Electrical connectors – Preformed panel circuit arrangement – e.g. – pcb – icm – dip,... – With provision to conduct electricity from panel circuit to...
Reexamination Certificate
1997-05-28
2001-05-01
Luebke, Renee (Department: 2833)
Electrical connectors
Preformed panel circuit arrangement, e.g., pcb, icm, dip,...
With provision to conduct electricity from panel circuit to...
C439S077000
Reexamination Certificate
active
06224395
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to electrical connectors and, more particularly, to a flexible interconnect cable having improved design flexibility and three-dimensional conformity.
2. Description of the Related Art
Thin, flexible cables for interconnecting electrical devices are well-known in the art. These articles, variously referred to as flex cables, flex circuits, flex circuit cards, or flex cable assemblies, are particularly useful for carrying electrical signals in compact electronics applications. In the computer industry, cable assemblies are used for many purposes including power distribution, low-speed signal communication, and high-speed signal communication. For example, in high-performance computer systems, specialized cable assemblies are used to transmit high-speed signals from one processor to another processor, from a processor to system memory (RAM), or from a processor to an input/output (I/O) device. These specialized high-speed cable assemblies are mechanically and electrically connected to the printed circuit boards that support these components.
A typical flex cable has many conductive traces (thin conductive layers) placed on an insulative substrate, in a pattern appropriate for the particular interconnection, to form an elongated and flexible circuit structure. The conductive traces can be formed of any conductive material, as gold or copper, and the substrate can be any flexible material, usually a durable polymer, including polyester or polyimide, such as MYLAR or KAPTON, flexible insulation films. The conductors can be coated with an overlying layer of insulative material or hermetically sealed. Electrical contacts (or pads formed on the conductive traces) are provided at the ends of and along the conductive traces, including signal and ground plane contacts.
Interconnection with the contacts or pads formed on the flex cable may be provided in a temporary manner, e.g., using a switch or other mechanism that results in a physical wiping action by a component contact to achieve connection with the flex cable contact, or in a permanent manner, e.g., soldering. The contacts may be provided for through hole connection or surface-mount connection. A flex cable can have a multi-layer construction, i.e., conductive traces and contacts on upper and lower surfaces of the substrate or buried in the substrate. More complicated three-dimensional conductive traces can be constructed by, e.g., laser ablation or etching operations. Multiple flex cables can be used in parallel, stacked, and staggered assemblies.
FIG. 1
depicts a conventional flex cable design
10
for interconnecting a computer system to a CD-ROM (compact disk, read-only memory) device. Flex cable
10
includes a plurality of conductive traces
12
formed on an insulative substrate
14
. The conductive traces terminate in through-holes
16
which have been plated with a conductive material. Two sets of holes define first and second connectors
18
and
19
at one end of the cable, and a third set of holes defines a third connector
20
at the other end of the cable. A fourth set of holes defines a fourth connector
22
at the end an extension
24
integrally formed with substrate
14
. Conductive traces may be provided on the underside of the substrate (not shown) for connection to, e.g., the fourth connector
22
.
The propagation delay for high-speed signals between electronic components affects overall performance of the computer system, so the propagation delay is decreased by reducing the total path length for the signal to travel, as well as by improving the dielectric properties of the cable assemblies. Reducing the path length is also generally desirable to provide more compact systems. Using shorter flex cables can, however, introduce other problems. Short flex cables have some ability to conform along the length of the flex but little flexibility perpendicular to the cable surface; for example, the flex cable
10
of
FIG. 1
can easily flex (or bow) between the ends at connectors
18
and
20
, but it has little ability to conform in the left-right direction. The ability to accept rotation from connector to connector is thus limited by the bending characteristics of the flex cable. Cable stiffness places stresses on the flex cable assembly and mating hardware when flex is bent or any dimensional mismatch occurs, and so can lead to defects if sufficient tolerance is not provided, and limits packaging density.
Because of the foregoing limitations, different cable designs are made to fit each application. For example, even with a single product, a first cable may be needed for system test, and a second cable needed for manufacturing volumes. Cable and hardware stresses are reduced by altering the construction of the cables, but this impacts electrical performance, presenting additional tolerances must be considered. Cable routings must also be based on standard flex characteristics. It, therefore, would be desirable to design a flex cable having improved physical conformity to lessen tolerance demands. It further would be advantageous if the improved flex cable provided increased interconnection design flexibility for additional functionality.
SUMMARY OF THE INVENTION
It is therefore one object of the present invention to provide an improved flex cable, particularly one that is adapted to interconnect computer components.
It is another object of the present invention to provide such a flex cable having improved physical conformity, particularly in three dimensions.
It is yet another object of the present invention to provide such a flex cable which can be used in a wider variety of interconnection designs, including interconnections on both sides of the cable.
The foregoing objects are achieved in a flex cable generally comprising an electrically insulative, flexible, generally planar substrate having a first (upper) surface and a second (lower) surface, and conductor traces formed on at least the first surface of the substrate, the substrate having a plurality of slits located to provide at least one conformable strip for supporting one of the conductor traces. In one embodiment of the flex cable, portions of the slits are skewed with respect to a lengthwise direction of the cable. The slit flex can reduce forces on the cable and mating hardware and reduce torsional force for dynamic or static applications. Jumper tabs can be used to interconnect ground planes at the slits. A portion of the conformable strip may be twisted such that the supported conductor trace faces away from a normal to the first surface, e.g., that portion of the strip can be twisted approximately 180° to face the same direction as the second surface. The strip can have another conductor trace formed on the second surface of the substrate which is exposed at twisted portion toward the first surface. Contacts can be formed on the supported conductor trace at the twisted portion to create connections. The strip further can have a second portion which is also twisted such that the supported conductor trace at the second portion also faces away from the normal to the first surface, providing multiple contact points along the conductor trace facing the same direction as the second surface. Slitting of the trace strips in this manner allows a single flex cable to be easily adapted to different connector configurations. Twisting allows interconnection through the substrate without laser ablation or etch operations.
The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.
REFERENCES:
patent: 3818122 (1974-06-01), Luetzow
patent: 3836415 (1974-09-01), Hilderbrandt
patent: 4065199 (1977-12-01), Andre et al.
patent: 4251683 (1981-02-01), Oughton, Jr. et al.
patent: 4871315 (1989-10-01), Noschese
patent: 4954100 (1990-09-01), McCleerey
patent: 5163835 (1992-11-01), Morlion et al.
patent: 5197902 (1993-03-01), Cesar
patent: 5675888 (1997-10-01), Owen et al.
paten
Dahlen Paul E.
Dangler John R.
Kidd Thomas D.
Swain Miles F.
Felsman Bradley Vaden Gunter & Dillon, LLP
International Business Machines - Corporation
Luebke Renee
LandOfFree
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