WO1996031921A1

WO1996031921A1 - Flexible printed circuit board connector

Info

Publication number: WO1996031921A1
Application number: PCT/IB1996/000285
Authority: WO
Inventors: Dolf Campschroer; Randy Verbeet
Original assignee: The Whitaker Corporation
Priority date: 1995-04-06
Filing date: 1996-04-04
Publication date: 1996-10-10
Also published as: KR19980703651A; GB9507127D0; DE69603019D1; EP0819324A1; CN1179857A; EP0819324B1; CN1071947C; DE69603019T2; JPH11507468A

Abstract

An electrical connector assembly according to the present invention is shown generally at (2). The assembly (2) includes an electrical connector (4) having a housing (6) wherein multiple electrical contacts (8) are disposed and an actuator (10). A flexible printed circuit (12) is shown having a plurality of circuit traces (14) thereupon for interconnection with the contacts (8) of the connector and an electronic component (16) upon the flexible printed circuit (12). Additional circuit traces (18) exit the electronic component (16) and are interconnected with a device (20). The electrical connector (4) enables the disconnection and replacement of the electronic component (16) and the device (20).

Description

FLEXIBLE PRINTED CIRCUIT BOARD CONNECTOR

This invention relates to an electrical connector and in particular to an electrical connector for a flexible printed circuit.

There are numerous electrical connectors directed to forming interconnections with the circuit traces upon a flexible printed circuit. One example of this is disclosed in US Patent 4,734,053 where an electrical connector includes a housing wherein fork-shaped contacts are disposed. The contacts are adapted for through-hole mounting upon a printed circuit board (PCB) . The flexible printed circuit is disposed between the forks of the contact and an actuator member, having a wedge and a guide shoulder, is wedged therebetween for retention and electrical engagement. The flexible printed circuit extends outward and away from the housing at some angle relative the PCB upon which the housing would be located. While the connector works very well, there are numerous areas that it can use improvement for particular applications.

PCBs are typically assembled using a pick-and-place machine. This involves a head removing an electrical or electronic component from a tape feed dispenser and the machine moving either the head or the PCB being assembled to a particular X-Y coordinate of a plane represented by the PCB where the component is to be placed. The machine then makes a relative Z-axis move to place the component upon the PCB such that the leads of the component correspond to solder pads upon the PCB so that a surface mount interconnection may be achieved. These machines move very quickly and repeat quite accurately making for a highly automated and rapid assembly process. However, one of the constraints of this pick-and-place operation is that the head of the assembly tool may only move up and down relative to the face of the PCB. It would be desirable be able to utilize a pick-and-place assembly tool to fully install an electrical connector for a flexible printed circuit and insert the flexible printed circuit therein.

In order to take advantage of the pick-and-place assembly techniques upon a surface mount PCB all contact pads of contacts within an electrical connector must be co-planar, thereby assuring that the solder bonds with the solder pads are full and complete. The co-planarity of requirement is sometimes as little as 0.1 mm. This co- planarity requirement exceeds the capability of the stitching machine so it would be desirable to assure that the co-planarity of the contact pads is maintained.

While the surface mount techniques provide for adequate electrical interconnection at the solder pads, it is also desirable that an electrical connector be securely anchored to the PCB. In certain applications the electrical interface is insufficient to mechanically anchor the connector to the housing. In this operation it is not desirable to include a board lock structure that may require a second operation to secure or interfering features that may not be conducive to the robotic assembly techniques of a pick-and-place machine. Therefore, it is desirable to assure that the electrical connector may be securely anchored by operations compatible with pick-and- place operations of locating the electrical connector upon the PCB and the soldering associated with surface mount soldering techniques (SMT) .

In certain applications, due to the density of adjacent apparatus, it is necessary that the flexible printed circuit exit the connector in a plane parallel to that of the PCB. This plane is typically perpendicular to the Z-axis defined by the PCB. In connectors of this type it is common that the flexible printed circuit must first be placed at the proper Z axis height relative the PCB and then inserted from the side (i.e. with an X or Y axis move) . This is not possible with the commonly used equipment. Therefore, it would be desirable to provide an electrical connector where the flexible printed circuit may be inserted into the connector and terminated therewith in response to Z-axis moves of the assembly tool where the flexible printed circuit exits the connector in a plane approximately parallel with the PCB.

In the automatic assembly operations envisioned, the actuator that wedges the circuit traces of a flexible printed circuit into engagement with the contact arm of the electrical connector within the connector should be formed in a symmetrical manner. A problem with this construction is that when a forked shaped contact is utilized and the flexible printed circuit is inserted into the fork area, the symmetrical wedge will be subjected to unbalanced forces tending to cock the actuator. It would be desirable to provide an electrical connector having contacts therein with a forked contact portion where a flexible printed circuit is to be wedged against one arm thereof, where the forces are balanced so that during insertion of the actuator the forces exerted thereagainst remain balanced.

Therefore, it is an object of this invention to provide an electrical connector for a flexible printed circuit that is fully assemblable upon a substrate, such as a PCB by way of automatic pick and place techniques. This object is accomplished by providing an electrical connector comprising a housing and at least one contact disposed therein, each contact having a fork shape with a contact arm and a back-up arm between which the flexible printed circuit is to be disposed where the fork shape is open opposite a pair of spaced apart surface mount feet, and an actuator receivable from above and wedgeable between the two arms for retaining the flexible printed circuit in engagement with the contact.

It is an object of this invention to provide an electrical contact having coplanar surface mount feet that are electrically engageable with solder pads of a PCB. This object is accomplished by providing an electrical connector comprising a connector housing having contact receiving sections and a plurality of contacts individually receivable within the contact receiving sections, where each contact is retained therein in an interference fit and includes a pair of spaced apart surface mount feet all of which are indexable with a block having a flat surface thereupon of the desired planarity that is used to push the partially positioned and initially stitched contacts to their fully seated position within the housing.

It is an object of this invention to provide an electrical connector that is fully mountable, both mechanically and electrically, using surface mounting techniques. This object is accomplished by providing an electrical connector having a housing and contacts disposed therein where the contact includes a plurality of surface mount feet and at least one of the feet is for mechanical anchoring of the connector.

It is an object of this invention to provide an electrical connector for connecting to a flexible printed circuit in a manner that requires minimum clearance above the connector side of the board. This object is accomplished by providing an electrical connector wherein the flexible printed circuit is top loadable therein relative to a PCB upon which the connector is mounted, where the flexible printed circuit is wedged into engagement with contacts therein, and the flexible printed circuit extends generally parallel to the PCB.

It is an object of this invention to provide an electrical connector that is top loadable. This object is accomplished by providing an electrical connector fixable upon a PCB and loadable thereupon with a flexible printed circuit that is wedged into engagement with electrical contacts housed therein such that the actuator is insertable therein to hold the flexible printed circuit against the contact in a manner that balances the forces exerted thereupon during insertion. It is another object of this invention to provide a connector that is simple to manufacture. It is yet another object to provide an electrical connector that enables high speed assembly operations. It is yet still another object to provide an electrical connector where the solder pads are accurately located relative the connector housing. It is still yet another object to provide an electrical connector where the flexible printed circuit is attachable thereto in a pre-loaded position such that insertion of the actuator produces reliable interconnection.

The invention will now be described by way of reference to the following figures, wherein; Figure 1 is an upper perspective view of an electrical connector according to the present invention attached to a flexible printed circuit;

Figure 2 is a partially exploded upper perspective view of the electrical connector of Figure 1; Figure 3 is a side perspective view of an electrical contact incorporated into the connector of Figure 1;

Figure 4 is a cross-sectional view of the electrical connector of Figure 2;

Figure 5 is an upper plan view of a section of the flexible printed circuit of Figure 1;

Figure 6 is an upper plan view of the solder pattern layout upon a PCB to which the electrical connector is mated;

Figure 7 is an upper perspective view of the electrical connector showing the flexible printed circuit attached thereto;

Figure 7a is an upper perspective detailed view of the electrical connector of Figure 7 showing the flexible printed circuit anchored to the connector housing; Figure 8 is a side sectional view showing the flexible printed circuit within the connector of Figure 1 with the actuator in its fully seated position; and

Figure 9 is a side view of electrical connector with the flexible printed circuit therein attached to a PCB. With reference first to Figure 1, an electrical connector assembly according to the present invention is shown generally at 2. The assembly 2 includes an electrical connector 4 having a housing 6 wherein multiple electrical contacts 8 are disposed and an actuator 10. A flexible printed circuit 12 is shown having a plurality of circuit traces 14 thereupon for interconnection with the contacts 8 of the connector and an electronic component 16 upon the flexible printed circuit 12. Additional circuit traces 18 exit the electronic component 16 and are interconnected with a device 20. The electrical connector 4 enables the disconnection and replacement of the electronic component 16 and the device 20. With reference now to Figure 2, the electrical connector 4 is shown. The electrical connector housing 6 retains a plurality of contacts 8. The housing 6 includes side rails 22,24 interconnected by a plurality of webs 26 that act as partitions to form a plurality of contact receiving seats 28 wherein the contacts 8 are disposed. The housing 6 includes a receiving region 30 between the rails 22,24 that is bounded by end walls 32,34. Located along an outer surface of the end walls are latch members 36 having an upper locating post 38, ramp surface 40 and catch surface 42. Along rail 22 towards each of the end walls 32,34 are positioners 44,46 for cooperating with the flexible printed circuit 12 as described below. Each of the positioners 44,46 extend above a guide surface 48 of the rail 22 and are configured with a first and second overhanging latch 50,52 for preventing removal of the flexible printed circuit 12 therefrom.

The actuator 10 is a symmetrical component about its length and width which decreases the need for complex sorting and orientation during assembly. The actuator 10 includes an upper plate 54 and a wedge 56 extending therefrom in a T-shaped manner such that portions 58,60 of the upper plate 54 overhang the wedge 56. The wedge includes chamfered surfaces 62 that run therealong for enhancing assembly. The wedge 56 is receivable within the receiving region 30 of the connector housing 6, whereby the flexible printed circuit 12 is captivated in electrical engagement with the contacts 8 as will be described below. When inserted into the receiving region 30 the actuator 10 is retained in place by catches 64 that are U-shaped members cantilevered from the upper plate 54 in a downward manner where the opening defined thereby extends into the upper plate 54. As the actuator 10 is assembled with the housing 6, the catches 54 are splayed outward by ramp surfaces 40 until they pass over catch surface 42. In this position, the catch 64 snaps under the catch surface 42 and the post 38 extends upward through the portion of the opening included in the upper plate 54 for locating the actuator 10 therewith.

With reference now to Figure 3, the electrical contact 8 is shown. The electrical contact 8 includes a fork-shaped contact portion 66 having a contact arm 68 and a spring arm 70 defining an opening 72 therebetween. The contact arm 68 and spring arms 70 extend from a body 74 in a U-shaped manner. Extending outward from either side of the body are bar sections 76,78 that carry a biasing post 80 and a positioning post 82 respectively. Outward from the biasing post 80 and the positioning post 82 are oppositely directed surface mount feet 84 that extend beyond a lower surface 86 of the contact 8 such that the lower surface 86 is relieved relative to the surface of the feet 84.

The contact arm 68 and the spring arm 70 are of different configuration and height, as best seen in Figures 4 or 8. The contact arm 68 is slightly lower than the spring arm 70. The contact arm 68 includes a contacting head 88 that includes a supporting surface 90 and an engagement nose 92 of sufficient sharpness to bite through any oxides or contamination that may be formed upon the circuit traces 14 of the flexible printed circuit 12. The spring arm 70 includes a biasing head 94 having a nose portion 96 constructed to interact with the wedge 56 of the actuator 10 in such a manner that the resilience utilized to maintain engagement with the circuit traces 14 is maintained by not allowing the biasing head 94 to bite into the material that forms the actuator 10. As the actuator 10 is typically a moulded plastic component having a sharp nose portion 96 would result in the spring forces decreasing over time as the biasing head 94 displaces the material used to form the wedge 56.

The biasing post 80 and the positioning post 82 extend from the bar sections 76,78 in the same direction as the contact arm 68 and spring arm 70. Each of the posts 80,82 include a barb 98,100 respectively thereupon for interfering with the housing 6 for retention of the contact 8 therein. The barbs 98,100 act to increase the cross-section of the respective post 80,82. The barbs 98,100 face the same direction on each of the posts 80,82 such that during insertion, the reaction to the forces produced by the interference fit bias the contact 8 in the same direction. Each of the posts 80,82 include a slightly rounded nose portion 102 for guiding the contact 8 during insertion into the housing 6. The posts 80,82 are of different configuration to assure proper assembly and function. The biasing post 80 is shorter than the positioning post 82 and includes a resilient portion 104 enabling some compliance of the post 80 relative to the bar 76. The biasing post 80 provides the function of stabilizing the contact 8 within the housing 6 and exerting a force that tends to bias the contact in the direction of the positioning post 82. The positioning post 82 is higher and of larger cross-section than the biasing post 80 such that it cannot be inadvertently seated in the wrong orientation. Furthermore, the positioning post 82 includes a locating surface 106 constructed to be essentially perpendicular with the PCB upon which the connector is mounted in such a manner that a reference location is provided with respect to the housing 6 so that reliable pick-and-place assembly techniques may be used. As the interference fit between the posts 80,82 and the housing 6 along with the resiliency of the biasing post 80 at the resilient portion 104 assure that the contact 8 is constantly being biased in the direction of surface 106, a reliable location is defined.

Opposite the aforedescribed structure a pair of surface mounting feet 84 are provided at the extreme ends of the contact structure 8. The surface mount feet 84 act as points to define a line thereacross. In addition, the surface mount feet 84 would enable electrical connection to multiple solder pads 108 upon a PCB 110 (Figure 6) . While each of the solder pads 108 could be electrically interconnected, it is not necessary and may not be desirable. It is possible that at least one of the solder pads 108 is simply for providing a mechanical anchor with the contact 8 as the connector 4 is to utilize surface mount soldering techniques for anchoring. In addition, the surface mount feet 84 provide stability thereacross for the contact and connector upon the PCB. In addition, the surface mount feet are utilized in the manner described below to assure co-planarity of all of the electrical contact surface mount feet 84 in order to assure reliable and effective surface mounting upon the PCB 110.

With reference now to Figure 4, a cross-sectional view of the connector 4 is shown with the contact 8 disposed within the housing 6 and the actuator 10 positioned thereover. The contact 8 is stitched within the connector housing 6 in a pre-loaded position short of the fully seated position shown in the Figures. In this position, the biasing post 80 and the positioning post 82 are received within respective cavities 112,114 contained within rails 24,22. These cavities are aligned with the seat sections 28 that are defined between webs 26. In order to assure proper co-planarity of all of the surface mount feet 84 in this partially stitched position, an insertion block (not shown) having one surface with the desired flatness is brought into position against all of the contacts 8 and pushes the contacts home to their fully seated position as shown in Figure 4. The contacts 8 are still floating within the housing 6 while the feet 84 are within a plane having the proper tolerance. During the insertion process the barbs 98,100 and the biasing post 80 causes the contact to be pressed in the direction of locating surface 106 which has a corresponding surface 116 within cavity 114. This provides positive location of the surface mount feet 84 relative to the connector housing 6. In addition, as there are a pair of surface mount feet at the extreme ends of the contact 8, the co-planarity is easier to define with the insertion block (not shown) as can further be seen in Figure 4, guide surface 48 upon rail 22 is displaced lower than the corresponding surface 118 on rail 24.

A portion of the flexible printed circuit 12 that is to be received within the connector 4 is shown. The flexible printed circuit 12 includes a front edge 120 and side edges 122 bounding a mating interface 124 of the traces 14. The front edge 120 and the side edges 122 define a tongue 126 that is receivable within the receiving region 30 of the connector 4. Along the side edges 122 of the tongue 126 are anchoring notches 128 that cooperate with the positioning posts 46 of the connector housing 6 (Figure 2) in such a manner to retain the flexible printed circuit 12 when initially positioned by a pick-and-place machine relative to the connector housing and during insertion by a pick-and-place machine of the actuator 10. The interaction between the positioning posts 44,46 and the notches 128 is best seen and described with reference to Figure 7 and Figure 7a. With reference now to Figure 6, a PCB is shown generally at 110 having a plurality of solder pads 108 corresponding to the surface mount feet 84 of the contacts 8 of the connector 4. The PCB 110 includes a face 130 upon which the solder pads 108 are located. The co-planarity of all of the surface mount feet 84 is to correspond with the planarity of the upper surface 130. When the surface mount solder techniques are used, such as re-flow soldering, the surface mount feet 84 are anchored to the solder pads 108 in such a manner that the connector is reliably retained therewith.

With reference now to Figure 7, once the electrical connector 6 is mounted upon PCB 110 as described above, the flexible printed circuit 12 possibly with the electrical device 20 attached thereto, may be top loaded with a pick-and-place machine. As shown in Figure 7a, the tongue 126 of the flexible printed circuit is directed downward from above the connector 6 such that the notch 128 formed along the side walls 122 corresponds to the post 46. As the post includes at least two overhanging latches 50,52 when the tongue 126 is pressed thereover, the flexible printed circuit 12 is positively captivated thereupon. In addition, as the overhanging latches 50,52 extend from the body (not shown) of the post 46, it is not possible to displace the flexible printed circuit 12 in the direction of its plane of positioning. In the position received, the front end 120 of the tongue 126 overhangs the cavity 30 and the contact arms 68. The flexible printed circuit 12 is also overlying the guide surface 48 of rail 22.

With Reference now to Figure 8, the electrical connector assembly 2 is shown in cross-sectional fully assembled view. With the assembly as shown in Figure 7, the actuator 10 is brought down upon the connector and flexible printed circuit 12. As this occurs the flexible printed circuit is pressed within the cavity 30 by the wedge 56 along the chamfered surface 62. During the insertion of the actuator 10, the flexible printed circuit 12 is formed over the supporting surface 90 of the contact arm 68. It is important to note that as the contact arm 68 is lower than the resilient spring arm 70 and the support surface 90 is of different configuration than the nose portion 96 of the resilient spring arm 70, a balance of reactionary forces is achievable. This is because the flexible printed circuit 12 has the effect of building up the height of the contact arm 68. It is important to keep the forces in balance so that the actuator may be fully and properly inserted. In addition, it is also important to note that during the insertion of the actuator 10, all of the forces are directed to the contact 8. All downward forces (in the direction of insertion) pass into the fork- shaped contact portion 66 and any forces perpendicular to the direction of insertion are absorbed within the resiliency of the arms 68,70. This prevents any undue stresses being imposed upon the solder joints formed at the solder feet 84. Upon further insertion of the actuator 10, the flexible printed circuit 12 is bent around sufficiently that the circuit traces 14 thereupon come into contact with the sharper nose 92 of the contact arm 68 that bites into the circuit trace 14. While this is occurring, the gentler biasing head 94 and the more smoothly rounded nose portion 96 thereupon are passing over the wedge 56 due to the smoother shape of the biasing head 94, the head 94 does not bite into the wedge 56, even over time, and therefore the reliable electrical interconnection is maintained. One other feature of the contact structure that can be observed in Figure 8 is that the transverse engagement points of the engagement nose 92 and the nose portion 96 are basically in line thereby balancing the forces such that the actuator 10 may be reliably retained therebetween, thereby eliminating the need for the retention members 36 and the catches 64. Furthermore, the chamfer 62 provides relief about which the flexible printed circuit 12 is bent such that the free end 120 is not distorted through a path that would result in forces being exerted on the actuator 10 that would tend to expel the actuator 10 from the connector housing 6. Finally, as the actuator 10 is installed, an overhanging portion 58 of the upper plate 54 comes into close proximity of the upper surface 118 of rail 24. As the corresponding surface 48 on rail 22 is lower than the surface 118 on rail 24 in the fully seated position, the overhanging portion 60 of the upper plate 54 and the guide surface 48 define a passageway 132 exiting generally perpendicular to the direction of insertion and assembly of the components making up the assembly 2. With reference now to Figure 9, the electrical connector 4 is shown mounted upon a PCB 10 with the flexible printed circuit extending generally parallel to the PCB 110. The contact 8 is mounted to solder pads 108 upon the printed circuit 110 and the latching structure comprising the retention members 36 and the catch 64 are positively engaged providing additional assurance that the actuator 10 does not become dislodged from the connector housing 6.

Claims

1. An electrical connector assembly (2) for electrically connecting at least one circuit trace (14) on a flexible circuit (12) to respective contact pads on a substrate (110) , the electrical connector assembly (2) comprising a connector housing (6) having a receiving region (30) therein, at least one contact (8) seated in the housing (6) with a contact portion (66) exposed in the receiving region (30) and a mounting foot (84) that extends beyond a surface (86) of the housing for engaging the contact pads of the substrate (110) , and an actuator (10) for retaining the flexible circuit (12) in the receiving region (30) with the contact portion (66) engaged to the corresponding circuit trace (14) thereupon; the connector assembly characterized in that the flexible circuit (12) is loadable into the connector housing (6) in a direction generally perpendicular to the substrate.

2. The electrical connector of claim 1, characterized in that the connector is configured such that the flexible circuit (12) will extend generally parallel to the substrate (110) .

3. The electrical connector of claim 1 or claim 2, characterized in that the contact portion (66) is of fork- shaped structure with a contact arm (68) and a spring arm (70) opposite thereto and the actuator (10) is fittable therebetween such that flexible circuit (12) is wedged against the contact arm (68) .

4. The electrical connector of claim 3, characterized in that the actuator (10) and the contact portion (66) are configured such that with the flexible circuit (12) positioned between the actuator (10) and contact arm (68) , the insertion forces for the actuator (10) result in essentially balanced reactionary forces.

5. The electrical connector of claim 4, characterized in that the contact arm (68) and the spring arm (70) are of different configuration.

6. The electrical connector of any one of the preceding claims where the contact (8) includes a biasing post (80) and a positioning post (82), these posts (80,82) being receivable in the housing (6) on opposite sides of the receiving region (30) such that the contacts (8) are suspended from the housing (6) and biased in a single direction transverse thereto.

7. The electrical connector of any one of the preceding claims wherein the contact (8) includes a second foot (84) on the opposite side of the receiving region (30) .

8. The electrical connector of any one of the preceding claims, further characterized in that the actuator (10) includes a pair of depending latch arms (64) on either end thereof for engaging lugs (42) on the housing (6) to retain the actuator (10) in the housing.

9. The electrical connector of any one of the preceding claims, wherein the housing (6) includes a pair of post and latch structures (44,46) for anchoring the flexible printed circuit (12) .

10. The electrical connector of any one of the preceding claims, wherein the spring arms (70) includes a blunt nose (96) for abutting the actuator (10) and the contact arm (68) includes and engagement nose (92) of sufficient sharpness to bite into the corresponding circuit trace (14).