U.S. patent application number 11/933759 was filed with the patent office on 2009-05-07 for disk drive comprising a double sided flex circuit wherein a first side lead provides an etching mask for a second side lead.
This patent application is currently assigned to WESTERN DIGITAL TECHNOLOGIES, INC.. Invention is credited to Dennis W. Hogg.
Application Number | 20090113702 11/933759 |
Document ID | / |
Family ID | 40586650 |
Filed Date | 2009-05-07 |
United States Patent
Application |
20090113702 |
Kind Code |
A1 |
Hogg; Dennis W. |
May 7, 2009 |
DISK DRIVE COMPRISING A DOUBLE SIDED FLEX CIRCUIT WHEREIN A FIRST
SIDE LEAD PROVIDES AN ETCHING MASK FOR A SECOND SIDE LEAD
Abstract
A method of manufacturing a flex circuit is disclosed for a disk
drive comprising a disk, a head actuated radially over the disk,
and control circuitry. The flex circuit is for electrically
coupling the head to the control circuitry and comprises a
substrate. An electrical coating applied to a first side of the
substrate is etched to form a first electrical lead. The first side
of the substrate is irradiated with radiation such that the first
electrical lead masks the radiation from passing through the
substrate to prevent curing of a photoresist applied to the second
side of the substrate to form an uncured photoresist and a cured
photoresist on the second side of the substrate. The uncured
photoresist is removed from the second side of the substrate to
form a groove, and the groove is filled with electrically
conductive material to form the second electrical lead.
Inventors: |
Hogg; Dennis W.; (Laguna
Hills, CA) |
Correspondence
Address: |
WESTERN DIGITAL TECHNOLOGIES, INC.;ATTN: LESLEY NING
20511 LAKE FOREST DR., E-118G
LAKE FOREST
CA
92630
US
|
Assignee: |
WESTERN DIGITAL TECHNOLOGIES,
INC.
Lake Forest
CA
|
Family ID: |
40586650 |
Appl. No.: |
11/933759 |
Filed: |
November 1, 2007 |
Current U.S.
Class: |
29/846 ;
360/245.9 |
Current CPC
Class: |
Y10T 29/49156 20150115;
H05K 3/06 20130101; Y10T 29/49124 20150115; H05K 2201/09672
20130101; G11B 5/486 20130101; H05K 3/048 20130101; Y10T 29/49147
20150115; H05K 3/184 20130101; H05K 3/0082 20130101; H05K 2201/0108
20130101; Y10T 29/49025 20150115; Y10T 29/49155 20150115; H05K
2203/0551 20130101; Y10T 29/49165 20150115 |
Class at
Publication: |
29/846 ;
360/245.9 |
International
Class: |
H05K 3/02 20060101
H05K003/02; G11B 5/48 20060101 G11B005/48 |
Claims
1. A method of manufacturing a flex circuit for a disk drive, the
disk drive comprising a disk, a head actuated radially over the
disk, and control circuitry, wherein the flex circuit is for
electrically coupling the head to the control circuitry and
comprises a substrate, the method comprising: etching an electrical
coating applied to a first side of the substrate to form a first
electrical lead; irradiating the first side of the substrate with
radiation such that the first electrical lead masks the radiation
from passing through the substrate to prevent curing of a
photoresist applied to the second side of the substrate to form an
uncured photoresist and a cured photoresist on the second side of
the substrate; removing the uncured photoresist from the second
side of the substrate to form a groove; and filling the groove with
electrically conductive material to form the second electrical
lead.
2. The method as recited in claim 1, wherein the first electrical
lead is substantially aligned with the second electrical lead such
that the substrate forms a capacitive dielectric.
3. The method as recited in claim 1, wherein the substrate
comprises a polyimide.
4. The method as recited in claim 3, wherein the polyimide is
sufficiently transparent to pass the radiation.
5. The method as recited in claim 1, wherein the radiation
comprises ultraviolet light.
6. The method as recited in claim 1, wherein the radiation
comprises visible light.
7. A disk drive comprising: a disk; a head actuated radially over
the disk; control circuitry; and a flex circuit for electrically
coupling the head to the control circuitry, the flex circuit
comprising: a substrate; a first electrical lead coupled to a first
side of the substrate, wherein the first electrical lead is
operable to conduct a first signal of a differential signal; a
second electrical lead coupled to a second side of the substrate
opposite the first side, wherein the second electrical lead is
operable to conduct a second signal of the differential signal; and
wherein the first electrical lead provides an etching mask for
etching the second electrical lead and the first electrical lead is
substantially aligned with the second electrical lead such that the
substrate forms a capacitive dielectric.
8. The disk drive as recited in claim 7, wherein the substrate
comprises a polyimide.
9. The disk drive as recited in claim 8, wherein the polyimide is
sufficiently transparent to pass a curing radiation.
10. The disk drive as recited in claim 7, wherein the radiation
comprises ultraviolet light.
11. The disk drive as recited in claim 7, wherein the radiation
comprises visible light.
12. The disk drive as recited in claim 7, further comprising an
actuator arm, wherein: the head is coupled to a distal end of the
actuator arm; the control circuitry comprises a preamp circuit
mounted on the actuator arm; and the flex circuit for electrically
coupling the head to the preamp circuit.
13. The disk drive as recited in claim 7, wherein the control
circuitry is mounted on a printed circuit board.
Description
BACKGROUND
[0001] FIG. 1A shows a prior art disk drive comprising a disk 2 and
a head 4 connected to a distal end of an actuator arm 6 which is
rotated about a pivot by a voice coil motor (VCM) 8 to position the
head 4 radially over the disk 2. The head 4 may comprise an
inductive write element (write coil) and a magnetoresistive read
element (MR element) fabricated in very small dimensions using
semiconductor fabrication techniques. A flex circuit 10 is
typically employed to electrically couple the head 4 to control
circuitry within the disk drive. In the example shown in FIG. 1A, a
first flex circuit 10A couples the head 4 to a preamp 12A mounted
on the actuator arm 6, and a second flex circuit 10B couples the
preamp 12A to other control circuitry 12B mounted on a printed
circuit board, wherein the second flex circuit 10B facilitates the
movement of the actuator arm 6. In other disk drives, the preamp
12A may be integrated with control circuitry 12B such that flex
circuit 10A couples the head 4 directly to the control circuitry
12B mounted on the printed circuit board.
[0002] FIG. 1B shows a magnified cross-sectional view of the flex
circuit 10A as comprising electrical leads for carrying
differential signals, such as a differential write signal 14A and
14B and a differential read signal 16A and 16B for the head 4. The
electrical leads are supported by a substrate 18 which may comprise
any suitable material, such as a polyimide. The electrical leads
are typically formed using conventional etching techniques on one
side of the substrate 18 such that the electrical leads for
carrying the differential signal are separated by an air gap (e.g.,
air gap 20A and 20B).
[0003] As the data rate in disk drives increases into the microwave
region, the transmission properties of the electrical leads for
carrying the differential signals has become more significant. For
example, it is desirable to reduce the impedance of the electrical
leads in order to increase power efficiency as well as the
signal-to-noise ratio (SNR) of the differential signal.
[0004] There is, therefore, a need in a disk drive to reduce the
impedance of the electrical leads fabricated on a flex circuit in
order to improve the power efficiency and SNR in transmitting
differential signals along the electrical leads.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1A shows a prior art disk drive comprising a head
actuated over a disk and a flex circuit for coupling the head to
control circuitry.
[0006] FIG. 1B shows a prior art flex circuit comprising electrical
leads for carrying differential signals fabricated on a single side
of a substrate.
[0007] FIG. 2A shows a disk drive according to an embodiment of the
present invention comprising a head actuated over a disk and a flex
circuit for coupling the head to control circuitry.
[0008] FIG. 2B shows a flex circuit according to an embodiment of
the present invention wherein the electrical leads for carrying
differential signals are fabricated on opposite sides of a
substrate, wherein a first electrical lead provides an etching mask
for etching the second electrical lead.
[0009] FIGS. 3A-3H show a method of manufacturing the flex circuit
according to an embodiment of the present invention wherein a first
electrical lead provides an etching mask for etching the second
electrical lead.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0010] FIG. 2A shows a disk drive according to an embodiment of the
present invention including a disk 22, a head 24 actuated radially
over the disk 22, control circuitry 26A and 26B, and a flex circuit
28A for electrically coupling the head 24 to the control circuitry
26A (a preamp in the example shown in FIG. 2A). The flex circuit
28A (FIG. 2B) comprises a substrate 30, a first electrical lead 32A
coupled to a first side of the substrate 30, wherein the first
electrical lead 32A is operable to conduct a first signal of a
differential signal, and a second electrical lead 32B coupled to a
second side of the substrate 30 opposite the first side, wherein
the second electrical lead 32B is operable to conduct a second
signal of the differential signal. The first electrical lead 32A
provides an etching mask for etching the second electrical lead
32B, and the first electrical lead 32A is substantially aligned
with the second electrical lead 32B such that the substrate 30
forms a capacitive dielectric.
[0011] In the embodiment of FIG. 2A, the head 24 is connected to a
distal end of an actuator arm 36 which is rotated about a pivot by
a voice coil motor 38 in order to actuate the head 24 radially over
the disk 22. A first flex circuit 28A couples the head 24 to a
preamp 26A mounted on the actuator arm 36, and a second flex
circuit 28B couples the preamp 26A to other control circuitry 26B
mounted on a printed circuit board. As the actuator arm 36 rotates,
the second flex circuit 28B bends to facilitate the movement of the
actuator arm 36. In an alternative embodiment, the preamp 26A is
integrated with the other control circuitry 26B such that flex
circuit 28A couples the head 24 directly to the control circuitry
26B mounted on the printed circuit board.
[0012] The flex circuit 28A may comprise electrical leads for
carrying any suitable differential signal. In one embodiment, the
head 24 comprises a magnetoresistive (MR) head comprising a write
element having a first differential signal interface (e.g., 32A and
32B) and a read element having a second differential signal
interface (e.g., 34A and 34B). As described above, it is desirable
to reduce the impedance of the electrical leads carrying a
differential signal in order to increase power efficiency as well
as the signal-to-noise ratio (SNR) of the signals. The impedance
can be reduced by increasing the capacitance between the electrical
leads, and in the embodiment shown in FIG. 2B, the impedance is
reduced due to the increased capacitance of the substrate 30.
However, in order to take full advantage of the capacitive
dielectric property of the substrate 30, in one embodiment the
first electrical lead (e.g., 32A) is substantially aligned with the
second electrical lead (e.g., 32B).
[0013] FIGS. 3A-3H show a method of manufacturing the flex circuit
28A according to an embodiment of the present invention so that the
electrical leads carrying a differential signal are substantially
aligned. Referring to FIG. 3A, an electrical coating 40 is applied
to a first surface of a suitable substrate 30 (e.g., a polymide),
wherein the electrical coating 40 may comprise any suitable
material, such as a metal alloy comprising copper, beryllium
copper, nickel, or compositions thereof. A suitable photoresist 42
(e.g., a suitable polymer) is applied over the electrical coating
40, and a mask 44 is placed over the photoresist 42 (FIG. 3B). A
suitable radiation source (e.g., ultraviolet light or visible
light) is directed at the first surface so as to cure the
photoresist 42 not covered by the mask 44. Referring to FIG. 3C,
the uncured photo resist 42 and underlying electrical coating 40
are removed (etched) using a suitable etchant solution, such as
acid ferric chloride. The cured photoresist 42 shown in FIG. 3C is
then removed (FIG. 3D) using a suitable solution, such as an
organic solvent (e.g., methylene chloride), leaving the first
electrical lead 32A shown in FIG. 2B.
[0014] During the step of etching the electrical coating 40 applied
to the first side of the substrate 30 to form the first electrical
lead 32A as described above with reference to FIGS. 3A-3D the mask
44 may be inverted if a positive photoresist 42 is employed. In
this embodiment, the masked part of the photoresist 42 is cured
when developed and the unmasked (and uncured) photoresist 42 is
removed together with the underlying electrical coating 40 as shown
in FIG. 3C.
[0015] Continuing now with FIG. 3E, the substrate 30 is flipped
over so that the second side is facing up, and a photoresist 46 is
applied to the second side. The first side of the substrate 30 is
then irradiated as shown in FIG. 3E such that the first electrical
lead 32A masks the radiation from passing through the substrate 30
to prevent curing of the photoresist 46 applied to the second side
of the substrate 30, thereby forming an uncured photoresist and a
cured photoresist on the second side of the substrate. In this
embodiment, the substrate 30 is sufficiently transparent to pass
the radiation, whereas the first lead 32A masks the radiation.
Referring to FIG. 3F, the uncured photoresist 46 is removed from
the second side of the substrate 30 to form a groove 48. Referring
to FIG. 3G, the groove 48 is filled with electrically conductive
material 50 using any suitable technique, such as a suitable
deposition process (e.g., a liquid bath plating process or
sputtering process). The cured photoresist 46 shown in FIG. 3G is
then removed as shown in FIG. 3H, thereby forming the second
electrical lead 32B shown in FIG. 2B.
[0016] As seen in FIG. 3H, the first electrical lead 32A is
substantially aligned with the second electrical lead 32B such that
the substrate 30 forms a capacitive dielectric. In one embodiment,
the capacitive dielectric of the substrate 30 increases the
capacitance of the electrical leads 32A and 32B as compared to the
air dielectric shown in the prior art of FIG. 1B. Increasing the
capacitance reduces the impedance of the electrical leads in order
to increase power efficiency as well as the signal-to-noise ratio
(SNR) of the differential signals.
* * * * *