Patent Publication Number: US-2004048504-A1

Title: Electrical connector having a solder-array interface surface

Description:
TECHNICAL FIELD OF THE INVENTION  
       [0001] The present invention relates generally to electrical connectors and, more particularly, to an electrical connector having an interface surface with a plurality of arrayed solder points.  
       BACKGROUND OF THE INVENTION  
       [0002] Electrical connectors are used to place electrical devices, such as printed circuit boards, in communication with one another. An electrical connector may be thought of as having two portions, one portion of which connects to a first electrical device and the second portion of which connects to a second electrical device to be put into communication with the first device. To connect the two devices, the two portions of the electrical connector are mated together.  
       [0003] Each portion of the connector includes one set of contacts adapted to communicatively couple to an electronic device and a second set of contacts adapted to matingly couple to the other connector portion. This can be readily accomplished by designating one portion of the connector as having “male” contacts adapted to couple to the other connector portion&#39;s “female” contacts. Regardless of the specifics of the contact design, the two connector portions should be adapted to be easily connected and disconnected from each other to respectively electrically link and unlink the electrical devices to which they are connected.  
       [0004] Accordingly, each connector portion is fixedly connected to an electronic device through it&#39;s remaining set of contacts. The contacts may be removably or permanently connectable to the electrical device; however, it is usually desired that the connector portion be secured to the electrical device through some physical mechanism. Typically, the connector portions are secured to electrical devices by fusing the contacts to contact pads or the like formed on the electrical device.  
       [0005] Recently, there has been a trend toward the miniaturization of most electrical devices. As electrical devices become smaller and more complex, the electrical connectors used with these devices must also become smaller and be able to accommodate the more complex devices. One problem with miniaturized electrical connectors arises from the increased precision of placement necessary to produce the proper positioning and connection of the connector contacts onto the device. This problem is exacerbated by the ever increasing input/output (I/O) density requirements demanded of the progressively smaller electrical connectors by increasingly miniaturized electrical devices.  
       [0006] One means of addressing the need for increased I/O density is to provide an arrayed connector. Such a connector can provide a high-density two-dimensional array of contact terminals for interfacing with an electrical device. However, arrayed connectors present attachment difficulties regarding connection to devices (i.e., circuit boards or substrates) since most of the contact terminals must necessarily be positioned in the interior of the two-dimensional array area and are accordingly difficult to align upon connection, visually inspect, and/or repair.  
       [0007] One attempt to provide a high-density electrical connector interface has been to use a ball grid array (BGA). The BGA offers the advantages of a precisely formed high-density array of solder contacts available to interconnect with a substrate. However, variation in the dimensions and/or placement of solder balls at the interface can lead to an uneven or non-coplanar interface and intermittent or poor electrical contact. Also, the presence of oversized or extra solder balls present in the connector interface can result in shorted connections and degraded connector performance.  
       [0008] There is therefore a need for an electrical connector design that reliably provides increased I/O density with an even, coplanar interface characterized by an array of precisely positioned solder balls. The present invention is directed towards meeting this need.  
       SUMMARY OF THE INVENTION  
       [0009] The present invention relates to an electrical connector adapted to fusingly attach to an electrical device, such as a printed circuit board. The electrical connector includes an insulating substrate having a first major face and an oppositely disposed second major face. A plurality of non-recessed apertures extend through the insulating substrate from the first major face to the second major face. A plurality of elongated electrically conducting members or pins extend through the respective apertures into a plurality of reflowable electrical conductors disposed adjacent the first major face. The tails of the pins extend from the second major face, and can be connected to an electrical device. The first major face may be fusingly connected to a second electrical device having electrical contact pads arrayed to match the positioning of the reflowable electrical conductors disposed on the first major face. The reflowable electrical conductors are heated and reflowed onto the respective electrical contacts and then cooled to fusingly connect the electrical connector to the second electrical device. A first electrical device connected to the electrical connector will thusly be put into electrical communication with the second electrical device.  
       [0010] One object of the present invention is to provide an improved electrical connector device. Related objects and advantages of the present invention will be apparent from the following description.  
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a top plan view of a first embodiment electrical connector of the present invention.  
     [0012]FIG. 2 is a partial side perspective view of the embodiment of FIG. 1.  
     [0013]FIG. 3 is a partial side sectional schematic view of the embodiment of FIG. 1.  
     [0014]FIG. 4 is a partial side perspective view of a second embodiment of the present invention.  
     [0015]FIG. 5 is a partial side sectional view of three pins extending through a substrate and to different lengths into three solder balls.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0016] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.  
     [0017] FIGS.  1 - 3  illustrate a first embodiment of the present invention, an electrical connector  10  including two matable electrical connector portions  20 , each having a substantially planar electrically insulating substrate plate  22 . A plurality of apertures  24  are formed extending through each substrate plate  22 . The apertures  24  are preferably non-recessed (i.e., the apertures do not widen substantially at their ends) and more preferably have walls that extend directly through the substrate plate  22  substantially perpendicularly to the major plane of the plate  22 . The apertures  24  may be chamfered at the surface of the plate  22  due to machining requirements. Elongated electrically conducting members or pins  26  extend through the apertures  24 . The pins  26  and apertures  24  preferably have the same or similar cross-sectional shapes, such as circular or rectangular (see FIG. 4), to accommodate a tight fit. Preferably, the pins  26  are inserted snugly into the apertures  24 . More preferably, each pin  26  enjoys an interference fit in an aperture  24 .  
     [0018] Each connector portion  20  also includes a plurality of posts  28  extending from its surface. Each connector portion  20  further includes a plurality of reflowable electrical conductors  30 , such as solder balls, positioned over the apertures  24 . The posts  28  are preferably positioned to substantially surround each aperture  24 , effectively limiting the size of the solder ball  30  positioned thereover. Additionally, the posts  28  are preferably arrayed such that there is room for only one solder ball  30  over each aperture  24  and more preferably, the posts  28  are positioned such that each solder ball  30  may only sit over an aperture  24 . In other words, the posts  28  are disposed such that the presence of the posts  28  prevents extra solder balls  30  from sitting on the surface of the connector portion  20  where they might potentially participate in an unplanned electrical connection (i.e., an electrical short circuit) on the connector portion  20 .  
     [0019] Each post  28  is preferably regularly shaped and preferably includes a flattened conical surface  32  at its apex, although the posts  28  may have any convenient shape. In the illustrated embodiment, the posts  28  are generally rectangular pillars with a flattened conical surface  32  formed at each corner at the top (for a total of four surfaces  32 ). Alternately, the posts  28  may have the general shape of right circular cylinders ending in flattened conical surfaces  32  (see the second embodiment of the present invention illustrated in FIG. 4). However, any convenient cross-sectional shape may be chosen that allows the posts  28  to define spaces over each of the apertures  24  large enough for solder ball occupation while reducing the remaining probability of solder ball occupation elsewhere on the surface of the connector portion  20 . It is contemplated that by precisely controlling post size, cross-sectional shape, and positioning, the surface of the connector portion  20  may be tailored such that only solder balls  30  of precisely controlled sizes may be placed thereupon without any excess space remaining for unintentional solder ball occupancy.  
     [0020] The reflowable electrical conductors  30  are preferably solder in composition and are preferably spherical in shape. However, the reflowable electrical conductors  30  may be formed of any convenient low melting or low-temperature softening electrically conducting composition that may be resolidified without experiencing a substantial shift in its electrical properties. The reflowable electrical conductor  30  composition may likewise include fusible electrically conducting ceramic compositions or polymers.  
     [0021] The electrically insulating substrate plate  22  preferably includes a first major surface  36  from which the posts  28  extend and upon which the reflowable electrical conductors  30  sit. The plate  22  also preferably includes a second major surface  38 , oppositely disposed from the first major surface  36  and from which the tails of the pins  26  extend. The first major surface  36  is adapted to face a first electrical device (not shown) having electrical contact pads oriented such that the array of solder balls  30  may be heated and reflowed to fuse each solder ball  30  to both a pin  26  and a pre-selected electrical pad. In other words, solder balls  30  are impaled upon pins  26  extending from the first major surface  36  to define a fusing interface  40 , i.e., an interface that is fusingly connectable to an electrical device. The second major surface  38  is adapted to be removably electrically connected to another connector portion  20  connected, either directly or indirectly, to a second electrical device (not shown). Therefore, the two connector portions  20  matingly join to put the two devices in electrical communication with each other. In other words, the second major surface  38  of one connector portion  20  hosts a non-fusing interface  42 , removably connectable to the second major surface  38  of another connector portion  42 . The major surfaces  38  of the connector portions may be of any convenient removably couplable design, such as interconnectable male and female contacts or the like.  
     [0022] The connector portion  20  also includes one or more alignment posts  50  extending therefrom. The alignment posts  50  are adapted to extend into alignment receptors (not shown) formed in the surface of the electrical device to which the electrical connector portion  20  is to be joined. The alignment posts  50  serve to guide the solder balls  30  onto the arrayed contact pads (not shown) of the electrical device to ensure proper alignment and good electrical connection of the connector portion  20  to the electrical device.  
     [0023] The solder balls  30  are preferably reflowed onto the ends of the pins  26  extending from the first major surface  36  of a respective connector portion  20 . This is accomplished by heating the solder balls  30  sufficiently to soften the solder balls  30  and then extending the pins  26  thereinto. The so-impaled solder balls  30  are then cooled and resolidified. The pins  26  may be extended substantially into the solder balls  30  (see FIG. 5, configuration A) or just far enough in to secure the resolidified solder balls  30  onto the pins (see FIG. 5, configurations B and C).  
     [0024] In operation, the first major surface  36  is aligned with a first electrical device (not shown) having electrical contact pads in a predetermined configuration (i.e., wherein each contact pad is positioned to receive a solder ball  30 ) by sliding the contact posts  50  into the contact post receptors in the surface of the device. The solder balls  30  are heated and reflowed onto the respective contact pads. The reflowed solder balls  30  are then cooled such that they are each fused to both a respective pin  26  and a respective contact pad, thereby forming an electrical connection between the two. The second major surface  38  may then be removably matingly connected to the second major surface  38  of a compatible electrical device, such as another connector portion  20  likewise connected to an electrical device, such that the first and second electrical devices are put into electrical communication by the coupled electrical connector portions  20 . The second major surface  38  could also be connected to an intermediate device, such as an electrical cable having a matable interface, or even directly to a second device such a circuit board adapted to matingly connect to the second major surface  38 .  
     [0025] Referring to FIG. 4, a second embodiment of the present invention is shown. FIG. 4 illustrates an electrical connector portion  20  similar to the one described above but having smaller posts  28  disposed around the solder balls  30 . In this illustrated embodiment, the posts  28  are generally cylindrical with flattened top surfaces  32 . The posts  28  of FIG. 4 are also shorter than the solder balls  30 . In other words, the diameter of the average solder ball  30  is greater than the height of the average post  28 . However, the posts of other embodiments may be taller than the solder balls. The posts  28  of this embodiment are regularly arrayed so as to restrain the solder balls  30  in position over the apertures  24 . FIG. 4 further illustrates an alignment post  50  adapted to extend into an alignment post receptor formed in the surface of an electrical device to which the connector portion  20  is to be coupled.  
     [0026] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are to be desired to be protected.