Pad on pad type contact interconnection technology for electronic apparatus

A pad on pad type contact, and technology therefor, for electronic apparatus wherein a spring member, that by its shape and material in the motion when the contact comes together wipes the mating pad surfaces across each other and then retains them under permanent compressive force in service. In high density and high performance electronic apparatus interwiring, array quantities of the spring member of contact are fabricated in unitary assembly elements for connection assemblies between both rigid and flexible type wiring.

FIELD OF THE INVENTION 
The invention relates to the interconnection of devices and arrays of 
devices in electronic apparatus and in particular to the technology of 
interconnections employing the pad on pad type of contact and to the pad 
on pad type of contact to the "flex tape" type of electronic apparatus 
wiring. 
BACKGROUND AND RELATION TO THE PRIOR ART 
As the performance, density and cost considerations of electronic apparatus 
become more stringent the structure is evolving into a tightly packed 
arrangement of interconnected device bearing boards with a large quantity 
of very closely positioned contacts. Those contacts cannot be permitted to 
introduce impedance into the interconnecting system and the conductors, in 
turn, in the interconnecting system cannot be permitted to introduce an 
impedance limitation on the transmission of the signals. Further, the 
large numbers of contacts must be such that they can be fabricated without 
introducing non-uniformity and reliability problems as is the situation 
where meticulous care is not taken to prevent metal oxides, grease, 
corrosion, insulating material particles and other debris from getting 
between the mating surfaces. 
One contacting technique receiving attention in the art involves a pad on 
one member contacting a pad on another member with the pads being held in 
position in service by a structure that supplies approximately constant 
pressure. The technique is known in the art by the terminology "pad on 
pad". In high density electronic apparatus there is very little space to 
accommodate structure associated with contacts. The pad on pad type 
contact occupies a small area. 
In the pad on pad type of contacting, reliability, uniformity and impedance 
minimization is greatly improved where a wiping operation of one pad on 
the other can be supplied when the pads are brought together. Heretofore 
in the art however, the providing of constant pressure in service and the 
providing of a wiping operation introduce considerable added structure in 
an interconnecting system. In many applications there just isn't room for 
any added structure. 
One type of electronic apparatus wiring employs a dielectric supporting 
member with flexible conductors on or embedded in it. It is known in the 
art as "flex tape". In the "flex tape" the dielectric supported wiring 
conductors are available with precision electric transmission line 
properties and with ground planes where desired. The flexibility 
simplifies large array assembly. The wiring benefits of "flex tape" wiring 
in electronic apparatus are somewhat offset by the difficulty and added 
structure needed for connection to "flex tape" and between "flex tapes". 
One example of that added structure in applying constant pressure in 
service is shown in U.S. Pat. No. 4,948,374 wherein pads on a "flex tape" 
are retained in contact with pads on a printed circuit board in a housing 
that has a bow spring and a deformable pad urging the pads together. 
Pad on pad connections to "flex tape" conductors where there is also wiping 
of the pads as they are assembled has heretofore in the art been confined 
to structures where the "flex tape" conductors are supported by a rigid 
supporting member. 
As an example, in U.S. Pat. No. 4,740,867 a connecting structure is shown 
where the "flex tape" is clamped in a slotted housing and a rigid 
connector member enters the slot, wipes and makes contact with the flex 
tape conductors. 
There is a need in the art for the ability to make reliable, uniform, and 
low cost, pad on pad connections, to all types of substrates, both rigid 
and flexible, without complex associated structure. 
SUMMARY OF THE INVENTION 
A pad on pad type of contact technology is provided wherein each pad on pad 
contact combination wipes one pad with respect to the other as the contact 
comes together and the combination is held in place under permanent 
compression in service. The contact of the invention has a spring member 
that has, serially, a support portion, an elongated spring portion that is 
at an angle to the direction of the support portion, and a compression 
portion that is about the size of, and essentially parallel to, the 
surfaces of the pads. There is a friction relationship between the 
compression portion and the substrate supporting one of the pads. The 
stress in the motion bringing the pads together, changes the angle the 
elongated spring portion makes with the support portion causing the 
compression portion of the spring member to move in a direction parallel 
to the pad surfaces because of the fixed length of the elongated spring 
portion which in turn moves one pad surface with respect to the other in a 
wiping motion; and then in service the mated pads are retained in contact 
under permanent compression by the spring properties under deflection in 
the spring portion of the spring member. The technology permits high 
density spring arrays of contacts with spring members being formed as part 
of a common sheet. The technology also permits high density high 
performance contacting between flexible substrates which in turn permits 
"flex tape" interwiring throughout extensive electronic apparatus.

DESCRIPTION OF THE INVENTION 
In connecting large numbers of contacts in arrays and in particular where 
at least one of the substrates supporting at least one of the contacts is 
flexible, a contact technology is provided through the invention where 
each electrically contacting portion of the contact is a pad, and the 
mating surfaces of the pad pairs of each contact are caused to wipe across 
those mating surfaces by the construction of the parts of a spring member 
that also then provides a permanent compressive force across those mating 
surfaces in service. The wiping operation dislodges any debris or 
corrosion that if not removed may introduce impedance, unreliability 
and/or non uniformity to the contacts. The spring members may be made of a 
material selected only for spring properties. The spring members in arrays 
may be made out of a single sheet of material in a simple stamping 
operation into a single array size pressure plate assembly component. 
Referring to FIG. 1 there is shown a line representation of the relative 
relationship of the portions of the spring member of the pad on pad 
contact of the invention. The spring member 1 has, in serial relationship, 
a support portion 2, a spring portion 3, shaped to be at an angle to the 
direction of the support portion 2 and a compression portion 3, shaped to 
be essentially in the direction of the support portion 2 and the size of 
the pads in the contact. The support portion 2 is fixed with respect to 
motion in the plane of portion 2 by support such as element 5 as 
symbolically illustrated, or by being part of a larger object. The spring 
portion 3 has one end connected to the support portion 2, has a fixed 
length and is shaped to be at an angle to the plane of support portion 2. 
The compression portion 4 is attached to the remaining end of the spring 
portion 3 and is shaped to be essentially parallel to the plane of the 
support portion 2. In service, relative motion as depicted by the 
bidirectional arrow 6, essentially perpendicular to the plane of support 
portion 2 and compression portion 4, because of the fixed length of the 
spring portion 3, will result in a displacement, as shown by the 
bidirectional arrow 7, of the compression portion 4. 
Referring to FIG. 2 there is shown a perspective view of the pad on pad 
contact of the invention with the contact in the open or unconnected 
position. The spring member 10 of the contact, is made up as discussed in 
connection with FIG. 1; of a planar support portion 11, which may be a 
portion of a larger array member; a spring portion 12, with one end 
attached to the portion 11 and shaped to be at an angle to the plane of 
portion 11; and, a compression portion 13 attached to the remaining end of 
the spring portion 12 and shaped to be essentially parallel to the plane 
of the support portion 11. The compression portion 13 in service will 
provide constant compressive force on the pad 14 on pad 15 contact 
assembly and will provide wiping motion across the contacting surfaces 16 
and 17 when the pads 14 and 15 are brought into contact with each other. 
The pads 14 and 15 are each an electrical contact or a portion of a 
conductor on substrates 18 and 19 respectively such as a semiconductor 
component, a printed circuit board, or a "flex tape". 
The pads 14 and 15 in FIG. 2 are shown with a separation 20 between them. 
The compression portion 13 of the spring member 10 is provided with a 
friction capability to facilitate the physical wiping movement of the pad 
surfaces 16 and 17 as they are brought together in the contact. The 
friction capability is shown as an adhesive member 22 which operates to 
urge the substrate 19 to move with the compression member 13 and in turn 
to move the surface 17 across the surface 16 as the pads 14 and 15 come 
together. The member 22 is shown having multiple layers such as a double 
sided 23 and 24 adhesive film each side with properties related to 
adhesion to the type of material it contacts. Where convenient the 
adhesive capability could also cover the entire surface of the substrate 
19 or alternatively the entire surface of the spring array. Element 23 
would contact the metal of portion 13 of spring member 10 whereas element 
24 would contact the dielectric backing of the substrate 19. 
Referring next; to FIG. 3, using the same reference numerals as in FIG. 1 
where appropriate, there is shown a line representation of the portions of 
the spring member 1 when the pad on pad contact is in the closed or 
contacting position; together with FIG. 4, which is a perspective view of 
the pad on pad contact in the closed or contacting position and where, the 
same reference numerals as in FIG. 2 where appropriate are used. Contact 
closing motion shown by the arrow 30 in FIG. 4 operates to produce 
vertical displacement as shown by the arrow 31 of FIG. 3 of the 
compression portion 4 which, in turn because it is attached through spring 
portion 3 and then support portion 2, results in a change in the angle the 
spring portion 3 makes with the support portion 2 and produces a 
displacement of the compression portion 4 as shown by the arrow 32. The 
displacement is labelled 32 in FIG. 4 and operates to move the compression 
portion 13 which motion is translated through the adhesive member 22 to 
the substrate 19 thereby providing relative wiping motion of the contact 
surfaces 16 and 17 of the contacts 14 and 15 as they come together. The 
spring deflection properties of the spring portion 12 in FIG. 4 then 
provide permanent compressive force across the pads 14 and 15 contact 
combination while they are in service. 
There are a number of unique features and benefits derived therefrom that 
are associated with the contact and technology of the invention. 
The spring member 1 does not have to carry current and consequently the 
properties of the material used does not have to be subject to 
resistivity, corrosion, metal migration or any other similar 
considerations of a current carrying contact. Freedom from resistivity 
considerations, in turn, permits a wider range of available materials with 
predictable and durable spring properties. The spring member 10 may be of 
a material such as spring steel. The substrates 18 and 19 may be rigid 
such as printed circuit board or even semiconductor material or they may 
be flexible such as "flex tape". Where all substrates are flexible, a 
rigid backing member, not shown, would be provided under element 18. 
Registration for assembly would be provided by dowels or equivalent, not 
shown. A clearance of less than the width of a pad, for the displacement 
32, would be provided at the dowel openings in the substrate 19. It should 
be noted that registration between the substrate 18 and the spring array 
40 must be established and maintained. Appropriate alignment is achieved 
and maintained through use of a friction capability. 
The friction capability can be provided by the adhesive member 22 which may 
be of a frictional, pressure sensitive, or permanent type interface, or it 
can be provided by an element such as a ridge or protrusion on the side of 
the substrate 19 next to the compression member 13. It is essential only 
that as the compression portion 13 is displaced, it moves the substrate 19 
along with it. The spring members 10, in array increments, may be stamped 
from a single piece into a spring array assembly component. Alternatively, 
small arrays may be grouped into larger arrays to improve registration and 
reduce die types. 
In FIGS. 5 and 6, top and side section views, respectively are shown of a 
portion of an array of spring members in a single piece. Referring to 
FIGS. 5 and 6 a single sheet piece of spring steel 40 has a plurality of 
spring members of which elements 41-46 are shown as an example and where 
the support portion 11 is part of the common portion 47 of the sheet 40 
with the spring portion 12 and the compression portion 13 being formed 
displaced from the plane of the sheet. In the section view of FIG. 6 the 
portions are labelled with the reference numerals of FIGS. 2 and 4, with 
each spring portion angularly attached to the common support portion and 
each compression portion offset from but essentially parallel to the 
common support portion. For dimensional perspective, contact spring 
members such as elements 41-46 can be stamped to spacings as small as die 
manufacturing can achieve which at the present time is approximately a 
1.27 mm center to center dimension. The compression portion 13 corresponds 
to the size of a pad which is an about 0.127 by 0.254 millimeter (mm) 
rectangle. 
Referring to FIG. 7 a perspective schematic view of the connector assembly 
is shown of the elements of the pad on pad technology of the invention as 
they are assembled. In the connector assembly 50 there is a rigid 
supporting base member 51 having registration dowels 52 and 53 extending 
vertically therefrom. A first substrate 54, corresponding to substrate 18 
in FIGS. 2 and 4, is positioned over the dowels 52 and 53 and in contact 
with the base member 51 with the pad contact array 55 on the side that is 
away from the support member 51. A second substrate 56, corresponding to 
the substrate 19 of FIGS. 2 and 4 is next positioned over the dowels 52 
and 53, with the pad contact array 57 in contact with the pad contact 
array 55. In the assembly of FIG. 7 the pad contact array 57 is on the 
underside of the substrate 56 and would not be directly visible so that 
only the outline of the location of the contacts is shown as array 57 in 
the upper surface. The openings 58 and 59 for dowels 52 and 53 
respectively are elongated about half a pad width to accommodate the 
displacement of the substrate 56 when the pad surfaces in arrays 55 and 57 
wipe across each other. Adjacent substrates 54 and 56 enter the assembly 
50 from opposite sides. 
A punch and die fabricated spring array assembly component 60 is positioned 
with the dowels 52 and 53 passing through registration holes therein. The 
spring array assembly component 60 has an array 61 of contact spring 
members for each pad combination in arrays 55 and 57. The spring array 
assembly component 60 is a structure with spring member features 
corresponding to element 40 of FIG. 5 and is positioned with the side 
having the spring members in contact with the substrate 56. While the 
substrate 54 is shown as being rigid and the substrate 56 is shown as 
being a "flex tape" or both, as desired. 
A rigid upper member 62 is positioned over the dowels 52 and 53. The 
assembly 50 is then drawn together with compression and retaining elements 
such as bolts, not shown, that extend through holes 63-70. The compression 
causes each spring member in the array 61 of the pressure plate 60 to 
displace each contact in the array 57 on the substrate 56 and thus to wipe 
the surfaces across each other of each of the contact pairs in the mating 
arrays 55 and 57 and then to retain each of the contact pairs under 
permanent compression in service. 
The principles of a spring array assembly component contact spring member 
array in providing a contact displacement wiping and then permanent 
compression as, discussed connection with FIG. 7, is further illustrated 
in FIGS. 8 and 9, for single and double sided pad arrays. 
Referring to FIG. 8, in a schematic side view, before compression, a 
connector assembly 71 has a rigid base 72 with vertical registration 
dowels 73 and 74. A rigid substrate 75 is positioned over the dowels 73 
and 74 with an array of contacts 76, one row of which being visible in 
this view. The contacts of array 76 are on the side of the substrate 75 
that is away from the base 72. A "flex tape" type substrate 77 is 
positioned over the dowels 73 and 74 with displacement clearance in the 
dowel accommodating openings and with the contacts of the array 78 in 
contact with the contacts of the array 76. In the "before compression" 
condition of this view the contact pad pairs are about half a pad width 
out of alignment. The spring array assembly component 79 with a spring 
member for each contact pair in arrays 76 and 78 is positioned with the 
dowels 73 and 74 through the registration holes therein, and with the side 
with the spring members protruding being in contact with the substrate 77. 
A rigid upper member 80 is positioned over the dowels 73 and 74, and 
compression and retention bolt type members 81 and 82 are used to draw the 
assembly 71 together. The drawing together of the assembly 71 causes the 
spring members in the pressure plate 79 to wipe the pad surfaces across 
each other of each contact pair bringing them into alignment and then hold 
each contact pair under permanent compressive force. 
Referring to FIG. 9 a schematic side view, before compression, is shown of 
a connector assembly where there are arrays of contact pads on both sides 
of a rigid substrate that mate with an array of contact pads on each of 
two "flex tape" type substrates. The connector assembly 90 includes a 
rigid base member 91 with vertical registration dowels 92 and 93. A first 
spring array assembly component 94 is mounted with the dowels extending 
through the registration holes therein and with the side opposite to the 
spring members in contact with the base member 91. A first "flex tape" 
type substrate 95 is positioned with the dowels 92 and 93 through 
displacement clearance elongated holes, and with the side opposite to the 
contact pads in contact with the pressure plate 94 spring members. A rigid 
substrate 96 with contact pads on both sides, is positioned, entering the 
assembly 90 from the side opposite to the side entered by the substrate 
95, with the dowels 92 and 93 extending through registration holes therein 
and with the contact pads on one side in contact with the contact pads of 
the substrate 95. A second "flex tape" type substrate 97 is positioned, 
entering the assembly 90 from the same side as the "flex tape" type 
substrate 95, with the contact pads in contact with the contact pads on 
the remaining side of the substrate 96, and with the dowels 92 and 93 
through displacement clearance elongated holes. A second spring array 
assembly component 98 is mounted with the dowels 92 and 93 extending 
through the registration holes therein and with the side opposite to the 
spring members in contact with the side opposite to the contact pad side 
of the substrate 97. A rigid upper member 99 is positioned over the dowels 
92 and 93 and the assembly is drawn together with bolt type members 100 
and 101. The drawing together of the assembly causes the spring members of 
both spring array assembly components 94 and 98 to move the contact pads 
with respect to each other and become aligned, and then to retain all 
contact pad mating pairs under permanent compressive force. 
What has been described is a pad on pad type contact for electronic 
apparatus wherein a spring member is provided, that by its shape and 
material, in the motion when the contact comes together wipes the mating 
pad surfaces across each other and then retains them under permanent 
compressive force and a technology of high density and high performance 
interwiring where array quantities of the spring member of the pad on pad 
contact of the invention is employed in unitary assembly elements in 
connection assemblies between both rigid and flexible wiring.