SURFACE MOUNT ELECTRICAL CONNECTOR

Abstract: A connector (10) connects printed circuits (22) on a printed circuit board (24) to a flat flex cable (32). Each circuit (22) is provided with at least two spaced apart solder-bearing contact pads (20) having a reflowable amount of solder thereon. A connector housing (14) having a board engaging surface (80) (see Fig. 2) includes a plurality of stamped metal terminals (18) each having a pair of depending solder contact projections (72, 74) one of which depends from the board engaging surface (80). The connector (10) is positioned on the circuit board (24) with pressure sensitive adhesive strips (82) so that the contact projections (72, 74) engage the contact pads (20). Upon reflow of the solder material a balanced shock resistant mechanical attachment and electrical connection of the connector (10) to the circuit board (24) is provided. No additional mounting structures are required so the arrangement occupies less board surface area. The arrangement is well suited for robotic assembly operations.

Description: The present invention relates to a surface mountable electrical connector for connecting circuits on a printed circuit board to another circuit member, e.g. the conductors of a flat flex cable, in one embodiment to a connector arrangement comprising the connector and a printed circuit board and to a method of constructing such a connector arrangement using a connector of the present invention. Flat flexible cable or flexible printed circuits including parallel spaced electrical conductors disposed between upper and lower planar webs of insulation are known. Connectors for connecting the individual conductors of flat flexible cable to printed circuits on printed circuit boards are also known. Typically, in these connector arrangements an end of the flat flexible cable is pre-stripped so that the top layer of insulation is removed. This leaves the lower layer of insulation and exposed portions of the cable conductors extending along the upper surface of the lower insulative layer. Cable-to-board connectors for use with flat flexible cable typically include a unitary dielectric housing having a front end with an opening and a rear end with an opening, a lower board engaging surface and a socket extending between said openings. A plurality of metallic terminals are mounted in the housing, corresponding in number and spacing to the cable conductors. Each terminal typically includes a base portion disposed in the rear end of the housing, a pair of upper and lower spaced apart cantilever beams unitary with the base extending forwardly from opposed sides of the base into the socket. The separation between the upper and lower beams of the terminal define an insertion slot for receiving the pre-stripped end of the cable disposed in the socket. In addition, a rear contact portion extends rearwardly from the base of the terminal to provide for electrical engagement with the printed circuit on the printed circuit board. A connector of this type further includes a cable actuator including a base and a forwardly projecting nose portion with an upper surface adapted to receive the flat flexible cable so that the exposed conductors of the prestripped end portion face away from the upper surface of the nose portion. The cable actuator is moveable toward the board mounted connector housing so that the nose portion of the actuator and the cable end are received into said socket and into said insertion slot defined between the cantilever beams of the terminal. As the nose portion of the actuator is inserted into the insertion slot it effectively pushes the exposed conductors on its surface into electrical engagement with the upper cantilever beams of the terminals within the housing. Typically latch means are provided on the actuator adapted to cooperate with latch recesses on the housing to lock the actuator and cable in mated position to the housing. Connectors of this type may be fixed to a printed circuit board by soldering the board contact portion of each terminal to a conductive region on a printed circuit board. The terminal is affixed to the underlying printed circuit at a single point. Often a substantial length of the board contact portion extends along the upper surface of the circuit board. Typically the terminal to circuit solder connections are disposed to the rear of the connector housing. In use, the terminals may be easily raised up off the surface of the board if an external force is applied to a mated cable or to the housing. Unfortunately this may cause part of the printed circuit pattern to which the terminal is fixed to be removed from the printed circuit substrate. In an effort to prevent terminals from rising and removing the underlying portions of the printed circuit pattern from the substrate, prior art connector housings have typically been provided with laterally extending flange members including depending mounting boss projections. The printed circuit board is also provided with mounting apertures which need to be drilled at precise locations in the substrate. Thereafter, the depending mounting projections must be press fitted into the mounting apertures to retain the housing in position on the printed circuit board. Alternative methods of securing a connector housing to a printed circuit board have included the provision of side mounting flanges including an aperture which is aligned with a printed circuit board mounting aperture, fixing members such as a nut and bolt or rivet arrangements are passed through the aligned apertures to permanently mount the connector to the printed circuit board, and the provision of V-shaped spring members (such as the connectors described in EP O214830, this being a document as defined by Article 54(3) EPC). These prior art methods of retaining the connector housing onto the printed circuit board have a number of disadvantages. The housing must be broader than the width of the circuits it is intended to overlie. This takes up real estate on the board surface area which could be used for additional circuitry. In addition, extra manufacturing steps are required to fix the connector housing to the printed circuit board and extra steps are required to provide mounting apertures in the printed circuit board. All of these requirements increase the manufacturing cost of the prior art connector arrangements. Moreover, these mounting arrangements do not meet the modern demand for increasing miniaturization of the connectors and for high density circuit boards having increased surface area utilized for bearing circuit patterns. It is an object of the present invention to mitigate one or more of these difficulties. The present invention provides, in one aspect, an electrical connector for electrically connecing printed circuits on a printed circuit board to another circuit member. The electrical connector includes a dielectric housing having a plurality of terminal receiving cavities. The housing has a circuit board engaging surface and a plurality of electrical terminals are mounted in cavities of the housing. Each terminal includes a board contact portion adapted to contact solder contact pads of a printed circuit on a printed circuit board. Each circuit on the printed circuit board is provided with at least two spaced-apart solder contact pads having excess solder material thereon. Each terminal mounted in the connector housing includes at least two spaced-apart board contact portions adapted to engage said contact pads. The board contact portions and the solder contact pads interconnect upon reflow of said soldering material to provide a balanced mechanical attachment of the connector to the printed circuit board and electrical connection between the terminals and the printed circuits. Temporary hold down means may be provided on the board engaging surface of the housing to temporarily hold the housing in position overlying the printed circuits preparatory to permanent soldering, such as by vapor phase reflow soldering methods. Adequate mechanical attachment of the connector to the board is provided by a double mechanical and electrical engagement between each terminal and each circuit provided in the arrangement. No further mounting means for permanently retaining the connector to the board surface are required. The assembled connector arrangement exhibits effective force shock load resistance and the tendency to remove portions of printed circuitry provided on the substrate by the prior art surface mount connector arrangements having an offset single solder point is avoided. The present invention still further includes a method of constructing a connector arrangement. A connector of the present invention for flat flexible cable may have a width which does not substantially exceed the width of the flat flexible cable and the targeted printed circuitry. No additional mounting flanges are required, so that the connector takes up far less printed circuit board surface area and is effectively miniaturized. In one embodiment of a connector according to the present invention for flat flex cable to board applications, a cable conductor contact portion of each of the terminals is disposed within the connector housing and is adapted for electrical engagement with an exposed conductor of a flat flex cable member. According to another embodiment of the present invention, a connector arrangement comprises a connector of the present invention and a printed circuit board mounting the connector. One way of carrying out the present invention in both its apparatus and method aspects will now be described in detail with reference to drawings which show one specific embodiment. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of a connector housing of a connector of the present invention shown mounted on a printed circuit board and forming a connector arrangement; FIG. 2 is a bottom plan view of the board engaging surface of the connector housing; FIG. 3 is a side elevation view of the connector arrangement taken from the right side as shown in Fig. 1; FIG. 4 is an elevated cross sectional view of the connector arrangement taken along view line 4-4 in Fig. 1; FIG. 5 is a front elevation view of an actuator member for use with the connector housing; FIG. 6 is a top plan view of the cable actutor shown in Fig. 5; FIG. 7 is a side elevation view taken from the right side of the connector actuator shown in Fig. 5; FIG. 8 is a front elevation view of the connector arrangement with the cable actuator positioned thereon in a pre-load position ready to accept a pre-stripped cable; FIG. 9 is a bottom plan view of the connector and actuator in the first pre-load position ready to receive the flat flex cable; FIG. 10 is an elevated cross-sectional view of the connector arrangement in the pre-load state taken along lines 10-10 in Fig. 9; FIG. 11 is a similar elevated cross-sectional view of the connector arrangement similar to the view shown in Fig. 10 illustrating the fully mated condition of the connector arrangement; and FIG. 12 is an elevated side view of the terminal used in the connector of the present invention. The connector arrangement 10 (see Figs. 10 and 11) includes a connector 12 including a dielectric housing member 14 and a separate actuator member 16. A plurality of terminals 18 mounted in the connector housing 14 are in turn mounted to solder-bearing contact pads 20 associated with printed circuits 22 on a printed circuit board 24. Referring now to Figs. 1 to 4, the connector arrangement 10 firstly comprises a unitary integrally molded dielectric housing member 14. Connector housing 14 includes a front end 26 with an opening 28 and a socket 30 adapted to receive a flat flex cable 32 (Fig. 8) and actuator 16. Socket 30 extends rearwardly in the housing from the front opening 28 in the front end 26 to a rear surface 52. Socket 30 is further defined by a bottom wall 34, spaced opposed upstanding side walls 36, 38 and an opposing top wall 40. The opposed upstanding sidewalls 36 and 38 each include an actuator groove 42 on the outer surfaces thereof which further include a pre-load latch projection 44 and a spaced locking retainer projection 46 adapted to co-operate with resilient latch arms 48, 50 (FIGS. 5-6) provided on the actuator member 16, to be more particularly described below. Connector housing 14 includes a plurality of spaced terminal receiving cavities 54 extending along the length of the socket 60. A plurality of stamped metal electrical terminals 18 are mounted one in each cavity 54 in a press fit engagement. The electrical terminals 18 are shown more particularly in FIG. 12. As shown therein, each terminal 18 is integrally formed from a metallic stamping to include a vertically extending base portion 56 and having forwardly projecting, spaced cantilever arms or beams 58, 60 extending unitarily from opposed sides of base 56 to a free end. The upper arm 58 is adapted to make resilient electrical contact with a bared conductor 62 of a cable 32 at a conductor contact portion 64 disposed at the free end 66 of the upper cantilever beam 58. A printed circuit board contact portion 68 extends rearwardly from the base 56 in alignment with the lower cantilevered beam 60. Disposed at the forward end 70 of the lower cantilever beam 60 is a solder contact projection 72 which is disposed in alignment with a solder contact projection 74 depending from the rearwardly extending board contact portion 68 of the terminal 18. As shown in FIG. 2, the lower surface 76 of the metallic terminal 18 disposed between the spaced apart solder projections 72, 74 is elevated from the surface of the printed circuit board. The connector housing 14 includes a board engaging surface 80 shown in FIG. 2. Board engaging surface 80 is preferably provided with strips of pressure sensitive adhesive 82, typically an epoxy based material, to temporarily attach the connector housing 14 with terminals 18 in position on printed circuit board 24, so that solder contact projections 72 and 74 of each terminal 18 engage the solder-bearing contact pads 20 of each printed circuit 22 prior to vapor phase reflow or other permanent soldering operation. The connector housing 14 is adapted to cooperate with a cable actuator 16 shown in FIGS. 5, 6 and 9-11. As shown in FIGS. 5 and 6, cable actuator 16 comprises a elongate base 84 extending the width of the connector housing. A forwardly extending cable support projection 86 extends from the base 84 including a beveled nose portion 88. In addition, a pair of resilient latch arms 48 and 50 extend from the opposed ends of the base 84 on the same side as the forward cable supporting projection 86. The actuator 16 is adapted to be fitted into the front end 26 of the connector housing 14 in either the preload position shown in FIGS. 9 and 10 or in the fully mated position shown in FIG.11. As shown in FIGS. 9 and 10 the preload position of the actuator 16 is achieved when the actuator 16 is moved towards the front end 26 of the connector housing 14 so that the projecting nose portion 88 of the actuator 16 is received within the socket 30 and within the insertion slot 90 defined between the spaced upper and lower cantilever beams 58 and 60 of the metallic terminals 18. As shown in FIG. 9, this position is achieved by outwardly deflecting the resilient latch arms 48 and 50 over the pre-load latch projections 44 on the housing 16 until the latch wings 92 on latch arms 48 and 50 are received within a first preload recess 94 in the actuator slide grooves 42 on the outside surfaces of sidewalls 36 and 38. As shown in FIG. 10 in the preload position of the actuator 16, an insertion space 96 is provided between the actuator 16 and top wall 40 for receiving a pre-stripped end portion 98 of a flat flex cable 32 shown in FIG. 8. The prestripped cable end portion 98 includes a lower insulating web 100 and the upwardly facing exposed conductor portions 62. The top layer of insulation of the cable has been removed to expose the cable conductors 62. The exposed end portion 98 is inserted into the insertion space 96 shown in FIG. 10 so that the bottom insulating web 100 is disposed on the upper surface of the beveled nose portion 88 with the exposed cable conductors 62 facing the cable conductor contact portions 64 disposed on the free ends 66 of the upper cantilever beams 58. With the conductors 62 inserted in to the socket 30, the actuator is urged inwardly towards the connector housing to the fully mated position shown in FIG. 11. As shown in FIG. 11, the nose projection 88 is moved forwardly into the socket 30 so that resilient electrical contact is made between contacts 64 on upper contact beams 58 and the exposed conductors 62, along the level surface of the cable support portion 86 beyond the beveled nose portion 88. The underside surface of the cable support portion 86 of the actuator 16 engages the lower cantilever beam 60 of the connector terminals 18. As can be appreciated from FIG. 9, as the actuator 16 is moved from the preload position shown therein, to the fully mated position shown in FIG. 11, the resilient wings 92 are once again resiliently deflected over the locking retainer projections 46 to retain the electrical cable 32 in mated relationship to the electrical terminals 18 of the housing 18. This mated position will be maintained, until a sufficient withdrawal force is applied on the actuator 16 to overcome the resistance of the locking retainer projections 46 on the resilient latch arms 48 and 50 in the side grooves 42 on the housing. A minor amount of a pressure sensitive adhesive 82 is applied to the board engaging surface 80 of the connector housing 14 as shown in FIG. 2 to temporarily attach connector housing 14 in the proper position over the contact pads 20 on the printed circuit board 24 preparatory to reflow soldering. The connector terminals 18 are mounted in the rear end of connector housing 14 and connector housing is positioned by means of the adhesive strip over the footprint of conductive solder pads 20 and associated circuits 22 provided on the upper surface 78 of the printed circuit board 24 as shown in FIG. 1. A plurality of connectors 12 may be temporarily mounted onto the surface 78 of the circuit board 24 at appropriate locations by, for example, robotic arm placement and thereafter the entire circuit board assembly may be moved into a vapor phase reflow chamber to cause the excess solder provided on the solder pad contacts 20 to flow forming a mechanical and electrical connection between the stamped metallic terminals 18 and the printed circuits 22 of the printed circuit board 24. Thereafter, the actuator 16 may be assembled on to the connector housing 14 in its preload position. The overall arrangement is ready to receive the prestripped end 90 of a flat flex cable 32 to connect the individual conductors 62 thereof to the printed circuits 22. The connector housing 14 may be molded in a miniaturized form. The housing 14 needs only be as large as is required to overlay the printed circuits 22 on the substrate 24 and provide effective electrical insulation between the stamped metallic terminals 18. Very close center to center spacings may therefore be accommodated. Housing 24 has no side flange projecting portions, as there are in the prior art connectors for mounting the connectors to the board. The connector 12 is directly vertically positioned on the board and then soldered in place without requiring extra board real estate. As a result, the connector arrangement is well suited for use in high circuit density circuit board arrangements. The provision of the redundant solder connections 72 per circuit, spaced apart from the rear end of the connector housing and lying close to the front end of the housing, provides effective electrical and mechanical engagement for each terminal and circuit. The cumulative effect of having two well spaced mechanical solder joints attaching each terminal, and therefore the housing 14, to the board surface is effective to provide a balanced, substantially force shock-load resistant surface mounted connector arrangement immovably fixing the connector housing 14 to the printed circuit board 24 to render the connector capable of withstanding the strain of repeated mating and unmating in use. Only a minor amount of adhesive is used to temporarily retain the connector housing on the board in position for reflow. Increasing the amount of adhesive is not advantageous because the cost of the overall connector arrangement is increased. Excess adhesive may tend to interfere with the formation of a good reflow solder joint between the solder projections 72 and 74 and the solder contact pads 20 provided on the upper surface 78 of the printed circuit board 24 during reflow. Although the present invention has been described in detail with reference to a specific embodiment, i.e. an arrangement for electrically connecting individual conductors of a flat flexible cable to printed circuits on a printed circuit board, other contact configurations for engaging circuit members other than flat flexible cables may be used. All that is required is that the terminals each include at least two surface mountable solder projections which are appropriately balanced in position with respect to the front and rear edges of the board engaging surface of the connector housing to effectively mount the housing on the board upon reflow and resist the shocks caused by actuating an actuator or other aspects of mating. There has been described with reference to the drawings a surface mount connector arrangement for mounting a multicircuit connector to a printed circuit board and for electrically connecting the terminals mounted in the connector to printed circuits on the printed circuit board. Costly drilling of the printed circuit board or extra molding steps to provide mounting projections for attachment of the connector on the board are not required. These features facilitate robotic placement and vapor phase reflow operations in a cost effective, miniaturized manner. The connector is fixed in a stable way, without increasing its physical size, which prevents the connector terminals from rising and removing the underlying printed circuits from the substrate when an external force is applied on the connector housing or on the flat flexible cable connected by the connector. Thus, the connector exhibits stable attachment to an associated printed circuit board in use and requires no extra manufacturing steps and hence cost for installation. The connector is miniaturized in the sense that it is adapted to overlie the printed circuits on a printed circuit board without requiring extra surface area surrounding the printed circuits for mounting its housing to the board, thereby permitting full use of the printed circuit board area for containing desired circuit patterns.

Claims: A connector (12) for soldering to printed circuits (22) on a printed circuit board (24) at solder contact pads (20) on the printed circuits to electrically connect the printed circuits to another circuit member, the connector including a dielectric housing (14) having a circuit board engaging surface, a plurality of terminal-receiving cavities (54), one for each printed circuit to be connected, and a plurality of electrical terminals (18) mounted one in each of said cavities, the terminals (18) including board contact portions adapted to contact the solder contact pads (20) of the printed circuits (22) for soldering to same, each terminal (18) including a pair of said board contact portions which are spaced apart from one another and at least one of which depends from said board engaging surface whereby a balanced permanent mechanical attachment of the connector (12) to the printed circuit board (24) is effected by the spaced pairs of soldered connections between each terminal (18) and each printed circuit (22) in use of the connector as well as electrical connection between the terminals (18) and the printed circuits (22). A connector (12) as claimed in claim 1 including hold down means comprising a temporary hold down means (82) provided on said board engaging surface for retaining the board engaging surface in position on the printed circuit board (24) preparatory to a soldering treatment to provide said permanent mechanical attachment. A connector (12) as claimed in claim 2 in which the hold down means is a strip of pressure sensitive adhesive (82) on the board engaging surface. A connector (12) as claimed in any preceding claim in combination with a printed circuit board (24) having a plurality of printed circuits (22) defined thereon, each circuit having a solder contact pad (20); the electrical connector (12) including a dielectric housing (14) having a plurality of terminal-receiving cavities (54) one for each printed circuit (22) and a circuit board engaging surface, a plurality of electrical terminals (18) one mounted in each of said cavities, each terminal (18) including a board contact portion adapted to contact a solder pad (20) of a printed circuit, and hold down means (82) for retaining the board engaging surface in position on the printed circuit board (24) preparatory to a permanent soldering treatment, each circuit including at least one other solder contact pad (20) spaced from the first said solder contact pad (20), both pads having a reflowable amount of solder material thereon; and each terminal (18) including at least one other board contact portion spaced from the first and depending from the board engaging surface for engaging said other solder contact pad (20), both of said board contact portions and said contact pads (20) interconnecting upon reflow of the solder material to provide a balanced mechanical attachment of the connector (12) to the printed circuit board (24) and electrical connection between the terminals (18) and the printed circuit. A connector (12) in combination with a printed circuit board (24), according to claim 4, wherein the solder material has been subjected to permanent soldering treatment. A connector (12) in combination with a printed circuit board (24) according to claim 4 or 5 for electrically connecting the printed circuit board (24) with conductors (62) in a flat flexible cable (32), wherein each of said terminals (18) further includes a cable conductor contact portion (64) in said housing (14) for electrically engaging a conductor in said cable. A method for constructing a connector arrangement for electrically connecting printed circuits (22) on a printed circuit board (24) to another circuit member, said arrangement including a printed circuit board (24) having a plurality of printed circuits (22) defined thereon, each circuit (22) having a solder contact pad (20); and an electrical connector (12) according to any one of claims 1-3, the method comprising securing the connector housing (14) to the printed circuit board (24) thereby to locate the terminal board contact portions in contact with the printed circuit contact pads (20), providing each printed circuit with at least one other solder contact pad spaced from the first said solder contact pad, providing both pads with a reflowable amount of solder material thereon; providing each terminal (18) with at least one other board contact portion spaced from the first and depending from the board engaging surface for engaging said other solder contact pad, and then reflow soldering both of said board contact portions and said contact pads of all the terminals (18) and printed circuits (22) together to provide a mechanical attachment of the connector (12) to the printed circuit board (24) and electrical connection between the terminals (18) and the printed circuits (22). A method as claimed in claim 7 in which the securing step comprises introducing adhesive between said circuit board engaging surface and the circuit board (24) temporarily to retain the board engaging surface in position on the printed circuit board (24) preparatory to the reflow soldering step.

Inventors: KANESIGE, AKIRA, SETO, MASASHI
Applicants: MOLEX INCORPORATED
Application year: 1988
Main classification: H01R23
IPC codes: H05K3, H01R12