US20160217814A1

US20160217814A1 - Disk drive head suspension tail with ground pad outside of bonding region

Info

Publication number: US20160217814A1
Application number: US15/090,880
Authority: US
Inventors: Yih-Jen Dennis Chen; Yanning Liu; Kia Moh Teo
Original assignee: Western Digital Technologies Inc
Current assignee: Western Digital Technologies Inc
Priority date: 2013-12-10
Filing date: 2016-04-05
Publication date: 2016-07-28
Also published as: US9324344B1

Abstract

A head gimbal assembly for a disk drive includes a flexure tail terminal region having flexure bond pads in electrical communication with the head. Each of the flexure bond pads is aligned with one of a plurality of flexible printed circuit (FPC) bond pads. An anisotropic conductive film is disposed between the FPC and the flexure tail terminal region. The flexure tail terminal region overlaps the anisotropic conductive film in a bonding area. Each of the flexure bond pads is bonded to one of the plurality of FPC bond pads by the anisotropic conductive film in a bonding area. A conductive layer of the flexure tail terminal region includes an exposed conductive ground pad that is disposed outside of the bonding area, and/or disposed outside of an application area of a thermode tool that is pressed against the flexure tail terminal region during the bonding process.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No. 14/322,616 (Atty. Docket No. T6982.X1) filed Jul. 2, 2014, entitled “DISK DRIVE HEAD SUSPENSION TAIL WITH GROUND PAD OUTSIDE OF BONDING REGION” which claims priority under 35 U.S.C. §120 as a continuation-in part to U.S. patent application Ser. No. 14/209,909, now U.S. Pat. No. 9,165,580, (Atty. Docket No. T6982) filed on Mar. 13, 2014, entitled “DISK DRIVE HEAD SUSPENSION TAIL WITH STIFFENED EDGE ALIGNMENT FEATURES,” and thereby also claims priority to provisional U.S. patent application Ser. No. 61/914,315 (Atty. Docket No. T6982.P), entitled “DISK DRIVE HEAD SUSPENSION TAIL ALIGNMENT FEATURE,” filed on Dec. 10, 2013. All applications referenced above are hereby incorporated by reference.

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, but other information storage devices also include heads—sometimes including heads that cannot write.
In a modern magnetic hard disk drive device, each head is a sub-component of a head gimbal assembly (HGA) that typically includes a suspension assembly with a laminated flexure to carry the electrical signals to and from the head. The HGA, in turn, is a sub-component of a head stack assembly (HSA) that typically includes a plurality of HGAs, an actuator, and a flexible printed circuit. The plurality of HGAs are attached to various arms of the actuator.
Modern laminated flexures typically include conductive copper traces that are isolated from a stainless steel structural layer by a polyimide dielectric layer. So that the signals from/to the head can reach the flexible printed circuit (FPC) on the actuator body, each suspension assembly includes a flexure tail that extends away from the head along a corresponding actuator arm and ultimately attaches to the FPC adjacent the actuator body. That is, the flexure includes traces that extend from adjacent the head and continue along the flexure tail to a plurality of flexure bond pads for electrical connection to the FPC. The FPC includes conductive electrical traces that terminate in a plurality of FPC bond pads that correspond to and are electrically connected to the flexure bond pads.
To facilitate electrical connection of the conductive traces of the flexure tails to the conductive electrical terminals of the FPC during the HSA manufacturing process, the flexure tails must first be properly positioned relative to the FPC so that the flexure bond pads are aligned with the FPC bond pads. Then the flexure tails must be held or constrained against the FPC bond pads while the aforementioned electrical connections are made, e.g., by ultrasonic bonding, solder jet bonding, solder bump reflow, or anisotropic conductive film (ACF) bonding.
An anisotropic conductive film is typically an adhesive doped with conductive beads of similar size or diameter. As the doped adhesive is compressed and cured, it is heated and 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 axially, i.e. in a direction normal to the bonded surfaces, since each bead is forced to contact both of the surfaces to be bonded. However, the cured adhesive film may not conduct electricity parallel to the bonded surfaces, since the beads may not touch each other laterally—hence the term “anisotropic”.
Prior to HSA assembly, HGAs are typically tested for acceptable function. For example, the HGAs may undergo so-called dynamic electrical testing (DET) to ensure acceptable function (and/or to characterize HGA performance for subsequent optimization or compensation in the HSA and/or in the assembled disk drive). Such testing may require a reliable electrical ground connection to the HSA. In some cases, the flexure tail may include an extra length with enlarged testing pads that include a ground pad for testing. However, such extra length must be cut-away as an extra processing step before or during HSA assembly, and the ground pad is therefore not part of the assembled HSA or the assembled disk drive.
Hence, there is a need in the art for a head suspension assembly flexure tail design that can provide a reliable ground connection, without the need for an extra length (e.g. with enlarged testing pads) that must be cut away as an extra processing step before or during HSA assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a disk drive capable of including an embodiment of the present invention.

FIG. 2 is a perspective view of a head stack assembly (HSA) capable of including an embodiment of the present invention.

FIG. 3 is a perspective view of a portion of a flexible printed circuit (FPC) capable of use with an embodiment of the present invention.

FIG. 4A is an assembled plan view of a flexure tail terminal region, according to an embodiment of the present invention.

FIG. 4B is an exploded perspective view of the flexure tail terminal region of FIG. 4A.

FIG. 5A depicts a plan view of a flexure tail terminal region according to another embodiment of the present invention, facing the conductive layer side.

FIG. 5B depicts a plan view of the flexure tail terminal region of FIG. 5A, facing the structural layer side.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a top perspective view of a disk drive 100 capable of including an embodiment of the present invention. The disk drive 100 includes a disk drive base 102 and two annular magnetic disks 104. The disk drive 100 further includes a spindle 106, rotatably mounted on the disk drive base 102, for rotating the disks 104. The rotation of the disks 104 establishes air flow through recirculation filter 108. In other embodiments, disk drive 100 may have only a single disk, or alternatively, more than two disks.
The disk drive 100 further includes an actuator 116 that is rotatably mounted on disk drive base 102. Voice coil motor 112 rotates the actuator 116 through a limited angular range so that at least one head gimbal assembly (HGA) 114 is desirably positioned relative to one or more tracks of information on a corresponding one of the disks 104. In the embodiment of FIG. 1, the actuator 116 includes three arms upon which four HGAs 114 are attached, each corresponding to a surface of one of the two disks 104. However in other embodiments fewer or more HGAs 114 may be included depending on the number of disks 104 that are included and whether the disk drive 100 is depopulated.
Each HGA 114 preferably includes a head 150 for reading from one of the disks 104. The head 150 may be referred to herein as a read head, even though it may also perform other functions and contain other structures such as a writer for writing data, a microactuator, a heater, a lapping guide, etc. The actuator 116 may occasionally be latched at an extreme angular position within the limited angular range, by latch 120. Electrical signals to/from the HGAs 114 are carried to other drive electronics via a flexible printed circuit that includes a flex cable 122 (preferably including a preamplifier circuit) and flex cable bracket 124.
FIG. 2 is a perspective view of a head stack assembly (HSA) 200 capable of including an embodiment of the present invention. The HSA 200 includes an actuator body 232 and a plurality of actuator arms 226, 236, 238 extending from the actuator body 232. The actuator body 232 includes a pivot bearing cartridge 220 disposed in the actuator bore, and a coil support 234 that supports a coil 235 and extends from the actuator body 232 in a direction that is generally opposite the actuator arms 226, 236, 238. The HSA 200 also includes a plurality of head gimbal assemblies (HGA) 240, 242, 244, 254, attached to the actuator arms 226, 236, 238. For example, such attachment may be made by swaging. Note that the inner actuator arm 226 includes two HGAs 242, 244, while each of the outer actuator arms 236, 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. HGA 254 includes head 280). The head 280 is attached to a tongue portion 272 of a laminated flexure 270. The laminated flexure 270 is part of the HGA 254, and is attached to a load beam (the part of the HGA 254 to which the numerical label 254 points). The laminated flexure 270 may include a structural layer (e.g. stainless steel), a dielectric layer (e.g. polyimide), and a conductive layer into which traces are patterned (e.g. copper). The HSA 200 also includes a flexible printed circuit (FPC) 260 adjacent the actuator body 232. The FPC 260 includes a flex cable 262 and a preamplifier 266. The FPC 260 may comprise a laminate that includes two or more conventional dielectric and conductive layer materials (e.g. one or more polymeric materials, copper, etc.). The laminated flexure 270 includes a flexure tail 274 that runs along the actuator arm 238 to a terminal region 278 of the laminated flexure 270 that is electrically connected to bond pads of the FPC 260.
Methods of electrical connection of the flexure tails (e.g. flexure tail 274) to the FPC 260 include ultrasonic bonding of gold coatings thereon, solder reflow, solder ball jet (SBJ), and anisotropic conductive film (ACF) bonding, and are preferably but not necessarily automated. To electrically connect and securely attach the flexure tails to the FPC 260, the flexure tails are first aligned with the FPC 260, and then pressed against the FPC 260 (at least temporarily) while electrical connection is established and secure attachment is completed. Maintaining alignment and sufficient uniform pressure and temperature to groups of bond pads may be desirable during this process.
FIG. 3 depicts the FPC 260 before flexure tail terminal regions (i.e. the portion of each flexure tail that overlaps the FPC, for example, flexure tail terminal region 278) are bonded thereto. The FPC 260 includes electrical conduits 382 that terminate at FPC bond pads 380, which are aligned with and connected to flexure bond pads of the terminal regions (e.g. flexure tail terminal region 278) of the HGA flexure tails. The FPC electrical conduits 382 may connect to a pre-amplifier chip 315 (shown exploded from the FPC 260 in FIG. 3). Two of the HGA flexure tails may pass through the FPC slit 310 to help facilitate their support and alignment.
The FPC 260 may include an optional insulative cover layer 320 having windows exposing the regions where the flexure tail terminal regions and the pre-amplifier chip 315 are bonded thereto. The cover layer 320 is shown cut away in the view of FIG. 3, so that the electrical conduits 382 can be better depicted.
FIG. 4A is an assembled plan view of a flexure tail terminal region 400, according to an embodiment of the present invention. FIG. 4B is an exploded perspective view of the flexure tail terminal region 400. Now referring to FIGS. 4A and 4B, the flexure tail terminal region 400 includes a structural layer 410 (e.g. stainless steel), a conductive layer 430 (e.g. copper), and a dielectric layer 420 (e.g. polyimide) between the structural layer 410 and the conductive layer 430. The flexure tail terminal region 400 may also include an optional cover layer 440 that comprises an electrically insulative material (e.g. an insulative polymer).
The flexure tail terminal region 400 may also include other layers, such as an additional conductive layer and an additional dielectric layer (e.g. in the case of a dual conductive layer flexure), but the layers described herein would still be included as described. In certain embodiments, the thickness of the structural layer 410 may be preferably less than 20 microns, the thickness of the dielectric layer 420 may be preferably less than 15 microns, the thickness of the conductive layer 430 may be preferably less than 15 microns, and a total thickness of the flexure tail terminal region 400 at each of the plurality of flexure bond pads 432 may be preferably at least 25 microns.
Now referring to FIGS. 3, 4A and 4B, the flexure tail terminal region 400 is preferably configured to at least partially overlap the FPC 260. The flexure tail terminal region 400 preferably includes a plurality of flexure bond pads 432 that are defined in the conductive layer 430 and that are aligned with corresponding ones of the plurality of FPC bond pads 380. Some or all of the plurality of flexure bond pads 432 are in electrical communication with a head (e.g. head 280 of FIG. 2).
In certain embodiments, a conventional anisotropic conductive film is disposed between the FPC 260 and the flexure tail terminal region 400, and the flexure tail terminal region 400 overlaps the anisotropic conductive film in a bonding area 460 (the portion of the flexure tail terminal region 400 having the bonding area longitudinal span 478). In such embodiments, each of the plurality of flexure bond pads 432 is bonded to the corresponding one of the plurality of FPC bond pads 380 by the anisotropic conductive film in the bonding area 460.
Still referring to FIGS. 3, 4A, and 4B, during the head stack assembly process an anisotropic conductive film may be disposed between the FPC 260 and the flexure tail terminal region 400. Optionally, this may be done by overlaying a rectangular strip of the anisotropic conductive film on the FPC 260. Next, a thermode tool may be pressed against a thermode tool application area of the flexure tail terminal region 400 (which in the embodiment of FIG. 4A is preferably but not necessarily coincident with the bonding area 460), to press the flexure bond pads 432 against the FPC bond pads 380 for a period. Since all of the plurality of flexure bond pads 432 are preferably disposed within the thermode tool application area of the flexure tail terminal region 400, the thermode tool simultaneously applies heat and increased pressure to all of the plurality of flexure bond pads 432, to preferably simultaneously bond them to corresponding ones of the plurality of FPC bond pads 380 by the anisotropic conductive film (ACF).
In certain embodiments, the anisotropic conductive film may comprise an adhesive material that includes a plurality of electrically conductive beads. In such embodiments, the electrically conductive beads may be of substantially similar size, and the plurality of electrically conductive beads may be arranged in a monolayer with each of the plurality of electrically conductive beads in electrical contact with one of the plurality of flexure bond pads 432 and the corresponding one of the plurality of FPC bond pads 380. The dielectric layer 420 may optionally include a plurality of through openings 422, for example to control the spread of ACF material used to make electrical connections to the flexure bond pads 432.
In the embodiment of FIGS. 4A and 4B, the structural layer 410 includes a plurality of discontinuous bond pad backing islands 412 that are disposed in alignment with the plurality of flexure bond pads 432. In the embodiment of FIGS. 4A and 4B, the flexure tail terminal region 400 also optionally includes a discontinuous edge stiffener island 413 in the structural layer 410 that does not overlap any of the flexure bond pads 432. In the embodiment of FIGS. 4A and 4B, the flexure tail terminal region 400 further comprises a narrow peninsula 417 in the structural layer 410 that is contiguous with the structural layer 410 in the flexure tail as it runs outside of the flexure tail terminal region (e.g. contiguous with the structural layer that runs along the actuator arm 238 in flexure tail 274 of FIG. 2).
Now referring to FIGS. 3, 4A and 4B, in certain embodiments the FPC 260 preferably may be designed so that the FPC conductive traces 382 are not disposed in locations that would overlap with the discontinuous edge stiffener island 413 or the narrow peninsula 417. Otherwise, such locations may be subject to undesirably high pressure from a thermode tool during the process of bonding the flexure tail terminal region 400 to the FPC 260, which may undesirably reduce the pressure or uniformity of pressure applied to the flexure bond pads by the thermode tool during head stack assembly.
In the embodiment of FIGS. 4A and 4B, the total longitudinal span 474 of the flexure tail terminal region 400 may optionally be in the range of 3 mm to 8 mm, and may include a bonding area longitudinal span 478 in the range of 2 mm to 7 mm. In certain embodiments, an adjacent area 494 of the flexure tail terminal region 400, outside the bonding area 460, may have an adjacent area longitudinal span 476 in the range of 1 mm to 3 mm.
Referring to FIGS. 3, 4A, and 4B, the conductive layer 430 may further comprise an exposed conductive ground pad 436 that is disposed outside of the bonding area 460. In the embodiment of FIGS. 4A and 4B, the exposed conductive ground pad 436 is disposed within the adjacent area 494. In the embodiment of FIGS. 4A and 4B, the adjacent area 494 of the flexure tail terminal region 400 may include a bent portion 496 extending approximately normally from a major plane of the flexure tail terminal region 400. In certain embodiments, and as shown in FIG. 4A, the bent portion 496 optionally longitudinally spans the exposed conductive ground pad 436.
In the embodiment of FIGS. 3, 4A, and 4B, since the exposed conductive ground pad 436 is disposed outside of the bonding area 460, pressing the thermode tool against the thermode tool application area of the flexure tail terminal region 400 does not bond the exposed conductive ground pad 436 to any of the plurality of FPC bond pads 380. Instead, the conductive ground pad 436 may be exposed and hence accessible to be contacted by a test probe, for example to make a temporary electrical connection for testing. The exposed conductive ground pad 436 of the conductive layer 430 may be electrically connected to the structural layer 410 of the flexure thru vias 426 through the dielectric layer 420.
FIG. 5A depicts a plan view of a flexure tail terminal region 500 according to another embodiment of the present invention, facing the side that includes its conductive layer 530. FIG. 5B depicts a plan view of the flexure tail terminal region 500, facing the side that includes its structural layer 510. Now referring to FIGS. 5A and 5B, the flexure tail terminal region 500 includes a structural layer 510 (e.g. stainless steel), a conductive layer 530 (e.g. copper), and a dielectric layer 520 (e.g. polyimide) between the structural layer 510 and the conductive layer 530. The flexure tail terminal region 500 may also include an optional cover layer 540 that comprises an electrically insulative material (e.g. an insulative polymer).
In the embodiment of FIGS. 5A and 5B, the flexure tail terminal region 500 is bounded by two opposing longitudinal outer edges 580, 590. The flexure tail terminal region 500 includes a plurality of flexure bond pads 532, 534 that are aligned with corresponding ones of a plurality of FPC bond pads (e.g. FPC bond pads 380 of FIG. 3). The dielectric layer 520 may optionally include a plurality of through openings 522, for example to control the spread of ACF material used to make electrical connections to the flexure bond pads 532, 534.
In the embodiment of FIGS. 5A and 5B, an exposed conductive ground pad 536 of the conductive layer 530 may be electrically connected to the structural layer 510 of the flexure thru a via in the dielectric layer 520 (e.g. polyimide layer) that is disposed between the conductive layer 530 and the structural layer 510.
In the embodiment of FIGS. 5A and 5B, each of the plurality of flexure bond pads 532, 534 comprises a corresponding one of a plurality of widened regions of a plurality of electrical traces 538 in the conductive layer 530. The flexure tail terminal region 500 further includes a plurality of discontinuous bond pad backing islands 512, 514 in the structural layer 510. Note that each of the discontinuous bond pad backing islands 512, 514 in the structural layer 510 overlaps and is aligned with a corresponding one of the flexure bond pads 532, 534 in the conductive layer 530. The structural layer islands 512, 514 may serve to transfer heat and pressure from a flat thermode tool to the plurality of flexure bond pads 532, 534 (simultaneously) during the HSA assembly process, for example to facilitate ACF bonding.
In the embodiment of FIGS. 5A and 5B, the flexure tail terminal region 500 also optionally includes a plurality of discontinuous edge stiffener islands 513, 515 in the structural layer 510 that do not overlap any of the flexure bond pads 532, 534. In the embodiment of FIGS. 5A and 5B, the flexure tail terminal region 500 further comprises a narrow peninsula 517 in the structural layer 510 that is contiguous with the structural layer 510 in the flexure tail as it runs outside of the flexure tail terminal region (e.g. contiguous with the structural layer that runs along the actuator arm 238 in flexure tail 274 of FIG. 2).
Now referring to FIGS. 3, 5A and 5B, in certain embodiments the FPC 260 preferably may be designed so that the FPC conductive traces 382 are not disposed in locations that would overlap with the discontinuous edge stiffener island 513 or the narrow peninsula 517. Otherwise, such locations may be subject to undesirably high pressure from a thermode tool during the process of bonding the flexure tail terminal region 500 to the FPC 260, which may undesirably reduce the pressure or uniformity of pressure applied to the flexure bond pads by the thermode tool during head stack assembly.
In the embodiment of FIGS. 5A and 5B, the total longitudinal span 574 of the flexure tail terminal region 500 may optionally be in the range of 3 mm to 8 mm, and may include a bonding area longitudinal span 578 in the range of 2 mm to 7 mm. In certain embodiments, an adjacent area 594 of the flexure tail terminal region 500, outside the bonding area, may have an adjacent area longitudinal span 576 in the range of 1 mm to 3 mm. In the embodiment of FIGS. 5A and 5B, the exposed conductive ground pad 536 is disposed within the adjacent area 594.
In the embodiment of FIGS. 5A and 5B, the adjacent area 594 of the flexure tail terminal region 500 includes a bent portion 596 extending approximately normally from a major plane of the flexure tail terminal region 500. In certain embodiments, and as shown in FIG. 5A, the bent portion 596 optionally longitudinally spans the exposed conductive ground pad 536.
In the foregoing specification, the invention is described with reference to specific exemplary embodiments, but those skilled in the art will recognize that the invention is not limited to those. It is contemplated that various features and aspects of the invention may be used individually or jointly and possibly in a different environment or application. The specification and drawings are, accordingly, to be regarded as illustrative and exemplary rather than restrictive. For example, the word “preferably,” and the phrase “preferably but not necessarily,” are used synonymously herein to consistently include the meaning of “not necessarily” or optionally. “Comprising,” “including,” and “having,” are intended to be open-ended terms.

Claims

What is claimed is:

1. A method of manufacturing a head stack assembly for a disk drive, the method comprising:

providing an actuator including at least one actuator arm and a flexible printed circuit (FPC) that includes a plurality of electrically conductive FPC bond pads;

attaching at least one head gimbal assembly to the at least one actuator arm, the at least one head gimbal assembly comprising a head for reading and writing data on the disk and a suspension assembly that comprises a load beam and a laminated flexure, the laminated flexure including a structural layer, a conductive layer, and a dielectric layer between the structural layer and the conductive layer, the laminated flexure including a tongue portion that connects to the read head and a flexure tail that extends to the plurality of FPC bond pads;

aligning a terminal region of the flexure tail with the FPC so that it at least partially overlaps the FPC, the flexure tail terminal region including a plurality of flexure bond pads in electrical communication with the head, with each of the plurality of flexure bond pads being aligned with a corresponding one of the plurality of FPC bond pads;

disposing an anisotropic conductive film between the FPC and the flexure tail terminal region; and

pressing a thermode tool against a thermode tool application area of the flexure tail terminal region to bond each of the plurality of flexure bond pads to the corresponding one of the plurality of FPC bond pads by the anisotropic conductive film;

wherein the conductive layer further comprises an exposed conductive ground pad that is disposed outside of the thermode tool application area.

2. The method of claim 1 wherein the thermode tool applies heat and increased pressure to the plurality of flexure bond pads in the thermode tool application area.

3. The method of claim 1 wherein the total longitudinal span of the flexure tail terminal region is in the range of 3 mm to 8 mm, and a longitudinal span of the thermode tool is in the range of 2 mm to 7 mm.

4. The method of claim 2 wherein the flexure tail terminal region includes a bent portion extending approximately normally from a major plane of the flexure tail terminal region, the bent portion being disposed outside the thermode tool application area, wherein the bent portion longitudinally spans the exposed conductive ground pad.

5. The method of claim 1 wherein all of the plurality of flexure bond pads are disposed within the thermode tool application area of the flexure tail terminal region, so that all are bonded simultaneously by pressing the thermode tool.

6. The method of claim 1 further comprising contacting a test probe with the exposed conductive ground pad to make temporary electrical connection with the exposed conductive ground pad for testing.

7. The method of claim 1 wherein disposing the anisotropic conductive film between the FPC and the flexure tail terminal region comprises overlaying a rectangular strip of the anisotropic conductive film on the FPC.

8. The method of claim 1 wherein pressing the thermode tool against the thermode tool application area of the flexure tail terminal region does not bond the exposed conductive ground pad to any of the plurality of FPC bond pads.