Head suspension assemblies (HSA) in rotatable data storage devices are spring structures that perform the difficult task of accurately holding and positioning a floating head assembly nanometers away from the rapidly spinning and seemingly smooth but microscopically irregular surface of a rotatable data storage device. The HSA can be part of a magnetic hard disk drive, which is the most common data storage medium today, or other type of drives such as an optical or magneto-optic medium in an optical disk drive system. Examples of such HSA's are disclosed in U.S. Pat. Nos. 5,491,597 and 5,645,735, portions of which are included herein, which patents are also incorporated herein in their entirety by their reference.
A HSA comprises different elements, the most common being a suspension beam assembly and a head assembly. A suspension assembly, which includes a spring element, usually includes a load beam which is attached to a gimbal or the gimbal is a unitary part of the load beam, with each composed of a carefully balanced combination of rigid regions and flex spring regions. A typical head assembly usually includes a "head", comprising of a highly sensitive read/write transducer, that is incorporated into an air bearing slider. Thus, the slider comprises a self-acting hydrodynamic air bearing and an electromagnetic transducer for recording and retrieving information on a rotating magnetic disk. The slider is attached to the gimbal and the gimbal is compliant in the slider's pitch and roll axes in order that the slider follows the topology of the disk surface, but is rigid in the yaw and in-plane axes for maintaining precise slider positioning. The load beam is attached to or is made as an integral part of the gimbal, and the load beam is attached to or includes a mounting arm which attaches the entire HSA to an actuator of a disk drive actuator drive assembly. The gimbal also usually includes a portion for the support of electrical traces connected to the transducer and extending along the length of the load beam to its mounted end.
In a magnetic disk drive, the slider supports a read and write transducer. A write transducer transforms electrical pulses to small magnetic fields which it then "writes" on a magnetic disk. A read transducer decodes these magnetic fields back into electrical pulses. The order of the magnetic fields and their subsequent orientation, aligned along the circumference of the disk in a diametrical configuration, defines a bit code that the transducer detects as the head floats on a cushion of air over the magnetic disk. As indicated, the head assembly includes electrical terminals, via traces, to send and receive these electrical pulses.
A HSA generally attaches at its proximal end to a rigid arm manipulated by a linear or rotary motion actuator designed to position the head at any radial location above the disk. The spinning disk coupled with the actuator movement allows the head to gain access to multiple tracks across the disk surface, each track capable of containing large amounts of densely stored data.
Positioned at the distal end of the suspension assembly, a gimbal holds the head assembly level and at a constant distance over the contours of the disk. This gimbal is the most critical of the spring regions in a HSA. The closer the head assembly can fly to the surface of a magnetic disk, the more densely can information be stored (the strength of a magnetic field is proportional to the square of the distance, thus the closer the head flies, the smaller the magnetic "spot" of information). Today's disk drives strive to reach flying clearances close to 100 nanometers=0.1 micrometers (a human hair is about 100 micrometers thick). Greater data densities allow for greater storage and smaller size. But the head assembly must not touch the disk ("crash"), as the impact with the rapidly spinning disk (rotating at about 3600 rpm or faster) could destroy both the head and the surface of the disk, along with the data stored on it.
In order to achieve this delicate and precise positioning, a suspension assembly, and specially the gimbal flexure, must carefully balance the load applied to the head assembly against the upward lift of the air stream on the slider. Since at this microscopic level, the seemingly smooth surface of the disk is full of peaks and valleys, the gimbal spring must be very responsive in order to maintain a level flying height. To avoid delays and errors, it must also resist torsion and momentum forces, and maintain the head parallel to the surface even after rapid repositioning movements. The best suspension assemblies are low in mass, to reduce momentum on the floating head, and very flexible along the Z-axis, perpendicular to the medium surface, to quickly adjust to surface undulations. They also are balanced carefully to reduce static roll and pitch to acceptable levels and to avoid applying an initial twist to the head.
A conventional gimbal flexure, sometimes referred to as a Watrous gimballing flexure design, is formed from a single sheet of material, such as stainless steel, and includes a pair of outer flexible arms about a central aperture, with a cross piece extending across and connecting the arms at a distal end of the flexure. A flexure tongue is joined to the cross piece and extends from the cross piece into the aperture. A free end of the tongue is centrally located between the flexible arms. The slider is mounted to the free end of the flexure tongue. The slider must be mounted to the flexure tongue so that the head assembly is in a predetermined (e.g., planar and parallel) relationship to the disk surface to assure accuracy and overall planarity. As the head writes and reads to and from the disk, it receives and sends electrical pulses of encoded information. Complex head assemblies may require four or more different input and output terminals. The electrical signals are relayed to appropriate amplifying and processing circuitry. Signal transmission requires conductors between the dynamic "flying" slider and the static circuitry of the data channels. However, while conductors can be routed fairly easily along the rigid actuator arm, providing the final interconnections through the suspension assembly, and specially those over the gimbal to the head, it is often extremely troublesome with current interconnect schemes, particularly as head structures become smaller in size and, correspondingly, becomes more fragile and acceptable to mechanical damage or heat damage. Thus, the interconnection of head components becomes more critical due to higher potential to damage from mechanical connection stresses or thermal stresses, such as is occurred during head component (load beam/gimbal/slider) attachment.
Specially designed HSA interconnect assemblies are required in order to relay electrical signals accurately while not disturbing the precise balance of the HSA components. The term interconnect assembly refers to the entire interconnect system in a HSA, including conductors, insulators, and other features. In order to assure data precision, interconnect assemblies must transmit the electrical signals free from interference or signal loss due to high inductance, high capacitance, or high resistance. Optimal interconnect assemblies must be attached securely in order to reduce movement and vibration which cause varying electrical characteristics and affect mechanical performance. They must have low resistance and be well insulated from electrical ground.
Also, as technology advances, an interconnect system also must be capable of handling a plurality of signals. A basic interconnect assembly for a transducer having a single read/write inductive element calls for two conductors. More complex transducer designs may incorporate a separate magneto-resistive read element and an inductive write element, thus requiring a minimum of three conductors if the elements are tied together or a minimum of four conductors if the elements are completely separate. More advanced systems require even more conductors.
Thus, HSA-interconnect assemblies must be planned around competing and limiting design considerations. The interaction of all the elements of an HSA forms a carefully balanced system. An ideal interconnect assembly must satisfy strict mechanical and manufacturing requirements.
The general technology trend in disk drive data storage devices is continual shrinking of the physical size of the HSA while providing increased data storage capacity. The down-sizing of the HSA has required smaller components, especially the principal components such as disks, sliders and load beams or flexures. Additionally, disk drive designers seek to add capacity to their designs by incorporating as many disks as possible within defined package dimensions. As the number of disks in the unit increases, the spacing between the disks decreases, thus further driving the need for smaller sliders and flexures. Smaller sliders and suspension beam assembly means more critical assembly requirements such as, for example, less application of applied heat in the case of assembled head components secured by epoxy adhesive that is cured at a high temperature. The slider bonding surface, in general, covers a large area over the center of the slider. The slider is typically attached to the load beam or flexure with an adhesive, such as epoxy, and, in order to reduce the cure time of the adhesive, the assembly is usually heated in an oven (e.g. oven curing) or by exposing epoxy in the slider to UV radiation. Depending upon the application, an electrically conductive or non-conductive adhesive or the like may be used. The time of applied heat to achieve curing is critical and should be sufficiently small so as not to damage the slider transducers or associated conductors but sufficiently large to permit proper completion of the curing step.
Another industry trend is to provide the user of disk drives with high data storage capacity at low cost. This requires developing improved data recording technology and finding lower cost ways of manufacturing the components of the disk drive including increase efficiency in the manufacturing steps.
A principal object of this invention is to provide an improved method and apparatus for the attachment of the slider and the distal end of the suspension beam/gimbal assembly that is time-efficiently accomplished without damage to the assembled components.
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