Dynamic magnetic information storage or retrieval – Head mounting – Disk record
Reexamination Certificate
2000-05-09
2002-11-12
Cao, Allen (Department: 2652)
Dynamic magnetic information storage or retrieval
Head mounting
Disk record
Reexamination Certificate
active
06480359
ABSTRACT:
FIELD OF THE INVENTION
The invention disclosed herein relates generally to hard disk drive suspensions. More specifically, the invention relates to hard disk drive suspension assemblies and circuit assemblies with an integral flexible circuit and integral support member.
BACKGROUND OF THE INVENTION
Suspension assemblies in hard disk drives include a head gimbal assembly (HGA). The HGA includes a gimbal assembly, a head assembly, and an interconnect assembly. The head assembly includes a highly sensitive read/write transducer, commonly referred to as a head, attached to an air bearing slider. The head assembly also includes electrical terminals configured for interconnection to the interconnect assembly for receiving and relaying data signals. The head assembly facilitates reading and writing of information on a surface of a rotating magnetic disk. The interconnect assembly includes a plurality of transmission elements, such as wires or traces, for transmitting data to and from the head assembly. The suspension assembly positions the head assembly at a generally constant distance away from the moving surface of the rotating disk. The suspension assembly permits the head assembly to “fly” at a height above the surface of the disk, including surface irregularities.
Most conventional suspension assemblies, also referred to herein as a support member, include a load beam and a gimbal portion. The load beam is a resilient spring plate designed to provide lateral stiffness. The load beam is calibrated to apply a force on the head assembly that counteracts a lift force on the head that is provided by the air stream generated by the rotating disk. Accordingly, the head assembly flies above the surface of the disk at a height established by the equilibrium of the load beam force and the lift force.
The gimbal portion is positioned adjacent to an end of the load beam and has the head assembly attached thereto. The gimbal portion permits roll and pitch deflections of the head assembly in response to flying over surface imperfections and warping of the rotating disk. By permitting these deflections, the gimbal portion aids in maintaining the proper orientation and distance of the head assembly relative to the rotating disk, even when the load beam exhibits a slight amount of flexing and twisting.
The suspension assembly can be attached at its proximal end to a rigid arm or directly to a linear or rotary motion actuator. The actuator rapidly moves and then abruptly stops the HGA over any position on a radius of the disk. The radial HGA movement and the rotation of the disk allow the head to quickly reach every location above the disk. However, the rapid stop and go movement causes very high stresses on the HGA.
An ideal HGA comprises components low in mass. Excessive inertial momentum caused by excessive mass can cause overshoot errors. Overshoot errors occur when momentum carries the whole HGA past the intended stopping point during positioning movement. Low-in-mass HGA's are easier to move, resulting in power savings in multiple platter disk drives. Furthermore, lighter weight HGA's permit the head to be flown closer to the surface of the disk. The closer the head assembly can fly to the surface of the disk, the more densely information can be stored on the disk. Accordingly, a lightweight HGA is desirable in high performance disk drives.
It is known that the strength of a magnetic field in a disk drive varies proportionally to the square of the fly height of the head. Manufacturers of disk drives strive to reach flying clearances less than 100 nanometers, which is 0.1 micrometers. For comparison, a human hair is about 100 micrometers thick. However, the head assembly must not touch the disk, since the impact with the spinning disk, which rotates at about 10,000 rpm or faster, can damage the head and the surface of the disk.
Amplifying and control circuits process, send and receive the data signals to and from the head assembly. Signal transmission requires conductors to extend between the head assembly and the related circuitry of the disk drive. Traditional head assemblies use a read-write circuit loop with two conductors, usually copper wires encapsulated in plastic sheeting. Newer types of magnetic read-write heads, commonly referred to as magneto-resistance head assemblies, require four or more independent conductors.
The increasing need for more wires, lower disk stack height and less stiffness and mass of the suspension assembly has forced the manufacturers to consider different suspension design approaches. In one design approach, a suspension assembly has signal traces that are etched from a stainless steel based material and an insulating layer is subsequently formed over the signal traces. The stainless steel base material is also etched to form the load beam portion and head gimbal portion of the suspension. A key limitation of this type of construction is excessive yield rates due to the integrated fabrication process and poor conductivity of stainless steel. In another design approach, a conventional flex circuit is attached to a separately fabricated suspension assembly using an adhesive. A key drawback with this type of construction is the cost associated with the precision required for assembling the flexible circuit to the suspension assembly.
Designers and manufacturers of HGA's face competing and limiting design considerations. During operation, the suspension assembly should be free of unpredictable loads and biases which alter the exact positioning of the head assembly. The suspension assembly should respond instantaneously to variations in the surface topology of a disk. Alterations to the flying height of the head can significantly affect data density and accuracy and even destroy data stored on the disk if the head collides with the surface of the disk.
The rigidity and stiffness of a load beam increase in relation to the cross-sectional thickness by the third power. To respond to air stream changes and to hold the flying head at the appropriate orientation, suspension assemblies are very thin and flexible, especially around a sensitive spring portion of the load beam. Interconnect assembly conductors have a large effect on the performance of the suspension assembly. Conductor stiffness alone greatly affects the rigidity of the spring regions and flight performance.
A standard wire conductor attached atop the suspension can more than double the stiffness of a load beam and significantly limit the ability of the load beam to adjust to variations in the surface of the disk, vibrations, and movement. The effect of the conductors on a gimbal region, the thinnest and most delicate spring in the suspension assembly, is even more pronounced. Furthermore, conductors placed over spring regions of the load beam and gimbal portion of the suspension assembly must not plastically deform when the spring regions flex. Plastic deformation prevents the return of the load beam or gimbal portion to its normal position and applies a biased load on the suspension assembly.
In HGA's that use conventional wire interconnect assemblies, two to five lengths of wire to the head assembly are manually connected to the head. Fixtures are used to manage the wires while they are being bonded to the head assembly. The lengths of wire are manually shaped using tweezers and tooling assistance to form a service loop between the head assembly and the suspension assembly and to position the wire along a predetermined wire path on the suspension assembly. The wires are tacked to the suspension using an adhesive or wire capture features formed into the suspension.
Special care is taken to avoid pulling the service loop too tight or leaving it too loose. A tight service loop places an unwanted torque on the head assembly causing errors associated with the fly height. A loose service loop allows the wire to sag down and scrape the adjacent spinning disk. Both conditions are catastrophic to disk drive performance.
Throughout the process of handling the head assembly, interconnect assem
Dunn Christopher G.
Kreutter Nathan P.
3M Innovative Properties Company
Cao Allen
Fonseca Darla P.
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