Abstract:
Provided herewith a method for terminating a conductor of a cable to a tail portion of a contact terminal, comprises the steps of a) providing a fine-pitch connector with a plurality of contact terminals assembled to a housing thereof; b) exposing a tail portion of the contact terminal assembled in the housing; c) deploying conductors to each of the tail portion of the contact terminals; d) providing a transferring layer provided with a plurality of bodies of conductive material over the conductors and tail portions; and e) treating the bodies of reflowable material to electrically bond the conductors to the tail portions of the contact terminals.

Description:
FIELD OF THE INVENTION 
   The present invention relates to a method, and more particularly to a method of terminating an ultra-fine conductor of a cable to a tail portion of a contact terminal of a connector. The method features an arrangement such that solderable reflowable material can be limited to certain area benefiting fine pitch and even ultra-fine pitch application. 
   DESCRIPTION OF PRIOR ART 
   Male and female electrical connector assemblies have been used for many years in a variety of applications, wherein a plug or male connector is mateable with a receptacle or female connector. A common type of plug and receptacle connector assembly employs pin and socket contacts or terminals. 
   In most of the applications, the plug connector, which carries a plurality of pins, is mounted on the board, such as a printed circuit board; while the receptacle, which carries a plurality of socket or box contact is terminated to a cable having a plurality of wires which conductors enveloped with insulation. U.S. Pat. No. 5,176,528 issued to Fry on Jan. 5, 1993 discloses both the receptacle connectors, see FIGS. 2, 4 and 5 in which the plug connector is mounted onto the printed circuit board, while FIG. 1 discloses a receptacle connector, right-hand side is terminated to a cable. Of course, the plug connector can also be terminated to a cable. 
   Termination between contact terminals, either plug or receptacle, and conductors of a cable can be categorized by mechanical, such as bolting, cramping, IDC, and soldering. Before getting more details on the method of termination, let discuss a little more regarding the dimension of the cable. 
   Generally, the diameter of a conductor of a wire ranges from 0.5 inches to 0.0010 inches. In order for easily referring those wires with different diameters, a wire gauge, such as American Wire Gauge (A.W.G), has been introduced. For the diameter of 0.5 inches, the AWG No. is 0000000 (7/0), while the diameter of 0.0010, the AWG No. is 50, the small the AWG number, the larger the diameter of the wire, and vice versa. For those wire with larger diameter, they are generally bolted to certain termination, such as switchboard, and transformer; while for those wire with smaller diameter, cramping, such as disclosed in the Fry&#39;s &#39;528 patent, soldering, and IDC have been widely applied. 
   U.S. Pat. No. 5,766,033 issued to Davis on Jun. 16, 1998 disclosed a typical example for IDC termination, as it can be best illustrated by FIGS. 1, 2 and 3. U.S. Pat. No. 6,062,896 issued to Huang on May 16, 2000 discloses a similar IDC termination. 
   For those conductors directly soldered to the tail portions of the contact terminals, such as disclosed in U.S. Pat. No. 5,980,308 issued to Hu et al. on Nov. 9, 1999; and U.S. Pat. No. 6,206,722 issued to Ko et al. on Mar. 27, 2001. These conductors have been widely associated with liquid crystal display (LCD), and the so-called micro-coaxial cable features an AWG numbers ranging from 34 to 42. The manufacturing processes are extremely laborious, and complicated. In generally, solder paste is directly applied to tail portion of the contact terminal, then the conductors are placed over the solder paste, then heat is applied to make the final joint. However, in the mobile phone and other palm digital device (PDA), the market uses an even small pitch connector, such as 0.4 mm pitch or even 0.3 mm pitch connector. The wire associated with these ultra-fine pitch connector is AWG 42, 0.0025 inches. 
   While, the consumer electronic device keeps pushing smaller and smaller, it is believed that in near future, cable assembly with wire gauge of 46, i.e. 0.0016 inches, which is approximately one fourth of human hair, or even higher will be applied. 
   Handling and treatment of such tiny wires is extremely laborious and delicate, and even beyond of imagination by the existing and available termination processes. For example, the smallest diameter of a drop of a solder paste available to the market is about 0.01 inches (about 0.0254 mm), which is comparably larger than the dimension of the wire of AWG 46. As a result, if the connector is further pushed to be featured with a pitch of below 0.3 mm, it is very much likely that wire of AWG of 44, 45, etc need to be applied. Accordingly, termination for those fine, or even ultra fine conductor to contact, is really a challenge to the industry. Unless it is overcome, it is unlikely to see another miniaturization of the consumer electronic devices. 
   U.S. Pat. No. 5,730,606 issued to Sinclair teaches the use of solder attached to contact tails. U.S. Pat. No. 4,678,250 issued to Romine on Jul. 7, 1987; and U.S. Pat. Nos. 6,024,584 and 6,042,389 issued to Lemke on Feb. 15, 2000 and Mar. 28, 2000 disclose a pre-formed solder mass attached to the contact tail of the connector. Specially, Lemke disposes solder mass and or solder paste within a well and or recess. 
   U.S. Pat. No. 6,793,506 issued to Hirata et al. on Sep. 21, 2004 discloses a so-called board-to-board connector, which generally have a 0.4 mm pitch. Soldering these fine-fine pitch connectors onto printed circuit board is sill doable since the solder paste can be deployed onto the footprint by stencil. However, if someone wants to attach cable or printed circuit onto this ultra-fine pitch connector, at least when the present invention is conceived, there is no doable processes available in the market. 
   Once the wire used become smaller and smaller, such as AWG 44 and beyond, there is also a concern that whether the solder joint formed during reflown is robust and durable. Accordingly, it is would be preferable that at least two electronic bonding can be formed between the tail portion of the contact and the conductor of the wire so as to ensure the durable electrical interconnection can be reached and ensured. 
   Nevertheless, in view of the dimension of the AWG 44 and beyond, it is unlikely to attach a preformed solder mass onto a tiny wire, which has merely one fourth of our human hair based on the existing termination technologies. 
   SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a method for terminating ultra-fine conductor to a tail portion of a contact terminal in which reflowable conductive material administered onto two adjacent tail portions of the contact terminals are offset from each other thereby allowing ultra-fine solder process to be properly performed. 
   It is further of the present invention to provide a connector suitable for terminating with an ultra-fine connector in which arrangement is provided adjacent to mounting portion of the contact terminal such that reflowable process of solderable material can be smoothly performed. 
   In accordance to a method of the current invention, provided herewith a method for terminating a conductor of a cable to a tail portion of a contact terminal, comprises the steps of a) providing a fine-pitch connector with a plurality of contact terminals assembled to a housing thereof; b) exposing a tail portion of the contact terminal assembled in the housing; c) deploying conductors to each of the tail portion of the contact terminals; d) providing a transferring layer provided with a plurality of bodies of conductive material over the conductors and tail portions; and e) treating the bodies of reflowable material to electrically bond the conductors to the tail portions of the contact terminals. 
   Still in accordance with an aspect of the current invention, the transferring layer is defined with a plurality of openings for receiving the bodies of the conductive material. 
   Still in accordance with an aspect of the current invention, wherein the bodies of conductive material is solder ball. 
   Yet still in accordance with an aspect of the current invention, the transferring layer is defined with a plurality of recesses for receiving the bodies of the conductive material. 
   Yet still in accordance with the present invention, wherein the step of treating includes the step of heating the reflowable material. 
   According to a second embodiment of the current invention, a method for terminating a conductor of a cable to a tail portion of a contact terminal, comprising the step of a) providing a fine-pitch connector with a plurality of contact terminals assembled to a housing thereof; exposing first and second open areas of a tail portion of the contact terminal assembled in the housing; c) deploying a plurality of conductors corresponding to each of the tail portion of the contact terminals; d) administering, a reflowable material to the second open area; and e) welding the conductor to the tail portion at the first open area, and simultaneously reflowing the reflowable material administered to the second open area. 
   According to one aspect of the second embodiment, wherein deploying the plurality of conductors to each of the tail portion of the contact terminals is by blowing compressed air. 
   Yet still in accordance with the second embodiment, wherein every two adjacent second open areas are offset from each other. 
   Other objects, features and advantages of the invention will be apparent from the following detailed description taken in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective and exploded view of a cable assembly made in accordance with the present invention; 
       FIG. 2  is similar to  FIG. 1 , but viewing from bottom of the connector; 
       FIG. 2A  is an enlarged view of a housing shown in  FIG. 2 ; 
       FIG. 3  is an assembled view in which the cable is organized and disposed on the bottom of the connector; 
       FIG. 3A  is an enlarged view illustrating the arrangement between a conductor and a tail portion of a contact terminal; 
       FIG. 3B  is an enlarged view showing the transferring layer in  FIG. 1  in up-side-down arrangement; 
     FIG.  3 B 1  is a top view of the transferring layer in  FIG. 3B ; 
       FIG. 3C  is an enlarged cross-sectional view showing the well arranged on the bottom surface of the connector along with a solder pre-form disposed above the conductor and the tail portion of the contact; 
       FIG. 3D  is similar to  FIG. 3C  but showing the solder pre-form is reflown and electrically attaching the conductor to the tail portion of the contact terminal; 
       FIG. 3E  is a perspective view similar to  FIG. 3 , while disclosing an alternative embodiment in which the organizer is removed; 
       FIG. 4  is a similar to  FIGS. 1 and 2 , with transferring later assembled to the connector so as to electrical interconnect the conductor with the tail portion; 
       FIG. 5  is similar to  FIG. 4 , with a wire end block finally attached to the connector to completely cover ends of tail portion and conductors; 
       FIG. 5A  is a cross-sectional view taken along line I-I of  FIG. 5 ; 
       FIG. 5B  is a cross-sectional view taken along line II-II of  FIG. 5 ; 
       FIG. 6  is an illustration of a second embodiment made according to the present invention; and 
       FIG. 7  is an illustration of a third embodiment made according to the present invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1 through 5 , a cable assembly  1  made in accordance with the present invention includes a connector  10 , a micro coaxial cable  20  made up by a plurality of micro coaxial wires  21 , and a transferring layer  30 , and finally a wire end block  40 . 
   The connector  10  can be of any type. In the present invention, a board-to-board connector is used for illustration, while it can be also of the type disclosed in U.S. Pat. No. 5,980,308 issued to Hu et al.; and U.S. Pat. No. 6,206,722 issued to Ko et al. The connector  10  includes an insulative housing  11 , defining a mating portion  12  and a mounting portion  13 . Extending therebetween is a plurality of passageway (not labeled). And each passageway has a slit  15  at mounting portion  13  of the housing  11 . Each of the slits  15  is provided with a wide-opened space  15 A, such as a cup  15 A which is comparably larger than the width of the slit  15 . As best illustrated in  FIGS. 3A and 3C , the cup  15 A of each slit  15  is arranged in a manner that every two adjacent cups  15 A are offset from each other. By this arrangement, the distance L between two cups  15 A is larger than the pitch P between two contacts  16 . It should be understood that if the connector  10  is made through process of insert-molding, then the passageway will not apparent as conventional connector. In the present invention, the connector  10  is made from insert-molding, and only a slit  15  is defined at the mounting portion  13  exposing the contact terminal  16 . The mounting portion  13  is further defined with a receiving space  13 A, and a plurality of notches  13 B which has pitch corresponding to the pitch of the contact terminal  16 . 
   A plurality of contact terminals  16  is assembled to each of the passageways of the housing  11  or integrally formed with the housing, with a mating section  16 A arranged in the mating portion  12  of the housing  11 , and a tail portion  16 B located at the mounting portion  13  of the housing  11 . Since the passage is provided with a slit  15 , the tail portion  16 B of the contact terminal  16  in the mounting portion  13  is accessible through the slit  15  and the cup  15 A. 
   The micro coaxial cable  20  is configured by a plurality of coaxial wires  21  each has an electrical conductor  21 A, an insulator  21 B, a braiding  21 C, and a jacket  21 D encapsulates the braiding  21 C, ad the insulator  21 B and the conductor  21 A. The wires  21  can be bundled by a coat  22  for easily handling and processing. On the other hand, during the processing, each of the wires  21  is properly disposed within an organizer  24  such that the wires  21  can be pre-arranged to a pitch identical to the pitch of the connector  10 , i.e. in this case to the pitch P of the tail portion  16 B. Before the conductor  21 B can be properly interconnected to the tail portion  16 B, the insulator  21 B, the braiding  21 C, and the jacket  21 D have to been stripped off a certain distance so as to expose the conductor  21 B. During the assembly, the organizer  24  can be properly and snuggly received within the receiving space  13 A defined in the mounting portion  13  of the housing  11 , while the cable  20  can be each properly supported by those notches  13 B defined on the edge of the mounting portion  13 . In addition, according to a preferred embodiment of the present invention, the organizer  24  can be made of conductive material, such as die cast such that the braiding of each wire  21  can be electrically interconnected to enhance the shielding effect. 
   Once the cable  20  is properly processed, each of the conductor  21 A can be properly run through the slit  15  so as to in contact with the tail portion  16 B of the contact terminal  16 , as shown in  FIGS. 3A and 3C . In addition, ends of the tail portion  16 B extends outside of the slit  15 , and an end of the conductor  21 B extends also out of the slit  15  along with the slit  15 . However, this exposure of the ends of both the conductor  21 A and the tail portion  16 B can be finally covered by a wire end block  40 . As shown in  FIG. 1 , the wire end block  40  is defined with a plurality of slots  41  dimensioned to the width of the tail portion  16 B of the contact terminal  16 . When the wire end block  40  is attached to the housing  11 , the tail portion  16 B is properly received in each of the slot  41 . 
   One of the features of the first embodiment of the present invention is that the transferring layer  30  is introduced. In the past, solder paste is stenciled onto the tail portion, such as shown in U.S. Pat. No. 5,980,308 issued to Hu et al.; and U.S. Pat. No. 6,206,722 issued to Ko et al. However, administration of solder paste is critical and uncontrollable when creating a ultra fine drop of solder paste. Theoretically, the solder paste has to be in physical contact with the tail portion and adhere thereto. Then when the dispenser is lifted, a certain amount drop of solder paste is left on the tail portion. As discussed in the Description of the Prior Art, it is very difficult and tedious to do this in a mass production. The introduction of transferring layer  30  with preformed solder mass thereon properly resolves this problem. 
   Accordingly, the transferring layer  30  in accordance with the present invention includes a substrate  31 , which can be made of any suitable material, such as paper sheet, Kevlar sheet, etc. Then, pre-formed conductive material, such as solder nuggets  32  are disposed and adhere to the substrate  31  in a pre-arranged pattern which is identical to the cup  15 A on the mounting portion  12  of the housing  11  such that when the transferring layer  30  is disposed over the mounting portion  12 , each of the solder nugget  32  is in alignment with the corresponding cup  15 A and properly received therein. After the transferring layer is properly disposed over the mounting portion  12 , properly heating process can be applied to permanently joint the conductor  21 B and the tail portion  16 B. 
   On the other hand, it can also apply some mechanic force such that the conductor  21 B is pressed to the tail portion  16 B, and this can still create a permanent and electrical connection therebetween. 
   In addition, the transferring layer  30  further includes a ground bar  33  distant to the preformed conductive mass  32  and in contact with a grounding braiding  21 C of each of the coaxial wire  21 . This also resolve another laborious process as in the existing process, a very tiny lead wire has to be firstly flattened, and then solder to the braiding. It is extremely difficult in view of such a tinny connector and tiny exposure of the braiding. However, then the ground bar  33  is attached to the substrate  31 , this problem is smoothly and completely resolved. By the way, the ground bar  33  can be applied onto both surfaces for advanced advantages. The other side of the substrate  31  is then provided with a ground plane  34  which provides further electromagnetic interference (EMI) shielding, providing a continuous EMI from micro-coaxial cable  20  to the connector  10 . None of the existing and/or relevant prior art provides such a feature. According to a preferred embodiment of the present invention, the substrate  31  can be facilitated without ground bar  33  if the wire  20  is organized with the organizer  24  which is electrically conductive. Only when the wires  20  are not organized with the organizer  20 , then the substrate  31  can be provided with a ground bar  33  so as to electrically interconnect the braiding  31 C of the wire  20 . 
   The manufacturing process of the cable assembly  1  in according to the present invention starts from organizing and processing the micro-coaxial cable  20 . Each of the wires  21  are prearranged and organized with an organizer  24 . The organizer  24  is provided with plurality of through holes (not shown) for receiving therein the wires  21 . Then glue or the like can be administered to securely position the wires  21  within the organizer  24 . The organizer  24  can be later properly and snuggly disposed within the receiving space  13 A so as to properly position the conductors  20  onto the mounting portion  13  of the housing  11 . 
   After the cable  20  is processed with wires  21  are properly held by the organizer  24 , firstly jacket  21 D is stripped off for a predetermined length. Then a certain braiding  21 C is further stripped off from the insulator  21 B, and finally a certain length of insulator  21 B is stripped and the conductor  21 A is finally exposed. Since the conductor  21 A is very tiny and slim, care has to be taken so as to prevent the conductors  21 A from being broken. 
   As described above, each passageway has a slit  15  at mounting portion  13  of the housing  11 . Each of the slits  15  is provided with a wide-opened space  15 A, such as a cup  15 A which is comparably larger than the width of the slit  15 . The connector  10  is held with the mounting portion  13  held upward. Then, each of the conductors  21 A is then aligned and disposed into each of the slit  15  such that the conductor  21 A runs through the whole slit  15  and with ends extending outside of the slit  15 . 
   Once the conductors  21 A is properly and smoothly disposed within the corresponding slit  15 , a solder paste dispenser, as shown in  FIG. 6  can be used to administer a drop of solder paste into the cup  15 A. After the solder administration, the connector  10  along with the cable  20  can undergo a heat process so as to reflow the solder paste and eventually, a solder joint will be formed between the conductor  21 A and the tail portion  16 B of the contact  16 . This is one of the manufacturing processes to electrically and mechanically interconnect the conductors  21 A and the tail portions  16 B. 
   Alternatively, instead of using solder paste dispenser, the transferring layer  30  can be used. It is really convenient to have the solder mass or nugget  32  preformed onto the substrate  31  of the transferring layer  30 . The solder mass or nuggets  32  are disposed over the substrate  31  in a mirror-image manner such that when the substrate  31  is disposed over the mounting portion  13  of the housing  11 , each of the nuggets  32  will be properly aligned with each of the cup  15 A, and further smoothly received within the cup  15 A. 
   Then after the transferring layer  30  is properly disposed over the mounting portion  13 , and with each of the solder nuggets  32  properly received within the cup  15 A, then heating process can be applied so as to reflow the solder paste and eventually, a solder joint will be formed between the conductor  21 A and the tail portion  16 B of the contact  16 . 
   As discussed above, ends of the tail portion  16 B extends outside of the slit  15 , and an end of the conductor  21 B extends also out of the slit  15  along with the slit  15 . This is advantageous as heat can be transferred and conduct to the solder nuggets  32  through the exposed ends of tail portion  16 B. However, after the process is completed, this exposure of the ends of both the conductor  21 A and the tail portion  16 B can be properly covered by a wire end block  40 . 
   In addition, ground bar  33  can be also disposed on the substrate  31  with a predetermined distance with respect to the preformed solder nuggets  32 . This is specially advantageous as once the solder nuggets  32  properly sit into the cup  15 A, the ground bar  33  is also properly aligned and overlapped with the braiding  21 C of the wire  21 . When the heat process proceeds, solder joint will also be formed between the braiding  21 C and the ground bar  33 . 
   Although the preferred embodiment illustrated above using micro-coaxial cable as an example, it should be understood that others can be used as long as it fits its field requirements. For example, a flexible printed circuit can be used to replace the micro-coaxial cable. 
   In this case, the flexible printed circuit board can be provided with preformed solder nuggets  32 , and then properly disposed over the mounting portion  13  of the connector  10  with the solder nuggets  32  properly enter the cup  15 A. Then a heat process can be performed to electrically and interconnect the connector  1  and the flexible printed circuit. 
   On the other hand, for easily and readily handling the placement of the transferring layer  30  over the mounting portion  13  of the connector  10 , guiding arrangements, such as dowel post and guiding notch or holes can be used to easy alignment and placement of the transferring layer  30  over the mounting portion  13 . 
   According to a third embodiment in accordance with the present invention as shown in  FIG. 7 , the interconnection between the conductor  21 A and the tail portion  16 B of the contact  16  can be performed by both laser welding as well as soldering. By this arrangement, it features a dual-joint interconnection between conductor  21 A and the tail portion  16 B of the contact  16 . By providing at least two electrical interconnections between the conductor  21 A and the tail portion  16 B of the contact  16 , the concern can be put aside. 
   As discussed above, ends of the tail portion  16 B extends outside of the slit  15 , and an end of the conductor  21 B extends also out of the slit  15  along with the slit  15 . As a result, laser welding of the conductor  21 A to the tail portion  16 B of the contact  16  can be easily and effectively performed on a fraction of second. Meanwhile, the heat conducted to the tail portion  16 B by the laser welding is also high and sufficient enough the reflow the solder nugget  32  previously disposed within the cup  15 A. Accordingly, not only the conductor  21 B is welded to the tail portion  16 B, but also the conductor  21 B is soldered to the tail portion  16 B around the area within the cup  15 A. This dual-joint interconnection ensure robust and durable interconnections for such a tine wire to the connector. As clearly shown in  FIG. 7 , welding joints are formed on the exposed tail portion  16 B, while the solder joint is formed within the cup  15 A. As a result, two electrical interconnections are formed between the conductor  21 A to the tail portion  16 B of the contact  16  ensuring the reliability and durability can be performed by a single laser welding. 
   As discussed above, the conductor  21 A is very tiny, and handling and processing that is tremendously laborious. In order to properly position and place the conductor  21 A into the slit  15 . Each of the slit  15  is provided with a lead-in edge or chamfer  15 B, see  FIG. 3C . Accordingly, with an assistance of compressed air toward the conductor  21 A, the air pressure from the compressed air can properly direct the conductor  21 A to rest onto the tail portion  16 B of the contact  16 . 
   The connector  10  made in accordance with the present invention is by way of insert-molding in case of ultra-fine pitch arrangement. As discussed, the method suggested by the present invention can also be applied to other existing connectors, such as discussed in the Description of the Prior Art, i.e. the contact terminals can be assembled into a pre-molded housing. During the insert-molding process, the slit  15  and the cup  15 A are simultaneously formed on the mounting portion  13 . 
   It should be noted that even a micro coaxial cable is used in the preferred embodiment, it should be noted that others can be used as well, such at flexible printed cable (FPC). In this embodiment, then the solder pre-form can be directly disposed on the FPC, and then the connector made in accordance with the present invention can readily sit onto the solder pre-form, and then go through certain process so as to electrically interconnect the FPC and the connector. 
   It will be understood that the invention may be embodied in other specific forms without departing from the spirit or central characteristics thereof. The present examples and embodiments, therefore, are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.