a2) United States Patent
`US 7,453,045 B2
`(0) Patent No.:
`Nov.18, 2008
`(45) Date of Patent:
`Myoungetal.
`
`US007453045B2
`
`RIGID-FLEXIBLE PCB HAVING COVERLAY
`
`MADEOF LIQUID CRYSTALLINE POLYMER
`AND FABRICATION METHOD THEREOF
`
`(58) Field of Classification Search ................. 174/254,
`174/259; 361/749-751
`See application file for complete search history.
`
`(54)
`
`(75)
`
`Inventors: Bum-Young Myoung,Seoul (KR);
`Dek-Gin Yang, Chungcheongbuk-do
`(KR); Dong-Kuk Kim, Kyunggi-do
`(KR)
`
`(73)
`
`Assignee: Samsung Electro-Mechanics Co. Ltd,
`Kyunggi-Do (KR)
`
`(*)
`
`Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21)
`
`Appl. No.: 11/440,806
`
`(22)
`
`Filed:
`
`May25, 2006
`
`(65)
`
`(62)
`
`(30)
`
`Prior Publication Data
`
`US 2006/0213683 Al
`
`Sep. 28, 2006
`
`Related U.S. Application Data
`
`Division of application No. 10/969,407, filed on Oct.
`20, 2004, now Pat. No. 7,082,679.
`
`Foreign Application Priority Data
`
`Jul. 26, 2004
`
`(KR) occ eect renee 2004-58315
`
`(51)
`
`(52)
`
`Int. Cl.
`
`(2006.01)
`HOS5K 1/00
`UWS. C1.
`ciececccccecceeescsecnscnsenes 174/254; 361/748
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`6,440,542 BL*
`7,348,492 B1*
`2003/0177635 Al*
`2004/0118596 Al*
`
`8/2002 Kariya oo... eee 428/209
`3/2008 Kawaietal. oe. 174/254
`9/2003 Arrington et al. oo... 29/830
`6/2004 Fuller et al. oe. 174/255
`
`JP
`JP
`JP
`JP
`JP
`
`FOREIGN PATENT DOCUMENTS
`2-92976
`7/1990
`04-026190
`1/1992
`2000-183506
`6/2000
`2002-280733
`9/2002
`2003 -264369
`9/2003
`
`* cited by examiner
`
`Primary Examiner—Jeremy C Norris
`(74) Attorney, Agent, or Firm—Gottlieb Rackman &
`Reisman, P.C.
`
`(57)
`
`ABSTRACT
`
`Disclosed are a rigid-flexible PCB and a methodfor fabricat-
`ing the rigid-flexible PCB. Characterized by using a liquid
`crystalline polymer for the formation of coverlay over flex-
`ible regions, the all-layer processing method has the advan-
`tage ofpreventing interlayer delamination, thereby providing
`a highly reliable rigid-flexible PCB which thus meets the
`recent requirements of electric appliances for low energy
`consumption, high frequency adoption, and slimness.
`
`6 Claims, 8 Drawing Sheets
`
`600
`
`400
`
`1
`
`APPLE 1029
`Apple v. Koss
`IPR2021-00381
`
`APPLE 1029
`Apple v. Koss
`IPR2021-00381
`
`1
`
`

`

`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 1 of 8
`
`US 7,453,045 B2
`
`FIG. 1
`
`PRIOR ART
`
`
`
`2
`
`

`

`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 2 of 8
`
`US 7,453,045 B2
`
`FIG. 2
`
`PRIOR ART
`
`
`
`3
`
`

`

`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 3 of 8
`
`US 7,453,045 B2
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`FIG. 3
`
`PRIOR ART
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`

`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 4 of 8
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`US 7,453,045 B2
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`FIG. 4
`
`
`
`
`Providing of a first
`base board including
`a liquid crystalline
`olymer whose one or
`
`both sides are cover
`with a copper foil layer
`
`
`Conduction of an image processing process
`on the copperfoil layer to form
`
`
`an
`tone
`Daten
`
`
`
`iti
`idrate ota cover ay Wl
`.
`of|tvvanercircult pattemn which corresponds
`to a flexible region ofthe first base board
`
`iquid crystalline polymer
`
`over a portion
`
`
`ding of
`
`
`another first base boar aro
`the first base bo
`
`an adhesive material
`
`
`
`Deposition of a second base board,
`.
`followed by conducting an umage, processing
`
`
`process to form an outer circuit pattern
`
`Formation of a coverlaywith a liquid.
`crystalline polymerover the flexible region
`
`
`
`
`ng
`of a photo imageablesolder resist
`oatin
`
`
`mask ink to protect theouter circuit pattern
`
`from a soldering process
`
`End
`
`$100
`
`$200
`
`5300
`
`5400
`
`$500
`
`S600
`
`$700
`
`5
`
`

`

`U.S. Patent
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`Nov. 18, 2008
`
`Sheet 5 of 8
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`US 7,453,045 B2
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`
`
` 110
`
`
`
`6
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`

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`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 6 of 8
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`US 7,453,045 B2
`
`HoST=
`a
`
`ROAAAARAAAAAAAARN.O.ONOOOh}INEMANS:
`
`400
`
`130'
`
`200
`
`7
`
`

`

`U.S. Patent
`
`Nov. 18, 2008
`
`Sheet 7 of 8
`
`US 7,453,045 B2
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`FIG. 5h
`
`400
`
`500
`
`130'
`
`200
`
`
`
`
`—_
`
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`
`
`
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`
`120'
`
`130
`110
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`
`400
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`
`510
`
`
`
`
`8
`
`

`

`U.S. Patent
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`Nov. 18, 2008
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`Sheet 8 of 8
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`US 7,453,045 B2
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`FIG. 5k
`
`400
`
`200"
`
`600
`
`SSK
`
`NEES EY
`
`
`
`
`
`
`600
`
`100
`
`
`
`9
`
`

`

`US 7,453,045 B2
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`10
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`25
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`1
`RIGID-FLEXIBLE PCB HAVING COVERLAY
`MADEOF LIQUID CRYSTALLINE POLYMER
`AND FABRICATION METHOD THEREOF
`
`This application is a Division of U.S. Ser. No. 10/969,407
`filed Oct. 20, 2004, now U.S. Pat. No. 7,082,679, the content
`of which is incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates to a rigid-flexible printed
`circuit board (PCB) which employsa liquid crystalline poly-
`mer. Moreparticularly, the present invention relates to a rigid-
`flexible PCB in which a coverlay is formed of a liquid crys-
`talline polymer over a flexible region by an all
`layer
`processing process. Also, the present invention is concerned
`with a methodfor fabricating such a rigid-flexible PCB.
`2. Description of the Prior Art
`With today’s ever smaller and slimmer packaging require-
`ments, various multilayer printed circuit boards have recently
`been developed which can have integrated electronic devices
`mounted on their surfaces. Particularly, rigid-flexible PCBs
`are underintensive study becausethey have the advantage of
`space economyand spatial variability.
`Extensively used in personal computers, PDAs and mobile
`phones, rigid-flexible PCBs usually comprise rigid regions
`which are supported by prepreg to impart mechanical
`strength to the PCBs, andflexible regions which connect the
`rigid regions to each other.
`In rigid flexible circuit boards are found coverlay films
`whichare responsible for the protectionofthe circuit patterns
`formed in the flexible regions and are usually madeof poly-
`imide.
`In orderto better understand the backgroundofthe inven-
`tion, a description will be given of conventional rigid-flexible
`PCBs andtheir fabrication with reference to FIGS. 1 to 3,
`below.
`FIG. 1 describes a partial coating method for forming a
`coverlay film on a predetermined portion ofa flexible region
`in a rigid-flexible PCB.
`First, while being masked, a copper foil layer 12 which,
`together with a polyimide layer 11, constitutes a polyimide
`copperfoil laminate 10, is patterned to form a predetermined
`inner circuit pattern (not shown) thereon.
`In order to protect the inner circuit pattern, then, a polyim-
`ide film 20 is provided as being larger in size than a flexible
`region within which the circuit pattern is confined.
`The polyimide film 20 is placed on the flexible region ofthe
`copperfoil layer 12 interleaved with an adhesive 21, followed
`by pseudo-bonding the polyimide film 20 to the flexible
`region manually with the aid of a soldering iron.
`After the bonding of the polyimide film 20 to the flexible
`region, a prepreg 30 is provided to give mechanical strength
`and bonding powerto the polyimide copperfoil laminate 10,
`as shownin FIG. 1.
`
`Afterwards, another copper foil laminate 10' in which a
`polyimide layer is open is pressurized against the prepreg 30
`to afford a single rigid-flexible PCB wherein therigid regions
`interleaved with the prepreg 30 are connected to each other
`via the flexible region whichis partially covered by the poly-
`imide coverlay.
`Construction ofa multilayer PCB can be achieved by bond-
`ing a single rigid-flexible PCB to anotherinterleaved with a
`prepreg 30' positioned at the axis of mirror symmetry, with
`the aid of a press. As seen in FIG.1, the multilayer PCB has
`rigid regions which are supported by prepregs 30 and 30' to
`
`2
`impart mechanical strength to the PCB, and flexible regions
`whichare partially covered with polyimide film 20 and con-
`nect the rigid regions to each other.
`Subsequently, etching and plating results in a via-hole for
`electrical interlayer connection while forming a predeter-
`minedouter circuit pattern, as shownin FIG.3.
`Next, a coverlay is formed of a polyimide film over a part
`ofthe outer circuit pattern which corresponds to the flexible
`region.
`Afterward, the PCBis coated with a photoimageable solder
`resist mask ink 160 to protect the outer circuit pattern 150 as
`well as to prevent solder bridge formation across the outer
`circuit pattern 150. As a result, there is obtained a single or
`multi-layer rigid-flexible PCB in which coverlays made of a
`polyimide film are formed overthe flexible region.
`Such rigid-flexible PCBs, however, require a long manu-
`facturing time and high production cost due to the coverlay
`processing and pseudo-bonding processes. In addition, the
`PCBs showslowreliability in circuit formation and stacking
`becauseofthe steps caused bythe partially deposited cover-
`lay films.
`To solve the problems, the overall portion of the flexible
`region is covered with a coverlay film, which is described
`with reference to FIG.2.
`
`First, while being masked, a copper foil layer 12 which,
`together with a polyimide layer 11, constitutes a polyimide
`copperfoil laminate 10, is patterned to form a predetermined
`inner circuit pattern (not shown) thereon.
`In orderto protectthe inner circuit pattern, a polyimide film
`20 is bonded using an adhesive 21 onto the inner circuit
`pattern, covering the entire flexible region.
`After the formation ofthe polyimidefilm colerlay 20 on the
`flexible region, a prepreg 30 is provided to give mechanical
`strength and bonding power to the polyimide copper foil
`laminate 10, as shownin FIG.2.
`Afterwards, another copper foil laminate 10', in which a
`polyimidelayeris open, is pressurized against the prepreg 30
`to afford a single rigid-flexible PCB wherein therigid regions
`supported by the prepreg 30 are connected to each other via
`the flexible region which is fully covered by the polyimide
`coverlay.
`Construction ofa multilayer PCB can be achieved by bond-
`ing a single rigid-flexible PCB to anotherinterleaved with a
`prepreg 30' positioned at the axis of mirror symmetry, with
`the aid of a press. As seen in FIG.2, the multilayer PCB has
`rigid regions which are supported by prepregs 30 and 30' to
`impart mechanical strength to the PCB, and flexible regions
`whichare fully covered with polyimide film 20 and intercon-
`nect the rigid regions to each other.
`Subsequently, etching and plating results in a via-hole for
`electrical interlayer connection while forming a predeter-
`minedouter circuit pattern, as shownin FIG.3.
`Next, a coverlay is formed of a polyimide film over a part
`ofthe outer circuit pattern which corresponds to the flexible
`region.
`Afterward, the PCBis coated with a photoimageable solder
`resist mask ink 160 to protect the outer circuit pattern 150 as
`well as to prevent solder bridge formation across the outer
`circuit pattern 150. As a result, there is obtained a single or
`multi-layer rigid-flexible PCB in which coverlays made of a
`polyimide film are formed overthe flexible region.
`When a coverlay madeof the polyimide film is deposited
`overthe entire flexible region, the fabrication of PCB can be
`simplified comparedto the partial coating process described
`in FIG. 1 because the pseudo-bonding and coverlay process-
`ing can be omitted.
`
`10
`
`10
`
`

`

`US 7,453,045 B2
`
`4
`a plurality offirst coverlays, each deposited over a portion of
`the inner circuit pattern which corresponds to a flexible
`region; a plurality of adhesives through which the first base
`boards are bonded to each other in such a waythat the crys-
`talline liquid polymers face each other; a plurality of second
`base boards, each having an outer circuit pattern and being
`deposited overthe first base board using an adhesive material;
`a plurality of second coverlays, each deposited over a portion
`of the outer circuit pattern, covering the flexible region of the
`second base board; and a plurality of solder masks for pro-
`tecting the outercircuit pattern.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates the position of a flexible region in a
`rigid-flexible PCB fabricated according to a conventional
`partial coating process using a polyimidefilm.
`FIG. 2 illustrates the position of a flexible region in a
`rigid-flexible PCB fabricated according to a conventionalfull
`coating process using a polyimidefilm.
`FIG. 3 is a cross sectional view of a rigid-flexible PCB
`according to the conventional process.
`FIG.4 is a flow chart showingtheall-layer processing for
`fabricating a rigid-flexible PCB according to the present
`invention.
`
`FIG. 5 provides cross sectional views showing the fabrica-
`tion of a rigid-flexible PCB according to the present inven-
`tion.
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`An all-layer processing processfor the fabrication ofrigid-
`flexible PCBs according to the present invention will be
`described in detail with reference to the accompanying draw-
`ings.
`With reference to FIGS. 4 and 5, there are a flow chart and
`cross sectional viewsillustrating the fabrication of a rigid-
`flexible PCB according to the present invention.
`Provided first is a liquid crystalline polymer copperfoil
`laminate 100 which will act as a first base board for the
`
`3
`However,the face ofthe coverlay polyimidefilm 20, which
`is not coated with the adhesive 21, has such a low surface
`energy dueto its characteristic stiff molecular structure as to
`weakly bond with the prepreg 30 and 30'. Accordingly, the
`coverlay is easily delaminated from the prepreg 30 and 30'"
`which deteriorates productreliability. That is, when the poly-
`imidefilm 20 for coverlay is bonded with the adhesive 21 to
`the flexible region, delamination between the polyimide film
`20 and the adhesive 21 occurs because of the different coef-
`
`ficients of thermal expansion therebetween andthe low ther-
`mal stability thereof.
`Problems with the conventional processes also include
`poor dimensional stability in products and high dielectric
`constant in insulation layers because the polyimide film 20
`has low surface energy and polar polyermic chains. Thus, it is
`difficult to achieve low power consumption, high frequency
`adoption, and slimness for conventional products.
`Further, the high cost of the polyimide film impedes the
`price competitiveness of the conventional products.
`
`SUMMARYOF THE INVENTION
`
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`Leading to the present invention, the intensive and thor-
`ough research on rigid-flexible PCBs, conducted by the
`present inventors, resulted in the finding that an all layer
`process employing liquid crystalline polymers can avoid
`interlayer delamination as well as achieving light, slim, short
`and small rigid-flexible PCBs.
`It is an object of the present invention to provide a rigid-
`flexible PCB which shows low power consumption and high
`frequency availability as well as being highly reliable, inex-
`pensive and slim.
`It is another object of the present invention to provide a
`methodfor fabricating the rigid-flexible PCB.
`According to one aspect of the present invention,there is
`provided a method for fabricating a rigid-flexible printed
`circuit board, comprising the steps of: providing a first base
`board including a liquid crystalline polymeroneor both sides
`of which are covered with a copperfoil layer; conducting an
`image processing process on the copperfoil layer to form an
`inner circuit pattern; forming a coverlay with a liquid crys-
`rigid-flexible PCB (S100). The liquid crystalline polymer
`talline polymer over a portion of the inner circuit pattern
`copper foil laminate 100 comprises a liquid crystalline poly-
`which correspondsto a flexible region of thefirst base board;
`merlayer 110 one or both sides of which are covered with a
`bondingthe first base board to anotherfirst base board using
`copperfoil layer 120.
`an adhesive material in such a waythat the liquid crystalline
`For convenience, the description will continue using as an
`polymers of the resulting structure are interleaved with the
`examplealiquid crystalline polymer copperfoil laminate 100
`adhesive material and face each other, said adhesive material
`which has a copperfoil layer 120 formed on oneside of the
`being open at a portion correspondingto the flexible region;
`liquid crystalline polymer layer 110, as shown in FIG. 5a.
`depositing a second base board, consisting of a copper foil
`However, it should be understood that a liquid crystalline
`layer and a liquid crystalline polymerlayer, over each side of
`polymer copper foil laminate having two copper foil layers
`the bondedfirst base board structure in such a way that the
`interleaved with a liquid crystalline polymer layer therebe-
`liquid crystalline polymerlayer of the second base board is
`tweenalso falls into the spirit and scope of the present inven-
`positioned to face to the inner circuit pattern ofthefirst base
`tion.
`board, said liquid crystalline polymerbeing openat a portion
`Then, image processing is conducted on the copperfoil
`corresponding to the flexible region; conducting imagepro-
`layer 120 ofthefirst base board 100 (S200).
`cessing on the copperfoil layer of the second base board to
`form an outer circuit pattern; forming a coverlay with a liquid
`In more detail, a photosensitive dry film is thermally pres-
`crystalline polymerovera portion ofthe outer circuit pattern
`surized against the copper foil layer 120 by use ofahotroller,
`which correspondsto the flexible region; and coating the PCB
`followed by the close adherence of an artwork film having a
`with a photo imageable solder resist mask ink to form a solder
`predetermined inner circuit pattern to the photosensitive dry
`mask for protecting the outer circuit pattern from a soldering
`film. Subsequently, when exposed to UV light through the
`process.
`patterned artwork film, the photosensitive dry film is cured.
`According to another aspect of the present invention, there
`Treatment with a developing solution such as sodium carbon-
`is provided a rigid-flexible printed circuit board, comprising:
`ate or potassium carbonate dissolves the uncured region ofthe
`aplurality offirst base boards, each having a liquid crystalline
`photosensitive dry film to make the copperfoil layer 120 of
`polymerlayer one or both sides of which are covered with a
`the liquid crystalline polymercopperfoil laminate 100 open.
`copperfoil layer on which an innercircuit pattern is formed;
`With the remaining cured photosensitive film pattern serving
`
`11
`
`

`

`US 7,453,045 B2
`
`5
`as a mask, the open copper foil layer 120 is etched to form a
`predeterminedinnercircuit pattern 130, as shown in FIG.58.
`Afterwards, a coverlay 200 is provided for protecting from
`the external environment a part of the inner circuit pattern
`130' at which a flexible region will be formed (S300).
`The coverlay 200 is formedofthe same material used in the
`liquid crystalline polymer layer 110 of the first base board
`100. In this regard, the liquid crystalline polymeris deposited
`at 230-300° C. for 20-120 min under a pressure of 10-60
`kgf/cm overall or part of the flexible region, as seen in FIG.
`5c.
`
`Using a liquid crystalline polymer which can be molded at
`the above temperature (e.g., 240° C.), the coverlay 200 may
`be formed in a single layer or a multi-layered structure. In the
`latter case, an adhesive may be used to bond the coverlay
`layers. Exemplified by epoxyoracryl, adhesives suitable for
`use in the formation of such a multiple layer structure have a
`melting point similar to the molding temperature (e.g., 240°
`C.). When the coverlay 200 is constructed in a multilayer
`structure, to prevent the interlayer conjunction oftheflexible
`regions upon subsequent molding processes, materials for the
`coverlay and the adhesive may be liquid polymers if the
`coverlay material has a higher melting point (e.g., 275° C.)
`thanthat of the adhesive material(e.g., 240° C.).
`In addition, the coverlay 200 interleaved with an epoxy or
`acrylic adhesive may be formedat a slightly lower tempera-
`ture, e.g., 120-150° C. for 20-120 min, overall or part of the
`flexible region.
`Following the formation of the coverlay 200 over the flex-
`ible region,the resulting structure is bonded to anotherresult-
`ing structure through an adhesive material 300, in such a way
`that the base boards 110 of the twostructures face each other
`(S400). The adhesive material 300 is open at a position cor-
`responding to the flexible region of the base board 110, as
`seen in FIG. 5d. The adhesive material 300 is preferably a
`liquid polymer which showsa strong adhesive strength when
`pressurized at a predetermined temperature. Also, the adhe-
`sive material 300 imparts mechanicalstrength to the resulting
`rigid-flexible PCB.
`Both the top and bottom sides of the resulting structure
`consisting oftwoofthefirst base boards 100 interleaved with
`the adhesive material 300, are covered with a second base
`board 100", followed by conducting image processing to form
`an outer circuit pattern (S500).
`In detail, a second base board 100'", in which an outer circuit
`pattern will be formed, is stacked on each ofthe first base
`boards which are bonded using the adhesive material 300,
`facing each other, as seen in FIG. 5e. The second base board
`100' comprises a liquid crystalline polymer 110' which is
`open at a portion corresponding to the flexible region of the
`first base board. One or both sides of the second base board
`are covered with a copper foil layer 120'. Upon stacking the
`second base board 100' onto the first base board 100, the
`liquid crystalline polymer 110' of the second base board 100'
`is positionedto face to the innercircuit pattern 130 ofthefirst
`base board 100.
`
`Pressing the stacked resulting structure includingthefirst
`base boards 100 and the second base boards 100' forms a
`single- or multi-layer rigid-flexible PCB in which a rigid
`region supported by the adhesive material 300 imparts a
`mechanical strength and a flexible region covered with the
`coverlay 200 connects the rigid region, as seen in FIG. 5f
`Subsequently, a via-hole 400 is formed through which the
`layers of the rigid-flexible PCB are electrically intercon-
`nected, as seen in FIG. 5g. The formationof the via-hole 400
`is conducted at a spindle speed of 70,000-120,000, at a feed
`speed of 1.5-3.0 m/min ata retract rate of 11-13 m/min.
`
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`6
`Lowerin thermal expansion than polyimideresin, the liquid
`crystalline polymer showsexcellent laser drill processability.
`Preferably, laser drilling is conducted in a short time and
`manytimesin order to prevent deterioration ofthe sidewall of
`the via-hole formed.
`
`Next, plating is conducted over the resulting structure
`including the via-hole 400 to give form a plate layer 500
`which will be provided for the formation of an outer circuit
`pattern as seen in FIG. 5h.
`After a masking process on the plate layer 500, a predeter-
`minedouter circuit pattern 510 is formed, as shown in FIG.5i.
`A detailed description of the formation of the outer circuit
`pattern 510 is omitted because its procedure is the same as
`described with reference to FIG. 58.
`
`Using the liquid crystalline polymer as described above, a
`coverlay 200' is formed over a portion of the outer circuit
`pattern 510 which correspondsto the flexible region (S600).
`At 230-300° C. for 20-120 min undera pressure of 10-60
`kgf/em?, the liquid crystalline polymer for the formation of
`the coverlay 200' is deposited overall or part of the flexible
`region, as shown in FIG.57.
`Using a liquid polymer which can be moldedat the above
`temperature (e.g., 240° C.), the coverlay 200' may be formed
`ina singlelayer or a multi-layerstructure. In the latter case, an
`adhesive maybe used to bond the coverlay layers. Exempli-
`fied by epoxyor acryl (not shown), adhesives suitable for use
`in the formation of such a multiple coverlay structure have a
`melting point similar to the molding temperature (e.g., 240°
`C.). When the coverlay 200' is constructed in a multilayer
`structure, to prevent the interlayer conjunction oftheflexible
`regions upon subsequent molding processes, materials for the
`coverlay and the adhesive may be liquid polymers if the
`coverlay material has a higher melting point (e.g., 275° C.)
`thanthat of the adhesive material (e.g., 240° C.).
`Alternatively, the coverlay 200' interleaved with an epoxy
`or acrylic adhesive may be formedat a slightly lower tem-
`perature, e.g., 120-150° C. for 20-120 min,overall or part of
`the flexible region.
`Finally, a photo imageable solder resist mask ink 600 is
`selectively applied to the resulting structure to protect the
`outer circuit pattern 510 from a soldering process (S700). In
`this regard, the photo imageable solder resist mask ink 600
`protects the outer circuit pattern 610 as well as serving to
`prevent a solder bridge across the outer circuit pattern 610
`during a soldering process.
`FIGS. 54 and 5/ show structures of the rigid-flexible PCBs
`fabricated according to the all-layer process of the present
`invention, which employ a base board 100 having a copper
`foil layer deposited over one face of a liquid crystalline poly-
`mer and a base board 100 having two copper foil layers
`interleaved with a liquid crystalline polymer, respectively.
`Characterized by using a liquid crystalline polymerfor the
`formation of coverlay overflexible regions, the all-layer pro-
`cessing method according to the present invention has the
`advantage ofpreventing interlayer delamination,thus provid-
`ing a highly reliable rigid-flexible PCB.
`Also, the rigid-flexible PCB fabricated according to the
`all-layer processing of the present invention meets the recent
`requirementsofelectric appliances for low energy consump-
`tion, high frequency adoption, and slimness.
`Additionally, the use of liquid crystalline polymers reduces
`the production cost because the polymers are inexpensive.
`Although the preferred embodimentof the present inven-
`tion has been disclosed forillustrative purposes, those skilled
`in the art will appreciate that various modifications, additions
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`US 7,453,045 B2
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`and substitutions are possible, without departing from the
`scope andspirit of the invention as disclosed in the accom-
`panying claims.
`The invention claimedis:
`1. A rigid-flexible printed circuit board, comprising:
`a plurality of first base boards, each having a liquid crys-
`talline polymer layer one or both sides of which are
`covered with a copperfoil layer on which an innercircuit
`pattern is formed;
`a plurality of first coverlays, each deposited over a portion
`ofthe innercircuit pattern which correspondsto a flex-
`ible region;
`aplurality of adhesives through whichthefirst base boards
`are bondedto each other in such a waythat the crystal-
`line liquid polymers face each other;
`a plurality of second base boards, each having an outer
`circuit pattern and being deposited over the first base
`board through an adhesive material;
`aplurality of second coverlays, each deposited over a por-
`tion of the outer circuit pattern, covering the flexible
`region of the second base board; and
`a plurality of solder masks for protecting the outercircuit
`pattern.
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`2. The rigid-flexible printed circuit board as set forth in
`claim 1, wherein the first and the second coverlays are depos-
`ited in a multi-layer structure with the use of an adhesive by
`pressing a liquid crystalline polymer at a predetermined
`molding temperature against a portion of the inner and the
`outer circuit patterns which correspondto the flexible region.
`3. The rigid-flexible printed circuit board as set forth in
`claim 2, wherein the adhesive is selected from among a liquid
`crystalline polymer, an epoxy resin and an acryl resin.
`4. The rigid-flexible printed circuit board as set forth in
`claim 2, whereinthefirst and the second coverlays are respec-
`tively deposited over the inner and the outercircuit patterns,
`overlapping the flexible region.
`5. The rigid-flexible printed circuit board as set forth in
`claim 2, whereinthefirst and the second coverlays are respec-
`tively deposited over the inner and the outercircuit patterns,
`fully covering the flexible region.
`6. The rigid-flexible printed circuit board as set forth in
`claim 1, wherein the adhesive for bonding the first base
`boards to each other is a liquid crystalline polymer.
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