Patent Publication Number: US-9853383-B2

Title: Conductive polymer contacts for surface mount technology connectors

Description:
BACKGROUND OF INVENTION 
     The invention provides a robust connection interface for surface mount technology (SMT) contacts used in the manufacture of electronic devices that have high area densities or high wear environments, and that accommodates contact surface irregularities without significant wear to the either contact surface. 
     In SMT contacts, connector components are applied directly to the surface of a circuit board. The components are secured at specified locations on the circuit board by solder pads that are placed on the circuit board in a suitable process, such as by printing the pads on the board forming a printed circuit board (PCB). The solder pads are then heated and the various components are placed onto the solder pads to be secured to the PCB by the cooling solder pads bonding the components to the PCB. 
     In the manufacture of the PCBs, to provide electrical connection to external or peripheral components various SMT style connectors are used, including but not limited to: Land Grid Arrays (LGAs), Ball Grid Arrays (BGAs), Pin Grid Arrays (PGAs), Flexible Flat Cable (FPC) connectors, and Pogo™ contacts. These connectors or components are usually soldered to one side of the circuit board and require a mating connector affixed to the external component. 
     In one prior art embodiment, as illustrated in  FIG. 1 , the component secured to the PCB  10  is a connector  18  used to interconnect the PCB  10  with another PCB or with a cable/flex circuit  20  having a complementary connector  26  thereon that is operably connected to another part of the device. These connectors  18 , 26  each include a body with complementary connecting structures thereon, as well as tabs  14  utilized to connect the connector body  18 , 26  to the associated PCB  10 , 20  using the solder pads  12 . The connecting structures  16 , 24  can take various forms, such as POGO pins and rigid metal contacts, or the tubular mating sockets configured to receive the pins or rigid metal contacts, which in  FIG. 1 —are tensioned, U-channels or sockets of metal,  16  and rigid, U-shaped tabs,  24 . The pins, contacts, e.g., a bed-of-nails contact array, or other connectors  24  are pressed into engagement with a suitably formed mating connector, such that an electric connection can be formed between the pin or contact  24  and socket  16  of the mating connector. To facilitate the connection between the contact  24  and the socket  16 , the contact and/or the socket, of whatever form, often include a electrical connection-enhancing surface coating on the exterior of the contact(s)  24  and/or socket(s)  16 . 
     One significant drawback with regard to these connectors is that the materials utilized to form the contacts are normally formed of a rigid material in order to facilitate the conductivity or electrical connections between the contacts and the other PCB or device with which the contacts are engaged. As a result, the contacts are formed with various surface irregularities that, when subjected to repeated connect/disconnect cycles, can damage the materials forming the contacts themselves or the contact that is pressed into engagement with the contact containing the surface irregularity. Also, if an excessive or shear force is inadvertently exerted to engage the connectors with one another, it is possible to permanently deform and/or damage the shape of the contacts and/or the coatings on the contacts, thereby degrading the connection between the contacts and other contacts that may be subsequently engaged with the damaged contacts. 
     Further, even without significant damage to the structure of either contact surface, surface irregularities can cause the interface to be unstable or not possible without exerting additional, potentially destructive force to the contacts already engaged. 
     Additionally, as with all surface mount devices employing rigid electrical traces, bending or flexing due to thermal expansion, pressure or vibration can cause solder and metal trace materials to fracture, irreparably damaging the contact; which in the case of many connection styles will require full replacement of the connector. 
     Accordingly, it is desirable to develop an electrical contact structure for use in SMT applications and in the devices constructed thereby that can successfully accommodate structural irregularities on other contact structures to minimize potential damage to the various contact structures and to maximize the electrical connections formed between the contacts. 
     BRIEF DESCRIPTION OF THE INVENTION 
     There is a need or desire for an improved contact structure for use in SMT applications where repeated connect/disconnect cycles or contact surface irregularities cause increased wear on the contact surface or connector contacts. The above-mentioned drawbacks and needs are addressed by the invention embodiments in the following descriptions. 
     According to one exemplary aspect of the invention, an improved contact structure for use in SMT applications is formed from a z-axis conductive polymer. The conductive polymer, forming the contacts of a connector, can conduct an electric signal from and function as the connection to an exposed circuit contact/connector. The polymer can self-heal when physically deformed by engagement with another circuit contact/connector. Thus, the conductive polymer contact can accommodate repeated engagement with rigid circuit contacts without any permanent deformation of either contact surface, to which PGA, FFC and Pogo™ (e.g. spring tension) connectors are susceptible. 
     According to another aspect of an exemplary embodiment of the invention, the conductive polymer is capable of engaging a contact having a contact-enhancing surface coating thereon without damaging the coating, due to the malleable nature of the polymer. The polymer does not create significant friction when engaged with a rigid contact, such that the contact coating is not damaged during connection or upon disengagement of the contact from the polymer contact. 
     According to yet another exemplary embodiment of the invention, the malleable conductive polymer is able to conform around surface irregularities of rigid and flexible circuit contacts. The polymer is thus able to form a better connection at lower overall contact pressures than are required by LGA or FFC or other prior art SMT connectors. 
     Another exemplary embodiment of the invention, the conductive polymer exhibits a degree of surface tension with the intended contact surface. The connector can therefore maintain better contact in environments with mechanical vibration or warping due to the attractive force of the surface tension unlike BGA or other various prior art soldered SMT connections. 
     Another exemplary embodiment of the invention, the polymer acts to reduce empty space between the contact surfaces. The action of deformation due to the surface tension of the polymer effectively self-seals the contact surfaces from the environment. Thus, the conductive polymer helps to prevent contamination of the contacts. 
     According to yet another exemplary embodiment of the invention, the aforementioned conductive polymer connectors do not require complex manufacturing technology to produce. The connector body can be easily manufactured using any process that can produce channels in a material (e.g. additive, multi-part, or chemically-etched construction, etc.). The channels are then filled (e.g. through injection, deposition or vacuum-drawn fill methods, among others) with the conductive polymer to form the contact surface features described herein. 
     According to still another aspect of one exemplary embodiment of the invention, complex branching and connective patterns can be created through the use of axis-limited conductive polymers (e.g. z-axis conductive polymer) in single or multiple layers; thus allowing for high contact densities to break-out into different connector styles. 
     According to still a further aspect of one exemplary embodiment of the invention, a surface mount technology (SMT) connector for a printed circuit board (PCB) includes a body formed of a non-conductive material a connection member disposed on the body and adapted to engage the body with a mating surface and at least one terminal disposed on the body formed from a conductive polymer. 
     According to still another aspect of one exemplary embodiment of the invention, a surface mount technology (SMT) connector set for joining a printed circuit board (PCB) and/or a flexible printed circuit (FPC) to one another includes a first connector including a set of conductive polymer contacts thereon and a second connector including a set of electrical contacts thereon, wherein the set of conductive polymer contacts is alignable with the set of electrical contacts to provide an electrical connection therebetween. 
     According to still a further aspect of one exemplary embodiment of the invention, a method for forming a surface mount technology (SMT) connector for a printed circuit board (PCB) or a flexible printed circuit (FPC includes the steps of forming a connector body including a number of channels extending completely through the connector body and filling the channels with an amount of a conductive polymer to form a conductive polymer contact in the connector body. 
     It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawings illustrate the best mode presently contemplated of carrying out the disclosure. In the drawings 
         FIG. 1  is an isometric view of a prior art surface mount technology flexible printed circuit (FPC) board-to-board female and male connector. 
         FIG. 2  is an isometric view of circuit board traces (left) and a matching connector according to one exemplary embodiment of the invention. 
         FIG. 3  is a cross-sectional view along line  3 - 3  of  FIG. 2 . 
         FIG. 4  is a cross-sectional view of a connector (gender neutral) in a form that interfaces with a rigid Printed Circuit Board (PCB) according to one exemplary embodiment of the invention. 
         FIG. 5  is a cross-sectional view of a mated pair of gender neutral connectors illustrated in  FIG. 4 . 
         FIG. 6  is an isometric view of another exemplary embodiment of the invention. 
         FIG. 7  is a cross-sectional view of the embodiment in  FIG. 6  showing the unmated and mated contact with a standard serial connector style. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific embodiments, which may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the embodiments, and it is to be understood that other embodiments may be utilized and that logical, mechanical, electrical and other changes may be made without departing from the scope of the embodiments. The following detailed description is, therefore, not to be taken in a limiting sense. 
     Further, the foregoing summary, as well as the following detailed description of certain embodiments, will be better understood when read in conjunction with the appended drawings. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings 
     Looking at  FIGS. 2, and 3  one exemplary embodiment of a connector  118  of the invention is illustrated in a connector set  101  including a female connector  103 . In the exemplary embodiment the connector  118  is formed as the male connector  118  mounted on flexible printed circuit (FPC)  122  and includes a body  102  formed in any desired or necessary configuration of a non-conductive and optionally flexible material. The body  102  is secured to the FPC in any suitable manner and includes a connection member providing pressure between mating surfaces, such as connector tabs  120  affixed thereto to guide and fix the connector  118  to a separate rigid printed circuit board (PCB)  110  using sockets  114  on the PCB  110 . The body  102  of the connector  118  also includes contacts  116  formed of a conductive, isotropic or non-isotropic polymer, or combinations of layers thereof, disposed within channels, apertures or other openings  111  formed in the body  102  of the connector  118 . The channels  111  extend completely through the body  102  such that the conductive polymer contacts  116  positioned therein extend the length of the channel  111  with a protrusion  113  on each end of the contact  116  that extend outwardly from each end of the channel  111 . The protrusions  113  opposite the FPC  122  each contacts a trace pad  112  on the female connector  103  on the printed circuit board  110 . In this manner, the contacts  116 , via the protrusions  113 , each make electrical contact between traces, wires or other electrical conductors (not shown) disposed in the FPC  122  and the traces  112  to facilitate an electrical connection between the FPC  122  the PCB  110  and can be, positioned in any way to afford contact with desired surfaces on the printed circuit board  110 . Further, the size of the protrusions  113  can be selected as desired in order to facilitate the electrical contact of the contacts  116  with the various traces  112  on the FPC  122  and the PCB  110 . In one exemplary embodiment, the protrusions  113  can extend outwardly from the channels  111  as shown in  FIG. 1  to contact the traces  112 , or can be positioned flush with the surface of the body  102 , such as shown in  FIG. 1  to contact the traces on the FPC  122 . In the embodiment where the protrusions  113  extend outwardly form the channel  111 , the properties of the polymer forming the contact  116  enable the protrusion  113  to be compressed upon contact with the trace  112  to create the electrical connection between the contact  116  and the trace  112 , while also returning to its original configuration upon removal of the compressive force on the protrusion  113 . Further, the surface tension of the polymer forming the contact  116  can operate to assist the protrusion  113  to contact the adjacent trace and form the required electrical connection. 
       FIG. 3  illustrates an exemplary embodiment of the connector  118  in which the flexible printed circuit board  122  is clamped between two halves  104 , 106  of the connector body  102 . Connector body part half  104  clamps in a suitable manner or is otherwise engaged onto body half  106 , such as using an adhesive or mechanical fastener, from the other side of the FPC  122  to retain the end of the FPC  122  therebetween. A thin, compressible, non-isotropic layer of conductive polymer, direct interface, or metal contacts  124  is positioned between the halves  104 , 106  and contacts the flexible printed circuit traces positioned between halves  104 ,  106  to electrically connect the FPC traces with the proper channels  116 . 
       FIGS. 4 and 5  illustrate another exemplary embodiment of a connector  218  employing conductive polymer contacts  216  formed of the conductive polymer disposed within channels  211  formed in the body  202 . In this construction, the connector  218  makes direct contact with traces  224  on a rigid printed circuit board  222 . The connector  218  is held onto the PCB  222  by a suitable fastener, such as a mechanical fastener  220  including, but not limited to a clip or screw that is directly engaged with a bore  221  in the PCB  222 , to provide enough pressure to engage and ensure direct contact between the conductive polymer disposed within the contacts  216  and the traces  224 . This exemplary embodiment illustrates a “gender neutral” embodiment of the connector  218  that makes use of a compressible, non-conductive polymer surface  228  located on the connector body  202  opposite the PCB  222  disposed around the protrusions  213  of the polymer contacts  216  after exiting the body  202  of the rigid connector  218 . In  FIG. 5 , the interface between two gender-neutral connectors  218  is illustrated where the connectors  218  are held together through a double-sided clipping mechanism  223  using mechanical fasteners  220  to hold the connectors  218  on the PCBs  210  as well as includes tabs  120  on one connector  218  that are insertable within and engageable with slots  226  formed in the opposite connector  218 . 
     In the illustrated exemplary embodiments, the conductive polymer is positioned in the circuit channel  111 ,  211  to form the terminal. While any suitable polymer can be utilized in forming the polymer, certain exemplary polymers for use as the polymer component of the conductive polymer include, but are not limited, to either an isotropic or non-isotropic loaded polymer, and combinations and layers thereof, as well as z-axis polymers. The particular polymer used can be any suitable elastomer, including but not limited to rubbers and thermoplastic elastomers with a range of varying viscosity, including a polydimethylsiloxane or equivalent low modulus silicone based polymer that is able to reflow back into shape after deformation. 
     Further, in order to provide the conductivity required for the formation of the terminal or contact  116 , 216  using the conductive polymer, the polymer component includes an amount of conductive particles (not shown) dispersed throughout the polymer component, and in the exemplary embodiment uniformly throughout the polymer component. The conductive particles can be selected as desired any suitable electrically conductive particle, such as from metal or other conductive material particle, but in an exemplary embodiment can be selected from the group consisting of copper, gold, silver, palladium, platinum, and alloys thereof. Further, the size of the particles can be 3 to 500 microns with optionally an electrically conductive sphere, flake or amorphous form or shape and can be present within the polymer component in an amount ranging from about 1% to about 99% w/w of the conductive polymer. 
     In addition, in exemplary embodiments where conductivity through the contact  116  and/or connector layer in only one direction is required, an electrically isolative polymer, such as Sil-194 can be used. In cases where a particular layer is required to conduct isotropically, such as a polydimethylsiloxane or equivalent low modulus silicone based polymer, can used. 
     Looking now at  FIGS. 6 and 7  another exemplary embodiment of the connector  312  is illustrated. In the connector  312 , as well as optionally in the other embodiments for the connectors  118  and  218 , channels  310  are formed through the solid connector body  302  through various methods of manufacture, including, but not limited to, injection molded techniques, additive deposition, or subtractive etching. The connector body  302  is held and/or secured to the PCB  222  by various mechanisms, including but not limited to adhesives or mechanical fasteners, such as those illustrated in  FIGS. 3 and 4  above, in order to electrically connect the conductive polymer contacts  320  with the traces  224  on the PCB  222  using various methods, similar to  FIGS. 3 and 4 . 
     The connector  312  is engaged with a plug  316  including a number of rigid, conductive pins  314  disposed within housing  318  for the plug  316  and connected to wires or other suitable conductive members (not shown). To engage the plug  316  with the connector  312 , the pins  314  are aligned with each of the channels  310  containing the conductive polymer contacts  320  and the pins  314  are forced or urges into the channels  310  to contact, deform and/or pierce the conductive polymer contact  320  within the channels  310 , thus electrically connecting the pins  314  to the contacts  320 . When the pins  314  are withdrawn from the channels  310 , due to the flexible and resilient nature of the polymer, the polymer contacts  320  self-heal and return to their original undeformed configuration within the channels  310  until the pins  314  are reinserted into the channels  310 . 
     To fill the channels  111 ,  211  or  310  in any of the illustrated exemplary embodiments with the conductive polymer to form the contact  116  within the channel  111 ,  211 ,  310 , injection, vacuum drawing, deposition, or any other suitable method can be used so long as the polymer completely fills the channel  111 ,  211 ,  310 , and in the illustrated exemplary embodiments of  FIGS. 2-5  is able to form a dome or protrusion  113 , 213  at the surface interface due to surface tension. Further, in the exemplary embodiment of  FIGS. 6 and 7 , the polymer can alternatively fill less than each of the entire channels  310  in order to accommodate the insertion of the pins  314  into the channels  310 , as desired. 
     Additionally, with regard to each of the exemplary embodiments of  FIGS. 2-7 , the flexible and resilient properties of the polymer forming the contacts  320  prevents any surface irregularities on the pins  314  from damaging the contacts  320 , and prevents the contacts  320  from damaging any coating applied to the exterior of the pins  314 . Further, in this and the other exemplary embodiments, the surface tension attributes of the polymer forming the contacts  320  promote the self-healing of the polymer contacts  320 , maintains a relatively constant insertion and disengagement force between the pins  314  and the contacts  320 , prevents contamination of the contacts, maintains better contact in environments with mechanical vibration or warping due to the attractive force of the surface tension, and provides better connection at lower overall contact pressures. 
     The written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.