Patent Application
20160344118
1. Field of the Invention
The present invention relates to separable electrical connectors used for the interconnection of circuit elements in electronic devices such as computers, mobile phones, tablets, laptop computers, medical electronics, opto-electronic assemblies, sensor electronics, or other devices requiring separable electrical interconnections for ease of testing, assembly, rework, repair, and/or for other reasons.
2. Background of the Invention
Complex electronic devices such as computers and mobile phones require electrical interconnection of various circuit elements, such as printed circuit boards, flexible printed circuit cables, rigid-flex circuits, ceramic substrates, semiconductor package substrates, opto-electronic devices, batteries, and other elements of electronic devices. Frequently, it is desired that these interconnections be separable in order to facilitate low cost and simplified assembly, test, rework, and repair, or to avoid high temperature interconnection methods such as soldering, brazing, or conductive adhesive curing when certain subcomponents or elements of the assembly are sensitive to elevated temperatures, or for other reasons or combinations of reasons.
For this reason, there is frequently a plurality of separable electrical connectors found in a single electronic device. As these electronic devices evolve to provide increased functionality in smaller form factors, such as for mobile consumer electronic products, the electrical connectors must simultaneously improve in function and performance while decreasing in size, including area of the connector's footprint (x by y area occupied on the mating circuit elements) and its profile (thickness). Low profile connectors also facilitate reduced electrical resistance across the connector, allowing them to carry more power with less temperature increase due to resistive losses, and often enable better signal integrity due to lower inductance and reduced impedance discontinuity.
It is frequently required that these electrical connectors meet stringent performance requirements, such as maintaining high signal integrity of the interconnected electronic signals at high operating frequencies, providing low electrical contact resistance to enable high current capacity with minimal temperature rise, surviving high levels of mechanical shock and vibration without transient or permanent interruptions in the electrical path, maintaining reliable interconnections through various environmental stresses during life of the product, and meeting other stringent performance requirements that are specific to various applications such as aerospace, medical electronics, and other demanding applications. As electronic devices continue to be miniaturized, the interconnection terminals or pads on the circuit elements being interconnected frequently are required to be reduced in size (area) and located on finer pitches (spaced closer together), requiring electrical connectors with improved means for precise and accurate alignment to the circuit elements and with very accurate true position of the contacts in the connector relative to each other and to the position of these alignment means. Manufacturing costs of these connectors must be low to keep pace with the competitive environment and endproduct pricing constraints, so connector materials and manufacturing processes must be simple, streamlined and/or low cost.
Many connectors used in present miniaturized electronic devices fall into one of two general categories: two piece ‘mezzanine’ connectors, and one piece ‘ZIF’ connectors, although other connectors including Neoconix PCBeam™ ‘normal force’ connectors are also frequently used. Both ZIF and mezzanine connectors frequently have difficulty surviving mechanical shock and vibration forces experienced during normal use of the device without transient or permanent interruptions in the electrical path, unless secondary retention elements are included which occupy additional space in the device. Since space in miniaturized devices is at a premium, this is not ideal. As these connectors continue to be miniaturized to fit into shrinking device form factors, the sensitivity to shock and vibration typically increases due to reduced area for application of retention forces. Frequently, the profile (thickness) of these connectors is well above 1 millimeter, which can be a limiting factor in shrinking the thickness of devices like high end mobile ‘smart-phones’. Commonly, ZIF and mezzanine connectors contribute to a reduction in signal fidelity at high frequencies due to relatively long, high inductance leads, and/or due to impedance discontinuities at the transitions from the mating circuit element terminals to the connector's electrical contacts. Frequently, the power handling capacity of these two connector types is less than or equal to 0.2 amps of current per individual contact due to high contact resistance and long current path, requiring an increase in the number of contacts and thus an increase in the connector's footprint size in order to function effectively as high power connectors, such as battery connectors, without unacceptable temperature rise during operation. In addition, contact true position of these connectors is frequently inadequate to enable the desired level of miniaturization in the system and of the circuit elements in the system. In many cases, these connectors are manufactured by stamping and forming electrical spring contacts into separate contact elements, before or during the insertion of those contacts sequentially or in ganged fashion into a pre-molded connector housing. In this situation, the true position tolerance of the contacts is defined cumulatively by any inaccuracies of the insertion process and inaccuracies in the precision of various dimensions of the molded connector housing structures that align and retain the electrical spring contacts, as well as inaccuracies in the dimensions or shape of the formed spring contacts and of the insertion process. In addition, the insertion process is frequently sequential and thus relatively time consuming and expensive, compared to batch processes. The retention of the contacts in the housing and their position in these mezzanine and ZIF connectors is typically maintained by frictional forces, rather than by true bonding of the contacts to the connector housing as would be the case if the housing were molded directly onto a portion of the contacts. It is desirable and would be an advance over the current state of the art to provide a connector structure and manufacturing process that offers high signal fidelity, high mechanical and electrical spring compliance and working range, high resistance to mechanical shock and vibration, fine contact pitch, low connector profile, high current capacity, very accurate and repeatable contact true position, low cost batch manufacturing processes, and reliability through environmental stresses during operating life in one connector type.
One objective of the present invention is to provide a low profile electrical connector for interconnecting two circuit elements in an electronic system or device, such as two printed circuit boards, or a printed circuit board and a flexible printed circuit, or a semiconductor package substrate and a printed circuit board, or a rigid-flex circuit and a flexible or rigid printed circuit, and which provides many or all of the characteristics including high electrical performance (including low electrical resistance, high signal fidelity at high operating frequencies), high current carrying capacity, high mechanical and electrical compliance and working range of the electrical spring contacts, high tolerance of mechanical shock and vibration without suffering transient or permanent opens, fine contact pitch for small connector footprint, positive retention and ease of assembly, and low connector profile. Another objective of the present invention is to maintain very tight true position tolerances for the electrical contacts in such a connector, relative to each other and to alignment features on the connector body, so that it is capable of interconnecting miniaturized circuit elements with interconnection terminals of small size and/or on a tight pitch. It is a further objective of this invention to provide the above features in a connector which can be manufactured in relatively few process steps and at lower cost than commonly used connectors, including by mass stamping and forming of the electrical spring contacts and mass integration of these electrical contacts into an insulative connector housing, and by other batch processing methods including surface finishing and singulation. It is a further objective of the present invention to reduce the impedance discontinuity at the interconnection by enabling smaller terminal mating pads on the mating circuit element, thereby reducing capacitance both between the connector structure and the mating terminal pad, and between the mating terminal pad and other circuit structures within the mating circuit element.
One aspect of the present invention comprises a plurality of patterned and formed electrical spring contacts which are created from a sheet or strip of electrically conductive spring material, such as a copper alloy, and which are integrated into a connector body or connector housing en masse while still integrally connected to the sheet or strip. The terms sheet and strip may at times be used interchangeably in further discussion of the present invention, and refer to a planar sheet of conductive spring material, typically with a thickness between 10 microns and 200 microns, but preferably between 25 and 50 microns. In general, a strip would be longer and narrower than a sheet, whereby a sheet width might be 50% or more of its length, and a strip more typically would have a width equal to less than 25% of its length. Strip can also refer to a very long length of contact sheet material which can be kept in and processed in coils, in reel to reel format, during manufacture of the connector. The terms connector body and connector housing may also be used interchangeably in further description of the present invention, and generally refer to an insulative structure that retains the spring contacts and maintains the integrity of the connector, including assisting with its alignment to other circuit elements. At times the connector body or housing may be referred to as a molded connector body or housing, but this should not be construed to limit the description of the process for creating the body or housing to molding or injection molding processes. Other means of creating the housing and integrating it with the contact strip may include deposition, 3D printing, lamination, adhesive bonding, or other fabrication means.
The integration of the plurality of electrical spring contacts into a connector housing may be accomplished with a molding process, such as injection molding or over-molding or film assisted over-molding, or by other molding processes, or by other means such as three dimensional printing, deposition, electrophoretic deposition, lamination, or by other common processes or combinations of these processes that can encapsulate or surround structures with an insulative material. In the present invention, the connector body is formed over an array of formed electrical contacts subsequent to the patterning and three dimensional forming of the plurality of electrical contacts, but while the electrical contacts are still integrated with and connected to the contact sheet as a unitary element.
The contacts in one embodiment of this invention have been formed into a three dimensional shape while one or more regions of each contact are still integrated into the contact sheet or strip, prior to molding or other means of applying the insulative connector body. The three dimensional contact of one embodiment includes a distal end comprising an elongated, flexible cantilever beam-like spring to enable separable electrical interconnection to electrically conductive terminals on a circuit element such as a printed circuit board, a flexible circuit, a rigid-flex circuit, or a semiconductor package substrate, through application of normal force between the mating circuit element and the connector. The distal end of the contact is designed so as to provide significant mechanical working range within the elastic limits of the spring sheet material, and likewise significant total electrical compliance whereby the contact spring provides low electrical resistance across a large range of compression distance. In one embodiment of the present invention, the distal end of the contact may take the shape of the PCBeam™ electrical contact technology previously disclosed by Neoconix, Inc. In another embodiment, the distal end of the contact resembles a cantilever beam.
In one embodiment of the present invention, the distal end of the electrical contact is preferably designed to provide wipe of the tip of the distal end across the mating terminal pad on the mating circuit element during compression. This wiping action assists in reducing contact resistance by breaking through any oxide layers or contaminants on the contact tip and/or the mating terminal pad. In a preferred embodiment, the distance of this wiping is 25 to 100 microns. The distal end of the contacts emanates from the original plane of the contact sheet and protrudes above a first surface of the contact sheet and above a first surface of the insulative connector body, at an angle of less than 90 degrees. In one embodiment, the distal end of the contact emanates from the plane of the contact sheet at an angle which gradually increases along a portion of the length of the distal end from where it is coplanar with the contact sheet toward the tip of the distal end. The three dimensional contact also comprises a proximal end. In one embodiment for a surface mount connector, the proximal end is a semi-rigid terminal or ‘solder tail’, approximately parallel to the plane of a second, opposing surface of the insulative connector body and parallel to the original plane of the contact sheet. The proximal end in this embodiment is used for permanently or semi-permanently joining the contacts of the connector to terminals on a second electronic circuit element using solder, conductive adhesive, or other means to provide an electrical and mechanical attachment and interconnection. The second electronic circuit element can be a printed circuit board, a flexible printed circuit, a rigid-flex circuit, a semiconductor package substrate, a semiconductor, a passive device, a battery, or other electronic circuit element. The electrical contact also comprises a middle section, which remains in the original plane of the contact strip or sheet after contact forming and which is integral with both the distal end and the proximal end of the electrical contact, such that the distal end, the middle section, and the proximal ends of the contact element form a unitary body. The middle section of the contact is substantially encapsulated on both surfaces by the connector body.
The formed, distal end of the contact emanates from the plane of the contact sheet at an angle of less than ninety degrees. The proximal end or solder tail emanates from the plane of the contact strip or sheet at an angle of approximately zero degrees, and hence is parallel but typically slightly elevated from the plane of the contact sheet or strip. In a preferred embodiment of this invention, the distal end of the contact emanates outward from a first surface of the contact sheet, and the proximal end of the contact is parallel to the contact sheet but protrudes above the second, opposing surface of the contact sheet.
In a preferred embodiment of the present invention, the design of the contact resembles a constant stress cantilever beam, with the width of the beam decreasing from its base, which emanates from the middle section of the contact, to its tip, where the mechanical and electrical connection is made to a mating circuit element. In a preferred embodiment, the width of the tip of the beam is less than 200 microns, and preferably is less than 150 microns.
The connector body is molded, deposited, laminated, or otherwise caused to encapsulate the plurality of electrical spring contacts of a quantity sufficient for the function of the specific interconnection requirement, this encapsulation occurring while the contacts are still integrated into the contact sheet or strip. This aspect of the present invention maintains the electrical contacts in precise alignment to one another, and enables very accurate true position of the contacts relative to one another and to the molded or otherwise formed connector body, which itself has integral alignment features to assist in integration of the finished connector into an electronic assembly. After molding or otherwise applying the connector housing or body, the distal ends of the electrical spring contacts emanate above the plane of a first surface of the molded connector body at an angle of less than ninety degrees, and preferably less than 60 degrees, such that it protrudes above the surface of the connector body. In one embodiment, for a surface mount connector, the proximal end of the contact emanates from a second, opposing surface of the connector body, ultimately becoming approximately parallel to the second surface but slightly proud of the plane of that second surface of the connector body. In a preferred embodiment of the present invention, the tip of the distal end of the contact protrudes substantially further from the first surface of the connector body than the distal end protrudes from the second surface of the connector body. In another embodiment of the present invention, there is a section of the proximal end of the contact immediately adjacent to the middle section of the contact which emanates from the second surface of the contact sheet for a short distance at an angle of approximately ninety degrees before the proximal end of the contact becomes oriented approximately parallel to the original plane of the contact sheet. This short section of the proximal end of the contact oriented 90 degrees to the plane of the contact sheet rigidifies the proximal end of the contact under application of normal force, such that it does not substantially compress, thereby functioning as a solder interconnection terminal for the contact rather than as a separable spring contact element, such as for use in surface mount connectors.
The molded or otherwise formed connector housing extends above both surfaces of the original plane of the contact sheet and encapsulates at least a portion of the middle section of the contact. In a preferred embodiment of the present invention, the molded connector body is designed with openings that allow the distal end of the contact to be unimpeded while it is fully compressed to a degree such that its tip is approximately co-planar with the first surface of the connector body. In a preferred embodiment, the distal end of the spring contact is designed such that when it is fully compressed to a degree where its tip is co-planar with the first surface of the connector body, it remains within its elastic range so that it does not deform plastically, and also so that it provides sufficient contact force between the contact tip of the distal end and the mating terminal such that it provides a low electrical contact resistance interconnection. In another embodiment of the present invention, the contact sheet material within the distal end of the contact remains in the elastic range during full compression of the contact distal end to the first surface of the connector body, but a plated surface finish layer or layers may not remain in its elastic range, and may therefore plastically yield a small amount during the first full compression of the contact distal end. In this embodiment, there would typically be no additional yielding of the plated surface finish material on subsequent compression cycles of the contact distal end.
Because the distal end of the contact preferably remains within its elastic range during full compression, it can therefore attain the same height above the first surface of the connector body when released as before compression. In this way, the contact element can survive and function through multiple mating cycles without plastic deformation or excessive fatigue or work hardening. The proximal end of the contact is preferably designed with a shape such that it does not deform or compress significantly during compression of the distal end of the contact through application of normal force through a first mating circuit element above the first surface of the connector body. The electrical connector of this embodiment of the present invention provides an electrical interconnection between two circuit elements by forming a permanent or semipermanent electrical interconnection between the proximal ends of the contacts to conductive terminals on one mating circuit element, and separable electrical interconnections between the distal ends of the contacts and conductive terminals on a second, opposing mating circuit element, through application of normal force between the two mating circuit elements toward one another.
In a preferred embodiment of the present invention, the distal and proximal ends of a single contact are adjacent to each other when viewed from a perspective normal to the surface of the contact sheet, and they are conjoined at a middle section of the contact at the end of the contact away from the tips of the distal and proximal ends of the contact. In another embodiment for a surface mount connector, the distal end of the contact is longer than the proximal end.
For another embodiment of the present invention, for a non-surface mount connector where both mating circuit elements are separably mated to, the distal end of the contact and the proximal end of the contact are of approximately the same length, and have approximately the same two dimensional and three dimensional shape and thickness, such that both distal and proximal ends can function as spring elements analogous to cantilever beams, and such that normal force required to compress the proximal end and the distal end of the contact is the same. In this embodiment of the present invention, the connector is designed to mate separably to each of two opposing, mating circuit elements. In this embodiment, the patterned and formed electrical contacts also remain integral to the contact strip during patterning, forming, and application of the connector housing.
The electrical contacts in the present invention may maintain their connection to the contact strip or sheet in various locations. In one embodiment, the contacts remain integral to the contact strip through an attachment point at the middle section of the contact. In another embodiment of the present invention, the contacts are integral to the contact sheet after stamping and forming of the contacts but before singulation, through a connection at the tip of the proximal end of the contact. This connection may be severed after the connector housing is applied to the plurality of contacts in the array for the connector. In a preferred embodiment, all the connections of all of the contacts to the contact sheet are severed en masse, using a stamping die or other cutting method, after the connector housing has been applied. In another embodiment, these connections are severed sequentially in rows.
In another embodiment, a power connector has a plurality of contacts n, where n is less than the total number of contacts in the connector, that are ganged together through conjoining of their middle sections, such that after singulation these ganged contacts remain electrically shorted together, for making high power interconnections and for grounding or return terminals. In another embodiment, n elastic distal contact ends are attached to m proximal contact ends, where n is greater than m. In another embodiment of this invention, the ganged contacts with conjoined middle sections remain connected to the contact sheet after stamping and forming of the contacts and through application of the connector housing, through an extension of the middle section at the edges of the contact array that remained integral with and connected to the contact sheet. After the connector housing is applied, the connector is singulated by cutting or otherwise separating or severing this extension of the middle section of the contacts at the edge of the connector array from the contact sheet or strip. In a preferred embodiment, all of these connections in a given connector are severed en masse, such as by use of a stamping die.
In another embodiment of this invention, both the distal ends and the proximal ends of the contacts are elongated, flexible cantilever beam-like springs to enable separable electrical interconnection of both sides of the connector to electrically conductive terminals on two opposing circuit elements such as printed circuit boards, flexible printed circuits, rigid-flex circuits, semiconductor package substrate, passive components, semiconductors, or batteries, to separably interconnect one electrical circuit element to the other. In this embodiment, both the distal end and the proximal end of the contact are designed so as to provide significant mechanical working range within the elastic limits of the spring sheet material, and likewise significant total electrical compliance whereby the contact spring provides low electrical resistance across a broad range of compression distance. The distal contact ends and the proximal contact ends in this embodiment emanate from opposing surfaces of the contact sheet, and are connected to one another with a middle contact section such that the distal end, proximal end, and middle section of the contact are a unitary body, and remain integral with the contact sheet through application of the connector housing or body, and are then singulated from the contact strip and, as needed, from one another.
Because the contacts are defined, formed, and incorporated into the connector housing while still integrated into the sheet or strip of contact material, and the tooling that molds, deposits, laminates, or otherwise applies the housing material is accurately aligned to the contact sheet or strip through high precision tooling features in the strip and in the tooling, the contact true positions are maintained very accurately with respect to one another and with respect to the connector housing alignment features, which can be comprised of integral features of the housing including protrusions, slots, holes, pins, or other alignment features. In a preferred embodiment of the present invention, the connector housing is applied by an injection molding process using a precision mold tool, said tool having precise alignment features and jigs to locate the mold over the contact array on the contact sheet or strip. This molding process thereby can provide a very accurate true position for the contacts relative to the alignment features molded as part of the housing, and allows the resulting connector to be used for electrical interconnection of highly miniaturized circuit elements with small mating terminal pads on a tight pitch and spacing.
The two dimensional shape of the electrical contacts of the present invention is defined in the sheet or strip using a patterning process which can include stamping, etching, laser machining, a combination of these processes, or other processes or combinations of processes that can cut or remove metal selectively without separating the contacts completely from the sheet or strip.
In one embodiment of the invention, during the patterning to achieve the two dimensional shape of the electrical contacts while they are still integrated in the contact sheet or strip, frangible sections are created at the locations where the contacts will ultimately be separated (singulated) from one another or from the contact strip or sheet, to enhance the ease of singulation of the contacts from one another for electrical isolation as needed for the specific connector function requirements, and/or for separation of the connector as a whole from the contact sheet or strip. The design of the frangible section may be created such that, when necessary, the frangible area can be more easily fractured or broken to achieve the isolation and separation of contacts from the contact strip or sheet and from each other. The frangible structure can in some embodiments be achieved by creating a weakened region, or a region of stress concentration, in the contact sheet material where the separation must occur. Such a frangible feature may be a sharp or sudden discontinuity in the thickness or width of the material immediately adjacent to, and in connection with, the contact. The stress concentrated or weakened region can be a sharp notch in the width of material section adjacent to the contact, such as a triangular cut outs with one point of the triangle normal to the edge of the material section connecting the contact to the sheet, and the two triangles pointing toward one another. In another embodiment, the frangible section can be created by a partial depth stamping of the material section adjacent to the contact and connected to the contact strip, to create a sharp discontinuity in the thickness of that connecting material section.
In one embodiment, the two dimensional contacts patterned and defined through means described above or through other means, are then configured into the desired three dimensional shape using a forming or other three dimensional shaping process, while the contacts are still attached integrally to the contact sheet or strip. The forming process can be performed en masse, where many contacts or all contacts in an array for one connector are formed simultaneously. In another embodiment, multiple contact arrays for multiple connectors are formed simultaneously using a large forming die or multiple smaller forming dies acting in parallel. Contact forming can also be performed in a series of forming steps, such as in a progressive die arrangement. In one embodiment, the strip is processed through the patterning, forming, plating or surface finishing, molding, contact singulation, and connector singulation in a reel to reel form factor, where the contact strip is very long and rolled out from a starting reel or spool, and then rewound onto an ending reel or spool. The contact strip can be unwound and rewound before, during, and/or after various process steps.
After forming the contacts, the connector body is applied over each array of contacts for an individual connector while the contacts are still integrated into the sheet or strip. The connector body material can be comprised of a polymeric material which is non-conductive. In a preferred embodiment, the connector body is a liquid crystal polymer. In another preferred embodiment, the liquid crystal polymer is applied through a molding process. In another preferred embodiment, the connector housing is over-molded onto the contact sheet after the contacts have been stamped and formed but are still integral to the contact strip. In another embodiment of the present invention, the connector body is applied to the contacts still in strip or sheet form using film assisted over-molding. In another embodiment, a portion of the outer surface of the connector housing has a conductive shield layer to serve as a faradaic cage, to minimize electromagnetic interference with or from other components in an electronic device.
After the connector body is applied to the connector contact array in the strip or sheet format through molding or other methods, the polymer material is fully cured and/or solidified. Subsequently, certain contacts, such as signal contacts, must be singulated from one another and from the contact strip such that they are no longer integral with the contact sheet or strip and are electrically isolated from all other signal contacts and power contacts, so that they are not electrically shorted. This can be accomplished by standard, low cost processes such as stamping, cutting, chemical etching, water jet abrasion, or laser ablation. In a preferred embodiment, all contact singulation is accomplished simultaneously using a stamping die. In another embodiment, in which the attachment point that has maintained the contacts integral to the contact strip or sheet has been made frangible during previous processing, the singulation may be accomplished with a simple die that provides a force adjacent to the frangible section to cause it to fracture and separate. Separation of the connector from the contact sheet or strip can be accomplished in a similar manner to, and in some embodiments, simultaneously with the contact singulation within the connector.
In one embodiment of the present invention, a connector has a plurality of electrical contacts, each contact having a distal end, a proximal end, and a middle section, these three sections of each individual contact forming a unitary body. In this embodiment, the middle section of the contact is located within an insulative connector housing, and the middle section is to some extent chemically and mechanically bonded to the connector housing, said housing having been solidified around the middle section of the contact during a molding or other application process, rather than simply being held in place by frictional forces and/or applied pressure. In a preferred embodiment, the connector housing has openings from which an elastic distal end of each of the contacts emanates above the plane of a first surface of the contact middle section and above a first surface of the connector housing. In another embodiment, the distal end of at least one contact emanates above the first surface of the connector housing at an angle of greater than zero degrees and less than ninety degrees, and preferably at an angle of less than 60 degrees, and approximates the shape of an elastic cantilever beam. In this embodiment, the contact distal end serves to make a separable electrical interconnection to at least one conductive terminal on a first surface of a first mating circuit element. In one embodiment of the present invention, the proximal ends of the contacts emanate from a second opposing surface of the middle section of the contact, and protrude slightly above but approximately parallel to the second surface of the connector housing, and function as solder terminals or ‘tails’ for permanent or semi-permanent attachment of the connector to terminals on a mating circuit element.
In another embodiment of the present invention, the proximal end and the distal ends of the contact emanate from opposing first and second surfaces of the connector housing respectively, at angles of greater than zero and less than ninety degrees, and preferably less than 60 degrees, and both function to make separable electrical interconnections to conductive terminals on a first and second mating circuit element, respectively.
According to one embodiment of the present invention, a separable electrical connector for interconnection of circuit elements in an electronic device is comprised of a plurality of electrical contacts that are created from a single strip or sheet of conductive material.
In one embodiment of the present invention, the contacts in the connector are arranged in an area array configuration. The contact shape is defined and formed while the contacts are integral with and attached to the contact strip, and an insulative dielectric connector body is added to the connector before the contacts are separated from the contact strip, so that the diametric true position error of the contacts relative to one another and to registration features on the connector housing is less than 0.250 mm and preferably less than 0.150 millimeter. In a preferred embodiment, the insulative connector body is molded onto the contact sheet. In another embodiment, the insulative connector body is created on the contact sheet through a three dimensional printing process. In a preferred embodiment, the insulative connector body is comprised of a liquid crystal polymer (LCP) molding material.
The contact strip or sheet is preferably comprised of a high conductivity, high strength copper alloy with good fatigue resistance and elasticity, such as copper-beryllium or copper-nickel-tin, with a thickness of 5 to 200 microns, and preferably 25 to 75 microns. This thickness range provides adequate spring load to ensure a suitable electrical connection is provided, without requiring excessive load such that it is not practical for an electrical connector for miniaturized electronics applications. In addition, contact sheet thickness in this range enables creation of fine pitch contact array patterns using stamping or etching, and enables forming of tighter radius contact shapes.
In one embodiment of this invention, the contact sheet is made of a heat-treatable alloy, whereby the hardness yield strength of the material increases after a heat treatment such as a precipitation hardening treatment. In one embodiment of the present invention, the material is fully hardened and heat treated before stamping and forming of the contact elements. In another embodiment of the present invention, the material is stamped and formed before it is fully hardened through heat treatment, and the heat treatment is performed prior to application of the connector housing.
In one embodiment of the present invention, the electrical contacts each have a common shape which approximates the shape of the letter U or C when viewed from a perspective normal to the plane of the connector surface. The contact is fully comprised of formed material from the contact strip or sheet, and includes a proximal end, and a middle section, and a distal end. The contact distal end is moveable elastically and emanates out of the plane of the contact sheet at an angle of less than ninety degrees and greater than zero degrees, and more preferably between 25 and 60 degrees, and approximates the shape of a cantilever beam. The contact also has a middle section which is coplanar with the original plane of the unformed contact sheet, and a proximal end which is parallel to the plane of the contact sheet and slightly raised from the plane of the contact sheet in the opposite direction from which the distal end emanates. The proximal end of the contact in this embodiment functions as a terminal for attachment of the contact to a connection pad on a circuit element using solder or conductive adhesive or similar semipermanent conductive interface as commonly used for surface mount connectors. The proximal end, middle section, and distal end of each contact form a unitary body. In one embodiment of this invention, the contact sheet is formed in part by a rolling process, which imparts a grain direction to the contact sheet. The grain direction of the spring contact sheet is oriented in the same direction in all three sections (distal end, proximal end, and middle section) of each contact, and preferably is parallel to the direction of the long dimension of the distal end of the contact, i.e. is parallel to the elastic cantilever beam. The middle section of the contact is captured and embedded in the insulative connector body during the molding or printing or lamination or other deposition process that causes the connector body or housing to be placed onto the contacts, and the housing is thereby mechanically and chemically bonded to and accurately positioned within the connector body. In one embodiment of the present invention, the insulative connector body is composed of a thermoset polymer, and is cured after being applied to the contact sheet, said curing causing a permanent bonding and attachment of the insulative connector body (housing) to at least a portion of the middle section of the contacts. In another embodiment, the thermoset polymer connector body forms a chemical and mechanical bond to portions of the contacts during curing. In another embodiment of the present invention, the insulative connector body is a thermoplastic polymer, and is solidified after being applied to the contact sheet, said solidification accomplished by cooling the melted thermoplastic and causing a substantially mechanically bonding of the thermoplastic body to at least a portion of the middle section of the contacts. In a further embodiment, the thermoplastic housing forms both a mechanical and a chemical bond to portions of the contact middle sections. In another embodiment, the contact sheet undergoes a pre-treatment process to chemically activate its surface to enhance the chemical bonding of the housing polymer to it. In another embodiment, the contact sheet undergoes a surface roughening treatment to enhance the mechanical bonding of the polymer connector body to the contacts. In another embodiment, both a surface activation treatment and a roughening treatment are applied to the contact sheet to enhance bonding of the connector body to the contact middle sections.
A first surface of the molded connector body defines the mating plane of one surface of the connector, and serves as the mating hard-stop for compression of the compliant distal end of the contact when the connector body bottoms out on the mating circuit element, such as a printed circuit board or flexible printed circuit. The mating plane defined by the molded connector body is parallel to the plane of the contact sheet but sits above it, and the elastic distal end of the electrical contact emanates above the first surface of the connector body. The connector housing has openings from which the distal ends emanate, and into which the distal ends can be compressed without impediment during mating of the connector to a mating circuit element through full compression of the distal ends of the contacts.
In a preferred embodiment, the distal end of the contact remains in the elastic range of deformation through full compression to the point where the connector body bottoms out on the mating circuit element, so that the distal end of the contact can approximately re-attain its original height above the connector body when it is fully separated from the mating circuit element. The distal end of the contact and the proximal end of the contact when viewed from a perspective normal to the connector mating surface are analogous to the ‘arms’ of the letter U or C depending on the orientation from which it is viewed, and one embodiment point in the same direction. In a preferred embodiment, the distal end of the contact is adapted to provide a low resistance separable interconnection to a conductive terminal on a mating circuit element. This adaptation can include plating of a noble metal such as gold over a barrier metal such as nickel. In another embodiment, the proximal end of the contact is adapted to accept solder. This adaptation can include plating of a solderable surface finish such as a noble metal such as gold or palladium over nickel, a solderable non-noble metal such as tin over nickel, use of an oxidation inhibitor on the contact sheet material, such as an organic solderability preservative (OSP) for copper, or other means. If desired, the same surface finish, such as nickel and gold plating, can used on both the distal end and the proximal end of the contact. If desired, the entire contact can be plated with nickel and gold or other common materials. The plating process can be electrolytic, electroless, or immersion in nature, or a combination of these various deposition methods.
In another embodiment of the present invention, the distal end and the proximal end of the electrical contacts are both designed to moveable elastically, and both emanate out of the plane of the of the contact sheet and above the planes of the connector housing surfaces in opposing directions, and at angles less than ninety degrees and greater than 0 degrees from the connector body surface from which they emanate, and preferably at angles between 25 and 60 degrees, such that the connector can separably connect to both circuit elements to which it is mating. In this embodiment, both the distal end and the proximal end of the contact resemble cantilever beams, and they are connected by and integral with the middle section of the contact, each contact's distal end and proximal end and middle section forming a unitary body. When viewed from the top of the contact sheet, normal to one surface of the sheet, the contact distal and proximal ends and its middle section form the approximate shape of a letter U or C. When viewed in a profile section view along the length of the elastic beams, the shape of the contact resembles the letter V.
A series of figures is provided to illustrate some, but not all, embodiments of the present invention.
Contact sheet tabs 200 formerly held the contact array and the molded connector body integral to the contact sheet or strip, prior to singulation of the connector from the sheet using stamping or other processes. The molded connector housing 9 is shown with a solid outline in this drawing. The conductive contact sheet and contact elements are shown with a hashed outline in this drawing.
Following forming of the contacts in the sheet or strip, each connector body is created using molding, 3D printing, over-molding, laminating, or other means of depositing or laminating an insulative material to create a connector body. The mold design allows the molding process to capture and bond to the middle section of each contact, but leaves an opening for the elastic distal end of each contact to enable it to be full compressed to the surface of the molded connector body without its movement being impeded. The mold design may also allow for formation of precise alignment features in the connector housing, to enable accurate alignment of the connector to mating circuit elements or to clamping and alignment hardware pre-aligned to the mating circuit element. The molding or other application of the connector body or housing is performed while the contacts are still integral with and connected to the contact strip or sheet. In a preferred embodiment, the contacts are provided with a surface finish in order to resist oxidation and that can accept solder to form a reliable joint on the proximal end and which enables reliable and low resistance separable interconnection to a connection terminal on a mating circuit element. In one embodiment, the surface finish is electroplated hard gold over an electroplated nickel barrier layer. In another embodiment, the surface finish is immersion gold plated over electroless nickel. The nickel thickness in both cases is preferably between 1 and 8 microns, and most preferably between 2 and 5 microns. The gold thickness is between 0.02 and 1.0 microns, and preferably between 0.05 and 0.5 microns. In another embodiment, nickel and gold plating is provided as a surface finish on the distal end of the contacts, and an organic solderability preservative is used on the proximal end. Other noble metals or metal alloys can also be used, such a palladium, platinum, or their alloys. In one embodiment, the surface finish is provided on the contacts prior to molding the connector body onto the contact array. In another embodiment, the surface finish is provided on the contacts after molding the connector body onto the contact array, as shown in
After surface finishing and application of the connector housing to the contact array, at least some of the electrical contacts must be singulated from one another, and the connector must be separated from the contact sheets. This separation can be done by separating the portions of the contact sheet that are still attached to the contacts, using a process such as stamping, etching, cutting, or laser ablation. In one embodiment, frangible sections are created during the initial patterning and forming of the contact strips or sheets in the regions where the contacts will be separated from the strip and from each other. These frangible sections can consist of thinned or narrowed regions in the contact sheet that substantially reduce the strength and/or increase the stress concentration in those regions, or can be weakened or made more brittle through work hardening or other means. The separation can then be accomplished by stamping the frangible regions with a die or by pushing the connector out of the contact strip or sheet or by other mechanical means.
Four center contacts 24 in
The preferred embodiment of the present invention has been described with some particularity in the preceding description of the preferred embodiment and some alternative structure and methods of manufacture have been presented within this description. Those of ordinary skill in the relevant art will appreciate that many modifications and substitutions can be made without departing from the spirit of the present invention. For example, the individual contacts can be separated from the sheet in a variety of different ways such as laser separation or singulation or stamping. The structure of the individual electric contact elements and the material from which they are formed can also a matter of design choice and, if a conductive material is added to the contact, the portions of the contact, the material chosen and the method of applying the conductive material can also be varied according to the design parameters and cost considerations. Accordingly, the foregoing description should be considered as merely illustrative of the principles of the present invention and not in limitation thereof, since the scope of the present invention is defined by the following claims.
The present patent claims the benefit of a previously-filed provisional patent application entitled “Low Profile, Normal Force Electrical Connector” filed by Ching-Ho Hsieh et al. on May 19, 2015, as Ser. No. 62/163,539. The specification and drawings from this provisional patent application are specifically incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62163539 | May 2015 | US |
