CONTACT HAVING A MASS OF REFLOWABLE SOLDERABLE MATERIAL THEREON

Abstract: A contact for an electrical connector is characterized by a mass of solder material (20) having a predetermined volume that is reflowed onto a predetermined localized portion of the tail (14). The tail may be generally linear or bent to define a concave portion thereon. If bent, the predetermined volume of solderable material is localized in the concave portion of the tail. Such a bent contact may be used advantageously with a connector mountable to a substrate in either a straddle mount (30) or in a surface mount (40) configuration.

Description: TITLE CONTACT HAVING A MASS OF REFLOWABLE SOLDERABLE MATERIAL THEREON BACKGROUND OFTHE INVENTION Field of the Invention The present invention relates to an electrical contact having a mass of a reflowed solder material having a predetermined volume disposed on a predetermined localized portion of the tail of the contact, to a connector having such a contact therein, and to a method of forming an electrical contact having a mass of a reflowed solder material having a predetermined volume disposed on a predetermined localized portion of the tail thereof. Description of the Prior Art Presently, the electrical contacts, whether of the spring or the post type, used in an electrical connector each have a tail portion that extends from the housing of the connector in which they are disposed. The tail portion may be generally linear if the connector is to be mounted into through openings provided in a substrate, such as a circuit board or a flexible member. Alternately, the tail portion of the contact may be bent to facilitate the mounting of the connector to either the surface or onto an edge of the substrate. When mounting the connector to a through hole in a substrate, it is common practice to press an annular preform of a reflowable solderable material onto the tail of the contact. When received onto the tail the preform produces a localized distended region along the tail of the contact. The tail is inserted into the through hole, and the substrate exposed to a environment suitable to cause the solderable material to reflow. This practice is exemplified in the pin alignment method disclosed in United States Patent 4,956,913 (Eck), assigned to the assignee of the present invention. WO publication 89/04071 discloses a receptacle contact for a connector in which the barrel of the contact is provided with a layer of a reflowable solderable material. The barrel accepts a linear tail portion of a mating pin. When subjected to reflow conditions the material in the barrel of the contact reflows to secure the contact -to the barrel. United States Patent 3,852,517 (Fava) and United States Patent 3,296,577 (Travis et al.) disclose members having a coating of solder thereon. It is known to provide a relatively thick coating of reflowed solder material onto the solder tail of an electrical contact by dipping the tails into a pool of molten solder. Although the resulting mass of material on the solder tail is intermetallically bonded to the base material of the contact, the volume, thickness, shape and location of the mass cannot be precisely controlled. In the case of surface mounted connectors and components it is a common practice to apply a layer of solder paste to the solder pads provided on a first surface of the substrate using screen printing techniques. That surface of the board is then populated with the connectors and/or components required. With the tail portions of the contacts embedded into the viscous solder paste, thereby temporarily securing the connector or component to the substrate, the populated substrate is exposed to a high temperature reflow environment. The solder paste melts and wets both the tail and the substrate. Upon cooling the solder solidifies, defining an intermetallically bonded solder joint that is both mechanically bonded and electrically conductive. The process is repeated on the opposite side of the substrate, if appropriate. This system is not totally satisfactory. In a typical situation a discrete component optimally requires a different volume of solder paste than does a connector. However, screen printing techniques are generally not available to permit selective application of differing volumes of paste to different regions of the substrate. Accordingly, the differing solder needs of discrete circuit components and connectors are accommodated by applying a layer of solder paste that is greater than the volume optimally required by a discrete component, but less than the volume of paste optimally required by a connector. Further complications arise in the situation where the connector is used in an edge, or straddle, mount configuration. In this case the pads adjacent to the edge of the first surface of the substrate are coated with paste simultaneously with the other pads on that surface. However, the straddle mounted connector is usually not mounted to that surface when the surface is populated with the required discrete components and/or connectors. Thus, when the solder paste is reflowed, the paste on the unpopulated pads forms mounds. Mounding makes difficult the subsequent insertion of the tails of the straddle mounted connector to that side of the substrate. Moreover, when paste is applied to the opposite side * of the substrate and the connector mounted thereon, care must be exercised to insure that the tails of the contacts do not plow the paste, leading to bridging of pads and the resultant short circuit. SUM ARY OF THE INVENTION The present invention relates to a contact for an electrical connector. The contact has a tail thereon. In accordance with this invention the tail of the contact is provided with a mass of a solder material having a predetermined, precisely controlled volume of solder material that is reflowed onto a predetermined localized portion of the solder tail. The tail of the contact may be generally linear or may be bent to define a concave portion thereon. When the tail of the contact is bent the mass of reflowable solder material is localized in the concave portion of the tail. Bent contacts in accordance with the present invention tail are advantageously used in a connector exhibiting either a straddle mount or a surface mount configuration. BRIEF DESCRIPTION OF THE DRAWINGS The invention will be more fully understood from the following detailed description thereof taken in connection with the accompanying drawings, which form a part of this application, and in which: Figures 1A, IB and 1C are, respectively, perspective views of a solder tail portion of a spring contact in accordance with the present invention for use with a connector or a component that is mountable either in a straddle mount, in a surface mount, or in a through mount configuration; Figures 2A, 2B and 2C are, respectively, sectional views taken along section lines 2A-2A, 2B-2B, and 2C-2C of respective Figures 1A, IB and 1C; Figure 3 is an end view of a connector or component having contacts of the type shown in Figure 1A mounted in a straddle mount configuration to a substrate: and Figure 4 is a perspective view of a portion of a fixture for fabricating contacts used in the connector of Figure 3. DETAILED DESCRIPTION OF THE INVENTION Throughout the following detailed description, similar reference numerals refer to similar elements in all figures of the drawings. Shown in each of Figures 1A, IB and 1C is an electrical contact, generally indicated by the reference character 10, that includes, in the general case, an electrical interconnection portion (not shown) and a solder tail portion 14. Although not illustrated in the Figures the electrical interconnection portion may take any one of a numbers of well-known forms, such as the receptacle configuration, the frictional wiping configuration, or the pin configuration. The solder tail portion 14 of the contact 10 is integrally formed with the electrical interconnection portion, typically by a stamping operation. The solder tail portion 14 may either be generally flattened, as illustrated in Figures 1A and IB, or may have a generally squared or rounded cross section, as illustrated in Figure 1C. Whatever the form taken by the electrical interconnection portion of the contact, the solder tail portion 14 thereof may exhibit a configuration which will facilitate the mounting of the contact using any of the well- known mount techniques. For example, the solder tail portion 14 may exhibit the configuration shown in Figure 1A which facilitates a straddle mount, the configuration shown in Figure IB which facilitates a surface mount, or the configuration shown in Figure IC which facilitates a through mount. In both the straddle mount configuration and the surface mount configuration the tail portion 14 is bent, as at 16, to define a generally concave region 18 on the contact 10. In the through mount configuration shown in Figure IC, the tail portion 14 is generally linear throughout its length. In accordance with the present invention a mass or predetermined volume 20 of solder material is reflowed onto a predetermined localized portion of the solder tail 14. Preferably the mass 20 of reflowable solder material is a tin lead solder although any reflowable material may be used. The application of the mass 20 to the tail portion 14 of the contact 10 is discussed hereinafter. In the straddle mount configuration and in the surface mount configuration the mass 20 of reflowable solder material is localized in the generally concave region 18 defined by the interior surface 22 of the tail 14. Moreover, as may be seen from Figures 2 A and 2B, the mass 20 of reflowed solder material does not uniformly surround the tail portion 14. The surface 22 has a relatively thick layer of the reflowed solder thereon while the exterior surface 24 of the tail (i. e., the surface 24 opposite to the interior surface 22 having the concavity 18) forms a relatively thin layer of the reflowed solder thereon. For example, the depth of the solder in the mass 20 on the concave interior surface 22 of the tail 14 may be on the order of 0.010 inch to 0.020 inch. At the same time the thickness of the layer of solder material on the surface 24 may on the order of 0.001 inch. In the case of the through mount configuration of Figure IC, the mass 20 of solder material is disposed at a convenient location along the linear tail portion 14. The mass 20 may substantially uniformly surround the linear tail portion pin. Figure 3 illustrates a component or connector 30 employing electrical contacts 10 of the straddle mount configuration as illustrated in Figure 1A and 2A. The component or connector 30 (which may be either a plug or a receptacle) 30 includes a housing 32 in which electrical contacts 10 are disposed. The solder tail portions 14 of the contacts 10 extend from the housing 32. In Figure 3 the solder tail portions 14 straddle the edge of a substrate S, such as a printed circuit board or a flexible member, and are in physical contact with the conductive pads P on the surface of the substrate S. With the solder tail portions 14 of the contacts 10 in the position shown the mass 18. The tails 14 and the pads P, when fluxed, are exposed to a high temperature reflow environment, causing the mass 20 to reflow and thereby to become mechanically and electrically connected to the pads P. Figure 4 illustrates a fixture 40 whereby the mass 20. of solder material may be reflowed onto a predetermined localized portion of the tail 14 of the contact 10. The fixture 40 is a plate-like member formed of a material that is nonwettable by the particular solder material being applied to the tails 14. Typically, stainless steel is suitable for this purpose. As will be developed, the mass 20 of solder material is may be reflowed onto the tail 14 after the contacts 10 have been inserted into the housing 32 of the connector or component 30, or while the contacts 10 still reside on their associated carrier strip, whichever is the more convenient. The fixture 40 includes an array of wells 42, arranged to correspond to the arrangement of the tails 14. For a surface mount configuration the wells are arranged on only one surface of the fixture, while for a straddle mount configuration the wells are placed on opposite surfaces of the sixture. Each well 42 has a central step 43 that separates the well into a shallow end 44 and a deep end 46. The width dimension 48 of each well 42 is slightly larger than the transverse dimension of the solder tail 14, while the relative depths of the shallow end 44 and of the deep end 46 are indicated by the respective reference characters 52, 54. To form the mass 20 integrally onto the tail 14, the wells 42 are filled with the selected paste. This may typically be accomplished by a screen printing process. The tail 14 of each contact 10 is placed into one of the wells 42, with the planar exterior surface 24 of the tail being received and supported on the shallow end 44 of the well 42. The tails 14 are secured in this position by any convenient arrangement. The fixture 40, with the tails 14 therein, are then placed in a suitable reflow environment, such as an infrared or vapor phase oven. Owing to the nonwettability of the fixture, the solder paste reflows onto the tails 14, forming an intermetallically bonded mass 20 having the predetermined volume on the predetermined localized portion of the tail 14. To provide the mass 20 on a linear tail portion (Figure IC), the tail may either be laid across the well 42, or else the deep end 46 of the well provided with a relatively precisely formed opening 49 (shown in dashed lines). The linear tail 14 is inserted into the opening 49, the well filled, and the solder reflowed onto the tail. By judicious selection of the depth dimensions 52, 54, the volume of reflowed solder mass, the location of the reflowed solder mass, the thickness of the reflowed solder mass, and- the shape of reflowed solder mass 20 may all be precisely controlled. Moreover, since the surface 24 of the tail 14 is supported on the shallow end 44 of the well 42, the solder mass 20 forms only as a thin layer on the exterior surface 24, assuring the continued planarity of that surface 24. Those skilled in the art having the benefit of the teachings of the present invention as hereinabove set forth may effect numerous modifications thereto. For example, it should be understood also that the method and the contact formed in accordance with the present invention may be used to provide a predetermined volume of reflowed solder material in a predetermined localized portion of other members, such as a metallic hold down fixture or a strain relief. These and other modifications are construed to lie within the contemplation of the present invention as defined by the appended claims.

Claims: WHAT IS CLAIMED IS: 1. A contact for an electrical connector, the contact having a tail thereon, the improvement comprising a mass of solder material having a predetermined volume refiowed onto a predetermined localized portion of the tail. 2. The contact of claim 1 wherein the tail has a first, interior, surface thereon and has a bend therein, the bend defining a concave portion on the first surface, a relatively thick laye of the mass of solder material being localized in the concave portion of the tail. 3. The contact of claim 2 wherein the tail has a second, exterior, surface thereon, the exterior surface being disposed oppositely to the interior surface, a relatively thin layer of the mass of reflowed solder material being localized on the exterior surface. 4. The contact of claim 3 wherein the tail is bent into a straddle mount configuration. 5. The contact of claim 3 wherein the tail is bent into a surface mount configuration. 6. The contact of claim 2 wherein the tail is bent into a straddle mount configuration. 7. The contact of claim 2 wherein the tail is bent into a surface mount configuration. 8. The contact of claim 1 wherein the tail is generally linear. 9. An electrical connector having a housing with a plurality of electrical contacts received therein, each contact having a tail extending from the housing, the improvement comprising: a mass of solder material having a predetermined volume reflowed onto a predetermined localized portion of the tail. 10. The connector of claim 9 wherein each tail has a first, interior, surface thereon and has a bend therein, the bend defining a concave portion on the first surface, a relatively thick layer of the mass of solder material being localized in the concave portion of the tail. 11. The connector of claim 10 wherein each tail has a second, exterior, surface thereon, the exterior surface being disposed oppositely to the interior surface, a relatively thin layer of the mass of reflowed solder material being localized on the exterior surface. 12. The connector of claim 11 wherein each tail is bent into a straddle mount configuration. 13. The connector of claim 11 wherein each tail is bent into a surface mount configuration. 14. The connector of claim 10 wherein each tail is bent into a straddle mount configuration. 15. The connector of claim 10 wherein each tail is bent into a surface mount configuration. 16. The connector of claim 9 wherein each tail is generally linear. 17. A method comprising the steps of: (a) filling a well in a fixture with a predetermined volume of solder material, the fixture being formed from a material that is nonwettable by the solder material; (b) introducing a predetermined localized portion of tail of a contact into the well; (c) exposing the solder material in the well to a reflow environment thereby to cause the solder material to reflow onto the predetermined localized portion of the tail. 18. The contact produced as a product of the method of claim 17.

Inventors: HAHN MARLYN EUGENE, HAHN, MARLYN, EUGENE
Applicants: DU PONT, E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1992
Main classification: H01R3
IPC codes: H01R4, H01R12, H05K3