High density connector system

Abstract: An electrical connector illustrated as a plug and receptacle is disclosed. In one embodiment, the connector includes a base member having a plurality of bores. A first plurality of contact elements is positioned in certain of the bores. The tail portion of each contact element extends a distance beyond the base member. A second plurality of contact elements is positioned in others of the bores. Insertion of the tail portion of the second plurality of contact elements into a circuit board is sufficient to hold the tail portions of the first plurality of contact elements against the circuit board. It is preferred for the tail portions of the second plurality of contacts to be capable of axial movement when a compression force is applied. In another embodiment, the connector includes a frame and a layer of contact elements, wherein each of the contact elements includes a forward end and a tail portion. The ends of the tail portions are positioned proximate the bottom surface of the frame. A plurality of shaped fusible elements, for example, solder balls, are located proximate the ends of the tail portions. In such an embodiment, the solder balls preferably have a deformed spherical shape, wherein the aspect ratio is greater than one.

Description: Field of the Invention The present invention relates to electrical connectors, and more particularly, to high density connectors intended for the interconnection of daughter boards and back panels. Background of the Invention Continued advances in the design of electronic devices for data processing and communications systems have placed rigorous demands on the design of electrical connectors. Specifically, electrical connectors having higher densities and pin counts are needed for design advances which increase integration of solid state devices and which increase the speed of data processing and communication. Designing connectors to have higher densities and higher pin counts requires careful consideration of the problems which result from decreasing the distance between contacts. This is particularly true in applications involving daughter board/back panel interconnections where the connector functions to establish an electrical connection and functions to mechanically hold the daughter board in position. Density and pin count are often viewed interchangeably, but there are important differences. Density refers to the number of contacts provided per unit length. In contrast, the number of contact elements that can reasonably withstand the mating and unmating forces is referred to as the pin count. As more functions become integrated on semiconductor chips or on flexible circuit substrates and more chips are provided on printed circuit boards (PCBs), each PCB or flexible circuit must provide more inputs and outputs (I/Os). The demand for more I/Os directly translates to a demand for greater density without sacrificing electrical or mechanical performance, particularly when such devices and integration techniques are utilized in devices having back panels. The importance of electrical performance of high density connectors was recognized in U.S. Patent No. 4,824,383 - Lemke, incorporated herein by reference. This patent proposed designs for plug and receptacle connectors for multiple conductor cables or multiple trace substrates. In such designs electrical performance was assured by electrically isolating individual contact elements or groups of contact elements through the use of conductive walls to prevent or minimize crosstalk and signal degradation. Although, the connectors disclosed in U.S. Patent No. 4,824,383 increased contact element density, industry driven density demands continued to grow. U.S. Patent Nos. 5,057,028 - Lemke et al. and 5,169,324 - Lemke et al. (now U.S. Patent No. Re. 35.508), all incorporated herein by reference, disclose two row plug and receptacle connectors for attachment to printed circuit boards (PCBs), which connectors again exhibited good electrical performance through the use of conductive walls to provide isolation. Electrical performance for high density connectors was also the focus of U.S. Patent Nos. 4,846,727, 5,046,960, 5,066,236, 5,104, 341, 5,496,183, 5,342,211 and 5,286,212. These patents disclose various forms of stripline structures incorporated into a plug and receptacle system. In a high density stripline structure, columns of contact elements arranged in a side-by-side array with conductive plates disposed between each column. The connectors are designed so that the plug and receptacle ground plates contact one another, thereby providing isolation between columns. A further aspect of this system is the modular design of the receptacle. Each column of receptacle contact elements is formed by molding the contact elements into a frame of dielectric material. One of the problems with these types of connectors is that the use of conductive walls for electrical isolation requires space. In certain applications the space or volume necessary for such isolation is impractical. In those applications where space is critical, proposals for achieving desired electrical performance have included the use of high density connectors in which one pin, selected for signal transmission, is positioned between pins connected to ground. Such patterns are known as interstitial arrangements. Such contact element patterns are suggested in U.S. Patent Nos. 5,174,770, 5,197,893 and 5,525,067. It will be appreciated that while such isolation schemes can be implemented in more compact connectors, such schemes require greater numbers of pins than were available in the previously described connectors using conductive walls. The document GB 2 222 917 A, on which the preamble of claim 1 is based, shows an electrical connector with a plurality of contacts. At least one of the electrical contacts is adapted to form a press fit connection with a plated through hole of a printed circuit board. At least one other of the electrical contacts is bent sideways to form a high pressure connection with the surface of the printed circuit board. In the document US 4,978,308 a pin header for being surface mounted on a back panel is disclosed. The pin header is secured to the back panel by means of e.g. bolts or screws. The pin header includes contact elements having outwardly facing contact surfaces on generally C-shaped spring arms for engaging the circuits on a back panel. The contact elements are positioned in dielectric inserts which are positioned in a shell and further include pins for electrically engaging a receptacle connector. In back panel applications, increasing the number of pins has a direct impact on mechanical integrity. As the number of pins increases, the number of bores or through holes in the back panel and daughter board increases. As the number of bores in a printed circuit board increases while at the same time decreasing the distance between each bore, as will be the case in high density applications, the mechanical integrity of the board decreases. As mechanical integrity decreases the ability for the back panel to mechanically hold the daughter board in position decreases. It will be appreciated that in back panel applications, the daughterboard is held in position, i.e., vertical and horizontal orientation, sometimes exclusively, by the connector used to electrically interconnect the two. Daughterboard size, the number of daughterboards and the components mounted to the daughterboards combine to produce the stresses and moments acting on the back panel after assembly. If the amount of back panel material is reduced in particular locations due to larger numbers of closely spaced through bores, back panel failure can occur, i.e., the back panel could deform or even break. One might conclude that the solution to back panel mechanical failure would be to use surface mount techniques to establish electrical connection to the back panel. Since surface mount techniques do not require the use of through holes, such techniques would afford the ability to connect high density connectors to the back panel without impacting mechanical integrity. Unfortunately, such solutions would be unsuccessful. Surface mount techniques typically involve temporarily fixing a component to a printed circuit board using a paste. After pasting, the board and temporarily fixed components are heated in order to reflow solder material previously coated onto the leads of the surface mount components. In back panel applications, numerous connectors are attached to the back panel board, which is typically a relatively large circuit board. In order to assure adequate reflow, thereby establishing good electrical connection, for numerous components spread over a relatively large board, the back panel board would have to be subjected to significant heat. Unfortunately, heat which is too high or too long in duration can actually interfere with establishing good surface mount terminations. Consequently, surface mount techniques do not form the answer to the need for higher density connectors for back panel applications. Consequently, a need still exists for a connector system which maximizes the number of contact elements available for ground/signal assignment and which does not jeopardize either the electrical or mechanical integrity of back panel applications. One other consideration which must be taken into account when designing high density connectors, particularly for back panel applications is the design of the structure for attaching the receptacle portion of the connector. One important factor in receptacle attachment is alignment. When a single receptacle contact element is misaligned, insertion force increases a negligible amount. However, when misalignment occurs in a high density contact receptacle, insertion force could increase to unacceptable levels. In other words, if misalignment occurs during the mounting of a receptacle to a circuit board, it may become impractical for the board to be mounted to a plug or vice versa. Consequently, a need still exists for a high density connector system which provides sufficient alignment after mounting such that insertion force remains within acceptable limits. Summary of the Invention The above described problems are resolved and other advantages are achieved in novel high density electrical connectors. A connector according to the invention for connecting with a circuit board provided with bores and pads comprises a base member having a plurality of bores passing therethrough. The connector also comprises a first plurality of contact elements, positioned in certain of said bores, wherein each of said first contact elements has an insertion portion and a tail portion with a longitudinal axis substantially aligned with said insertion portion, wherein said tail portion extends a distance beyond said base member for contacting conductive material. The connector further comprises a second plurality of contact elements, positioned in other of said bores, wherein each of said second contact elements has an insertion portion and a tail portion, wherein when inserted in said bores the tail portions of said second plurality of contact elements hold the tail portions of said first plurality of contact elements against said pads. It is preferred for the tail portions of the first plurality of contacts to be capable of axial movement when a compression force is applied. In this later embodiment, it is especially preferred for the tail portions of the second plurality of contacts to include a serpentine structure. Brief Description of the Drawings The present invention will be better understood and its numerous objects and advantages will become apparent by reference to the following detailed description of the invention when taken in conjunction with the following drawings, in which: Figure 1 is a partial sectional view of a header constructed in accordance with the present invention; Figure 2 is a top view of the complete header depicted in Fig. 1; Figure 3 is a top view of the printed circuit board on which the header of Fig. 1 is to be mounted; Detailed Description of the Invention As was discussed above, one need which still exists in the industry is a connector having greater density. To this end, a new connector 10 has been developed and is generally depicted in Figure 1. Although depicted as a plug, it will be appreciated that the invention is applicable to either a plug or receptacle. Connector 10 is seen to include side walls 12 and 14 and base wall (base member) 16. A number of blades (contact elements) 18 and 20 are disposed in bottom wall 16. It is noted that blades (second contact elements) 18 include a deformable tail portion, preferably in the form of a press fit section which extends a distance below the bottom surface of bottom wall (base member) 16. By contrast, blades (first contact elements) 20 include a much shorter, compressible tail portion which extends only a short distance from the bottom surface of bottom wall 16. It is noted that the serpentine or S shape of the tail portion of blade 20 permits the tail portion to be compressed upon the exertion of force on the tail. Figure 2 is a top view of plug 10. Connectors constructed in accordance with the invention have the advantage of requiring only half the pins having through holes while the other half utilizes contact pads for establishing electrical connection. In back panel applications, such a construction preserves the mechanical integrity of the back panel while providing a significantly higher pin density. Figure 3 depicts the portion of printed circuit board 22 onto which plug 10 is to be mounted. Circuit board 22 includes a pattern of bores 24 and contact pads 26. It is noted that the diameter of the contact pad is smaller than the diameter of the bore and that the bores and contact pads are arranged in an alternating pattern. When plug 10 is mounted to circuit board 22, the tail portions of blades 18 are inserted into bores 24. The force of insertion causes the compressible end portions of blade 20 to establish electrical contact with pads 26. It is preferred for the tail portions of blades 18 to be either deformable or of a shape to cause a friction force between the tail portion and circuit board 22 sufficient to hold plug 10 in place and maintain electrical contact between the tail portions of blades 20 and contact pads 26. While the invention has been described and illustrated with reference to specific embodiments, those skilled in the art will recognize that modification and variations may be made without departing from the principles of the invention as described hereinabove and set forth in the following claims.

Claims: A connector (10) for connecting with a circuit board (22) provided with bores (24) and pads (26), comprising: a base member (16) having a plurality of bores passing therethrough; a first plurality of contact elements (20), positioned in certain of said bores, wherein each of said first contact elements (20) has an insertion portion and a tail portion; and a second plurality of contact elements (18), positioned in other of said bores, wherein each of said second contact elements (18) has an insertion portion and a tail portion, wherein when inserted in said bores (24), the tail portions of said second plurality of contact elements (18) hold the tail portions of said first plurality of contact elements (20) against said pads (26) characterised in that the tail portion of each of said first contact elements (20) has a longitudinal axis substantially aligned with said insertion portion, wherein said tail portion extends a distance beyond said base member (16) for contacting conductive material (26). The connector of claim 1, wherein the tail portions of said first plurality of contacts (20) are capable of axial movement when a compression force is applied to said tail portions. The connector of claim 2, wherein the tail portions of said second plurality of contacts (18) are deformable, in the form of a press fit section, which extends a distance below the bottom surface of said base member (16). The connector of claim 2, wherein the tail portions of said first plurality of contacts (20) comprises a serpentine structure.

Inventors: SHUEY JOSEPH B, SHUEY, JOSEPH B.
Applicants: FRAMATOME CONNECTORS INT, FCI
Application year: 1998
Main classification: H01R12
IPC codes: H05K3