Card edge connector using flexible film circuitry

A surface mountable card edge connector 10 includes a housing 16 having a transverse base 18 and opposed endwalls 28; a generally C-shaped outer shell member 44; a generally C-shaped inner support member 60; two resilient members 76 disposed in channels 74 defined between portions of the shell and support members 44,60; and a flexible film circuit assembly 80. Free ends 56 of the shell member 44 define a card receiving slot 58 of selected width greater than the thickness of a card 112 insertable thereinto. Facing portions 78 of each the resilient members 76 extend into the card receiving slot 58. The film assembly 80 is disposed in a loop extending into the card receiving slot 58 and around the sides 19 of the shell member 44 such that exposed circuitry 88,90 at selected regions of the film assembly 80 is located in the card receiving slot 58 and proximate the resilient members 76. Upon inserting a circuit board 112 having circuit pads 114 thereon in registry with the circuitry of the film assembly 80 into the card receiving slot 58, the resilient members 76 provide normal force to maintain electrical interconnection therebetween.

FIELD OF THE INVENTION 
This invention relates to card edge connectors and more particularly to 
surface mountable card edge connectors using flexible film circuitry. 
BACKGROUND OF THE INVENTION 
The use of flexible film circuitry i.e., circuitry disposed on a thin 
insulating material such as polyimide polyester, or the like, to 
interconnect one circuit array with another array to provide a means to 
achieve extremely high density interconnections is known in the art. 
Flexible film circuitry is particularly suitable for use when dealing with 
dense arrays of circuits having closely spaced centerlines. The circuitry 
on the film is easily reconfigurable and the film provides a seamless 
extension from the mother board to a daughter card. 
U.S. Pat. No. 3,922,054 discloses one early use of flexible film with a 
zero insertion force (ZIF) card edge connector in which a flexible circuit 
is looped around a channel and held taught against it by retaining it. The 
circuits wrapped around the spring portions are brought into contact with 
corresponding circuits on the daughter card by means of cams. 
Other more recent ZIF type connectors are disclosed in U.S. Pat. No. 
4,911,643 in which the camming action is provided by a shape-memory alloy 
that is activated by an electrical circuit; and U.S. Pat. No. 5,308,257 
that uses a camming slide member. 
U.S. Pat. No. 5,195,897 discloses a two-piece connector using flexible film 
circuitry in which the film is wrapped around a C-shaped spring member. 
The spring member is spread apart prior to engaging a circuit board by cam 
bearing surfaces on sidewalls of a support structure associated with the 
circuit board. A handle attached to the C-shaped spring member provides 
means for disconnecting the member from its associated circuit board. 
The use of a camming type mechanism however increases the complexity of the 
connector as well as the associated manufacturing cost. In addition, the 
camming mechanism generally occupies space on the board and at a minimum 
requires that there be sufficient room surrounding the connector to permit 
access to it in order to activate the mechanism to permit insertion and 
withdrawal of the daughter cards. It is desirable, therefore, to have a 
surface mountable card edge connector using flexible circuitry that does 
not require the use of a camming mechanism whether mechanically, 
electrically, or otherwise activated, thereby conserving board space and 
permitting closer stacking of daughter cards. 
SUMMARY OF THE INVENTION 
The present invention is directed to a surface mountable high density card 
edge connector using flexible circuitry that overcomes problems associated 
with the prior art. 
The connector of the present invention includes a housing having a 
transverse base and end walls, an outer shell member, an inner support 
member, a resilient member disposed between the support and shell members 
and a flexible film circuit looped within a card receiving slot and around 
the outer shell member. 
The housing includes an elongate transverse base having opposed ends walls, 
the end walls preferably including card receiving channels, and board lock 
members. The C-shaped outer shell member is configured to be received 
between the housing endwalls. The shell member includes elongate sides 
extending from a transverse base section and upwardly a selected first 
distance to leading ends and concluding at free ends defining a card 
receiving slot of a width greater than the thickness of a card insertable 
thereinto. The inner support member is also a generally C-shaped member 
and is disposed centrally within the C-shaped outer member. The support 
member includes elongate sides extending from a transverse base section 
upwardly a second selected distance to leading ends, the second distance 
being less than the first distance so that the sides of the support member 
are shorter than the corresponding sides of the shell member. The leading 
ends of the shell and support members are being spaced apart vertically to 
define a first pair of opposed longitudinal channels therebetween. A 
resilient member is disposed in each of the channels such that facing 
portions of the resilient members are spaced closer together than the 
thickness of the card to be inserted into the card receiving slot. The 
flexible film circuit assembly is disposed in a loop within the card 
receiving slot such that exposed circuit traces lie proximate the 
resilient members whereby upon insertion of a circuit card having circuit 
pads thereon in registry with the traces on the film, the resilient 
members provide normal force to maintain electrical interconnection 
therebetween. Preferably the flexible film layer further includes a 
plurality of apertured regions such as tabs extending outwardly from the 
sides, the apertured regions cooperating with film registration pegs on 
the housing base to accurately position the film in the connector. 
In the preferred embodiment, the flexible film circuitry, the inner support 
member, and the outer shell member are secured to the base by means of 
eyelets. It is to be understood other means can be used to secure the 
connector members together. The end walls of the housing in the preferred 
embodiment preferably include daughter card guide or receiving slots and 
board lock members or other means for securing a connector to a mother 
board. 
To assure accurate alignment of the circuits of the flexible film assembly 
and the contact pads of the mother board, the connector housing includes 
at least a pair of board mounting posts extending from the mounting face. 
One of the posts is used as a datum for the connector, that is the 
reference point from which measurements to the respective registration 
tabs are made to assure precise positioning of the film. The datum post 
cooperates with a datum mounting post aperture in the circuit board which 
is used as the reference point for the location of the circuit pads on the 
board and the other mounting apertures. 
To assure accurate alignment of the flexible film circuitry and the contact 
pads of the daughter card, one of the housing end walls further includes 
an internal wall extending across the short axis of the base, the circuit 
side of which is used as a datum, that is the reference point from which 
measurements are made to locate the apertures for the eyelets in the 
flexible film assembly and also as a base for locating the mounting posts, 
which are used as the datum for the registration pegs. The datum wall also 
functions as a polarization wall for the daughter card and cooperates with 
a daughter card datum along the circuit side of the slot. 
In an alternative embodiment of the invention the inner support member is 
configured to provide an additional pair of opposed channels for receiving 
additional resilient members thereby enabling the connector to be used 
with a daughter card having spaced apart rows of contact pads. The 
connector is also suitable for use with other configurations of flexible 
circuitry including circuit assemblies having one or more ground planes 
such as in a microstrip or stripline configuration as known in the art. 
It is an object of the present invention to provide a high density card 
edge connector for use with flexible circuitry that eliminates the need 
for a camming mechanism, whether activated mechanically, electrically or 
by other means known in the art. 
It is a further object of the invention to provide a connector that 
minimizes space requirements on the mother board. 
It is another object of the invention to provide a surface mount connector 
having flexible film circuitry that is compatible with conventional 
techniques used to surface mount connectors having terminal members. 
It is also an object of the invention to provide a connector having means 
to hold the flexible film in a precise position so that the respective 
traces in the film are precisely aligned with the corresponding circuit 
pads on the mother board and daughter card. 
It is a further object of the invention to provide a connector utilizing 
flexible film circuitry that will accommodate any unevenness in the 
daughter card. 
It is yet another object of the invention to provide a connector using 
flexible film circuitry that can readily accommodate the tolerance ranges 
associated with card sizes made in accordance with industry standards. 
Embodiments of the present invention will now be described by way of 
example with reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring now to FIGS. 1, 2 and 3 surface mountable high density card edge 
connector 10 is designed to interconnect a plurality of circuit traces 108 
on a mother board 106 to corresponding traces 114 on a daughter card. 112. 
Connector 10 has card receiving face 12 and an opposed mounting face 14. 
The connector 10 includes a housing 16, an outer shell member 44, an inner 
support member 60, at least one pair of resilient members 76 and a 
flexible film circuit assembly 80. 
Housing 16 includes an elongate transverse base 18 having sidewalls 19 and 
spaced apart end walls 28. Sidewalls 19 include a plurality of spaced 
apart radiused film supports 22 that provide support for the flexible film 
circuitry assembly 80 and to assure the film assembly 80 is maintained in 
the desired curve for engaging the circuit traces 108 on the mother board 
106. In the preferred embodiment end walls 28 include integrally molded 
card guides 30 for guiding the daughter card 112 into position within the 
connector 10 and a board lock receiving slot 34. The side surfaces 27 of 
the end walls 28 further include film mounting pegs 36 used to secure and 
align the flexible film circuit assembly 80 in the assembled connector 10. 
Transverse base 18 includes a plurality of apertures 20 extending 
therethrough for receiving eyelets 104 used in assembling the connector 10 
as more fully described below. 
In the preferred embodiment one of the end walls 28 includes a polarization 
wall 32 as known in the art to assure that the daughter card 112 is 
inserted correctly. The polarization wall 32 is also used as a datum or 
reference surface from which critical measurements are taken to register 
the film circuit traces 88,90 with circuit pads 114 of daughter card 
including the locations of the apertures 96,96' film assembly 80. One of 
the mounting posts 24 extending from the mounting face 14 of housing 16 is 
used to register the film traces 92,94 that are to be soldered to circuit 
pads 108 on mother board 106. In the preferred embodiment the mounting 
post 24 that is near datum wall 32 is used as the datum post. Datum post 
24 in polarization is used as the reference point for locating the film 
registration pegs 36. The base 18 further shows a board lock 38 having a 
body 40 and opposed beams 42 which are inserted into the board lock slot 
34 and extend through mounting posts 24 on the mounting face 14 of housing 
16. In the embodiment shown the mounting posts 24 include a pair of 
semicylindrical legs 26 joined together at the leading ends thereof. The 
board lock 38 shown in the preferred embodiment is more fully disclosed in 
copending patent application U.S. Ser. No. 08/248,262, filed concomitantly 
herewith. It is to be understood that other means for securing the 
connector to the housing may also be used. 
In the preferred embodiment the housing is made of dielectric material such 
as a liquid crystal polymer (LCP) or other suitable material that is 
highly temperature resistant, i.e. can withstand the high temperatures 
associated with standard soldering techniques for surface mounted 
connectors, is resistant to chemicals used for cleaning connectors and is 
flame retardant. One suitable LCP is XYDAR G930, available from Amoco 
Performance Products, Inc. Other materials as known in the art are also 
usable. 
Outer shell member 44 is a rigid generally C-shaped member configured to be 
received within the end walls 28 of the housing 16. The shell member 44 
has elongate sides 50 extending upwardly from a transverse base 46 for a 
selected first distance to leading ends 52. The leading ends of shell 
member 44 have inwardly directed portions 54 and conclude at free ends 56. 
As shown in FIGS. 3 and 5, the leading ends 56 are curved slightly to 
conform to the curve of resilient member 76. The parallel free ends 56 
define a card receiving slot 58, the slot 58 being of a width selected to 
be greater than the thickness of a daughter card 112 to be inserted into 
the slot. As can best be seen in FIG. 3 transverse base 46 also includes 
apertures 48 for receiving the eyelets 104 during assembly of the 
connector 10 as more fully described below. 
In accordance with the invention the outer shell member 44 is rigid and 
needs to have sufficient strength to withstand the normal forces 
associated with insertion of the daughter card 112 and compression of the 
resilient member 76. In the preferred embodiment, therefore, the shell 
member is formed of stainless steel having a thickness of about 0.025". 
Rib like detents 53 are formed along shell sidewalls 50 to further 
increase the rigidity of the outer shell member 44, as seen in FIGS. 1 and 
3. It is to be understood that the shell member may also be made of a 
dielectric material but in order to achieve the desired strength 
characteristics, the dielectric walls would need to be considerably 
thicker, thus increasing the overall size of the connector and the amount 
of space needed on the mother board. 
The inner support member 60 is also a generally C-shaped rigid member 
configured to be received within the outer shell member 44 and disposed 
centrally therein. The inner support member 60 has elongate sides 66 
extending from a transverse base section 62 that extend upwardly a 
selected second distance to leading ends 68. Sides 66 include slots 63 
which are configured to provide clearance for inwardly directed portion of 
ribs 53 of outer shell 44. The base 62 of inner support member 60 further 
includes a plurality of holes extending therethrough for use in assembling 
the connector as more fully described below. Leading ends 68 includes 
inwardly directed portions 70 at the leading edges thereof and conclude at 
free end 72 spaced apart not less than the width of the card receiving 
slot 58 defined by the outer shell member 44. The side walls of the inner 
support member 60 are shorter than those of the outer shell member 44 such 
that when inner support member 60 is positioned within outer shell member 
44 there respective inwardly directed portion 70,54 are spaced vertically 
apart to define a first pair of opposed longitudinal channels 74 
therebetween. The essential function of the inner support member 60 is to 
provide support preferably along the full length of the resilient members 
76 that are disposed in the opposed longitudinal channels 74. The free 
ends 72 of inner support member 60 are curved slightly upwardly to conform 
to the curve of the resilient member 76. In the preferred embodiment the 
inner support member is also made from stainless steel and has a thickness 
of about 0.010 inches, sufficient to withstand the forces exerted by the 
compression of the resilient members 76. 
The resilient members 76 when placed in the channels 74 have portions 78 
that face each other and extend into the card receiving slot 58 as best 
seen in FIG. 3. Suitable materials for the resilient members include 
extruded elastomeric materials such as for example a fluoroelastomer or 
the like. The material selected for the resilient members should be one 
that has minimum deflection, preferably not greater than 20% to prevent 
the material from taking a compression set, be resistant to chemicals 
typically used to clean connectors and be stable at the temperatures 
associated with standard practices for soldering surface mounted 
connectors. One suitable fluoroelastomer is VITON available from DuPont. 
Canted coiled springs or other suitable resilient materials may also be 
used. 
FIG. 5 illustrates connector 10 after daughter card 112 has been inserted 
into card receiving slot 58. As card 112 enters slot 58, the leading edge 
of the card engages resilient member portion 78, compressing resilient 
members 76, and forcing the member into the remaining space in channels 
74. The insertion of the card 112 provides wiping for the traces 88 and 90 
to assure good interconnection between traces 88 and 90 to card traces 
114. 
The flexible film circuit assembly 80 will be best understood by referring 
to FIGS. 1, 3, 4 and 6. The assembly 80 is made by means known in the art. 
The assembly includes a plurality of circuit traces 84 disposed between 
insulating layers 82,86 with the circuit traces being exposed at least at 
first selected areas 88,90 for interconnecting to corresponding circuit 
pads 114 of daughter card 112 and at second areas 92,94 at the outer edges 
of the continuous strip of film. As can best be seen in FIG. 1 assembly 80 
has two sets of circuit traces 84 separated by an insulating portion 85. 
This structure is intended to be used with a double sided daughter card 
112 having a plurality of contact pads 114 on both sides thereof as seen 
in FIG. 5. It is to be understood that only one set of traces 84 needs to 
be on the flexible film assembly when single sided daughter cards are 
used. It is also to be understood that the insulating cover layer 86 may 
also be eliminated in those applications where safety and environmental 
conditions permit. The circuitry of flexible film assembly 80 can be 
readily reconfigurable to meet the needs of a customer by changing the 
"artwork" used to photographically imaged or otherwise form the traces on 
the insulating layer, as known in the art. Thus the same housing structure 
can readily accommodate multiple circuit arrangements. 
The structure of the flexible film is more clearly shown in FIG. 4. When 
constructing the flexible film circuitry 80, as known in the art, a layer 
of adhesive is used to join the layers together. Thus layer 86 includes a 
layer of adhesive 87 adhering it to the conductive trace 92 on its upper 
surface and a layer of adhesive 83 adheres the lower layer of flexible 
material 82 to the trace 92 on its lower surface. As shown in FIG. 4 the 
underlying adhesive and insulating layers 83,82 extend beneath the exposed 
conductor layer 92. As can best be seen in FIGS. 3 and 4, only the upper 
layer 86 of the insulating material and its associated adhesive are 
removed to expose the circuit traces 92,94,88 and 90 for electrical 
engagement with a respective pads 108 and 114 on the mother and daughter 
cards 106,112 respectively. For purposes of clarity, the adhesive layers 
are not shown in the other figures. The central portion 85 of the flexible 
film circuitry further includes two apertures 96, 96' for receiving the 
eyelets 104 when assembling the connector as best seen in FIG. 3. As shown 
in FIG. 1, one of the apertures 96 is round and the other 96' is oval. As 
previously discussed, the round aperture 96 is positioned with reference 
to datum/polarization wall 32. The differences in shape allow for 
tolerance variations in manufacturing the parts for the connector. The 
corresponding apertures 48,64 (not shown) in shell member 44 and inner 
support member 60 have similar configurations. The accuracy in placement 
of aperture 96 in film assembly 80 is essential in maintaining 
registration of the closely spaced film circuit traces 88,90 with the 
daughter card traces 114. The eyelets extend through apertures 96, 96' in 
film assembly 80, inner support apertures 64, outer support apertures 48 
and housing apertures 20 to secure the parts together, as shown in FIG. 3. 
Circuit assembly 80 further includes outwardly extending tabs 98 proximate 
the outer traces 92, 94 that are to be connected to the mother board 106. 
Tabs 98 include apertures 102 which cooperate with the positioning posts 
36 of housing 16 to secure the flexible film assembly 80 to the outer 
surface of the housing preferably by heat staking. As previously 
discussed, the locations of the film positioning posts 36 are determined 
with reference to datum mounting post 24. Securing the film assembly 80 to 
the housing 16 thereby assures the outer traces positions 92,94 of the 
film assembly 80 are correctly registered for engagement with the 
corresponding traces 108 on the mother board 106. As can best be seen in 
FIGS. 3, 4 and 5, the traces 92,94 with the outer edge of the flexible 
film assembly 80 are preferably folded near the leading ends thereof so 
that a portion of the traces 92 will be disposed on the corresponding 
trace 108 of the circuit board. As seen in FIG. 3, an adjacent film 
portion extends from the connector housing at positioning posts 36 and 
past radiused film supports 22 to the far ends of the circuit pads to 
which the traces are to be soldered and is of a length greater than the 
straight-line distance from the posts to the far pad ends. In combination 
with the excess length adjacent film portion, the fold provides a flexible 
hinged area to relieve stress on the soldered connections as the connector 
flexes during insertion or withdrawal of the daughter card 112 or owing to 
differences in rates of thermal expansion of the various materials. It is 
to be understood that the word "solder" is used in the generic sense and 
includes other materials such as, for example, conductive adhesives or the 
like which may be used to effect interconnection of the film traces and 
circuit board pads. 
The traces 92,94 are secured to the outer board with solder, a conductive 
adhesive or other suitable material that will effect electrical and 
mechanical interconnection as known in the art. 
FIG. 7 is an alternative embodiment 110 of the connector in which the inner 
support member 160 is formed to include a second channel for receiving a 
resilient member, intermediate the base and leading ends thereof. In this 
embodiment the flexible film assembly 180 includes two sets of film 
circuit pads, 188, 190 for interconnection to two spaced apart rows of 
contact pads on the same side of a daughter card (not shown). 
FIGS. 8 and 9 show diagrammatic representations of two alternative 
embodiments of the flexible film assembly 280,380. In embodiment 280, 
shown in FIG. 8, the film assembly includes an upper insulating layer 186, 
adhesive layer 187 surrounding traces 192 and 197 (greatly enlarged), a 
middle insulating layer 182, a ground plane 195 and a lower insulating 
layer 189. Circuit trace 199 is interconnected to ground plane 195 by 
means of a via 197 shown in phantom. Embodiment 280 defines a micro-strip 
flexible circuitry. 
In embodiment 390, shown in FIG. 9, the film assembly includes two 
additional layers, a second ground plane 195 and a further insulating 
layer 189, such that the conductors 192,199 are sandwiched between ground 
planes 195. Selected circuit traces and ground planes are interconnected 
with vias (not shown) in the same manner as previously described. 
Embodiment 380 defines strip-line flexible circuitry. 
It is thought that the card edge connector having flexible circuitry of the 
present invention and many of its attendant advantages will be understood 
from the foregoing description. It is apparent that various changes may be 
made in the form, construction, and arrangement of parts thereof without 
departing from the spirit or scope of the invention, or sacrificing all of 
its material advantages.