 , thereby completing a conductive path between chip  120  and circuit board  130 .  
         [0026]     In the illustrated embodiment, each of the compliant members  114  is positioned within a recess  118 . As chip  120  is pressed against chip socket  110 , compliant member  114  retracts into recess  118 . Similar recesses (see, e.g.,  318 ,  FIG. 3 ) are provided on the lower surface of chip socket  110  to receive compliant members  314 .  
         [0027]     Recess  118  is surrounded by a seal  116 . Seal  116  is formed from a low durometer material such as is conventionally used in forming seals or gaskets. Preferably, seal  116  is formed from a material that is relatively impervious to oxygen and other gases from the ambient environment. In some embodiments, seal  116  is formed from a curable material, such a silicone, that may be molded in place. Examples of other suitable materials for forming seal  116  are rubber and rubberized plastic.  
         [0028]     As shown, seal  116  extends above surface  112 . As force F presses chip  120  against chip socket  110 , seal  116  presses against the lower surface of chip  120 . Because seal  116  is made of a compliant material, it conforms to the shape of chip  120 . Preferably, the force F is sufficient to form an environmental seal between chip socket  110  and chip  120 .  
         [0029]      FIG. 2  shows a side view connector system  100 . In this view, it may be seen that the illustrated embodiment of chip socket  110  includes symmetrical upper and lower surfaces. The upper surface includes compliant members  114  facing chip  120 . The lower surface includes compliant members  314  facing circuit board  130 . Each compliant member  114  is electrically connected to a compliant member  314 .  
         [0030]     Each of the compliant members  114  and  314  makes contact with a conducting pad. Compliant members  114  on the upper surface of chip socket  110  may contact with pads  124  on chip  120 . Compliant members  314  on the lower surface of chip socket  110  make contact with pads  134  on circuit board  130 . Pads  124  on chip  120  may be electrically connected to circuitry within chip  120 . Likewise, pads  134  may be electrically connected to traces or other circuit components within circuit board  130 . In this way, chip socket  110  completes an electrical connection between circuitry inside chip  120  and circuit board  130 .  
         [0031]     In the exploded view of  FIG. 2 , the compliant members such as  114  and  314  are shown extended. Compliant members  114  extend a distance T above the surface of housing  150 . When chip  120  is pressed against chip socket  110 , compliant members  114  may be compressed by a distance T. Distance T represents the “travel” of the compliant member.  
         [0032]     Having a large amount of travel ensures that compliant members  114  will make contact with pads  124  even if there are variations in the manufacture of the components. For example, variations that are the result of manufacturing tolerances may result in some compliant members extending above the surface of housing  150  by less then the amount illustrated. However, where T is sufficiently large, routine manufacturing variations will not preclude any of the compliant members from engaging with a pad on chip  120 . In some embodiments, the distance T may be between approximately 0.1 mm and 1 mm. In the embodiments pictured herein, the distance T is on the order of 0.5 mm.  
         [0033]     Providing a large amount of travel enables a large working deflection. The working deflection represents the difference between the minimum and maximum deflection of the compliant members  114  that may result because of manufacturing tolerances of the components. In the embodiment illustrated, the maximum travel T, taking into account manufacturing variations, is the working deflection.  
         [0034]     A traditional connector is designed so that the contact force is sufficient to form a reliable electrical connection. Sufficient contact force is desired to prevent gases from the ambient environment from reaching and interacting with the metals of the contact members in the contact region. Gases including oxygen, chlorine and sulfur are often present in the environments where printed circuit boards are used or manufactured and can interact with the contacts to form an oxide coating over the contacts. Because metal oxides are generally nonconductive, formation of an oxide in the contact region may increase the resistance of the contact or decrease the reliability of the connection between a compliant member  114  and pad  124 . To avoid the formation of oxide in the contact region, traditional connectors are often designed to provide approximately 50 grams of force for each contact.  
         [0035]     If 50 grams is the minimum acceptable contact force, this amount of force must be generated at the minimum deflection of compliant member  114 . At the maximum deflection of compliant member  114 , the contact force will be greater. The amount by which the contact force will increase over the minimum acceptable contact force will be related to the working deflection.  
         [0036]     The maximum possible contact force, multiplied by the total number of contacts, indicates the minimum value for the force F that should be applied to hold a chip  120  in socket  110 . Using conventional designs to provide a contact force of approximately 50 grams of force per contact while simultaneously providing relatively large working deflection leads to one of several problems. One possibility is that the total force F becomes unworkably large. Another possible negative result is that the compliant members may be too large for readily interfacing to the small contact areas traditionally available on an integrated circuit chip. Here, these problems are avoided by using an environmental seal to reduce the required contact force, allowing connectors to be made with a relatively large working deflection in a relatively small space.  
         [0037]      FIG. 3  illustrates how seals  116  may be used to increase the integrity of the electrical connections between chip socket  110  and a chip  120 . A similar seal  316  is used to increase the integrity of electrical connections between a chip socket  110  and circuit board  130 .  
         [0038]     In the configuration illustrated in  FIG. 3 , compliant member  114  is shown pressed into recess  118  by chip  120 . Chip  120  contacts seals  116  in the upper surface of housing  150 . Seals  116  provide sufficient compliance so that a relatively gas impervious seal is formed between seal  116  and chip  120 . Because the seal  116  encircles recess  118 , seal  116  in conjunction with the lower surface of chip  120  seals compliant member  114  within recess  118 . Oxygen and other gases are prevented from reaching compliant member  114 , thereby substantially reducing the rate at which oxide forms on compliant member  114  or pad  124 . When the mating interface between compliant member  114  and pad  124  is sealed within recess  118 , the amount of force needed to ensure a reliable connection is decreased. In some embodiments, the amount of force is less than about twenty five grams per contact. In other embodiments forces of 15-25 grams per contact may be used.  
         [0039]     Seal  316  in the lower surface of housing  150  forms a similar seal between housing  150  and circuit board  130 . Seal  316  seals compliant member  314  within recess  318 . The required contact force between compliant member  314  and pad  134  is therefore reduced.  
         [0040]      FIG. 3  also illustrates details of a possible method of manufacturing chip socket  100 . Housing  150  may be molded from plastic or other insulative material. Housing  150  may be molded with recesses such as  118  and  318  in each surface. A passage  310  may be formed, connecting the recesses. The recesses  118  are formed to align with the pads  124  on the lower surface of chip  120 . Recesses  318  on the lower surface are likewise centered around pads  134 . Pads  134  may be, but do not need to be, aligned with pads  124 .  
         [0041]     Contact members  312  are inserted into the passage  310 . Opposing ends of the contact member  312  may be formed into compliant portion  114  and  314 . Contact member  312  may be secured within passage  3 . 10  according to any suitable means. For example, contact member  312  may be held in place through an interference fit with the walls of passage  310 . Alternatively, barbs or other retaining structures formed in contact  310  may engage housing  150  to hold contact member  312  in place.  
         [0042]      FIG. 3  shows that each seal  116  and  316  has a portion positioned in a recess, such as grooves  340 , of a surface of housing  150 . Seal  116  and  316  may be held in place in any suitable manner. Seals  116  and  316  may be held in place through an interference fit with housing  150 . Alternatively, seals such as  116  and  316  may be glued or otherwise adhered to a surface of housing  150 .  FIG. 1  shows that each seal  116  has a raised portion encircling a compliant member  114 .  
         [0043]     The seal surrounding each compliant member could be formed from a separate structure. Alternatively, some or all of the seals surrounding compliant members may be formed from a single piece of compliant material. For example, seal portion  116 A includes a raised portion  330  and a raised portion  332 . Raised portions  330  and  332  are joined by a bridge  334  of material. Raised portion  330  forms a portion of the seal encircling contact member  312 A. Raised portion  332  forms a portion of the seal encircling contact member  312 . In this embodiment, bridge portion  334  does not contribute to forming a seal around either contact member  312  or  312 A. However, bridge portion  334  may facilitate forming raised portions  330  and  332  in a molding operation. Placing bridging material between the seals encircling the individual contact members facilitates the flow of material during molding and reduces the number of material inlets required for the molding operation.  
         [0044]     Seals  116  may be formed in housing  150  in a multi-step molding process. In a first step, housing  150  may be molded with grooves  340  formed in the surfaces in positions where seal members should be placed in the finished socket. In a second molding step, seal material may be deposited in the grooves  340 .  
         [0045]     Any suitable method of forming housing  150  may be used. For example, housing  150  may be molded in a two barrel molding machine. In a two barrel molding machine, the insulative material forming housing  150  is injected while inserts are positioned where grooves  340  are to be formed. Once the insulative material forming housing  150  sets, the inserts occupying grooves  340  are removed. Those inserts may, for example, be attached to camming mechanisms that slide the members in and out of the cavity as desired. With the inserts removed, a second type of material may then be injected into the voids formed by removing those inserts.  
         [0046]     As an alternative, a two cavity molding operation may be used. The first cavity may have a mold shaped to conform to the profile of insulative housing  150  alone. Once the insulative housing  150  is formed in this cavity, the work piece may be moved to a second cavity with a mold having a contour conforming to the shape of insulative housing  150  and seals  116  and  316  combined. When the work piece is placed in this mold, voids are left where the seals  116  and  316  are to be formed. Seal material is then inserted in these voids.  
         [0047]     Turning to  FIG. 4 , an alternative embodiment of chip socket  110  is shown. Here, chip socket  110  is formed with a housing  450 . Housing  450  is formed without passages  310  to receive contact members. In this embodiment, housing  450  is insert molded around the contact members  312 . In an insert molding operation, the contact members may be formed attached to a lead frame that holds the contact members in the desired positions. Once the housing is molded around the contact members, the lead frame can be cut away.  
         [0048]     Having thus described several aspects of at least one embodiment of this invention, it is to be appreciated various alterations, modifications, and improvements will readily occur to those skilled in the art.  
         [0049]     For example, each contact element is pictured as being formed from a single piece of metal that is bent to form contact portions on each end. Contact elements need not be formed in this way. Each contact element may be formed from multiple pieces of metal that are electrically coupled to each other. Each contact element may alternatively be formed from a combination of metal pieces and other conductive components that are coupled to form a conducting path.  
         [0050]     Likewise, the number of pieces from which other components are constructed may be varied. For example, each seal member is shown made from a single piece. However, seal members may be formed from multiple segments.  
         [0051]     As a further variation, surfaces of the chip carrier are shown to be planar. The invention is not limited to use in planar structures. Surfaces may be curved or may have projections or other non-planar portions. In use, the portions of the chip carrier having seals around contact elements may be pressed towards other structures that conform generally to the their shape. Compliance provided by the seal members or the surfaces themselves may allow an adequate seal to be formed even when the structures do not precisely conform.  
         [0052]     Further, it is not necessary that the seals be mounted at the highest point of the surface of the chip socket. For example, if a chip  120  or circuit board  130  contains projecting members, housing  150  may contain channels or other recesses to receive those projecting members. In this configuration, the seals could be mounted to the surface of the housing, even though positioned at the bottom or the walls of the channel.  
         [0053]     Furthermore, the drawings show connections to the chip socket being made through pads on the surface of a printed circuit board and a semiconductor chip. Connections are not so limited. Connections can be made to any structure that can be accessed from the surface, including conducting members that are positioned in recesses, cavities or holes within the surface.  
         [0054]     Further, embodiments are described in which seals are formed around contact members by molding compliant material in place. The compliant material may be first formed in the desired shape and then positioned as desired.  
         [0055]     As a further example, it was described that an advantage of an environmentally sealed chip package is that contact members may be designed to deliver reduced contact force. However, the motivation for incorporating the novel features described above is not a limitation on the invention. For example, the invention may be employed with contact members designed to provide contact forces comparable to those found in a traditional connector. Such a connector may be desirable for providing reliable connections in a harsh environment, such as one containing oxidizing gasses.  
         [0056]     Further, it is described that chip socket  150  has symmetrical upper and lower surfaces. The compliant members need not be symmetrically disposed. For example, the pitch of the compliant members may be greater on the lower surface to facilitate manufacture of circuit board  130 .  
         [0057]     Further, it is not necessary that both sides of the chip socket include contact elements that make an electrical connection by being pressed against a mating contact element. For example, contact elements on the lower surface of chip socket  110  may be soldered to contacts on circuit board  130  or attached in any other suitable fashion. Also, the invention is described in connection with a chip socket style connector. The invention is not so limited. For example, the invention may be employed in connection with a pressure mount or press-fit electrical connector. Seals may be formed in the connector housing that is pressed into a printed circuit board. Alternatively, seals may be formed in a connector housing that is pressed against a housing of a mating connector, such as occurs in a backplane—daughter card connector assembly or a mezzanine connector assembly.  
         [0058]     As an example of another variation, it is not necessary that the seals be formed as part of housing  150 . Seals could be formed in or attached to chip  120  or circuit board  130 .  
         [0059]     Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are by way of example only.