US007281328B2
`
`a2) United States Patent
`US 7,281,328 B2
`(10) Patent No.:
`
` Leeet al. (45) Date of Patent: Oct. 16, 2007
`
`
`(54) METHOD OF FABRICATING
`RIGID-FLEXIBLE PRINTED CIRCUIT
`BOARD
`
`(75)
`
`Inventors: Yang Je Lee, Chungcheongbuk-do
`(KR); Dek Gin Yang,
`Chungcheongbuk-do (KR); Jung Wook
`Hwang, Gyeongsangnam-do (KR); Kyu
`Hyok ‘Yim, Chungcheongbuk-do (KR);
`Jung Hun Chai, Jeollabuk-do (KR);
`Young Ho Lee, Daegu (KR); Kwang
`Yune Kim, Daejeon (KR); Dong Gi
`An, Chungcheongnam-do (KR)
`
`(58) Field of Classification Search .................. 29/846,
`29/847, 852; 174/262, 254, 255; 427/97.1,
`427/97.7
`See application file for complete search history.
`.
`References Cited
`U.S. PATENT DOCUMENTS
`
`(56)
`
`5,095,628 A *
`5,206,463 A *
`6,745,463 BL*
`
`........... 29/846
`3/1992 McKenneyet al.
`4/1993 DeMasoet al... 174/254
`6/2004 Chou ou... eeeeee 29/852
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`
`2003-101167 A
`
`4/2003
`
`(73) Assignee: Samsung Electro-Mechanics Co., Ltd.,
`Kyunggi-Do (KR)
`
`* cited by examiner
`
`(*) Notice:
`
`Subject to any disclaimer, the term ofthis
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`Primary Examiner—Richard Chang
`(74) Attorney, Agent, or Firm—Darby & Darby P.C.
`
`(57)
`
`ABSTRACT
`
`(21) Appl. No.: 11/253,973
`
`(22)
`
`Filed:
`
`Oct. 18, 2005
`
`(65)
`
`(30)
`
`Prior Publication Data
`
`US 2006/0101640 Al
`
`May 18, 2006
`
`Foreign Application Priority Data
`
`Oct. 28, 2004
`
`(KR) eee 10-2004-0086731
`
`(51)
`
`Int. Cl.
`(2006.01)
`HOIK 3/10
`(52) U.S. Ch cc eeeeeeees 29/852; 29/846; 29/847;
`174/254; 174/262; 427/97.1; 427/97.7
`
`The present invention is related to a methodof fabricating a
`rigid-flexible printed circuit board. Specifically, this inven-
`tion relates to a methodoffabricating a rigid-flexible printed
`circuit board, in which an internal circuit pattern exposed for
`use in an external pad and a mounting padis protected from
`external environments using a resist cover by window
`etching the base copper foil of a flexible region upon
`formation of an external circuit pattern as opposed to using
`a resist cover. Thus the numberof fabrication processes and
`the fabrication costs are decreased andthe increase in defect
`rates due to contamination is prevented, resulting in maxi-
`mizedreliability.
`
`5 Claims, 7 Drawing Sheets
`
`°,.05mm~5mm
`
`
`
`
`
`LLLLILLEELLEREA
`
`
`
`
`
` RMPMOoy}
`
`XXgCGCREMSN
`
`1
`
`APPLE 1028
`Apple v. Koss
`IPR2021-00381
`
`APPLE 1028
`Apple v. Koss
`IPR2021-00381
`
`1
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 1 of 7
`
`US 7,281,328 B2
`
`FIG. 1A
`
`Prior Art
`
`
`
`FIG. 1B
`
`Prior Art
`
`
`
`1¢C
`FIG.
`Prior Art
`
`20
`30
`
`
`
` BRRRARERSRhee SS
`
`
`
`FIG. 1D
`
`Prior Art
`
`2
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 2 of 7
`
`US 7,281,328 B2
`
`
`
`
`
`LLELLL pay eeeSDN
`VSftS]
`
` SS>>>
`. >N
`
`WE)GS
`LLLLL,
`
`
`
`
`
`
`
`ANK CLLMMLALLLLLLLILEELLSE
`RRROy
`
`
`
`
`40
`
`
`
`3
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 3 of 7
`
`US 7,281,328 B2
`
`FIG. 1G
`Prior Art
`
`4
`
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 4 of 7
`
`US 7,281,328 B2
`
`FIG. 11
`Prior Art
`
`
`
`FIG. 2A
`
`7
`RRRQEEESEEESSEEESSSESSSSSSEAoe12
`
`ts
`
`110
`
`FIG. 2B
`
`Llu. 120
`
`RkkhSESESSEESEEEESSSEES 112
`
`5
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 5 of 7
`
`US 7,281,328 B2
`
`
`
`130
`
`
`SSSSANNAANAAANUSANANNANSNARRNANNN
`
`S| ERSSs SE
`
`
`
`
`WTILLLLLLLLLLLL
`
`SS REET
`
`6
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 6 of 7
`
`US 7,281,328 B2
`
`aee
`
`RESETS
`
`IKB
`
`NEZ ROSS
`
` SDSMOHPMW Ea, a7
`
`
`WYLLLELLLLALALL
`stt|Ber
`
`
`NKKKK
`MLLLebelehueepeeKe
`
`FIG. 21
`
` LLLLLLPLEPELEKERBee
`
`
`
`
`S&Sissxws_ 8
`
`
`
`
`
`
`i
`
`ZX
`eSs
`
`.S
`
`
`
`SLLLLLALLALL
`
`7
`
`

`

`U.S. Patent
`
`Oct. 16, 2007
`
`Sheet 7 of 7
`
`US 7,281,328 B2
`
`pee)TIN
`
`BE
`DLE)
`
`FIG. 3
`
`140
`
`8
`
`
`
`
`

`

`US 7,281,328 B2
`
`1
`METHOD OF FABRICATING
`RIGID-FLEXIBLE PRINTED CIRCUIT
`BOARD
`
`INCORPORATION BY REFERENCE
`
`The present application claims priority under 35 U.S.C.
`§119 to Korean Patent Application No. 10-2004-0086731
`filed on Oct. 28, 2004. The content of the application is
`incorporated herein by reference in its entirety.
`
`10
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates, generally, to a method of
`fabricating a rigid-flexible printed circuit board (rigid-flex-
`ible PCB), and moreparticularly, to a methodoffabricating
`a flyingtail type rigid-flexible PCB that eliminates the need
`for a resist cover serving to protect a pad portion exposed for
`use in an external pad and a mounting pad from external
`environments, by window etching the base copperfoil of a
`flexible region upon the formation of an external circuit
`pattern, instead of using the resist cover.
`2. Description of the Related Art
`Recently, while the degree of integration of semiconduc-
`tor devices is gradually increasing,
`the number of pads
`provided on semiconductor devices to connect the semicon-
`ductor devices to external circuits is increasing and the
`mounting density is also increasing. For example, when a
`minimum processing dimension on the semiconductor
`device formed ofsilicon is about 0.2 tum, about 1000 pads
`maybe provided on a semiconductor device having a size of
`about 10x10 mm.
`
`Further, in semiconductor apparatuses, such as semicon-
`ductor packages, having the semiconductor devices mounted
`thereon, the size and thickness of the apparatus should be
`decreased to increase the mounting density. In particular,
`small and thin semiconductor packages are required for
`portable information apparatuses, such as notebook type
`PCs, PDAs, mobile phones, etc.
`For packaging the semiconductor device, while the semi-
`conductor device is mounted on a wiring substrate, the pad
`of the semiconductor device should be connected to the pad
`of the wiring substrate. However, in the case where about
`1000 pads are provided on the about 10x10 mm sized
`semiconductor device, they come to have fine pitches of
`about 40 ym. Hence, with the aim of connecting the pad
`having the fine pitch of the semiconductor device to the pad
`of the wiring substrate, very high accuracy is required for
`wiring on the wiring substrate or position-matching upon
`connection. Eventually, it is difficult to apply conventional
`wire bonding techniques or tape automated bonding (TAB)
`techniques.
`To solve the problem, the use of a rigid-flexible PCB
`having rigid and flexible regions interconnected without the
`use of an additional connector by structurally bonding a
`rigid substrate and a flexible substrate together is more and
`more frequently proposed. In particular, the rigid-flexible
`PCB is mainly applied to small terminals, such as mobile
`phones, realizing high integration by removing unnecessary
`space dueto the use of the connector, depending on require-
`ments offine pitches and high integration of mounting parts
`in proportion to high functionality of the mobile appara-
`tuses.
`
`Although the rigid-flexible substrate is manufactured in
`the most commonly used rigid-flexible-rigid form or the
`
`25
`
`30
`
`35
`
`40
`
`45
`
`65
`
`2
`rigid-flexible form, the present invention is directed to a
`flying tail type comprising only rigid-flexible regions.
`Referring to FIGS. 1A to 1], a conventional process of
`fabricating a flying tail type rigid-flexible PCB is sequen-
`tially shown.
`In a polyimide copper clad laminate 10 including a
`polyimide layer 11 and a copper foil 12, the copper foil 12
`is subjected to a photolithographic process to form an
`internal circuit pattern having a predetermined shape (FIG.
`1A).
`Then,to protect the internal circuit pattern corresponding
`to a flexible region, which is to be formed on the polyimide
`copper clad laminate 10, from the external environment, a
`polyimide film 20 is processed to suit the flexible region.
`The processed polyimidefilm 20 is attachedto the part of
`the flexible region having the corresponding internal circuit
`pattern, using an adhesive, after which the polyimidefilm 20
`is temporarily bonded through manual soldering, thereby
`completing the process of forming a coverlay (FIG. 1B).
`After the formation of the coverlay corresponding to the
`part of the flexible region using the polyimide film 20, a
`resist cover 30 is formed on the other part of the flexible
`region (FIG. 1C).
`Theresist cover 30 functions to protect the internal circuit
`pattern exposed for use in an external pad and a mounting
`pad from external environments, and includes, for example,
`heat-resistant tape or peelable ink. In addition, the resist
`cover 30 is removed after the completion of the substrate,
`unlike the polyimide film 20.
`Subsequently, to confer mechanical strength and adhesive
`strength to a rigid region, which is to be formed on the
`polyimide copper clad laminate 10, prepregs 40 and base
`copper plates 50 are laminated on the upper and lower
`surfaces of the base substrate to face each other.
`
`After the prepregs 40 and the base copperplates 50 are
`laminated, they are compressed using a press, to form both
`a rigid region, in which the circuit pattern is incorporated
`into the prepreg, and a flexible region, in which the circuit
`pattern is covered with the coverlay (FIG. 1D).
`Then, a through hole 60 for electrical connection between
`internal and external layers is formed (FIG. 1E). The base
`copper plate 50 and the through hole 60 are plated with
`copper to form a copper plated layer 70 (FIG. 1F). During
`the plating, an external circuit pattern having a predeter-
`mined shape is formed (FIG. 1G).
`The external circuit pattern is obtained using a predeter-
`mined photolithographic process, and the plated layer of the
`flexible region is etched therewith.
`After the external circuit pattern having a predetermined
`shape is formed, the resist cover 30 is removed.
`In the case where the resist cover is formed of peelable
`ink, peelable ink may be easily removed by further applying
`peelable ink on the formed peelable ink to form an ink layer
`having a predetermined thickness and then removing the ink
`layer (FIG. 1H).
`Thereafter, the resultant substrate is coated with PSR ink
`(photo imageable solder resist mask ink) and then surface
`treated, thereby finally completing a flying tail type rigid-
`flexible PCB, in whichthe flexible region is covered with the
`coverlay, including the polyimide film and the resist cover
`(FIG. 1D.
`However, in the flying tail type rigid-flexible PCB thus
`formed, since the external pad or mounting pad of the
`flexible region is internally exposed, processes of forming
`the resist cover on the flexible region using the heat-resistant
`tape or peelable ink and then removing it are required,
`
`9
`
`

`

`US 7,281,328 B2
`
`3
`causing problems of undesirably complicating fabrication
`processes and of increasing fabrication costs.
`Further, due to the residue remaining after the removal of
`the heat-resistant tape or peelable ink, contamination may
`occur, thus a defect rate is increased, resulting in drastically
`decreased reliability.
`
`SUMMARY OF THE INVENTION
`
`Accordingly, the present invention has been made keep-
`ing in mind the above problems occurring in the related art,
`and an object of the present invention is to provide a method
`of fabricating a flying tail type rigid-flexible PCB, which is
`advantageous because a resist cover is not used and a base
`copper foil of a flexible region is window etched after the
`formation of an external circuit pattern, thereby decreasing
`the numberoffabrication processes and the fabrication costs
`and preventing contamination, thus reducing a defect rate,
`resulting in maximizedreliability.
`In orderto achieve the above object, the present invention
`provides a method of fabricating a flying tail type rigid-
`flexible PCB without the need for a resist cover, which
`includes the steps of providing a base substrate including a
`polyimide film having an internal circuit pattern formed on
`at least one surface thereof; forming a coverlayto protect the
`internal circuit pattern corresponding to a flexible region of
`the base substrate, with the exception of a pad portion of the
`flexible region; placing prepregs on upper and lower sur-
`faces of the base substrate corresponding to a rigid region,
`placing base copperplates correspondingto the rigid region
`and the flexible region on the prepregs, and then collectively
`laminating the placed prepregs and base copperplates to
`form a rigid region and a flexible region; forming external
`circuit patterns electrically connected to each other on the
`rigid region, while protecting the base copper plate corre-
`sponding to the flexible region; and removing the base
`copper plate corresponding to the flexible region.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIGS. 1A to 1] are sectional views sequentially showing
`a conventional process of fabricating a flying tail
`type
`rigid-flexible PCB;
`FIGS. 2A to 21 are sectional views sequentially showing
`a process of fabricating a rigid-flexible PCB, according to
`the present invention; and
`FIG. 3 is a sectional view showing the structure of the
`rigid-flexible PCB,
`fabricated using the method of the
`present invention.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`Hereinafter, a detailed description will be given of a
`methodof fabricating a rigid-flexible PCB, according to the
`present invention, with reference to the appended drawings.
`FIGS. 2A to 21 are sectional views sequentially showing
`a process of fabricating a rigid-flexible PCB, according to
`the present invention.
`As shownin FIG. 2A, a polyimide copper clad laminate
`110 comprising a polyimide layer 111 and a copper foil 112
`is provided.
`Polyimide is a polymer material suitable for working
`under conditions of high temperature and high pressure,
`thanks to its excellent wear resistance, heat resistance,
`self-lubricating ability, creep resistance, electrical insulating
`properties, and plasma properties in a vacuum.
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`4
`As shownin FIG.2B, an etching resist pattern 120 for the
`formation of an internal circuit pattern is formed on the
`copper foil 112.
`To form the etching resist pattern 120, a circuit pattern
`printed on an artwork film should be transferred onto the
`substrate. Although the transferring process may be vari-
`ously conducted,
`it may be mainly carried out using a
`photosensitive dry film in such a mannerthat the circuit
`pattern printed on the artworkfilm is transferred onto the dry
`film using ultra violet (UV)light.
`Thus, the dry film having the transferred circuit pattern
`mayact as an etching resist. In the case where an etching
`process is performed using the dry film as an etchingresist,
`the copper foil 112 in the region on which the etching resist
`pattern 120 is not formed,
`is removed, thus forming an
`internal circuit pattern having a predetermined shape, as
`shown in FIG. 2C.
`
`After the internal circuit pattern having a predetermined
`shape is formed, the etching resist pattern 120 remaining on
`the non-etched copper foil 112 is removed, thereby com-
`pleting a base substrate, as shown in FIG. 2D.
`Then,
`in order to protect
`the internal circuit pattern
`corresponding to a flexible region, which is to be formed on
`the base substrate, with the exception of a pad portion of the
`flexible region required for use in an external pad and a
`mounting pad, from external environments, a coverlay 130
`is processed to suit the flexible region.
`The coverlay 130 may be formed by attaching a polyim-
`ide film to the flexible region having the corresponding
`internal circuit pattern, with the exception of the pad portion
`of the flexible region, using an adhesive, and then tempo-
`rarily bonding the polyimidefilm through manual soldering,
`as shown in FIG. 2E.
`
`the pad portion for use in an
`In the flexible region,
`external pad and a mounting pad is exposed as not covered
`with the coverlay 130.
`After the formation of the coverlay 130, prepregs 140 are
`placed on upper and lower surfaces of the base substrate
`corresponding to a rigid region, after which base copper
`plates 150 are placed on the prepregs 140 to correspond to
`the rigid and flexible regions.
`Each of the prepregs 140 has a window corresponding to
`the flexible region such that the prepreg 140 is laminated
`only on the portion where the rigid region is formed. As
`such, the prepreg 140 is formed in a semi-cured state by
`infiltrating a thermosetting resin into glass fibers, and thus
`functions to confer mechanical strength to the rigid region
`and also may act as an adhesive between the base substrate
`and the base copper plate 150 upon the subsequent com-
`pression procedure.
`The base copperplate 150 placed on the prepreg 140 does
`not have a window,to serve as the external circuit pattern of
`the rigid region and the protection plate of the pad portion
`of the flexible region.
`Thereafter, the base copper plate 150, the prepreg 140, the
`base substrate, the prepreg 140, and the base copper plate
`150,
`in that order, are laminated and compressed under
`conditions of predetermined temperature and pressure,
`thereby forming both the rigid region, in which the internal
`circuit pattern 112 is incorporated into the prepreg 140, and
`the flexible region having the internal circuit pattern 112,
`part of which is coated with the coverlay 130, the other part
`of which is exposed to form the pad portion, as shown in
`FIG, 2F.
`
`After the layers are compressed, a through hole 160 for
`electrical connection between internal and external layers of
`the substrate is formed, as shown in FIG. 2G.
`
`10
`
`10
`
`

`

`US 7,281,328 B2
`
`5
`The through hole 160 results from computer numerical
`control (CNC)drilling at the predetermined position of the
`rigid region, resulting in a plated through hole 160 penetrat-
`ing through the substrate.
`Thereafter, the through hole 160 and the base copperplate
`150 are plated with copper, thus forming a copper plated
`layer 170, as shown in FIG. 2H.
`The copper plated layer 170 formed on the through hole
`160 acts to realize the electrical connection between the
`
`internal and external layers, while the copper plated layer
`170 formed on the base copperplate 150, along with the base
`copper plate 150, constitutes a plated layer 180, which is
`then formed into an external circuit pattern.
`After the copperplated layer 170 is formed, a photolitho-
`graphic process is conducted on the plated layer 180 using
`a dry film,
`to form a desired external circuit pattern, as
`shown in FIG.21.
`
`Assuch,the external circuit pattern is formed only on the
`rigid region, so that the base copperplate 150 andthe plated
`layer 180 corresponding to the flexible region function to
`protect the pad portion exposed for use in an external pad
`and a mounting pad. That
`is, when the external circuit
`pattern is formed, the flexible region should be protected by
`the base copper plate 150 and the plated layer 180 so that the
`exposed pad portion thereof is not damaged by the etching
`process.
`In addition, for easy removal of the base copperplate 150
`and the plated layer 180 correspondingto the flexible region,
`the base copper plate 150 and the plated layer 180 corre-
`sponding to the flexible region are formed to be about
`0.05~5 mm larger than the flexible region. In addition, the
`edge portion of the base copper plate 150 and the plated
`layer 180 corresponding to the boundary between the flex-
`ible region and the rigid region is processed using a CNC
`drill or a steel rule die, whereby the subsequent removal
`procedure of the base copper plate 150 andthe plated layer
`180 becomes easier.
`Then, the base copper plate 150 and the plated layer 180
`corresponding to the flexible region remaining to protect the
`exposed pad portion for use in an external pad and a
`mounting pad are physically removed by manual labor or
`using an automated machine. Further, with the goal of
`preventing a solder bridge phenomenon between external
`circuit patterns during a soldering process while protecting
`the external circuit pattern, the resultant substrate is coated
`with PSR ink and then surface treated. Thereby, as shown in
`FIG.3, a flying tail type rigid-flexible PCB, without the need
`for a resist cover, is finally obtained.
`As described above,
`the present invention provides a
`methodoffabricating a rigid-flexible PCB. According to the
`method of the present invention, after an external circuit
`pattern is formed, the base copperfoil of a flexible region is
`windowetchedto protect the exposed padportion, instead of
`using a conventional resist cover formed of heat-resistant
`tape or peelable ink. Thereby,
`the inventive method is
`advantageous because the fabrication processes are simpli-
`fied and price competitive poweris increased.
`In addition, since heat-resistant tape and peelable ink are
`not used in the present invention, conventional problems,
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`6
`that is, contamination and damageofthe circuit pattern due
`to the presence of residue thereof, may be prevented, thus
`greatly increasing reliability.
`The embodiment of the present invention has been dis-
`closed for illustrative purposes, those skilled in the art will
`appreciate that various modifications, additions and substi-
`tutions are possible, without departing from the scope and
`spirit of the invention as disclosed in the accompanying
`claims.
`Whatis claimedis:
`
`1. A methodof fabricating a rigid-flexible printed circuit
`board, comprising the steps of:
`providing a base substrate having a polyimide layer and
`an internal circuit pattern formed on at least one of an
`upper or a lower surface thereof;
`forming a coverlay, to protect the internal circuit pattern,
`on a correspondingflexible region of the base substrate
`that excludes a pad portion of the corresponding flex-
`ible region;
`placing prepregs on the upper and lower surfaces of the
`base substrate on a correspondingrigid region, placing
`base copper plates on the prepregs on the correspond-
`ing rigid region and the corresponding flexible region
`on the prepregs, and collectively laminating the placed
`prepregs and base copperplates to form a rigid region
`and a flexible region;
`forming external circuit patterns electrically connected to
`each other on the rigid region, while the base copper
`plate serves to protect the flexible region; and
`removing the base copper plate corresponding to the
`flexible region after the forming step has formed the
`external circuit patterns.
`2. The method as set forth in claim 1, wherein the pad
`portion of the flexible region is a region for use in an external
`pad and a mounting pad.
`3. The method as set forth in claim 1, wherein the base
`copper plate on the corresponding flexible region is formed
`to be about 0.05 to 5 mm larger than the flexible region.
`4. The method as set forth in claim 1, wherein the
`removing step further comprises the steps of:
`processing a portion of the base copper plate correspond-
`ing to a boundary between the flexible region and the
`rigid region using a computer numerical control (CNC)
`drill or a steel rule die; and
`physically removing the base copperplate.
`5. The methodasset forth in claim 1, wherein the step of
`forming the external circuit patterns further comprises the
`steps of:
`forming a through hole through the rigid region;
`plating the base copperplate, on the corresponding rigid
`region having the through hole formed therethrough
`and the corresponding flexible region, with copper to
`form a plated layer; and
`partially removing the base copper plate and the plated
`layer on the corresponding rigid region to form the
`external circuit pattern, while the base copper plate
`serves to protect the flexible region.
`*
`*
`*
`*
`*
`
`11
`
`11
`
`