U.S. patent application number 13/473248 was filed with the patent office on 2012-09-13 for method of manufacturing a flexible printed circuit board.
This patent application is currently assigned to Samsung Electro-Mechanics Co., Ltd.. Invention is credited to Chang Hwan Choi, Jong Rip Kim, Choon Keun Lee, Kyung Ho LEE, Jeong Yeol Moon, Se Min Oh.
Application Number | 20120227888 13/473248 |
Document ID | / |
Family ID | 40751727 |
Filed Date | 2012-09-13 |
United States Patent
Application |
20120227888 |
Kind Code |
A1 |
LEE; Kyung Ho ; et
al. |
September 13, 2012 |
METHOD OF MANUFACTURING A FLEXIBLE PRINTED CIRCUIT BOARD
Abstract
An FPCB and a method of manufacturing the same, in which an
electrical signal-conductive portion of the FPCB is subjected to
little stress so as not to be broken by fatigue in spite of
repeated bending of the FPCB, thereby increasing the lifetime of
the FPCB.
Inventors: |
LEE; Kyung Ho; (Suwon,
KR) ; Oh; Se Min; (Suwon, KR) ; Choi; Chang
Hwan; (Sungnam, KR) ; Lee; Choon Keun; (Suwon,
KR) ; Moon; Jeong Yeol; (Gimhae, KR) ; Kim;
Jong Rip; (Suwon, KR) |
Assignee: |
Samsung Electro-Mechanics Co.,
Ltd.
Suwon
KR
|
Family ID: |
40751727 |
Appl. No.: |
13/473248 |
Filed: |
May 16, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12213570 |
Jun 20, 2008 |
8198542 |
|
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13473248 |
|
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Current U.S.
Class: |
156/64 |
Current CPC
Class: |
Y10T 29/49117 20150115;
Y10T 29/49126 20150115; H05K 2201/0715 20130101; H05K 2201/0352
20130101; Y10T 29/49124 20150115; H05K 1/0218 20130101; H05K
2201/0191 20130101; H05K 1/028 20130101; H05K 2201/09736
20130101 |
Class at
Publication: |
156/64 |
International
Class: |
B32B 37/12 20060101
B32B037/12 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 18, 2007 |
KR |
10-2007-133299 |
Claims
1. A method of manufacturing a flexible printed circuit board,
comprising: adhering a cover, which includes an adhesive layer and
at least one dielectric layer, to a conductive member, which
includes a conductive portion and at least one dielectric layer;
determining the elastic modulus and the thickness of a shield to be
layered on at least one of the conductive member and the cover, so
that a neutral plane is located within a predetermined range of the
thickness of the conductive portion, the neutral plane forming a
substantial interface of tension and compression in response to
bending; and layering the shield on at least one of the conductive
member and the cover, with the elastic modulus and the thickness of
the shield determined so that the neutral plane is located in the
conductive portion.
2. The method of claim 1, wherein the shield comprises: a first
shield layered on a top surface of the cover; and a second shield
layered on an underside of the conductive member.
3. The method of claim 1, wherein the elastic modulus and the
thickness of the shield are determined according to the following
Formula:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i)E.sub.i)),
and .SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c), where
Y.sub.n is a distance normally extending from a reference plane to
the neutral plane, T.sub.i is the thickness of a respective layer
of the flexible printed circuit board, E.sub.i is an elastic
modulus of a material placed in the respective layer of the
flexible printed circuit board, Y.sub.i is a distance normally
extending from the reference plane to the geometric center of the
respective layer, T.sub.x is the thickness of the respective layer
under the conductive portion, T.sub.c is the thickness of the
conductive portion, and the reference plane is an underside of the
flexible printed circuit board.
4. The method of claim 3, wherein the determining of the thickness
and elastic modulus of the shield comprises locating the neutral
plane in a range determined by the following Formula:
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.su-
b.c).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a U.S. divisional application filed
under 37 CFR 1.53(b) claiming priority benefit of U.S. Ser. No.
12/213,570, filed in the United States on Jun. 20, 2008, now
allowed, which claims earlier priority benefit to Korean Patent
Application No. 10-2007-133299 filed with the Korean Intellectual
Property Office on Dec. 18, 2007, the disclosures of which are
incorporated herein by reference.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to a flexible printed circuit
board (FPCB) and a manufacturing method thereof, and more
particularly, to an FPCB used in various electrical and/or
electronic devices such as a mobile communication device and a
method of manufacturing the same.
[0004] 2. Description of the Related Art
[0005] In general, an FPCB is a circuit board that is designed to
conduct various complicated signals, and includes a conductor layer
for conducting electrical signals and dielectric layers covering
the top surface and the underside surface of the conductive layer.
This type of FPCB can be manufactured to be thin and small, and is
used for a thin and small electrical device such as a mobile
communication device.
[0006] The FPCB has highly-flexible physical property, and thus is
used for a shape-changeable electrical device. Particularly, the
FPCB is used for electrical circuit connection between a body and a
slide (or a foldable member) in a slide-type or folder-type mobile
communication device.
[0007] That is, when the slide (or the foldable member) is moved
open or closed, the FPCB flexibly bends, so that the circuit can be
continuously connected.
[0008] As mentioned above, the FPCB maintains electrical circuit
connection when it repeats bending since it is used in a
shape-changeable device such as a mobile communication device.
[0009] However, when the FPCB is repeatedly bending, a conductor
layer inside the FPCB suffers from fatigue, caused by the repeated
bending. This as a result causes cracks in the conductor layer,
thereby reducing the lifetime of the FPCB.
SUMMARY
[0010] The present invention has been made to solve the foregoing
problems with the prior art, and therefore the present invention is
directed to an FPCB and a method of manufacturing the same, in
which an electrical signal-conductive portion of the FPCB is
subjected to little stress so as not to be broken by fatigue in
spite of repeated bending of the FPCB, thereby increasing the
lifetime of the FPCB.
[0011] According to an aspect of the present invention, the FPCB
includes a first dielectric portion forming a dielectric layer; a
second dielectric portion forming a dielectric layer opposite the
first dielectric portion; and a conductive portion conducting
electrical signals and having a neutral plane, wherein the neutral
plane is located within a predetermined range of the thickness of
the conductive portion, and has substantially zero strain due to
bending between the first and second dielectric portions.
[0012] On both sides of the neutral plane, the first dielectric
portion is substantially subjected to tension and the second
dielectric portion is substantially subjected to compression.
[0013] According to another aspect of the present invention, the
FPCB includes a first dielectric portion subjected to tension in
response to bending; a second dielectric portion subjected to
compression in response to bending; and a conductive portion
conducting electrical signals, and having a neutral plane, the
neutral plane is within a predetermined range of the thickness of
the conductive portion, and forms a substantial interface of
tension and compression between the first and second dielectric
portions.
[0014] Each of the first and second dielectric portions may include
at least one dielectric layer.
[0015] Here, a geometric center, obtained by converting the
thickness and the width of respective layer of the flexible printed
circuit board using same elastic modulus, may be located in the
predetermined range of the thickness of the conductive portion.
[0016] The position of the neutral plane may be determined
according to the following Formula:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i*)E.sub.i)),
and
.SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c)
[0017] where Y.sub.n is a distance normally extending from a
reference plane to the neutral plane, T.sub.i is the thickness of a
respective layer of the flexible printed circuit board, E.sub.i is
an elastic modulus of a material placed in the respective layer of
the flexible printed circuit board, Yi is a distance normally
extending from the reference plane to the geometric center of the
respective layer, T.sub.x is the thickness of the respective layer
under the conductive portion, T.sub.c is the thickness of the
conductive portion, and the reference plane is an underside of the
flexible printed circuit board.
[0018] The neutral plane may be located in a range determined by
the following Formula:
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.s-
ub.c).
[0019] According to a further aspect of the present invention, the
FPCB includes a conductive member including a conductive portion,
which conducts electrical signals, and at least one dielectric
layer; and a cover including a adhesive layer adhered to the
conductive portion and at least one dielectric layer, wherein the
thickness and the elastic modulus of the conductive member and the
cover are determined so that a neutral plane is placed within a
predetermined range of the thickness of conductive portion, the
neutral plane being substantially free from tension or compression
in response to bending of the conductive member and the cover.
[0020] The position of the neutral plane may be determined
according to the following Formula:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i*)E.sub.i)),
and
.SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c),
[0021] where Y.sub.n is a distance normally extending from a
reference plane to the neutral plane, T.sub.i is the thickness of a
respective layer of the flexible printed circuit board, E.sub.i is
an elastic modulus of a material placed in the respective layer of
the flexible printed circuit board, Y.sub.i is a distance normally
extending from the reference plane to the geometric center of the
respective layer, T.sub.x is the thickness of the respective layer
under the conductive portion, T.sub.c is the thickness of the
conductive portion, and the reference plane is an underside of the
flexible printed circuit board.
[0022] The neutral plane may be located in a range determined by
the following Formula:
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.s-
ub.c).
[0023] According to another aspect of the present invention, the
method of manufacturing an FPCB includes determining the elastic
modulus of a conductive portion and the elastic modulus of first
and second dielectric portions, which insulate the conductive
portion; determining the thickness of the conductive portion and
the first and second dielectric portions so that a neutral plane is
located within a predetermined range of the thickness of the
conductive portion, the neutral plane being substantially free from
tension or compression in response to bending of the conductive
member and the cover; and insulating the conductive portion
according to the determined thickness and the determined elastic
modulus.
[0024] The step of determining the thickness may design to locate a
geometric center in the predetermined range of the thickness of the
conductive portion, the geometric center obtained by converting the
thickness and the width of respective layer of the first dielectric
portion, the second dielectric portion and the conductive portion
using same elastic modulus.
[0025] The thickness of the first dielectric portion, the second
dielectric portion and the conductive portion may be determined
according to the position of the neutral position, which is
obtained by the following Formula:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i*)E.sub.i)),
and
.SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c),
[0026] where Yn is a distance normally extending from a reference
plane to the neutral plane, Ti is the thickness of a respective
layer of the flexible printed circuit board, Ei is an elastic
modulus of a material placed in the respective layer of the
flexible printed circuit board, Yi is a distance normally extending
from the reference plane to the geometric center of the respective
layer, Tx is the thickness of the respective layer under the
conductive portion, Tc is the thickness of the conductive portion,
and the reference plane is an underside of the flexible printed
circuit board.
[0027] The step of determining the thickness may locate the neutral
plane in a range determined by the following Formula:
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.s-
ub.c)
[0028] According to yet another aspect of the present invention,
the method of manufacturing an FPCB includes adhering a cover,
which includes a adhesive layer and at least one dielectric layer,
to a conductive member, which includes a conductive portion and at
least one dielectric layer; determining the elastic modulus and the
thickness of a shield to be layered on at least one of the
conductive member and the cover, so that a neutral plane is located
within a predetermined range of the thickness of the conductive
portion, he neutral plane forming a substantial interface of
tension and compression in response to bending; and layering the
shield on at least one of the conductive member and the cover, with
the elastic modulus and the thickness of the shield determined so
that the neutral plane is located in the conductive portion.
[0029] The shield may include a first shield layered on a top
surface of the cover; and a second shield layered on an underside
of the conductive member.
[0030] Here, the elastic modulus and the thickness of the shield
are determined according to the following Formula:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i*)E.sub.i)),
and
.SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c)
[0031] where Y.sub.n is a distance normally extending from a
reference plane to the neutral plane, T.sub.i is the thickness of a
respective layer of the flexible printed circuit board, E.sub.i is
an elastic modulus of a material placed in the respective layer of
the flexible printed circuit board, Y.sub.i is a distance normally
extending from the reference plane to the geometric center of the
respective layer, T.sub.x is the thickness of the respective layer
under the conductive portion, T.sub.c is the thickness of the
conductive portion, and the reference plane is an underside of the
flexible printed circuit board.
[0032] The step of determining the thickness and elastic modulus of
the shield may locate the neutral plane in a range determined by
the following Formula:
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.s-
ub.c)
[0033] In the FPCB of the present invention, even though the FPCB
is repeatedly bent, the conductive portion, which conducts
electrical signals, is not easily fractured by fatigue caused by
stress, thereby increasing the lifetime of the FPCB. The
manufacturing method of the present invention can newly manufacture
an FPCB having the above-described properties, and also provide the
above-describe properties to a previously-made FPCB.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] The above and other aspects, features and other advantages
of the present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0035] FIGS. 1 and 2 are perspective views illustrating example
operations of an FPCB according to an embodiment of the present
invention;
[0036] FIG. 3 is a cross-sectional view of the FPCB, taken along
the line I-I in FIG. 2;
[0037] FIG. 4 is a configuration view illustrating stress
distribution when an object is bent or curved;
[0038] FIG. 5 is a cross-sectional view of an FPCB according to an
embodiment of the present invention, illustrating physical
properties of materials of respective layers of the FPCB;
[0039] FIG. 6 is a graph illustrating the effects of an FPCB
according to an embodiment of the present invention; and
[0040] FIGS. 7 and 8 are cross-sectional views illustrating a
method of manufacturing an FPCB according to another embodiment of
the present invention.
DESCRIPTION OF EMBODIMENTS
[0041] Exemplary embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0042] FIGS. 1 and 2 illustrate the operation of a flexible printed
circuit board (FPCB) according to an embodiment of the present
invention. First, the FPCB according to an embodiment of the
present invention will be schematically described with reference to
FIGS. 1 and 2.
[0043] The FPCB illustrated in FIGS. 1 and 2 comprises first and
second connectors 1 and 2, each of which is connected to a main
circuit board or an auxiliary circuit board, and a flexible portion
3, which transmits electrical signals between the connectors 1 and
2 and is bent flexibly.
[0044] The FPCB illustrated in FIGS. 1 and 2 is characterized in
that it can realize various electronics, particularly compact slim
devices. For example, the FPCB can be applied to a slide type
mobile communication terminal.
[0045] In other words, assuming that the first connector 1 is
connected to a PCB installed in a terminal body (not shown) and
that the second connector 2 is connected to a slide (not shown)
performing operations such as slide-up/down on the terminal body,
the state illustrated in FIG. 1 can be regarded to be a slide-up
state, whereas the state illustrated in FIG. 2 can be regarded to
be a slide-down state.
[0046] A user repeats the slide-up and the slide-down while using
the slide type mobile communication terminal. In this case, the
flexible portion 3 repeats the flexure as illustrated in FIGS. 1
and 2.
[0047] In this manner, in the case in which the FPCB according to
an embodiment of the present invention is bent, the flexible
portion 3 is subjected to tension and compression at the same time.
A detailed mechanism of the operation will be described with
reference to FIG. 3.
[0048] FIG. 3 is a cross-sectional view taken the line I-I of the
FPCB illustrated in FIG. 1 or 2.
[0049] The FPCB is fundamentally divided into a conductive portion
for transmitting electrical signals, and a dielectric portion for
insulating the conductive portion. As illustrated in FIG. 3, the
FPCB according to an embodiment of the present invention comprises
a first dielectric portion 10, a conductive portion 30, and a
second dielectric portion 20.
[0050] The first and second dielectric portions 10 and 20 are
disposed with the conductive portion 30 in between, and serve to
protect and insulate the conductive portion 30.
[0051] When the FPCB is bent as illustrated in FIGS. 1 and 2,
tension T and compression C thereof occurs at the same time as
illustrated in FIG. 3.
[0052] In other words, the tension T occurs at the first dielectric
portion 10, and the compression C occurs at the second dielectric
portion 20. In the embodiment illustrated in FIG. 3, the first
dielectric portion 10 includes a first layer 11, a second layer 12,
and a third layer 13, and the second dielectric portion 20 includes
a fourth layer 24 and a fifth layer 25.
[0053] The embodiment of FIG. 3 illustrates that each of the first
and second dielectric portions 10 and 20 has, but not limited to, a
plurality of dielectric layers. For example, each of the first and
second dielectric portions 10 and 20 may include a single
dielectric layer.
[0054] More specifically, in the embodiment illustrated in FIG. 3,
the first layer 11 of the first dielectric portion 10 is an
electromagnetic interference (EMI) shield layer, the second layer
12 is a polyimide layer, and the third layer 13 is an adhesive
layer for adhering to the conductive portion 30.
[0055] Further, the fourth layer 24 of the second dielectric
portion 20 is a polyimide layer, and the fifth layer 25 is an EMI
shield layer.
[0056] However, the FPCB according to an embodiment of the present
invention is not essentially divided into the first dielectric
portion 10, the second dielectric portion 20, and the conductive
portion 30. Thus, the FPCB according to another embodiment of the
present invention can be divided into a conductive member 50 and a
cover 40.
[0057] The conductive member 50 includes the conductive portion 30
in addition to the fourth and fifth layers 24 and 25, both of which
are stacked beneath the conductive portion 30. The cover 40
includes the first, second and third layers 11, 12 and 13, which
are stacked in that order. At this time, the third layer 13
typically serves as an adhesive layer for adhering to the
conductive portion 30.
[0058] Meanwhile, the embodiment illustrated in FIG. 3 includes a
neutral plane 35, which is substantially subjected neither to the
tension nor the compression.
[0059] Any material will be extended or contracted to a certain
extent under tensile or compressive stress. However, the neutral
plane 35 substantially causes neither tension nor compression, so
that the strain thereof substantially becomes zero.
[0060] Here, the strain is expressed by a ratio of an original
length or volume to a deformed length or volume. Since no change is
caused from the neutral plane 35, the strain of the neutral plane
35 substantially becomes zero.
[0061] In other words, as illustrated in FIG. 3, when the FPCB is
bent, the first dielectric portion 10 (or the cover 40) is
subjected to the tension T, and the second dielectric portion 20
(or the conductive member 50, from which the conductive portion 30
is excluded) is subjected to the compression C. Further, the
neutral plane 35 substantially causes neither the tension nor the
compression.
[0062] Thus, according to an embodiment of the present invention,
since the neutral plane 35 is disposed within the conductive
portion 30, the FPCB experiences the tension and the compression to
the minimum extent in spite of the repeated bending thereof, very
slight deformation, and thus weak fatigue. Accordingly, the FPCB
can inhibit cracks caused by the fatigue, and thus increase its
life span.
[0063] In detail, the neutral plane 35 is preferably adapted to
exist within a predetermined range of the thickness of the
conductive portion 30. To this end, each of the first dielectric
portion 10, the second dielectric portion 20 and the conductive
portion 30 must be determined with respect to a thickness, an
elastic modulus, etc. thereof.
[0064] A method of determining the thicknesses and the elastic
moduli of the respective layers constituting the FPCB will be
described with reference to FIGS. 4 and 5.
[0065] FIG. 4 illustrates stress distribution when an object is
bent or curved, and FIG. 5 illustrates physical properties of
materials of the respective layers of an FPCB according to an
embodiment of the present invention.
[0066] As illustrated in FIG. 4, it is assumed that X and Y
materials are stacked, that width and elastic modulus of the X
material are b and Ex respectively, and that width and elastic
modulus of the Y material are b and E.sub.y respectively. When the
bending occurs from top to bottom, the neutral plane N is located
at a substantial interface between the tension T and the
compression C.
[0067] Further, the neutral plane N is not matched with a boundary
between the X and Y materials. This is because area and elastic
modulus of the X material are different from those of the Y
material.
[0068] Thus, as illustrated in FIG. 4, the position of the neutral
plane can be easily obtained by calculation based on the elastic
modulus of one material.
[0069] In other words, when calculated on the basis of the elastic
modulus Ex of the X material, the width of the Y material is nb,
where n=E.sub.y/E.sub.x.
[0070] The neutral plane N is a line passing through the geometric
centers of the X and Y materials which are represented by the width
calculated in this way.
[0071] However, since the FPCB has various layers such as the
conductive portion, the dielectric layer for insulating the
conductive portion, the shield layers for shielding the EMI, and so
on, the elastic moduli and thicknesses of which are different from
each other, it is difficult to find the whole geometric
centers.
[0072] Here, in order to find the position of the neutral plane,
i.e. the line passing through the geometric centers of the
materials represented by calculation based on the same elastic
modulus, the concept of the geometrical moment of area (i.e. the
moment of area) is used. This concept will be described below in
greater detail.
[0073] The FPCB of the present invention is designed so that the
neutral plane is located in the conductive portion as described
above, namely within a predetermined range of the thickness of the
conductive portion.
[0074] The positional relationship between the neutral plane and
the conductive portion of the FPCB according to an embodiment of
the present invention will be described in greater detail with
reference to FIG. 5. The embodiment illustrated in FIG. 5 is merely
provided for the illustrative purpose. Thus, the present invention
is not limited to this embodiment, and includes the case where each
of the first and second dielectric portions has one dielectric
layer as well as two or more dielectric layers.
[0075] As illustrated in FIG. 5, the thickness and the elastic
modulus of the first layer 11 of the FPCB according to an
embodiment of the present invention are T.sub.1 and E.sub.1,
respectively.
[0076] The thickness and the elastic modulus of the second layer 12
are T.sub.2 and E.sub.2, respectively. The thickness and the
elastic modulus of the third layer 13 are T.sub.3 and E.sub.3,
respectively. Further, the thickness and the elastic modulus of the
conductive portion 30 are T.sub.c and E.sub.c, respectively.
[0077] The thickness and the elastic modulus of the fourth layer 24
are T.sub.4 and E.sub.4, respectively. The thickness and the
elastic modulus of the fifth layer 25 are T.sub.5 and E.sub.5,
respectively.
[0078] The widths of these components are equal to each other, and
are expressed by L. Meanwhile, assuming that one outer surface, for
instance a lower surface, of the FPCB illustrated in FIG. 5 is a
reference surface, the distances from the reference surface to the
geometric centers of the respective layers can be expressed by
Y.sub.i, where "i" is the symbol denoting the respective layers.
Specifically, the symbol "i" denotes one of 1, 2, 3, c, 4 and
5.
[0079] Here, the geometric centers of the respective layers, of
which the FPCB is composed, refer to the distances from the
reference surface to the central lines of the respective layers
(i.e. lines passing through the centers of thickness of the
respective layers) in an uncalculated state, rather than the
geometric centers of the respective layers calculated on the basis
of the same elastic modulus.
[0080] In detail, the distance from the reference surface to the
geometric center of the first layer 11 is Y.sub.1, the distance
from the reference surface to the geometric center of the second
layer 12 is Y.sub.2, the distance from the reference surface to the
geometric center of the third layer 13 is Y.sub.3, the distance
from the reference surface to the geometric center of the fourth
layer 24 is Y.sub.4, and the distance from the reference surface to
the geometric center of the fifth layer 25 is Y.sub.5. Further, the
distance from the reference surface to the neutral plane 35 is
expressed by Y.sub.n.
[0081] Thus, Y.sub.1 is
T.sub.1/2+T.sub.2+T.sub.3+T.sub.C+T.sub.4+T.sub.5, and Y.sub.2 is
T.sub.2/2+T.sub.3+T.sub.C+T.sub.4+T.sub.5. According to the
embodiment illustrated in FIG. 5, Yi, i.e. one of the values
ranging from Y1 to Y5, is as shown in Tables 1 and 2.
[0082] In order to show the positional relationship between the
neutral plane and the conductive portion of the FPCB illustrated in
FIG. 5, it is necessary to calculate the geometrical moments of
area (i.e. the moments of area) of the respective layers of which
the FPCB is composed. Here, the geometrical moment of area is
defined as the product of the area by the geometric center.
[0083] The geometrical moment of area is the concept that is
introduced in order to obtain the geometric centers of the whole
materials represented by calculating the respective layers, of
which the FPCB according to the present invention is composed, on
the basis of the same elastic modulus (At this time, the materials
represented by calculating the respective layers on the basis of
the same elastic modulus may be further increased or decreased in
area).
[0084] For example, when conversion factors represented by
calculating the elastic moduli of the second layer 12, the third
layer 13, the conductive portion 30, the fourth layer 24, and the
fifth layer 25 on the basis of the elastic modulus of the first
layer 11 are applied to the respective layers in FIG. 5, the widths
of the respective layers are changed after this calculation. Thus,
when the calculated widths are applied to the respective layers,
some of the layers are calculated that the areas thereof are
further increased, and the other layers are calculated that the
areas thereof are further decreased.
[0085] When the geometric centers of the materials are found in
overall consideration of the calculated materials, the geometric
centers are matched with the neutral plane.
[0086] In order to obtain the geometric center for the whole
materials, the concept of the geometrical moment of area is
introduced. Thus, the geometric center is the ratio of an entire
area to an entire geometrical moment of area.
[0087] The entire area is the cross-sectional area of the materials
of the respective calculated layers, or the sum of cross-sectional
areas of the respective calculated layers. The entire geometrical
moment of area is the sum of the geometrical moments of area of the
respective calculated layers.
[0088] The following Table 1 shows thicknesses, elastic moduli,
conversion factors n, conversion widths, conversion areas, and
geometric centers of the respective layers of the FPCB illustrated
in FIG. 5. Here, the conversion is based on the elastic modulus
E.sub.1 of the material of which the first layer 11 is formed.
[0089] Further, the geometric centers refer to the distances from
the reference surface to the central lines of the respective layers
in an uncalculated state.
TABLE-US-00001 TABLE 1 T* EM* CF* CW* CA* Geometric center 1.sup.st
Layer T.sub.1 E.sub.1 1 L T.sub.1 * L (T.sub.1/2 + T.sub.2 +
T.sub.3 + T.sub.c + (EMI) T.sub.4 + T.sub.5) 2.sup.nd Layer T.sub.2
E.sub.2 E.sub.2/E.sub.1 L * (E.sub.2/E.sub.1) T.sub.2 * L *
(E.sub.2/E.sub.1) (T.sub.2/2 + T.sub.3 + T.sub.c + T.sub.4 +
T.sub.5) (polyimide) 3.sup.rd Layer T.sub.3 E.sub.3 E.sub.3/E.sub.1
L * (E.sub.3/E.sub.1) T.sub.3 * L * (E.sub.3/E.sub.1) (T.sub.3/2 +
T.sub.c+ T.sub.4 + T.sub.5) (adhesive layer) Conductive T.sub.c
E.sub.c E.sub.c/E.sub.1 L * (E.sub.c/E.sub.1) T.sub.c * L *
(E.sub.c/E.sub.1) (T.sub.c/2 + T.sub.4 + T.sub.5) portion (Cu)
4.sup.th Layer T.sub.4 E.sub.4 E.sub.4/E.sub.1 L *
(E.sub.4/E.sub.1) T.sub.4 * L * (E.sub.4/E.sub.1) (T.sub.4/2 +
T.sub.5) (polyimide) 5.sup.th Layer T.sub.5 E.sub.5 E.sub.5/E.sub.1
L * (E.sub.5/E.sub.1) T.sub.5 * L * (E.sub.5/E.sub.1) (T.sub.5/2)
(EMI) Note) T * : thickness, EM * : elastic modulus, CF * :
conversion factor (n), CW * : conversion width, CA * : conversion
area
[0090] With regard to the calculation of the respective layers, in
the present embodiment, the conversion factor n is applied to the
width L, thereby expressing the conversion width. Alternatively,
the conversion factor may be applied to the thickness instead of
the width, the result of which is the same.
[0091] Meanwhile, the following Table 2 shows conversion areas,
geometric centers, and the geometrical moments of area. Here,
A.sub.i and M.sub.i denote the conversion area of each layer and
the geometrical moment of area of each layer respectively, where
"i' is the symbol denoting each layer.
TABLE-US-00002 TABLE 2 CA* Geometric center GMA* 1.sup.st Layer
A.sub.1 = T.sub.1*L Y.sub.1 = (T.sub.1/2 + T.sub.2 + T.sub.3 +
T.sub.C + M.sub.1 = A.sub.1*Y.sub.1 = T.sub.1*L*(T.sub.1/2 + (EMI)
T.sub.4 + T.sub.5) T.sub.2 + T.sub.3 + T.sub.C + T.sub.4 + T.sub.5)
2.sup.nd Layer A.sub.2 = T.sub.2*L*(E.sub.2/E.sub.1) Y.sub.2 =
(T.sub.2/2 + T.sub.3 + T.sub.C + T.sub.4 + M.sub.2 =
A.sub.2*Y.sub.2 = T.sub.2*L*(E.sub.2/E.sub.1)* (polyimide) T.sub.5)
(T.sub.2/2 + T.sub.3 + T.sub.C + T.sub.4 + T.sub.5) 3.sup.rd Layer*
A.sub.3 = T.sub.3*L*(E.sub.3/E.sub.1) Y.sub.3 = (T.sub.3/2 +
T.sub.C + T.sub.4 + T.sub.5) M.sub.3 = A.sub.3*Y.sub.3 =
T.sub.3*L*(E.sub.3/E.sub.1)* (adhesive layer) (T.sub.3/2 + T.sub.C
+ T.sub.4 + T.sub.5) Conductive A.sub.c =
T.sub.c*L*(E.sub.c/E.sub.1) Y.sub.c = (T.sub.c/2 + T.sub.4 +
T.sub.5) M.sub.c = A.sub.c*Y.sub.c = T.sub.c*L*(E.sub.c/E.sub.1)*
portion (Cu) (T.sub.c/2 + T.sub.4 + T.sub.5) 4.sup.th Layer A.sub.4
= T.sub.4*L*(E.sub.4/E.sub.1) Y.sub.4 = (T.sub.4/2 + T.sub.5)
M.sub.4 = A.sub.4*Y.sub.4 = T.sub.4*L*(E.sub.4/E.sub.1)*
(polyimide) (T.sub.2/2 + T.sub.5) 5.sup.th Layer A.sub.5 =
T.sub.5*L*(E.sub.5/E.sub.1) Y.sub.5 = (T.sub.5/2) M.sub.5 =
A.sub.5*Y.sub.5 = T.sub.5*L*(E.sub.5/E.sub.1)* (EMI) (T.sub.5/2)
Note) CA*: conversion area, GMA*: Geometrical Moment of Area =
Area*Geometric center
[0092] As shown in Tables 1 and 2, the total area and the total
geometrical moment of area for all the layers of the FPCB
illustrated in FIG. 5 are expressed as follows:
A=.SIGMA.A.sub.i, and M=.SIGMA.M.sub.i
[0093] The position of the neutral plane 35 can be expressed as
follows.
Yn=M/A=(.SIGMA.M.sub.i)/(.SIGMA.A.sub.i)
[0094] When these formulas are applied in detail, the total area A
can be expressed as follows:
.SIGMA. A i = ( A 1 + A 2 + A 3 + A c + A 4 + A 5 ) = L * ( T 1 * E
1 + T 2 * E 2 + T 3 * E 3 + T c * E c + T 4 * E 4 + T 5 * E 5 ) / E
1 ##EQU00001##
[0095] The total moment M can be expressed as follows:
.SIGMA. M i = ( M 1 + M 2 + M 3 + M c + M 4 + M 5 ) = ( A 1 * Y 1 +
A 2 * Y 2 + A 3 * Y 3 + A c + A 4 * Y 4 + A 5 * Y 5 ) = L * ( T 1 *
E 1 * Y 1 + T 2 * E 2 * Y 2 + T 3 * E 3 * Y 3 + T c * E c * Y c + T
4 * E 4 * Y 4 + T 5 * E 5 * Y 5 ) / E 1 ##EQU00002##
[0096] The position Y.sub.n of the neutral plane 35 can be
expressed by the following formula (hereinafter, referred to as
"Formula 1").
Yn = ( .SIGMA. M i ) / ( .SIGMA. A i ) = T 1 * E 1 * Y 1 + T 2 * E
2 * Y 2 + T 3 * E 3 * Y 3 + T c * E c * Y c + T 4 * E 4 * Y 4 + T 5
* E 5 * Y 5 ) / ( T 1 * E 1 + T 2 * E 2 + T 3 * E 3 + E c * E c + T
4 * E 4 + T 5 * E 5 ) = ( .SIGMA. ( T i * E i * Y i ) ) / ( .SIGMA.
( T i * E i ) ) ##EQU00003##
[0097] The neutral plane 35 defined by Formula 1 is designed to be
within the thickness range of the conductive portion 30, and
preferably to satisfy the following formula (hereinafter, referred
to as "Formula 2").
.SIGMA.T.sub.x<Y.sub.n<(.SIGMA.T.sub.x+T.sub.c) Formula 2
[0098] Here, T.sub.x indicates the thickness of each dielectric
layer under the conductive portion 30. In the embodiment
illustrated in FIG. 5, T.sub.x is the sum of T.sub.4 and
T.sub.5.
[0099] In other words, T.sub.i, E.sub.i, and Y.sub.i are determined
such that Y.sub.n is greater than T.sub.4+T.sub.5 and is smaller
than T.sub.4+T.sub.5+T.sub.c. Thus, Yn exists between the lower and
upper surfaces of the conductive portion 30.
[0100] For example, if the materials of the first dielectric
portion 10, the second dielectric portion 20, and the conductive
portion 30 are predetermined before the FPCB is manufactured, the
elastic modulus E.sub.i of each layer constituting each component
is a fixed value, and the thickness of each layer constituting each
of the first dielectric portion 10, the second dielectric portion
20, and the conductive portion is determined by Formulas 1 and
2.
[0101] The determination of the thickness is conducted by a trial
and error method, or by changing the thickness of a changeable
layer on the basis of the aforementioned formulas if the
thicknesses of some of the layers are fixed, i.e., are not changed.
Thereby, the FPCB according to an embodiment of the present
invention can be manufactured.
[0102] Further, in the case of the cover 40 and the conductive
member 50, the elastic modulus is determined by the method similar
to the aforementioned method, and the thickness of each layer is
determined. The cover 40 and the conductive member 50, prepared on
the basis of this determination, are adhered to each other.
Thereby, the FPCB according to the present invention can be
manufactured.
[0103] However, the FPCB according to the present invention has a
very thin structure in which its thickness is several microns. As
such, although the FPCB is manufactured on the basis of the
thicknesses determined by the aforementioned formulas, there is no
alternative but to allow a tolerance to some extent.
[0104] Thus, the position Y.sub.n of the neutral plane 35 is
preferably adapted to be within a range limited to some extent in
spite of the thickness range of the conductive portion 30. Thereby,
the neutral plane 35 can be matched with the geometric center of
the conductive portion 30 as exact as possible, or be spaced apart
from the geometric center of the conductive portion 30 as near as
possible.
[0105] Thus, as illustrated in FIG. 5, the position Yn of the
neutral plane is preferably adapted to be determined by the
following formula.
D.sub.1.ltoreq.Y.sub.n.ltoreq.D.sub.2
[0106] Here, D1 is preferably selected by a distance ranging from
the reference surface to a position corresponding to about 20% of
the thickness of the conductive portion, and D2 is preferably
selected by a distance ranging from the reference surface to a
position corresponding to about 80% of the thickness of the
conductive portion. In other words, the position Y.sub.n of the
neutral plane is preferably adapted to be determined within a range
expressed by the following formula (hereinafter, referred to as
"Formula 3").
(.SIGMA.T.sub.x+0.2T.sub.c).ltoreq.Y.sub.n.ltoreq.(.SIGMA.T.sub.x+0.8T.s-
ub.c)
[0107] The reason D1 and D2 are determined as described above is
for selecting a more stable range in consideration of the tolerance
caused by the manufacturing, rather than the present invention has
no effect beyond the range.
[0108] Meanwhile, the effects of the FPCB according to an
embodiment of the present invention will be described with
reference to FIG. 6. FIG. 6 shows the results of lifespan
prediction simulation performed on an FPCB according to an
embodiment of the present invention and a known FPCB.
[0109] In the graph shown in FIG. 6, the abscissa denotes a
distance between the geometric center of the conductive portion and
the neutral plane in unit of micron, and the ordinate denotes the
number of times of repeating bending using a slide.
[0110] Further, the symbol A corresponds to the case where the
geometric center of the conductive portion and the neutral plane of
the FPCB according to an embodiment of the present invention are
matched with each other, and the symbol B denotes the result of a
bending test of the known FPCB.
[0111] The graph shown in FIG. 6 is obtained by simulating the case
where the thickness T.sub.c of the conductive portion 30 is set to
12 .mu.m. When the value of the abscissa is zero (0), this denotes
the case where the neutral plane is matched with the geometric
center of the conductive portion. As it proceeds to the right side
on the basis of the zero value of the abscissa, this denotes that
the neutral plane is gradually spaced apart from the geometric
center of the conductive portion in an upward or downward
direction.
[0112] For example, if the neutral plane is spaced 5 .mu.m apart
from the geometric center of the conductive portion in a downward
direction, the number of times of repeating the bending using the
slide corresponding to 5 of the abscissa on the graph shown in FIG.
6 becomes a predicted lifespan. If the neutral plane is spaced 5
.mu.m apart from the geometric center of the conductive portion in
an upward direction, the number of times of repeating the bending
using the slide corresponding to 5 on the abscissa of the graph
shown in FIG. 6 also becomes a predicted lifespan.
[0113] In other words, the range from 0 .mu.m to 6 .mu.m on the
abscissa of the graph shown in FIG. 6 is the thickness range of the
conductive portion. The symbol P of the graph denotes the range
between D.sub.1 and D.sub.2 illustrated in FIG. 5.
[0114] As shown in FIG. 6, although the neutral plane is within the
thickness range (from 0 .mu.m to 6 .mu.m) of the conductive
portion, the lifetime of the FPCB of the present invention is
longer than that of the conventional FPCB. Even in the range of P,
it is possible to achieve better effects than the conventional
FPCB.
[0115] When the range of D.sub.1 and D.sub.2 are selected to be
between 20% and 80% of the thickness of the conductive portion as
described above, P in the graph of FIG. 6 approximately ranges from
0 to 4.8.
[0116] The present invention aims to locate the conductive portion
in a plane, the elastic modulus of which is substantially zero (0).
This plane indicates the interface between one portion under
tension and another portion under compression when bending occurs,
or the neutral plane which is not subjected to tension or
compression in response to bending. Here, the neutral plane has
zero (0) elastic modulus.
[0117] Since the conductive portion has a predetermined thickness,
all of the conductive portion cannot serve as the neutral plane.
When the FPCB of the present invention is bent, a small amount of
tension and compression will be applied to the conductive portion,
thereby deforming the same in a very small range.
[0118] The present invention is directed to finally match the
neutral plane to the geometric center of the conductive portion.
When the neutral plane is not consistent with but close vicinity to
the geometric center of the conductive portion, the conductive
portion is not free from stress or strain in the bending. However,
as shown in FIG. 6, the stress applied to the conductive portion
will be very small, and the strain will be close to 0, so that
substantially no deformation occurs in the conductive portion,
thereby increasing the lifetime of the FPCB.
[0119] Table 3 below shows the result of lifetime experiments,
performed on FPCB specimens according to an embodiment of the
present invention. Here, the distance between the geometric center
and the neutral plane was 4.00 .mu.m in four of the specimens, and
1.26 .mu.m in two of the specimens.
TABLE-US-00003 TABLE 3 Distance from neutral plane 1 2 3 4 4.00
.mu.m 163,600 157,400 173,300 151,100 1.26 .mu.m 331,800
354,600
[0120] From the data reported in Table 3 above, it can be
appreciated that the average lifetime of the 4.00 .mu.m specimens
is 161,350 times, and the average lifetime of the 1.26 .mu.m
specimens is 343,200 times.
[0121] That is, the experiments reveal that the lifetime of the
conductive portion against bending may increase as the geometric
center thereof is farther from the neutral plane.
[0122] Referring to the drawings, the method of manufacturing an
FPCB of the present invention will be described in more detail.
[0123] The method of manufacturing an FPCB of the present invention
basically includes determining the thickness and the elastic
modulus of respective layers (i.e., dielectric, adhesive and
conductive layers) of the FPCB so that the neutral plane is located
within the thickness or a predetermined range of the thickness of
the conductive portion, and manufacturing the FPCB according to the
determined values of thickness and elastic modulus.
[0124] Accordingly, method of manufacturing an FPCB of the present
invention can be generally divided into two types.
[0125] First type is to manufacture an FPCB by suitably determine
the thickness and elastic modulus of a first dielectric portion, a
second dielectric portion and a conductive portion (or a cover and
a conductive member), and locating a neutral plane within a
predetermined range of the thickness of the conductive portion.
Second type is to stack a suitable thickness of dielectric layer
(or shield layer) on a previously made FPCB so that a neutral plane
is located within a predetermined range of the thickness of a
conductive portion.
[0126] A first type embodiment of the manufacturing method was
already described with reference to FIG. 5.
[0127] That is, the thickness and elastic modulus of respective
layers are determined based upon above-described Formulae, such as
Formulae 1 and 2 or Formulae 1 and 3, and an FPCB is manufactured
according to the determined values.
[0128] Here, it is frequent that the material of the respective
dielectric or shield layer is previously determined. When the
material is previously determined, the elastic modulus is
automatically determined as a unique value of the respective
material, and it is required to determine only the thickness of the
respective layer. The geometric center can be easily calculated
when the thickness and elastic modulus of the respective layer is
determined. The position Y.sub.n of the neutral plane is obtained
according to Formula 1 above, and it is designed so that the
position Y.sub.n is present in a predetermined range of the
thickness of the conductive portion.
[0129] If not only the elastic modulus of the respective layers but
also the thickness of any of the layers are fixed, the thickness of
the layer, which is variable, can determined according to
above-described Formulae 1 and 2 or Formulae 1 and 3 in order to
manufacture an FPCB.
[0130] Now, a second type embodiment of the method of manufacturing
an FPCB will be described with reference to FIGS. 7 and 8.
[0131] As shown in FIG. 7, the FPCB includes a cover 40 and a
conductive member 50, in which the cover 40 includes first and
second layers 41 and 42, and the conductive member 50 includes a
conductive portion 30 and a third layer 50.
[0132] The first layer 41 has a thickness T.sub.1 and an elastic
modulus E.sub.1, the second layer 42 has a thickness T.sub.2 and an
elastic modulus E.sub.2, the conductive portion 30 has a thickness
T.sub.c and an elastic modulus E.sub.c, and the third layer 53 has
a thickness T.sub.3 and an elastic modulus E.sub.3.
[0133] The position Y.sub.n of the neutral plane 35 is not present
in the range between D.sub.1 and D.sub.2 of the conductive portion
30. That is, neutral plane 35 is spaced from the conductive portion
30 at a predetermined distance, and this represents that the
conductive portion 30 is greatly subjected to tension or
compression by bending.
[0134] This embodiment is directed to a manufacturing method, which
causes the neutral plane 35 to be located in the range between
D.sub.1 and D.sub.2 by suitably adding a dielectric layer or a
shield layer to the FPCB, in the state shown in FIG. 7.
[0135] As shown in FIG. 8, the method of manufacturing an FPCB
involves suitably layering a shield on at least one of the top
surface and the underside of the FPCB shown in FIG. 7, so that the
neutral plane 35 is located within a predetermined range of the
thickness of the conductive portion 30.
[0136] Referring to FIG. 8, it is illustrated that the position of
the neutral plane 35 is adjusted using the shield, that is, a first
shield 61 layered on the top surface of the cover 40 and a second
shield 62 layered on the underside surface of the conductive member
50.
[0137] Preferably, the thickness and the elastic modulus of the
first and second shields 61 and 62 can be determined based upon
Formula 1 and/or Formula 2 above.
[0138] The first shield 61 has a thickness T.sub.s1 and an elastic
modulus E.sub.s1, the second shield 62 has a thickness T.sub.s2 and
an elastic modulus E.sub.s2. These values will be determined in the
following.
[0139] The thickness T.sub.1 and elastic modulus E.sub.1 of the
first layer 41, the thickness T.sub.2 and elastic modulus E.sub.2
of the second layer 42, the thickness T.sub.c and elastic modulus
E.sub.c of the conductive layer 30, and the thickness T.sub.3 and
elastic modulus E.sub.3 of the third layer 53 are previously
determined.
[0140] When the values T.sub.s1, E.sub.s1, T.sub.s2 and E.sub.s2
are inputted, respectively, into Formula 1:
Y.sub.n=(.SIGMA.(T.sub.i*E.sub.i*Y.sub.i))/(.SIGMA.(T.sub.i*E.sub.i))
[0141] Y.sub.s1 (the distance from a reference plane to the
geometric center of the first shield 61) can be expressed as in the
following Formula:
Y.sub.s1=T.sub.s1/2+T.sub.1+T.sub.2+T.sub.c+T.sub.3+T.sub.s2
[0142] In addition, Y.sub.s2 (the distance from the reference plane
to the geometric center of the second shield 61) can be expressed
as in the following Formula:
Y.sub.s2=T.sub.s2/2
[0143] As described above, a suitable value is selected based on
the relation with the position Yn of the neutral plane by inputting
T.sub.s1, E.sub.s1, Y.sub.s1, T.sub.s2, E.sub.s2 and Y.sub.s2. It
is preferable that the value of Y.sub.n satisfy Formula 2 or
Formula 3 above.
[0144] That is, the values T.sub.s1, E.sub.s1, T.sub.s2 and
E.sub.s2 are determined by suitably selecting from above-mentioned
formulas, and based upon the determined values, the first shield 61
and the second shield 62 are layered on the FPCT as shown in FIG.
7, so that the neutral plane 35 can be located within a
predetermined range of the thickness of the conductive portion 30
as shown in FIG. 8.
[0145] While the present invention has been shown and described in
connection with the exemplary embodiments, it will be apparent to
those skilled in the art that modifications and variations can be
made without departing from the spirit and scope of the present
invention as defined by the appended claims.
* * * * *