Trace interconnect array having increased bandwidth by...

Details Trace interconnect array having increased bandwidth by... Trace interconnect array having increased bandwidth by...

2002-11-21

2004-05-04

Chen, Tianjie (Department: 2652)

Dynamic magnetic information storage or retrieval

Head mounting

Disk record

Reexamination Certificate

active

06731467

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 trace interconnect array manifesting controlled inductance, capacitance and high frequency resistance in order to provide increased bandwidth and a process for making the array have the desired electrical characteristics by selective etching of conductive traces and adjacent dielectric materials.
BACKGROUND OF THE INVENTION
Contemporary mass storage devices such as magnetic hard disk drives present a data transducer in a confronting relationship with a relatively moving data storage medium. Magnetic flux transitions are written to, or read from the medium. Disk drives typically include a rotating rigid storage disk having at least one major surface carrying a deposition or coating of magnetic material. A head positioner, commonly referred to as an actuator, positions the data transducer at selected radial storage track locations of the disk. In-line rotary voice coil actuators are presently preferred because of their simplicity and high performance characteristics, due in substantial part to intrinsic mechanical rigidity and a characteristic of being mass balanced about an axis of rotation relative to a drive base. A closed-loop servo system within the disk drive controls a voice coil motor of the actuator in order to position the transducer head at each desired disk radial location during track following operations and to move the transducer among radial locations during track seeking operations.
The read/write transducer head of a magnetic hard disk drive is typically a dual element design and is selectively deposited by thin film deposition upon a ceramic slider having a portion defining an air bearing surface for supporting the transducer at a very small distance away from the disk surface upon an air bearing present during disk rotation. One element of the transducer is typically a thin-film inductive write element. The other element of the transducer is typically a magnetoresistive (MR) sensor. A flux transition field of a recorded data pattern proximate to the MR sensor causes a miniscule change in electrical resistance of the sensor. Change of resistance in the presence of a constant current flowing through the sensor results in a minute voltage change, on the order of 3-5 millivolts, and this voltage change, representing a data pattern, is amplified by a preamplifier. Since the sensed signal (read signal) is so small, care must be taken to reduce extraneous noise pickup along a circuit between the read sensor and the preamplifier.
A head suspension extending from the actuator includes a load beam and a gimbal or flexure. The load beam includes a spring portion which applies a desired preload force to the slider which biases the slider toward the disk surface. This preload or bias force is overcome by airflow resulting from disk rotation and the formation of the desired air bearing between the slider and the adjacent disk surface. The gimbal enables the slider to follow the contour of the disk in order to maintain constant a very small spacing, on the order of one half to several microinches, between the transducer and the storage surface.
In the past, very small diameter twisted solid copper wires have typically been used to connect head elements at the slider to other signal carrying and signal processing elements of the disk drive located on or adjacent to the actuator structure. The two-conductor twisted pair service loop is inherently self-shielding from external noise sources such as electromagnetic interference (EMI) and radio frequency interference (RFI) by virtue of the fact that the conductors are twisted around each other. Coaxial transmission line cables are also inherently self-shielding, but the center conductor is electrically unbalanced with respect to the outer cylindrical shield conductor. Two-conductor balanced coaxial transmission lines avoid this drawback but are typically too bulky and cumbersome to be used to connect to the write/read elements of the very small sliders in present use in hard disk drives. One drawback of wires and cables is that they can apply an unwanted bias force to the slider supporting structure. Another drawback of discrete wires is that their electrical characteristics are not precisely controllable.
To reduce unwanted drawbacks of discrete wire conductors and cables, head suspensions having integrated trace arrays have recently been adopted in disk drive designs. These designs have typically included a stainless steel flexure upon which conductor structures have been formed by selective deposition/removal of dielectric material and conductor material. As formed the trace conductors of a service loop extend longitudinally from the transducer element to an interconnect or a preamplifier/write driver circuit. One example of a preferred method for manufacturing a magnetic head suspension with integrated trace array wiring is described in U.S. Pat. No. 5,666,717 to Matsumoto et al., entitled: “Method for Manufacturing a Magnetic Head Suspension”, the disclosure thereof being incorporated herein by reference.
Because the conductive traces of a service loop are typically formed in a side-by-side arrangement on a dielectric layer or substrate of the trace array, the traces essentially form an open-wire or micro-strip transmission line. Micro-strip line technology teaches that the loop and inter-conductor capacitance may be changed by changing the dimensions of and/or spacing between micro strips forming a transmission line. In the case of integrated trace array wiring designs for use within, or as part of, head suspension assemblies of hard disk drives, the dimensions of conductors and dielectric substrates may be governed more by mechanical constraints rather than by desired electrical characteristics.
Disk drive technology is continually seeking ways to increase storage capacity and performance of hard disk drives. One way to increase performance, as noted above, is to make write/read elements very small, and to reduce the size of sliders and head suspension assemblies, thereby reducing overall actuator mass and reducing average seeking operation time. One way to increase capacity is to make track widths narrower, so that more tracks may be defined in a unit storage area. Yet another way to increase capacity is to increase linear data density as by increasing data transfer rates, for example. With increased data transfer rates, care must be taken to ensure that the interconnect structure and electrical service loop between head and preamplifier has sufficient bandwidth margin to support the higher data transfer rate. One parameter which limits the bandwidth of a head interconnect service loop is impedance, which in turn depends upon inductance and capacitance characteristics of the interconnect structure.
One known way to reduce losses and noise pickup caused by the interconnect is to make the interconnect as short in length as possible. This approach requires locating some or all of the preamplifier electronics as close to the read element of the head as possible. This usually means mounting and connecting an integrated circuit chip directly onto the head suspension, a so-called “chip-on-suspension” or COS approach. The COS approach has its own drawbacks, such as chip heat dissipation and electrical supply requirements and characteristics, issues which have not yet been fully developed and resolved.
FIG. 1
shows a present-day trace interconnect array
10
. This exemplary trace interconnect array
10
typically consists of two trace conductors for each read or write channel of the head. The
FIG. 1
enlarged cross-sectional view shows that the array
10
essentially comprises two copper conductor traces
12
and
14
separated from a stainless-steel substrate
16
by a dielectric layer
18
of polyimide, epoxy resin, acrylic resin, or other suitable polymeric dielectric material. The substrate
16
is typically of thi

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