Dynamic magnetic information storage or retrieval – Head mounting – Disk record
Reexamination Certificate
1999-03-31
2002-07-23
Ometz, David L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Head mounting
Disk record
C360S261100
Reexamination Certificate
active
06424499
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to flex circuits for connecting magnetic heads to read and write circuits of a magnetic recording device. More particularly, the present invention relates to a flexible trace interconnect array for a multi-channel tape head which manifests reduced inter-channel cross talk as well as controlled electrical impedance characteristics.
BACKGROUND OF THE INVENTION
Magnetic tape drives are typically employed to provide data backup and archival storage for user data records and programs. For digital data storage applications, tape drives typically employ either rotating heads, or non-rotating heads. One form of non-rotating head is the streaming tape drive. In a streaming tape drive multiple blocks of user data are typically written to tape in a single streaming operation, rather than in a series of start-stop operations of the tape transport. In the streaming tape drive, a magnetic tape head includes at least one read/write element. The head is typically positioned laterally relative to the tape path by a lead screw, which is controllably rotated by e.g. a stepper motor, or an equivalent arrangement. In this manner a single transducer element, or several spaced-apart elements, may write to, and read from, a multiplicity of linear tracks defined along the magnetic recording tape.
In order to permit the head to be moved laterally across the tape in order to confront the multiple parallel tape tracks, a flexible head interconnect arrangement is needed to connect the read/write elements of the head to electronic circuitry conventionally mounted on one or more printed circuit boards affixed to the tape drive base or housing. In the past, flexible wires, twisted together into pairs and gathered into a cable, have been employed as tape head interconnects.
Digital linear magnetic tape drives are an improved type of linear streaming magnetic tape drives. One well established digital linear magnetic tape drive is provided by Quantum Corporation as the DLT-7000 drive. This particular tape drive uses a single reel tape cartridge that supplies a stream of half-inch-wide tape via a leader and buckling mechanism. The Quantum DLT7000 tape drive has a four-channel head, with eight write elements and four read elements. A first set of four write elements are placed on one side of the four read elements, and a second set of four write elements are placed on an opposite side of the first set. This particular arrangement enables four data tracks to be written and then read-checked during a single forward tape streaming operation, and a second four data tracks to be written and read-checked during a single reverse tape streaming operation. Azimuth recording is employed to reduce cross talk between adjacent tape tracks. Therefore, the head is not only displaced laterally relative to the tape path, it is also rotated to a forward azimuth angle for forward direction, and rotated to a reverse azimuth angle for reverse direction data recording. Backward compatibility is achieved by orienting the head at a right angle to the tape path such that two non-azimuthal tracks may be simultaneously written and/or read during each tape streaming operation.
A flex circuit supporting the eight write elements and the four read elements of the Quantum DLT7000 tape drive product is described in commonly assigned U.S. Pat. No. 5,862,014 to Nute, entitled: “Multi-Channel Magnetic Tape Head Module Including Flex Circuit”, the disclosure thereof being incorporated herein by reference. The described flex circuit permitted the tape head freely to be laterally displaced and also to be rotated to the variously available azimuthal and linear tape confronting positions. In the arrangement described in the '014 patent, approximately 128 linear data tracks were provided on the half-inch recording tape.
Data rates and track densities are increasing. One way to increase data rate of a magnetic recording system is to increase the write frequency. Another way to increase data rate is to increase the number of parallel write and read elements of the head and data channels of the tape drive so that more tracks are simultaneously written during each tape streaming operation. A third way to increase data rates is to employ partial response, maximum likelihood signaling techniques of the type known in magnetic disk drives.
One way to increase track density is to reduce linear track width and spacing by aligning the write elements/read elements closer together. By employing thin film inductive write elements and magneto-resistive read elements, it is practical to increase the number of data tracks of a one-half inch magnetic recording tape from e.g., 128 tracks to e.g., 1000 or more tracks. Since the head carrying the write and read elements must still be displaced laterally relative to the tape path, a flexible interconnect arrangement is needed in order to connect the write and read elements of the movable head to write and read electronics affixed to the printed circuit board of the drive electronics.
A flex trace interconnect array is preferred, because it affords the opportunity to control the electrical impedance characteristics of the traces, as taught for example by commonly assigned U.S. Pat. No. 5,737,152 to Balakrishnan, entitled: “Suspension with Multi-Layered Integrated Conductor Trace Array for Optimized Electrical Parameters”, the disclosure thereof being incorporated herein by reference. Commonly assigned U.S. Pat. No. 5,754,369 to Balakrishnan, entitled: “Head Suspension with Self-Shielding Integrated Conductor Trace Array”, shows an arrangement wherein a read conductor pair is interleaved between two conductors of a write conductor pair in a disk drive flexible trace interconnect. (In disk drive operations, simultaneous writing and reading operations are not usually present, and thus the write traces offer a measure of shielding to the read traces during disk drive data reading operations). The disclosure of the '369 patent is also incorporated by reference herein.
Conventionally, the trace conductors connecting the preamplifiers to the read elements of the tape head are interleaved with the conductors connecting the write drivers to the write elements. Because of space restrictions, and the desire to reduce the interconnect mass, the trace conductors have to be placed close to each other. While it is desirable from an electrical viewpoint to space the conductors of any single channel as close to each other as possible, it is equally desirable to increase the spacing between adjacent conductors of separate channels.
FIG.
1
and
FIG. 3A
show a conventional layout of flex conductors on a flexible trace interconnect array
10
which connects two inductive write elements
12
and
14
and two magneto-resistive read elements
13
and
15
of a two-channel tape head
16
to a two-channel preamplifier/write driver circuit
18
of the tape drive. In this example one tape channel (track) is defined by write element
12
and read element
13
, and another tape channel (track) is defined by write element
14
and read element
15
. Further, in the
FIG. 1
simplified example a conductor pair
20
A-
20
B of flex interconnect
10
connecting read transducer
15
to its preamplifier in circuit
18
is interleaved between a conductor pair
22
A-
22
B connecting write transducer
12
to its write driver in circuit
18
and a conductor pair
24
A-
24
B connecting write transducer
14
to its write driver in circuit
18
.
Flexible trace interconnects are presently available having trace widths as narrow as 75 &mgr;m (approximately 3 mils). Thus, in the
FIG. 1
multi-channel flex interconnect
10
a flex trace interconnect conductor geometry would have a cross-sectional layout of traces formed on a flexible substrate
11
as shown in FIG.
3
A: - - - 75 &mgr;m read trace
26
A - - - 75 &mgr;m inter-conductor space - - - 75 &mgr;m read trace
26
B - - - 75 &mgr;m inter-pair space - - - 75 &mgr;m write trace
22
A - - - 75 &mgr;m inter-conductor space - - - 75 &mgr;m write trace
22
Balakrishnan Arun
Gunther Doug
Hertrich Gregory P.
Sheppard Mark
Law Office of Steven Roeder
Ometz David L.
Quantum Corporation
Roeder Steven G.
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