(12) United States Patent
`Yamato et al.
`
`US006388201 B2
`(10) Patent No.:
`US 6,388,201 B2
`(45) Date of Patent:
`May 14, 2002
`
`(54) WIRED CIRCUIT BOARD
`(75) Inventors: Takeshi Yamato; Kenichiro Ito, both
`of Ibaraki (JP)
`(73) Assignee: Nitto Denko Corporation, Osaka (JP)
`(*) Notice:
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/866,813
`(22) Filed:
`May 30, 2001
`(30)
`Foreign Application Priority Data
`Jun. 8, 2000 (JP) ....................................... 2000–172034
`(51) Int. Cl." .................................................. H05K 1/00
`(52) U.S. Cl. ....................... 174/255; 174/250; 174/254;
`174/258; 361/751; 361/792; 361/807
`(58) Field of Search ................................. 174/250, 254,
`174/255, 256, 261, 260, 258, 259, 262,
`265, 266, 72 A: 361/748, 749, 751, 792,
`752, 793, 807; 360/137
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`3/1996 Carpenter et al. ............ 29/830
`5,495,665 A *
`5,598.307 A *
`1/1997 Bennin .................... 360/245.9
`
`5,737,837. A * 4/1998 Inaba .......................... 29/884
`5,835,306 A * 11/1998 Bennin .................... 360/234.5
`5,879,787 A * 3/1999 Petefish ...................... 428/209
`5,978,177 A * 11/1999 Takasugi ................. 360/245.9
`6,100,582 A * 8/2000 Omote et al. ............... 257/699
`6,162.996 A * 12/2000 Schmidt et al. ............. 174/259
`6,198,052 B1 * 3/2001 Omote et al. ............ 174/245.9
`
`* cited by examiner
`
`Primary Examiner—Jeffrey Gaffin
`Assistant Examiner—Ishwar B Patel
`(74) Attorney, Agent, or Firm—Kubovcik & Kubovcik
`(57)
`ABSTRACT
`To provide a wired circuit board capable of surely prevent
`ing occurrence of a short circuit between a metal terminal
`layer and a metal supporting layer with a simple
`construction, to provide improvement in connection reliabil
`ity and in voltage proof property, a wired circuit board
`comprises a base layer formed on a supporting board, a
`conductive layer formed on the base layer, a surface of the
`conductive layer being exposed by opening the supporting
`board and the base layer, and a metal plated layer formed on
`the conductive layer exposed in the openings of the sup
`porting board and the base layer, wherein a specified space
`is defined between a periphery of the metal plated layer and
`a periphery of the opening of the supporting board.
`
`3 Claims, 9 Drawing Sheets
`
`
`
`
`
`18
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`N
`
`33
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`
`
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`Ø
`
`HUTCHINSON EXHIBIT 1008
`
`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 1 of 9
`
`US 6,388,201 B2
`
`
`
`#
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`HUTCHINSON EXHIBIT 1008
`
`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 2 of 9
`
`
`
`
`
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`% SN 19 ?N
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`5
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`FIG.2
`
`HUTCHINSON EXHIBIT 1008
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`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 3 of 9
`
`US 6,388,201 B2
`
`12
`
`13a
`
`(b)
`
`12
`
`13a [L-24
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`(c)
`C
`
`12
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`(d)
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`13a
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`* = 2-32
`13a
`12
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`! 3
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`3 |
`
`! 3
`12
`
`FIG.3
`
`HUTCHINSON EXHIBIT 1008
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`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 4 of 9
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`US 6,388,201 B2
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`20 31
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`
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`12 N 12
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`20
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`
`HUTCHINSON EXHIBIT 1008
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`

`

`US. Patent
`
`May 14, 2002
`
`Sheet 5 0f 9
`
`US 6,388,201 B2
`
`14
`r—"‘—fi
`14a
`14b 22
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`22
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`
`HUTCHINSON EXHIBIT 1008
`
`(61)
`
`(b)
`
`(c)
`
`(d)
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`HUTCHINSON EXHIBIT 1008
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`

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`US. Patent
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`May 14, 2002
`
`Sheet 6 0f 9
`
`US 6,388,201 B2
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`‘8
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`HUTCHINSON EXHIBIT 1008
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`(b)
`
`(c)
`
`
`
`14
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`
`HUTCHINSON EXHIBIT 1008
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`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 7 of 9
`
`US 6,388,201 B2
`
`FIG.7
`
`FIG.8
`
`FIG.9
`
`|| || || ||
`
`32a
`
`# ###
`
`32b
`
`# § § §
`
`32C
`
`FIG.10
`
`#:
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`HUTCHINSON EXHIBIT 1008
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`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 8 of 9
`
`US 6,388,201 B2
`
`4
`
`7
`
`(a)
`
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`(b)
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`
`(d)
`
`FIG.11
`Prior Art
`
`HUTCHINSON EXHIBIT 1008
`
`

`

`U.S. Patent
`
`May 14, 2002
`
`Sheet 9 of 9
`
`US 6,388,201 B2
`
`FIG.12
`
`19
`36
`18
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`13 Z
`
`12
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`HUTCHINSON EXHIBIT 1008
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`

`

`1
`WIRED CIRCUIT BOARD
`
`US 6,388,201 B2
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates to a wired circuit board and,
`more particularly, to a wired circuit board suitably used for
`a suspension board with circuit.
`2. Description of the Prior Art
`For example, a suspension board with circuit used for a
`hard disk drive comprises a supporting board 1 made of
`stainless steel foil, a base layer 2 formed of an insulating
`material formed on the supporting board 1, a conductive
`layer 3 formed on the base layer 2 in the form of a specific
`circuit pattern, and a cover layer 4, formed of an insulating
`material, for covering the conductive layer 3, as shown in
`FIG. 11(d).
`The suspension board with circuit, prevalent nowadays as
`the so-called Flying Lead, is formed to have terminals 5
`formed on both sides of the conductive layer 3, rather than
`in only either side thereof, in order to meet the demand of
`recent years for electronic equipment to have increasingly
`higher density and reduced size.
`Conventionally, the terminals 5 of the suspension board
`with circuit are formed on both sides of the conductive layer
`3 in the following manner. First, the cover layer 4 is formed
`and simultaneously opened by use of a photo-resist and the
`like to form a first opening 7 for forming the terminal 5 in
`the cover layer 4 and expose a front side of the conductive
`layer 3, as shown in FIG. 11(a). Then, a second opening 8
`for the terminal 5 to be formed in the supporting board 1 is
`formed in the supporting board 1 by a chemical etching and
`the like, as shown in FIG. 11(b). Sequentially, with the
`supporting board 1 as a mask, the base layer 2 exposed in the
`second opening 8 is opened by a plasma etching and the like,
`to form a third opening 9 for the terminal 5 to be formed in
`the base layer 2, so that a back side of the conductive layer
`3 is exposed, as shown in FIG. 11(c). Thereafter, metal
`plated layers 6 are formed on both sides of the conductive
`layer 3 thus exposed, as shown in FIG. 11(d).
`The metal plated layer 6 thus formed extends over the
`whole area of the conductive layer 3 exposed in the whole
`area of the third opening 9 in the base layer 2 formed by
`using the supporting board 1 as the mask, without leaving
`any space between the periphery of the metal plated layer 6
`and the periphery of the third opening 9 in the base layer 2.
`As a result of this, the metal plated layer 6 formed in the
`second opening 8 also extends in the thickness direction
`thereof, without leaving any space between the periphery of
`the metal plated layer 6 and the periphery of the second
`opening 8 in the supporting board 1. Due to this, depending
`on thickness of the metal plated layer 6 formed, the metal
`plated layer 6 can contact the periphery of the opening 8 in
`the supporting board 1 to cause a short circuit from the
`contact between the metal plated layer 6 and the supporting
`board 1.
`In practice, since the third opening 9 in the base layer 2
`is formed with the second opening 8 of the supporting board
`1 as the mask, the third opening 9 is sometimes made
`slightly larger than the second opening 8 in the supporting
`board 1, as shown in FIG. 11(d). This increases the risk of
`a short circuit being caused from contact between the metal
`plated layer 6 and the supporting board 1.
`It is the object of the invention to provide a wired circuit
`board capable of surely preventing occurrence of a short
`circuit between a metal terminal layer and a metal support
`
`10
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`50
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`55
`
`60
`
`65
`
`2
`ing layer with a simple construction, to provide improve
`ment in connection reliability and in voltage proof property.
`SUMMARY OF THE INVENTION
`The present invention is directed to a novel wired circuit
`board comprising an insulating layer formed on a metal
`supporting layer, a conductive layer formed on the insulating
`layer, a surface of the conductive layer being exposed by
`opening the metal supporting layer and the insulating layer,
`and a metal terminal layer formed on the conductive layer
`exposed in the openings of the metal supporting layer and
`the insulating layer, wherein a specified space is defined
`between a periphery of the metal terminal layer and a
`periphery of the opening of the metal supporting layer.
`With this construction, since the specified space is defined
`between the periphery of the metal terminal layer and the
`periphery of the opening of the metal supporting layer,
`contact between the periphery of the metal terminal layer
`and the periphery of the opening of the metal supporting
`layer can be surely prevented. This can surely prevent
`occurrence of a short circuit caused from the contact
`therebetween, thus providing improved connection reliabil
`ity and voltage proof property of the suspension board with
`circuit.
`It is preferable that the conductive layer has a terminal
`forming portion for forming the metal terminal layer and the
`terminal forming portion is hollowed toward the metal
`supporting layer with respect to the remaining portions of
`the conductive layer.
`With this construction, the distance from the front side of
`the metal supporting layer to the front side of the metal
`terminal layer is shortened to an extent corresponding to the
`hollowed portion from the remaining portion and, as a result
`of this, the metal terminal layer is placed closer to the
`outside of the metal supporting layer to that extent. This can
`produce the effect that for example when the connecting
`terminals of an external circuit are connected with the metal
`terminal layers in such a manner that those connecting
`terminals are laid over the metal terminal layers and are
`bonded to each other via supersonic vibration of a bonding
`tool, the pressure bonding can be well ensured, thus pro
`viding further improved connection reliability.
`The wired circuit board of the present invention can be
`used as a suspension board with circuit.
`BRIEF DESCRIPTION OF THE DRAWINGS
`In the drawings:
`FIG. 1 is a perspective view showing a suspension board
`with circuit presented in the form of an embodiment of a
`wired circuit board of the present invention,
`FIG. 2 is a sectional view taken along a longitudinal
`direction of the wiring, showing a magnetic head connecting
`terminal and an external connecting terminal of the suspen
`sion board with circuit shown in FIG. 1,
`FIG. 3 illustrates in section the steps of preparing a
`supporting board and forming on the supporting board a
`base layer with a specified pattern, of the method of pro
`ducing the suspension board with circuit presented as an
`embodiment of the method of producing a wired circuit
`board of the present invention,
`(a) shows the step of preparing a supporting board;
`(b) shows the step of forming a coating of a precursor of
`a photosensitive polyimide resin on the supporting
`board;
`(c) shows the step of exposing the coating to light through
`a photomask and developing it to form a specified
`pattern; and
`
`HUTCHINSON EXHIBIT 1008
`
`

`

`US 6,388,201 B2
`
`3
`(d) shows the step of curing the patterned coating to form
`the base layer,
`FIG. 4 illustrates in section the steps of forming on the
`base layer a conductive layer with a specified circuit pattern,
`(a) shows the step of forming a ground on the supporting
`board and the base layer;
`(b) shows the step of forming on the ground a plating
`resist of an opposite pattern to the specified circuit
`pattern;
`(c) shows the step of forming a conductive layer of a
`specified circuit pattern on a portion of the base layer
`in which no plating resist is formed, by using an
`electrolysis plating;
`(d) shows the step of removing the plating resist; and
`(e) shows the step of removing the ground,
`FIG. 5 illustrates in section the steps that after a surface
`of the conductive layer of the circuit pattern is protected by
`a thin metal film, the surface of the conductive layer is
`covered with a cover layer,
`(a) shows the step of forming the thin metal film on
`surfaces of the conductive layer;
`(b) shows the step of forming a coating of a precursor of
`a photosensitive polyimide resin on the base layer and
`the thin metal film;
`(c) shows the step of patterning the coating by exposing
`the coating to light through a photomask and develop
`ing it; and
`(d) shows the step of curing the patterned coating to form
`the cover layer,
`FIG. 6 illustrates in section the steps of forming the
`magnetic head connecting terminals and the external con
`necting terminals in the state of their both sides being
`exposed,
`(a) shows the step of opening the supporting board at
`portions thereof for the magnetic head connecting
`terminals and the external connecting terminals to be
`formed;
`(b) shows the step of peeling the thin metal film formed
`on the exposed conductive layer and supporting board;
`(c) shows the step of opening the base layer exposed in the
`opening of the supporting board, so as to correspond in
`position to the opening;
`(d) shows the step of peeling the ground exposed by
`opening the base layer; and
`(e) shows the step of forming a metal plated layer on each
`side of the exposed conductive layer,
`FIG. 7 is a schematic plan view of an embodiment of a
`photomask used for exposing the coating to light in the step
`of FIG. 3(b),
`FIG. 8 is a schematic plan View of another embodiment
`of the photomask used for exposing the coating to light in
`the step of FIG. 3(b),
`FIG. 9 is a schematic plan view of a further embodiment
`of a photomask used for exposing the coating to light in the
`step of FIG. 3(b),
`FIG. 10 is a schematic plan view of a yet another
`embodiment of a photomask used for exposing the coating
`to light in the step of FIG. 3(b),
`FIG. 11 illustrates in section the steps of forming the
`terminals in the state of their both sides being exposed in the
`producing method of a conventional suspension board with
`circuit,
`(a) shows the step of forming an opening for the terminal
`to be formed in the cover layer;
`
`10
`
`15
`
`20
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`25
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`30
`
`35
`
`40
`
`45
`
`50
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`55
`
`60
`
`65
`
`4
`(b) shows the step of forming an opening for the terminal
`to be formed in the supporting board;
`(c) shows the step of opening the base layer exposed in the
`opening of the supporting board, so as to correspond in
`position to the opening; and
`(d) shows the step of forming a metal plated layer on each
`side of the exposed conductive layer,
`FIG. 12 is a sectional view taken along a longitudinal
`direction of the wiring, showing another embodiment of the
`magnetic head connecting terminal and external connecting
`terminal of the suspension board with circuit shown in FIG.
`1, and
`FIG. 13 is a sectional view taken along a longitudinal
`direction of the wiring, showing a further embodiment of the
`magnetic head connecting terminal and external connecting
`terminal of the suspension board with circuit shown in FIG.
`1.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`Referring to FIG. 1, there is a perspective view showing
`a suspension board with circuit presented in the form of an
`embodiment of a wired circuit board of the present inven
`tion. The suspension board with circuit 11 mounts thereon a
`magnetic head of a hard disk drive (not shown) and suspends
`the magnetic head while holding a minute interval between
`the magnetic head and a magnetic disk against airflow
`generated when the magnetic head and the magnetic disk run
`relative to each other. The suspension board with circuit has
`lines of wire 14a, 14b, 14c, 14d, integrally formed therewith
`in the form of a specific circuit pattern, for connecting the
`magnetic head and a read/write board formed as an external
`circuit.
`In FIG. 1, the suspension board with circuit 11 has a base
`layer 13 formed as an insulating layer of insulating material.
`The base layer 13 is formed on a supporting board 12
`extending longitudinally as a metal supporting layer. The
`conductive layer 14 is formed on the base layer 13 in the
`form of a specific circuit pattern. The circuit pattern is
`provided in the form of the plurality of lines of wire 14a,
`14b, 14c, 14d arrayed in parallel and spaced apart at a
`predetermined interval.
`Gimbals 15 for fitting the magnetic head therein are
`formed in the supporting board 12 by cutting out the
`supporting board 12 at a front end portion thereof. Formed
`at the front end portion of the supporting board 12 are
`magnetic head connecting terminals 16 to connect the mag
`netic head and the lines of wire 14a, 14b, 14c, 14d. Formed
`at the rear end portion of the supporting board 12 are
`external connecting terminals 17 to connect the read/write
`board and the lines of wire 14a, 14b, 14c, 14d. Though not
`shown in FIG. 1, the conductive layer 14 is actually covered
`with a cover layer 18 made of insulating material.
`In this suspension board with circuit 11, the cover layer 18
`is opened to expose a front side of the conductive layer 14
`and also the supporting board 12 and the base layer 13 are
`opened to expose a back side of the conductive layer 14, so
`as to expose both sides of the conductive layer 14, and then
`the metal plating layers 19 as metal terminal layers are
`formed on both sides of the exposed conductive layer 14,
`whereby the magnetic head connecting terminals 16 and the
`external connecting terminals 17 are each formed as a
`terminal with its both sides being exposed, such as the
`so-called Flying Lead, as shown in FIG. 2. In FIG. 2, a
`ground 20 and a thin metal film 22 as will be mentioned later
`are omitted.
`
`HUTCHINSON EXHIBIT 1008
`
`

`

`5
`Referring now to FIGS. 3 to 6, a process for manufac
`turing the suspension board with circuit 11 will be described.
`Illustrated at the right side of FIGS. 3–6 are sectional views,
`taken along the longitudinal direction of the lines of wire
`14a, 14b, 14c, 14d, of a part of the suspension board with
`circuit 11 in which the magnetic head connecting terminals
`16 and the external connecting terminals 17 are formed.
`Illustrated at the left side of FIGS. 3–6 are sectional views,
`taken along a direction orthogonal to the longitudinal direc
`tion of the lines of wire 14a, 14b, 14c, 14d, of a certain part
`of the suspension board with circuit 11.
`First, the supporting board 12 is prepared and the base
`layer 13 is formed on the supporting board 12 in the form of
`a specified pattern, as shown in FIG. 3. A metal foil or a
`metal sheet is preferably used as the supporting board 12.
`For example, stainless steel, 42 alloy and the like are
`preferably used. The supporting board used preferably has a
`thickness of 10–60 um, or further preferably 15–30 u?um,
`and a width of 50–500 mm, or further preferably 125–300
`II li?m.
`Insulating material used for forming the base layer 13 is
`not limited to any particular insulating material. The insu
`lating materials that may be used include, for example,
`synthetic resins such as polyimide resin, acrylic resin, poly
`ether nitrile resin, polyether sulfonic resin, polyethylene
`terephthalate resin, polyethylene naphthalate resin and poly
`vinyl chloride resin. Of these synthetic resins, a photosen
`sitive synthetic resin is preferably used as the base layer 13.
`A photosensitive polyimide resin is further preferably used.
`Then, for example, in the case where the base layer 13 is
`formed in the specified pattern on the supporting board 12 by
`using photosensitive polyimide resin, a liquid solution of a
`precursor of the photosensitive polyimide resin is, as shown
`in FIG. 3(b), applied to the whole area of the supporting
`board 12 prepared as shown in FIG. 3(a), first, and then is
`heated at 60–150° C., or preferably at 80–120° C., to form
`a coating 13a of the precursor of the photosensitive poly
`imide resin.
`Then, the coating 13a is exposed to light through photo
`masks 24 and 32, as shown in FIG. 3(c). If required, the
`exposed part is heated to a specified temperature. Thereafter,
`the coating 13a is developed to form the coating 13a into a
`specified pattern. Preferably, radiation irradiated for the
`exposure has an exposure wavelength of 300–450 nm, or
`preferably 350–420 mm. An integrated quantity of exposure
`light is preferably of 100–1,000 m.J/cm3, or further prefer
`ably 200–700 m.J/cm3. Further, when the exposed part of the
`coating 13a irradiated is heated, for example, at temperature
`of not less than 130° C. to less than 150° C., it is solubilized
`(positive type) for the next processing procedure
`(development), while on the other hand, when heated, for
`example, at temperature of not less than 150° C. to not more
`than 180° C., it is non-solubilized (negative type) for the
`next processing procedure (development). The development
`can be performed by any known method, such as a dipping
`process and a spraying process, by using a known develop
`ing solution such as alkaline developer. Preferably, the
`manufacturing method uses the negative type to produce the
`circuit pattern. Illustrated in FIG. 3 is an embodiment using
`the negative type of process steps for patterning the circuit.
`As shown in FIG. 3(d), the coating 13a of the precursor
`of the polyimide resin thus patterned is finally heated, for
`example, to 250° C. or more to be cured (imidized), whereby
`the base layer 13 of polyimide resin is formed in the
`specified pattern.
`In this method, in the step of forming the base layer 13 on
`the supporting board 12 in the specified pattern, an opening
`
`10
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`US 6,388,201 B2
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`6
`portion 31 of the base layer 13, which is opened in the later
`stage to expose the conductive layer 14, is made to have a
`smaller thickness than the remaining portions of the base
`layer 13, for forming the magnetic head connecting termi
`nals 16 and the external connecting terminals 17.
`The opening portion 31 of the base layer 13 can be made
`to have a smaller thickness than the remaining portions of
`the base layer 13, for example by use of a photomask 32
`formed to have different transmissivity of irradiated light
`between the opening portion 31 of the coating 13a and the
`remaining portions of the coating 13a. After this photomask
`32 is positioned over the opening portion 31 of the base layer
`13, the coating 13a is exposed to light through the photo
`mask 32 so that the opening portion 31 and the remaining
`portions of the coating 13a can be exposed in different
`amount of light exposure, and then is developed and cured.
`The photomask 32 thus formed can allow the opening
`portion 31 and the remaining portions of the coating 13a to
`be exposed in different amounts of light exposure, thus
`enabling the opening portion 31 to have a smaller thickness
`than the remaining portions of the coating 13a in a simple
`and reliable manner.
`To be more specific, when the coating 13a is patterned
`with a negative image, as shown in FIG. 3(c) and 3(d), the
`photomask 32 may be so structured that the transmissivity of
`irradiated light in the opening portion 31 of the coating 13a
`can be reduced more (preferably not more than 80% of the
`remaining portions) than in the remaining portions of the
`coating 13a. After this photomask 32 is positioned over the
`opening portion 31 of the base layer 13, the coating 13a is
`exposed to light through the photomask 32, so that the
`amount of light exposure in the opening portion 31 of the
`coating 13a is reduced more than the amount of light
`exposure in the remaining portions of the coating 13a, as
`shown in FIG. 3(c). Then, the coating 13a is developed and
`cured, as mentioned above. This can produce a smaller
`thickness for the opening portion 31 of the base layer 13 than
`that of the remaining portions of the base layer 13.
`The photomask 32 may be formed to have difference
`transmissivity of irradiated light between the opening por
`tion 31 of the coating 13a and the remaining portions of the
`coating 13a by the following manner. For example, an area
`of the surface of the photomask 32 corresponding to the
`opening portion 31 is finely roughened so that components
`of irregular reflection on the area of the photomask 32 can
`be increased to thereby produce reduced components of the
`transmitted light in that area. Or, an irradiated light absorb
`ing film is stuck on the area of the surface of the photomask
`32 corresponding to the opening portion 31 so that the
`components of the transmitted light in that area can be
`reduced. Or, a pattern having a light transmiting area and a
`light shielding area is formed on the area of the surface of
`the photomask 32 corresponding to the opening portion 31
`so that the components of the transmitted light in that area
`can be reduced.
`Further, in the case a photomask 32 of a thin metal film
`having a specified pattern is used, a thin metal film smaller
`than the thin metal film of the photomask 32 may be formed
`on the area of the surface of the photomask 32 corresponding
`to the opening portion 31 so that the components of the
`transmitted light in that area can be reduced. In other words,
`this photomask 32 is formed in the manner that after a
`photomask 32 having no thin metal film formed in the area
`thereof corresponding to the opening portion 31 (a conven
`tional photomask) is formed, a resist is formed on that
`photomask 32 so as to expose only the opening portion 31,
`
`HUTCHINSON EXHIBIT 1008
`
`

`

`7
`a thin metal film made of e.g. chromium smaller than the
`above-mentioned thin metal film is formed by vapor depo
`sition or by plating and, thereafter, the resist is peeled.
`These photomasks 32 can permit the amount of light
`exposure in the opening portion 31 to be surely adjusted by
`one exposure.
`Of these photomasks, the photomask having the pattern
`including the light transmiting area and the light shielding
`area formed on the area of the surface thereof corresponding
`to the opening portion 31 is preferably used. Specifically, the
`photomasks 32a, 32b, 32c, 32d shown in FIGS. 7–10 are
`preferably used.
`Each of these photomasks 32a, 32b, 32c, 32d shown in
`FIGS. 7–10 is made of a sheet of glass, such as quartz glass
`or soda glass, of thickness of 2–5 mm, and a thin metal film
`having a pattern is formed on an area of the glass corre
`sponding to the opening portion 31, such that the transmis
`sivity in that area can be reduced more than in the remaining
`areas. The pattern of the thin metal film can be formed, for
`example, by the process that after a thin metal film made of
`e.g. chromium is formed on the whole area of the glass by
`vapor deposition or by plating, the thin metal film is pat
`terned by use of laser or electron beam. These photomasks
`32a, 32b, 32c, 32d can permit the light exposure in the
`opening portion 31 to be surely controlled with a simple
`Structure.
`For example, the photomask 32a shown in FIG. 7 has, at
`its area corresponding to the opening portion 31, a striped
`pattern presented in the form of light transmitting portions
`and light shielding portions being alternately arranged at a
`not more than 6 um pitch (width of the light transmitting
`portion and the light shielding portion) so that the averaged
`transmissivity of that area can be about 50% with respect to
`the remaining areas.
`The photomask 32b shown in FIG. 8 has, at its area
`corresponding to the opening portion 31, a lattice pattern
`presented in the form of the light transmitting portions and
`the light shielding portions being alternately arranged at a
`not more than 6 um pitch (width of the light transmitting
`portion and the light shielding portion) so that the averaged
`transmissivity of that area can be about 25% with respect to
`the remaining areas.
`The photomask 32c shown in FIG. 9 has, at its area
`corresponding to the opening portion 31, a staggered pattern
`presented in the form of round light transmitting portions
`having a diameter of not more than 6 um being arranged in
`zigzag with respect to the remaining light shielding portion
`so that the averaged transmissivity of that area can be about
`25% with respect to the remaining areas.
`The photomask 32d shown in FIG. 10 has, at its area
`corresponding to the opening portion 31, a staggered pattern
`presented in the form of round light shielding portions
`having a diameter of not more than 6 um being arranged in
`zigzag with respect to the remaining light transmitting
`portion so that the averaged transmissivity of that area can
`be about 70% with respect to the remaining areas.
`Of the photomasks 32a, 32b, 32c, 32d shown in FIGS.
`7–10, those shown in FIGS. 7–9 of not more than 6 um in
`width (pitch or diameter) of the striped, latticed or rounded
`light transmitting portion are preferable. The light transmit
`ting portion having a width of not more than 6 um permits
`the opening portion 31 to be uniformly irradiated with the
`irradiated light of exposure wavelength of 300–450 nm as
`mentioned above, and as such can allow the thickness of the
`opening portion 31 to be uniformly reduced. In contrast to
`this, the light transmitting portion having a width of more
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`US 6,388,201 B2
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`8
`than 6 um increases the resolving power of irradiated light,
`to thereby produce undulations in the opening portion 31
`and, as a result, the opening portion 31 is made uneven in
`thickness so that the etching may not be performed in the
`later stage. Preferably, the light transmitting portion has a
`width of not more than 4 um, or further preferably not more
`than 3 um.
`The averaged transmissivity in the opening portion 31 is
`preferably 50% or less, or further preferably 25% or less,
`with respect to the remaining portions.
`The photomask 32 may be formed to be integral with the
`photomask 24 used for the patterning or may be formed to
`be separated therefrom.
`When the coating 13a is patterned with a positive image,
`the photomask 32 may be so structured that the transmis
`sivity of irradiated light in the opening portion 31 can be
`increased more than in the remaining portions.
`The opening portion 31 of the base layer 13 can be made
`smaller in thickness than the remaining portions of the base
`layer 13, for example, by using a plurality of photomasks of
`different patterns to subject the opening portion 31 to light
`exposure or light shielding alternately at least two times,
`other than by using the photomask 32 formed to have
`different transmissivity of irradiated light between the open
`ing portion 31 and the remaining portions.
`Further, when a photosensitive resin is not used to form
`the base layer 13, for example a resin may be applied or
`layered in the form of a dry film on the supporting board 12
`in the specified pattern. The opening 31 of the base layer 13
`can then be made smaller in thickness than the remaining
`part of the base layer 13, for example, by layering the resin
`two or more times and also by layering the resin in the
`opening portion 31 a fewer number of times than in the
`remaining portions.
`Preferably, the base layer 13 thus formed has a thickness
`of e.g. 2–30 um, or preferably 5–20 um. The base layer 13
`usually has a thickness of about 10 um. The thickness of the
`opening portion 31 of the base layer 13 is usually 80% or
`less of the thickness of the remaining portions. For example,
`the opening portion 31 preferably has a thickness of not
`more than 8 um, or further preferably not more than 5 um.
`Suppose that the opening portion 31 has a thickness of 8 um
`or less, when the remaining portions have a usual thickness
`of 10 um, as mentioned above, the time required for the
`opening to be formed in the later stage can be shortened by
`the extent corresponding to 2 um.
`The opening portion 31 of the base layer 13 may have a
`lower limit of thickness or a minimum thickness to serve as
`a barrier layer against the conductive layer 14 when the
`suppor