Suspension tail design for a head gimbal assembly of a hard disk drive

A method of assembling a head stack assembly of a magnetic storage drive is provided. The method includes attaching a flexible printed circuit (FPC) with a suspension tail of a head gimbal assembly, wherein the suspension tail includes a plurality of discrete segments positioned within a bonding area and other portions of a structural layer outside of the bonding area, and pressing tail bond pads of the suspension tail against corresponding ones of FPC bond pads of the FPC by bringing a single flat surface of a thermode in contact with each of the discrete segments.

FIELD

Aspects of the present invention are directed toward a flexure of a head-gimbal assembly of a hard disk drive and, more particularly to a design of a flexure tail that facilitates bonding between the flexure and a flexible printed circuit.

BACKGROUND

Information storage devices are used to retrieve and/or store data in computers and other consumer electronics devices. A magnetic hard disk drive is an example of an information storage device that includes one or more heads that can both read and write from one or more rotating storage media. In a magnetic hard disk drive device, each head is a sub-component of a head-gimbal assembly (HGA) that typically includes a laminated flexure to carry electrical signals to and from the head. The HGA, in turn, is a sub-component of a head-stack assembly (HSA) that typically includes one or more HGAs, an actuator, and a flexible printed circuit (FPC). The one or more HGAs are attached to various arms of the actuator.

Each of the laminated flexures typically includes electrically conductive traces (e.g., copper traces) that are isolated from a stainless steel structural layer by a dielectric layer such as a polyimide layer, and the conductive traces transfer signals between the head and the FPC on the actuator body. Each HGA flexure includes a flexure tail that is attached to the FPC adjacent the actuator body. That is, the conductive traces extend from adjacent the head and continue along the flexure to electrical connection points (or pads) located at the tail portion of the flexure. The FPC includes conductive electrical terminals (or bond pads) that correspond to the electrical connection points of the flexure tail.

To facilitate electrical connection of the conductive traces of the flexure tails to the conductive electrical terminals of the FPC during an HSA manufacturing process, the flexure tails are first properly positioned relative to the FPC so that the connection points of the flexure tails are aligned with the conductive electrical terminals of the FPC. Then, the flexure tails are held or constrained against the conductive electrical terminals of the FPC while the electrical connections are made (e.g., by ultrasonic bonding, solder jet bonding, solder bump reflow, or anisotropic conductive film bonding).

An anisotropic conductive film (ACF) is an adhesive doped with conductive beads or cylindrical particles of uniform or similar diameter. As the doped adhesive is compressed and cured, it is squeezed between the surfaces to be bonded with sufficient uniform pressure that a single layer of the conductive beads makes contact with both surfaces to be bonded. In this way, the thickness of the adhesive layer between the bonded surfaces becomes approximately equal to the size of the conductive beads. The cured adhesive film may conduct electricity via the contacting beads in a direction normal to the bonded surfaces (though may not necessarily conduct electricity parallel to the bonded surfaces, since the beads may not touch each other laterally—though axially each bead is forced to contact both of the surfaces to be bonded—hence the term “anisotropic”).

In a high-volume manufacturing environment like the very competitive information storage device industry, there is a practical need for a fast and cost-effective method of bonding many bond pads simultaneously. In particular, there is a need in the art for an improved flexure design that may facilitate the bonding of many bond pads simultaneously or concurrently.

SUMMARY

Aspects of embodiments according to the present invention are directed toward an improved flexure of a head gimbal assembly, a disk drive including the same, and methods for manufacturing the same. In one embodiment, a suspension assembly of a head gimbal assembly for a disk drive includes a dielectric layer, a conductive layer, and a structural layer. The dielectric layer has a first side and a second side opposite the first side. The conductive layer is on the first side of the dielectric layer, and includes a plurality of bond pads at a tail portion of the suspension assembly. The structural layer is on the second side of the dielectric layer, and the structural layer consists of a plurality of discrete segments positioned within a bonding area and other portions positioned outside of the bonding area. The plurality of discrete segments respectively correspond in position to the bond pads. The bonding area extends beyond an area including the plurality of discrete segments by a preselected amount, and the preselected amount is selected such that the plurality of discrete segments are configured to receive a single flat surface without contacting the other portions of the structural layer.

In some embodiments, the suspension assembly may further include a cover layer on the conductive layer, and the cover layer may have a plurality of openings at locations corresponding to the bond pads. The dielectric layer may have a plurality of openings respectively corresponding to spaces adjacent to the bond pads. The dielectric layer may include polyimide. The conductive layer may include a plurality of electrically conductive traces connected between the bond pads and a head of the suspension assembly. The structural layer may include a stainless steel layer.

In another embodiment, a method of assembling a head stack assembly of a disk drive including a flexible printed circuit (FPC) and a head gimbal assembly is provided. The method includes applying an adhesive material on a component selected from the group consisting of a plurality of tail bond pads of a suspension tail of the head gimbal assembly and a plurality of FPC bond pads of the FPC, and attaching the FPC with the suspension tail, wherein the suspension tail includes a dielectric layer, the plurality of tail bond pads on a first side of the dielectric layer, and a structural layer on a second side of the dielectric layer, the structural layer consisting of a plurality of discrete segments positioned within a bonding area and other portions positioned outside of the bonding area, the plurality of discrete segments respectively corresponding in position to the tail bond pads. The method further includes aligning the plurality of tail bond pads with the plurality of FPC bond pads on the FPC, providing a flat surface against the FPC, and pressing the tail bond pads against corresponding ones of the FPC bond pads by bringing a single flat surface of a thermode in contact with each of the discrete segments and without contacting the other portions of the structural layer.

The FPC may include a cover layer on a side thereof facing toward the suspension tail, and the cover layer may have an opening corresponding to the bonding area. The cover layer of the FPC and the single flat surface of the thermode may not overlap with each other. The adhesive material may include an anisotropic conductive film (ACF). The dielectric layer may have a plurality of openings at respective locations adjacent to the tail bond pads.

The pressing the tail bond pads against corresponding ones of the FPC bond pads may include transferring heat from the thermode through the discrete segments in the bonding area to the tail bond pads to raise the temperature of the ACF to a preselected temperature.

The method may further include removing an elongated structural member from the suspension tail, the elongated structural member having a first end and a second end respectively connected to the other portions of the structural layer located outside of the bonding area of the suspension tail.

In another embodiment, a disk drive includes a disk drive base, a disk rotatably mounted to the disk drive base, an actuator rotatably mounted to the disk drive base, the actuator including a flexible printed circuit (FPC) having a plurality of FPC bond pads, and at least one head gimbal assembly as described above operatively attached to the actuator.

DETAILED DESCRIPTION

FIG. 1is an exploded perspective view of a disk drive according to an embodiment of the present invention. The disk drive includes a head disk assembly (HDA)10and a printed circuit board assembly (PCBA)14. The HDA10includes a base16and cover18that together house at least one annular magnetic disk20. Each disk20contains a number of magnetic tracks for storing data. The tracks are disposed upon opposing first and second disk surfaces of the disk20that extend between an inner disk edge22(corresponding to the inner diameter) and an outer disk edge24(corresponding to the outer diameter) of the disk20. The HDA10further includes a spindle motor26for rotating the disk20about a disk axis of rotation28. The spindle motor26includes a spindle motor hub that is rotatably attached to the base16of the HDA10. The disks20may be stacked and separated with one or more annular disk spacers12that are disposed about the hub, all held fixed to the hub by a disk clamp11.

The HDA10further includes a head stack assembly (HSA)30rotatably attached to the base16of the HDA10. The HSA30includes an actuator comprising an actuator body32and one or more actuator arms36extending from the actuator body32. The actuator body32includes a bore44and a pivot bearing cartridge engaged within the bore for facilitating the HSA30to rotate relative to the HDA10about an actuator pivot axis46. One or two head gimbal assemblies (HGA)38are attached to a distal end of each actuator arm36. Each HGA includes a head (e.g., head40) for reading and writing data from and to the disk20, and a load beam42to compliantly preload the head against the disk20. The HSA30further includes a coil support48that extends from one side of the HSA30that is opposite the head40. The coil support48is configured to support a coil50through which a changing electrical current is passed. The coil50interacts with one or more magnets54that are attached to the base16via a yoke structure56,58to form a voice coil motor for controllably rotating the HSA30. The HDA10also includes a latch52rotatably mounted on the base16to prevent undesired rotations of the HSA30.

The PCBA14includes a servo control system for generating servo control signals to control the current through the coil50and thereby position the HSA30relative to tracks disposed upon surfaces of the disks20. The HSA30is electrically connected to the PCBA14via a flexible printed circuit (FPC)60, which includes a flex cable62and a flex cable support bracket64. The flex cable62supplies current to the coil50and carries signals between the HSA30and the PCBA14.

In the magnetic hard disk drive ofFIG. 1, the head40includes a body called a “slider” that carries a magnetic transducer on its trailing end (not visible inFIG. 1). The magnetic transducer may include an inductive write element and a magnetoresistive read element. During operation the transducer is separated from the magnetic disk by a very thin hydrodynamic air bearing. As the motor26rotates the magnetic disk20, the hydrodynamic air bearing is formed between an air bearing surface of the slider of head40and a surface of the magnetic disk20. The thickness of the air bearing at the location of the transducer is commonly referred to as “flying height.”

FIG. 2is a perspective view of a head stack assembly (HSA)200according to an embodiment of the present invention. The HSA200includes an actuator body232and a number of actuator arms226,228,230,236,238extending from the actuator body232. The actuator body232includes a pivot bearing cartridge220disposed in the actuator bore, and a coil support234that supports a coil235and extends from the actuator body232in a direction that is generally opposite the actuator arms226,228,230,236,238. The HSA200also includes a number of head gimbal assemblies (HGA)240,242,244,246,248,250,252,254, attached to the actuator arms226,228,230,236,238. For example, such attachment may be made by swaging. Each of the inner actuator arms226,228,230includes two HGAs, while each of the outer actuator arms236,238, includes only one HGA. This is because in a fully populated disk drive the inner arms are positioned between disk surfaces while the outer actuator arms are positioned over (or under) a single disk surface. In a depopulated disk drive, however, any of the actuator arms may have one or zero HGAs, possibly replaced by a dummy mass.

Each HGA includes a head for reading and/or writing to an adjacent disk surface (e.g., HGA254includes head280). The head280is attached to a tongue portion272of a laminated flexure270. The laminated flexure270is part of the HGA254and is attached to a load beam258(another part of the HGA254). The laminated flexure270may include a structural layer (e.g., a stainless steel layer), a dielectric layer (e.g., a polyimide layer), and a conductive layer (e.g., a copper layer) into which traces are patterned. The HSA200also includes a flexible printed circuit (FPC)260adjacent the actuator body232, and the FPC260includes a flex cable262. The FPC260may include a laminate that includes two or more conventional dielectric and conductive layer materials (e.g., one or more polymeric materials, copper, etc). The laminated flexure270includes a terminal region (or flexure tail)300that is electrically connected to connection points (e.g., bond pads) of the FPC260.

Methods of electrical connection of the flexure tails to the FPC260include solder reflow, solder jet bonding (SJB), ultrasonic pad bonding (USPB) and anisotropic conductive film (ACF) bonding. To electrically connect and securely attach the flexure tails to the FPC260, the flexure tails are first aligned with the FPC260, and then pressed against the FPC260(at least temporarily) while electrical connection is established and secure attachment is completed, for example, by ACF bonding.

Embodiments of the present invention relate to a suspension tail of a flexure (i.e., flexure tail) of a HGA including bond pad designs for more effective and reliable ACF bonding, and methods for bonding the flexure tail with a FPC. According to the embodiments, isolated or discrete structural segments, e.g., stainless steel (SST) pads, are located in an ACF bonding area on a support side (e.g., the structural layer) of a dielectric layer, and other structural elements (e.g., SST frame or patch) are located outside of the bonding area. A number of bond pads (e.g., copper pads) are located on a side of the dielectric layer opposite the support side. Each of the discrete structural segments supports a corresponding one of the bond pads in the bonding area. Because the bonding area is clear of structural elements other than the discrete structure segments, a single flat surface of a thermode can be used to apply pressure and heat to all of the discrete structure segments for simultaneous bonding, hence greatly reducing the process complexity. In addition, no cover layer is required in a corresponding bonding area of the FPC, and therefore the distance or gap between the bond pads on the FPC and the bond pads on the flexure tail can be reduced.

FIGS. 3(a)-3(c) illustrate the flexure tail300(hereafter “suspension tail”) in a support layer plan viewFIG. 3(a), a side viewFIG. 3(b), and a signal layer (e.g., the conductive layer) plan viewFIG. 3(c), according to an embodiment of the present invention. Referring to the support layer plan view ofFIG. 3(a), a number of discrete segments302(e.g., stainless steel pads) are positioned on a dielectric layer303(e.g., a polyimide layer) in a bonding area304in which no other structural support element is present. The bonding area304extends beyond an area including only the plurality of discrete segments302by a preselected amount. For example, a support member306is located outside of the bonding area304and is not connected to the discrete segments302.

Referring to the side view ofFIG. 3(b), it can be seen that the discrete segments302are the tallest features in the bonding area304. Therefore, a single flat surface of a thermode or other suitable devices can be used to apply pressure and heat to all of the discrete segments302at the same time to improve the ACF bonding process efficiency and its long term reliability. Referring to the signal layer plan view ofFIG. 3(c), a number of bond pads308are located in the bonding area304on the dielectric layer303. The bond pads308may be copper bond pads plated with gold or made of other electrically conductive materials suitable for ACF bonding. The bond pads308are electrically connected with conductive traces (not visible inFIG. 3but seeFIG. 4)that are covered by a cover layer310to avoid undesirable shorting. The suspension tail shown inFIG. 3is to be attached to a FPC, and the bond pads308are each aligned with a corresponding bond pad on the FPC during an ACF bonding process.

During the ACF bonding process, the single flat surface of the thermode (not shown inFIG. 3) is configured to contact only the discrete segments302(e.g., isolated SST patch) that respectively support the bond pads308on the signal layer side. Pressure and heat applied by the thermode will pass through the discrete segments302, the dielectric layer303, and the bond pads308to the ACF bonding material located between the bond pads308and the bond pads of the FPC. The cover layer310on the suspension tail300has openings corresponding to the bond pads308. Therefore, the gap between the bond pads308and the bond pads of the FPC is reduced to the desired distance, and the adhesive of the ACF bonding material is cured to make a reliable joint between the suspension tail300and the FPC.

FIG. 4is a top view of a suspension tail400and each of four layers of the suspension tail400in more detail according to an embodiment of the present invention. InFIG. 4, the suspension tail400has a cover layer400a, a copper trace layer (e.g., conductive layer)400bcovered by the cover layer400a, a dielectric layer400con which the copper trace layer400bis formed, and a structural support layer400dunder the dielectric layer400c. That is, the various layers of the suspension tail400are arranged in the following order: the cover layer400a, the copper trace layer400b, the dielectric layer400c, and the structural support layer400d. The suspension tail400has a test terminal section400ehaving a number of test points to facilitate testing during manufacturing, and the test terminal section400emay be removed after assembly.FIG. 5is a schematic drawing illustrating the suspension tail400with the test terminal section400eremoved.

Referring toFIGS. 4 and 5, the copper trace layer400bis positioned on a first side of the dielectric layer400c. The copper trace layer400binclude a number of traces for transferring electrical signals. Portions of the traces are widened to form a number of bond pads408at preselected locations. For example, nine bond pads408arranged in three columns are formed by the widened portions of the traces, and each column includes three bond pads408. Here, the bond pads408have a substantially rectangular shape. However, the present invention is not limited thereto, and the bond pads408may have other shapes suitable for ACF bonding. In addition, the bond pads408are typically plated with gold for ACF bonding.

The copper trace layer400bis covered by the cover layer400awhich may be formed of a polyimide (PI) layer. The cover layer400ahas a number of open areas or openings409in a bonding area that expose the bond pads408to be bonded with a flexible printed circuit (FPC) during assembly. In the embodiment ofFIGS. 4 and 5, the cover layer400ahas three open areas409respectively corresponding in position to the three columns of bond pads408of the copper trace layer400b. For the FPC, there may be no cover layer in the bonding area according to one embodiment of the present invention.

The dielectric layer400cis positioned between the copper trace layer400band the structural support layer400d, and may be made of a PI layer. The dielectric layer400chas a number of openings405that are positioned adjacent to and/or between corresponding bond pads408. The structural support layer400dmay be made of stainless steel or other suitable structural materials. A number of discrete segments402(e.g., stainless steel pads) of the structural support layer400dare positioned in a bonding area404to support the bond pads408. Within the bonding area404, no other structural elements are present besides the discrete segments402. That is, the bonding area404extends beyond an area including only the discrete segments402by a preselected amount. Because the discrete segments402each correspond to the bond pads408in position, the openings405of the dielectric layer400care respectively positioned adjacent to and/or between corresponding ones of the discrete segments402. Therefore, the openings405may allow some of the ACF bonding material between the suspension tail400and the FPC to escape through it during ACF bonding.

Referring now toFIG. 5, the test terminal section400e(seeFIG. 4) has been removed, and the structural support layer400dincludes no support elements (e.g., stainless steel frame) in the bonding area404of the suspension tail400except the discrete segments402. That is, the discrete segments402are isolated from other support elements. For example, a first support element406ais not connected to any of the discrete segments402.

Referring back toFIG. 4, the first support element406ais connected to a second support element406bvia a third support element406c(e.g., an external strut). The third support element406cis optional, but the third support element406cmay be included to address a potential suspension tail distortion problem (i.e., flexing of the suspension tail300) during an HGA assembly process. The presence of the third support element406cmay reduce the risk of tail distortion because the third support element406cstrengthens a section of the suspension tail300that corresponds to the bonding area404. This third support element406cmay be cut off after the HGA assembly process.

FIG. 6is a perspective view of a number of suspension tails400that are electrically connected to a FPC260according to an embodiment of the present invention. Now referring toFIG. 6, the FPC260includes FPC bond pads (covered by the suspension tails400) that are aligned with and electrically connected to corresponding bond pads408(seeFIG. 4) of the suspension tails400. As shown inFIG. 6, a portion of each of the suspension tails400extends into one of the slits510. In the embodiment ofFIG. 6, each of the suspension tails400is bent upward or downward near a corresponding slit510so that each of the suspension tails400is substantially in parallel with the FPC260and has the discrete segments402facing away from the FPC260. Because the bonding areas of the suspension tails400are clear of other support elements besides the discrete segments402, a single flat surface of a thermode or other suitable tools may be used to apply pressure and heat to the discrete segments402of one or more of the suspension tails400simultaneously. As such, no alignment of individual discrete segments402is needed. Accordingly, efficiency and reliability of the process and resulting structure may be increased, and manufacturing costs may be reduced.

FIG. 7illustrates a method of assembling a head stack assembly of a hard disk drive according to an embodiment of the present invention. It is noted that the following method may not include all the various steps of assembling a head stack assembly because some steps or processes that are generally known in the art and not necessary for the understanding of the present invention may be omitted for clarity.

A flexible printed circuit (FPC) having a number of FPC bond pads is to be attached with a suspension tail of a head gimbal assembly (HGA). The suspension tail includes a dielectric layer, a number of tail bond pads on a first side of the dielectric layer, and a structural layer on a second side of the dielectric layer. The structural layer consists of a number of discrete segments positioned within a bonding area and other portions positioned outside of the bonding area. That is, no other structural elements are located inside the bonding area besides the discrete segments. According to the method, an adhesive material (e.g., an ACF bonding material) is applied on the FPC bond pads and/or the tail bond pads (S10). The discrete segments respectively correspond in position to the bond pads. Then, the FPC is attached with the suspension tail (S20). In several embodiments, process step S20includes installing the suspension tail of the head gimbal assembly over the adhesive material on the FPC. The tail bond pads are aligned with the FPC bond pads on the FPC (S30). Here, the FPC is placed against a flat surface (S40) that supports the FPC when the suspension tail is pressed against the FPC by a thermode. Then, the tail bond pads are pressed against corresponding ones of the FPC bond pads by bringing a single flat surface of a thermode in contact with each of the discrete segments simultaneously and without contacting the other portions of the structural layer (S50). In several embodiments, process step S50further includes bringing the single flat surface of the thermode over the suspension tails, and applying force and heat to the thermode to bring conductive particles in the adhesive material in contact with both the tail bond pads and the FPC bond pads and cure the adhesive material to form an electrical bond.

While the above description contains many exemplary embodiments of the present invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.