U.S. patent application number 16/147485 was filed with the patent office on 2020-02-27 for method of making flexible circuit board.
The applicant listed for this patent is Avary Holding (Shenzhen) Co., Limited., HongQiSheng Precision Electronics (QinHuangDao) Co., Ltd.. Invention is credited to MING-JAAN HO, HSIAO-TING HSU, FU-YUN SHEN.
Application Number | 20200068715 16/147485 |
Document ID | / |
Family ID | 69583942 |
Filed Date | 2020-02-27 |
United States Patent
Application |
20200068715 |
Kind Code |
A1 |
SHEN; FU-YUN ; et
al. |
February 27, 2020 |
METHOD OF MAKING FLEXIBLE CIRCUIT BOARD
Abstract
A flexible circuit board includes a substrate including a base
layer and a bonding layer formed on each of opposite sides of the
base layer. Each of the two bonding layers is formed by coating a
bonding solution and drying the bonding solution. The bonding
solution is composed of an adhesive and a solvent. A viscosity of
the adhesive is 5000 millipascal-seconds. The adhesive is composed
of a precursor having a mass fraction of 35%-65%, carboxyl modified
polyphenylene oxide having a mass fraction of 10%-15%,
bisphenol-F-epoxy resin having a mass fraction of 10%-15%, a silane
coupling agent having a mass fraction of 0%-1.5%, silica filler
having a mass fraction of 5%-20%, and a flame retardant filler
having a mass fraction of 10%-20%.
Inventors: |
SHEN; FU-YUN; (Shenzhen,
CN) ; HO; MING-JAAN; (New Taipei, TW) ; HSU;
HSIAO-TING; (New Taipei, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Avary Holding (Shenzhen) Co., Limited.
HongQiSheng Precision Electronics (QinHuangDao) Co., Ltd. |
Shenzhen
Qinhuangdao |
|
CN
CN |
|
|
Family ID: |
69583942 |
Appl. No.: |
16/147485 |
Filed: |
September 28, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H05K 2201/015 20130101;
H05K 3/429 20130101; H05K 1/028 20130101; H05K 2201/0162 20130101;
H05K 3/4676 20130101; Y10T 29/49155 20150115; H05K 2201/0158
20130101; H05K 2201/012 20130101; H05K 2201/0195 20130101; H05K
3/389 20130101; H05K 1/189 20130101; H05K 3/4635 20130101; H05K
3/386 20130101; H05K 3/0017 20130101; H05K 1/0218 20130101; H05K
1/0393 20130101; H05K 2201/0715 20130101 |
International
Class: |
H05K 1/18 20060101
H05K001/18; H05K 1/02 20060101 H05K001/02; H05K 3/46 20060101
H05K003/46; H05K 3/00 20060101 H05K003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 23, 2018 |
CN |
201810968814.2 |
Claims
1. A method of making a flexible circuit board, the method
comprising: providing a base layer; coating a bonding solution on
both of opposite sides of the base layer and drying the bonding
solution to form two corresponding bonding layers, the base layer
and the two bonding layers cooperatively forming a substrate;
forming a first copper layer on a surface of a first one of the
bonding layers facing away from the base layer, and forming a
second copper layer on a surface of a second one of the bonding
layers facing away from the base layer; etching the first copper
layer to form a first signal line layer, and etching the second
copper layer to form a second signal line layer; and forming an
insulating layer on a surface of each of the first signal line
layer and the second signal line layer; wherein forming the first
copper layer and the second copper layer on each the surfaces of
the first and the second bonding layers is solidified at 170
degrees Celsius, a time duration of solidifying the first copper
layer and the second copper layer is 30 minutes, and a pressure
value of forming the first copper layer and the second copper layer
is 5 pascals.
2. The method of claim 1, wherein the bonding solution is dried at
100 degrees Celsius, and a time duration of drying the bonding
solution is 5 minutes.
3. The method of claim 1, further comprising: laminating, on a
surface of each insulating layer, an additional substrate formed by
the process of claim 1; forming a third copper layer on a surface
of the bonding layer of a first one of the other substrates facing
away from a first one of the insulating layers, and forming a
fourth copper layer on a surface of the bonding layer of a second
one of the other substrates facing away from a second one of the
insulating layers; defining at least one through hole through the
three substrates, the first signal line layer, the second signal
line layer, the two insulating layers, the third copper layer, and
the fourth copper layer; electroplating an inner wall of the at
least one through hole to form an electroplating layer on the inner
wall of the at least one through hole, thereby forming a conductive
via; and etching the third copper layer to form a first ground
layer, and etching the fourth copper layer to form a second ground
layer.
4. The method of claim 3, further comprising: forming a cover film
on a surface of each of the first ground layer and the second
ground layer.
5. The method of claim 1, wherein the bonding solution is composed
of an adhesive and a solvent, and a viscosity of the adhesive is
5000 millipascal-seconds.
6. The method of claim 1, wherein the base layer is made of PI,
FR4, or PEEK.
7. (canceled)
8. A flexible circuit board comprising: a substrate; a first signal
line layer formed on a first side of the substrate; a second signal
line layer formed on a second side of the substrate opposite to the
first side; and two insulating layers, a first one of the
insulating layers formed over the first signal line layer, and a
second one of the insulating layers formed over the second signal
line layer; wherein: the substrate comprises a base layer and a
bonding layer formed on each of opposite sides of the base layer;
each of the two bonding layers is formed by coating a bonding
solution and drying the bonding solution; the bonding solution is
composed of an adhesive and a solvent; a viscosity of the adhesive
is 5000 millipascal-seconds; and the adhesive is composed of a
precursor having a mass fraction of 35%-65%, carboxyl modified
polyphenylene oxide having a mass fraction of 10%-15%,
bisphenol-F-epoxy resin having a mass fraction of 10%-15%, a silane
coupling agent having a mass fraction of 0%-1.5%, silica filler
having a mass fraction of 5%-20%, and a flame retardant filler
having a mass fraction of 10%-20%.
9. The flexible circuit board of claim 8, further comprising: two
additional substrates, a first one of the additional substrates
laminated on a first one of the insulating layers, and a second one
of the additional substrates laminated on a second one of the
insulating layers; a first ground layer formed on a surface of the
bonding layer of the first one of the additional substrates facing
away from the first one of the insulating layers; a second ground
layer formed on a surface of the bonding layer of the second one of
the additional substrates facing away from the second one of the
insulating layers; and at least one conductive via formed by
electroplating an inner wall of a through hole defined through the
three substrates, the first signal line layer, the second signal
line layer, the two insulating layers, the first ground layer, and
the second ground layer; wherein the conductive via electrically
interconnects the first signal line layer, the second signal line
layer, the first ground layer, and the second ground layer.
10. The flexible circuit board of claim 9, further comprising: two
cover films, a first one of the two cover films formed over the
first ground layer, and a second one of the two cover films formed
over the second ground layer.
11. The flexible circuit board of claim 8, wherein the adhesive
precursor is selected from one or more of fluoroalkyl-modified
polyamic acid and silsesquioxane-modified polyamic acid.
12. The flexible circuit board of claim 8, wherein the silane
coupling agent is selected from one or more of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, glycidyl
methoxypropyl trimethoxysilane, methylallyl propyl
trimethoxysilane, thiopropyl tri-methyl(ethyl) oxysilane.
13. The flexible circuit board of claim 8, wherein the solvent is
selected from one or more of carbitol acetate, cyclohexanone, and
methyl cyclohexane.
14. The flexible circuit board of claim 8, wherein the base layer
is made of PI, FR4, or PEEK.
15. The flexible circuit board of claim 8, wherein a thickness of
each bonding layer is 1-3 micrometers.
16. The flexible circuit board of claim 8, wherein the flame
retardant filler is selected from one or more of
hexaphenoxycyclotriphosphazene and melamine polyphosphate.
Description
FIELD
[0001] The subject matter herein generally relates to flexible
circuit boards, and more particularly to a flexible circuit board
having low transmission loss and a method for making the flexible
circuit board.
BACKGROUND
[0002] Material of a circuit board is an important consideration in
making the circuit board. Circuit boards made of polyimide
generally have a high dielectric loss factor (Df) and a high
dielectric constant (Dk). Thus, it is difficult to satisfy
requirements for high frequency signal transmission.
[0003] Therefore, there is room for improvement within the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Implementations of the present disclosure will now be
described, by way of example only, with reference to the attached
figures.
[0005] FIG. 1 is a cross-sectional view of an embodiment of a base
layer.
[0006] FIG. 2 is a cross-sectional view of the base layer having
two bonding layers formed thereon.
[0007] FIG. 3 is a cross-sectional view of a first copper layer and
a second copper layer formed on the bonding layers.
[0008] FIG. 4 is a cross-sectional view of the first copper layer
and the second copper layer etched to form a first signal line
layer and a second signal line layer.
[0009] FIG. 5 is a cross-sectional view of two insulating layers,
two additional substrates, a third copper layer, and a fourth
copper layer laminated onto the first signal line layer and the
second signal line layer.
[0010] FIG. 6 is a cross-sectional view of a through hole defined
through the substrates, the first copper layer, the second copper
layer, the insulating layers, the third copper layer, and the
fourth copper layer.
[0011] FIG. 7 is a cross-sectional view of an inner wall of the
through hole electroplated to form a conductive via.
[0012] FIG. 8 is a cross-sectional view of a protective layer
formed on a first ground layer and a second ground layer.
DETAILED DESCRIPTION
[0013] It will be appreciated that for simplicity and clarity of
illustration, where appropriate, reference numerals have been
repeated among the different figures to indicate corresponding or
analogous elements. Additionally, numerous specific details are set
forth in order to provide a thorough understanding of the
embodiments described herein. However, it will be understood by
those of ordinary skill in the art that the embodiments described
herein can be practiced without these specific details. In other
instances, methods, procedures and components have not been
described in detail so as not to obscure the related relevant
feature being described. The drawings are not necessarily to scale
and the proportions of certain parts may be exaggerated to better
illustrate details and features. The description is not to be
considered as limiting the scope of the embodiments described
herein.
[0014] Several definitions that apply throughout this disclosure
will now be presented.
[0015] The term "coupled" is defined as connected, whether directly
or indirectly through intervening components, and is not
necessarily limited to physical connections. The connection can be
such that the objects are permanently connected or releasably
connected. The term "comprising" means "including, but not
necessarily limited to"; it specifically indicates open-ended
inclusion or membership in a so-described combination, group,
series and the like.
[0016] A method for making a flexible circuit board 100 is provided
in the following steps.
[0017] FIG. 1 shows step S1. Abase layer 10 is provided. The base
layer 10 may be made of PI, FR4, or PEEK.
[0018] FIG. 2 shows step S2. A bonding solution is applied on each
of opposite surfaces of the base layer 10. The bonding solution is
dried to form two corresponding bonding layers 20. The base layer
10 and the two bonding layers 20 cooperatively form a substrate
200. The bonding solution is dried at 100 degrees Celsius, and a
time duration of drying the bonding solution is 5 minutes. The two
bonding layers 20 adhere to the opposite surfaces of the base layer
10. A thickness of each bonding layer 20 is 1-3 micrometers.
[0019] FIG. 3 shows step S3. A first copper layer 30 is formed on a
surface of one of the bonding layers 20 facing away from the base
layer 10, and a second copper layer 40 is formed on a surface of
the other one of the bonding layers 20 facing away from the base
layer 10. Forming the first copper layer 30 and the second copper
layer 40 on each the surfaces of the first and the second bonding
layers 20 is solidified at 170 degrees Celsius, a time duration of
solidifying the first copper layer 30 and the second copper layer
40 is 30 minutes, and a pressure value of forming the first copper
layer 30 and the second copper layer 40 is 5 pascals.
[0020] FIG. 4 shows step S4. The first copper layer 30 is etched to
form a first signal line layer 31, and the second copper layer 40
is etched to form a second signal line layer 41.
[0021] FIG. 5 shows step S5. An insulating layer 50 is formed on a
surface of each of the first signal line layer 31 and the second
signal line layer 41. The insulating layer 50 is formed over the
surfaces of the first signal line layer 31 and the second signal
line layer 41 and fills in the etched portions of the first signal
line layer 31 and the second signal line layer 41 over the
corresponding bonding layers 20. Material of the insulating layers
50 is selected from flexible insulating material, such as epoxy
resin. In one embodiment, the insulating layer 50 is partially
solidified resin applied over the surfaces of the first signal line
layer 31 and the second signal line layer 41 and then pressed to
fill in the etched portions of the first signal line layer 31 and
the second signal line layer 41 over the corresponding bonding
layers 20.
[0022] FIG. 5 shows step S6. Steps S1 and S2 are repeated to form
two additional substrates 200. Each additional substrate 200 is
laminated onto the surface of the corresponding insulating layer
50.
[0023] FIGS. 5-6 show step S7. A third copper layer 60 is formed on
a surface of the bonding layer 20 of a first one of the other
substrates 200 facing away from a first one of the insulating
layers 50, and a fourth copper layer 70 is formed on a surface of
the bonding layer 20 of a second one of the other substrates 200
facing away from a second one of the insulating layers 50. At least
one through hole 80 is defined through the substrates 200, the
first signal line layer 31, the second signal line layer 41, the
two insulating layers 50, the third copper layer 60, and the fourth
copper layer 70.
[0024] FIG. 7 shows step S8. An inner wall of the through hole 80
is electroplated to form an electroplating layer 81 on the inner
wall of the through hole 80, thereby forming a conductive via 82
for electrically interconnecting the first signal line layer 31 and
the second signal line layer 41. In one embodiment, material of the
electroplating layer 81 is copper. In other embodiments, the
electroplating layer 81 may be formed from other materials.
[0025] FIG. 7 shows step S9. The third copper layer 60 is etched to
form a first ground layer 61, and the fourth copper layer 70 is
etched to form a second ground layer 71.
[0026] FIG. 8 shows step S10. A cover film 90 is formed on a
surface of each of the first ground layer 61 and the second ground
layer 71, thereby completing formation of the flexible circuit
board 100. The cover film 90 protects the first ground layer 61 and
the second ground layer 71.
[0027] After step S6, additional signal line layers may be formed
over the first signal line layer 31 and the second signal line
layer 41 according to requirements.
[0028] Alternatively, steps S6-S10 may be omitted.
[0029] In one embodiment, the bonding solution is composed of an
adhesive and a solvent. A bonding strength of the adhesive is 5000
millipascal-seconds.
[0030] The adhesive is composed of a precursor having a mass
fraction of 35%-65%, carboxyl modified polyphenylene oxide having a
mass fraction of 10%-15%, bisphenol-F-epoxy resin having a mass
fraction of 10%-15%, a silane coupling agent having a mass fraction
of 0%-1.5%, silica filler having a mass fraction of 5%-20%, and a
flame retardant filler having a mass fraction of 10%-20%.
[0031] The adhesive precursor is selected from one or more of
fluoroalkyl-modified polyamic acid and silsesquioxane-modified
polyamic acid. Using an adhesive precursor made of material similar
to the material of the base layer 10 enhances the bonding strength
of the bonding layer 20 to the base layer 10.
[0032] The carboxyl modified polyphenylene oxide enhances a
relative dielectric constant (Dk) of the bonding layer 20.
[0033] The bisphenol-F-epoxy resin reduces fragility of the
carboxyl modified polyphenylene oxide and reduces fragility of the
bonding layer 20.
[0034] The silane coupling agent is selected from one or more of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, glycidyl
methoxypropyl trimethoxysilane, methylallyl propyl
trimethoxysilane, thiopropyl tri-methyl(ethyl) oxysilane. The
silane coupling agent enhances adhesiveness of the bonding layer 20
to the base layer 10.
[0035] The silica filler enhances dielectricity of the bonding
layer 20 and controls expansion and shrinkage of the bonding layer
20.
[0036] The flame retardant filler is selected from one or more of
hexaphenoxycyclotriphosphazene and melamine polyphosphate. The
flame retardant filler enhances flame retardation of the bonding
layer 20.
[0037] The solvent is selected from one or more of carbitol
acetate, cyclohexanone, and methyl cyclohexane. The solvent
dissolves the adhesive to form the bonding solution.
[0038] A method of making the bonding solution is provided as
follows.
[0039] The adhesive is placed within a container. A predetermined
volume of solvent is dispensed within the container and stirred to
form the bonding solution having a bonding strength of 5000
millipascal-seconds.
[0040] A first embodiment of making the bonding solution is
provided as follows.
[0041] A solvent selected from carbitol acetate is provided. 52.8
grams (g) of fluoroalkyl-modified polyamic acid, 13.2 g of
silsesquioxane-modified polyamic acid, 11.5 g of carboxyl modified
polyphenylene oxide, 10.3 g of bisphenol-F-epoxy resin, 0.7 g of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, 9.5 g of silica
filler, and 15 g of hexaphenoxycyclotriphosphazene are placed in a
container. A predetermined volume of carbitol acetate is dispensed
into the container and mixed to form the bonding solution.
[0042] A second embodiment of making the bonding solution is
provided as follows.
[0043] A solvent selected from carbitol acetate is provided. 39.6 g
of fluoroalkyl-modified polyamic acid, 26.4 g of
silsesquioxane-modified polyamic acid, 11.3 g of carboxyl modified
polyphenylene oxide, 10.3 g of bisphenol-F-epoxy resin, 0.7 g of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, 9.5 g of silica
filler, and 15 g of hexaphenoxycyclotriphosphazene are placed in a
container. A predetermined volume of carbitol acetate is dispensed
into the container and mixed to form the bonding solution.
[0044] A third embodiment of making the bonding solution is
provided as follows.
[0045] A solvent selected from carbitol acetate is provided. 33 g
of fluoroalkyl-modified polyamic acid, 33 g of
silsesquioxane-modified polyamic acid, 11.1 g of carboxyl modified
polyphenylene oxide, 10.3 g of bisphenol-F-epoxy resin, 0.7 g of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, 9.5 g of silica
filler, and 15 g of hexaphenoxycyclotriphosphazene are placed in a
container. A predetermined volume of carbitol acetate is dispensed
into the container and mixed to form the bonding solution.
[0046] A fourth embodiment of making the bonding solution is
provided as follows.
[0047] A solvent selected from carbitol acetate is provided. 65 g
of fluoroalkyl-modified polyamic acid, 11.5 g of carboxyl modified
polyphenylene oxide, 10.3 g of bisphenol-F-epoxy resin, 0.7 g of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, 9.5 g of silica
filler, and 15 g of hexaphenoxycyclotriphosphazene are placed in a
container. A predetermined volume of carbitol acetate is dispensed
into the container and mixed to form the bonding solution.
[0048] A fifth embodiment of making the bonding solution is
provided as follows.
[0049] A solvent selected from carbitol acetate is provided. 14 g
of fluoroalkyl-modified polyamic acid, 48 g of
silsesquioxane-modified polyamic acid, 15 g of carboxyl modified
polyphenylene oxide, 10.3 g of bisphenol-F-epoxy resin, 0.7 g of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, 9.5 g of silica
filler, and 15 g of hexaphenoxycyclotriphosphazene are placed in a
container. A predetermined volume of carbitol acetate is dispensed
into the container and mixed to form the bonding solution.
[0050] The bonding layer 20 formed from the bonding solution
provided in the first-fifth embodiments has a peel strength of 1.1
kgf/cm, 1.4 kgf/cm, 1.5 kgf/cm, 1.1 kgf/cm, and 1.4 kgf/cm,
respectively.
[0051] The bonding layer 20 formed from the bonding solution
provided in the first-fifth embodiments has a solder thermal
resistance of 320 degrees C., 300 degrees C., 300 degrees C., 300
degrees C., and 320 degrees C., respectively.
[0052] The bonding layer 20 formed from the bonding solution
provided in the first-fifth embodiments has a dielectric constant
(Dk) of 2.5, 2.6, 2.6, 2.6, and 2.9, respectively.
[0053] The bonding layer 20 formed from the bonding solution
provided in the first-fifth embodiments has a dielectric loss
factor (Df) of 0.003, 0.005, 0.005, 0.006, and 0.005,
respectively.
[0054] FIGS. 5-8 show the flexible circuit board 100 including the
base layer 10, the two bonding layers 20, the first signal line
layer 31, the second signal line layer 41, and the two insulating
layers 50. The base layer 10 is made of polyimide, fiberglass,
epoxy resin, or polyether ether ketone. The two bonding layers 20
are formed on opposite surfaces of the base layer 10. The bonding
layers 20 are formed by applying the bonding solution onto the
surfaces of the base layer 10 and drying the bonding solution. A
thickness of the bonding layer 20 is 1-3 micrometers. The base
layer 10 and the two bonding layers 20 cooperatively form the
substrate 200.
[0055] The bonding solution is composed of an adhesive and a
solvent. A bonding strength of the adhesive is 5000
millipascal-seconds.
[0056] The adhesive is composed of a precursor having a mass
fraction of 35%-65%, carboxyl modified polyphenylene oxide having a
mass fraction of 10%-15%, bisphenol-F-epoxy resin having a mass
fraction of 10%-15%, a silane coupling agent having a mass fraction
of 0%-1.5%, silica filler having a mass fraction of 5%-20%, and a
flame retardant filler having a mass fraction of 10%-20%.
[0057] The adhesive precursor is selected from one or more of
fluoroalkyl-modified polyamic acid and silsesquioxane-modified
polyamic acid. The precursor made of material similar to the
material of the base layer 10 enhances the bonding strength of the
bonding layer 20 to the base layer 10.
[0058] The carboxyl modified polyphenylene oxide enhances a
relative dielectric constant (Dk) of the bonding layer 20.
[0059] The bisphenol-F-epoxy resin reduces fragility of the
carboxyl modified polyphenylene oxide and reduces fragility of the
bonding layer 20.
[0060] The silane coupling agent is selected from one or more of
N-.beta.-.gamma.-aminopropyltrimethoxysilane, glycidyl
methoxypropyl trimethoxysilane, methylallyl propyl
trimethoxysilane, thiopropyl tri-methyl(ethyl) oxysilane. The
silane coupling agent enhances adhesiveness of the bonding layer 20
to the base layer 10.
[0061] The silica filler enhances dielectricity of the bonding
layer 20 and controls expansion and shrinkage of the bonding layer
20.
[0062] The flame retardant filler is selected from one or more of
hexaphenoxycyclotriphosphazene and melamine polyphosphate. The
flame retardant filler enhances flame retardation of the bonding
layer 20.
[0063] The solvent is selected from one or more of carbitol
acetate, cyclohexanone, and methyl cyclohexane. The solvent
dissolves the adhesive to form the bonding solution.
[0064] The first signal line layer 31 is formed on the
corresponding bonding layer 20, and the second signal line layer 41
is formed on the corresponding bonding layer 20. The two insulating
layer 50 are formed over the first signal line layer 31 and the
second signal line layer 41 and fill in the exposed portions of the
first signal line layer 31 and the second signal line layer 41.
[0065] A first one of two additional substrates 200 is laminated
onto the surface of one of the corresponding insulating layers 50,
and a second one of the two additional substrates 200 is laminated
onto the surface of a second one of the corresponding insulating
layers 50. A first ground layer 61 is formed on a surface of the
bonding layer 20 of the first one of the additional substrates 200
facing away from a first one of the insulating layers 50, and a
second ground layer 71 is formed on a surface of the bonding layer
20 of the second one of the additional substrates 200 facing away
from a second one of the insulating layers 50. The substrates 200,
the first signal line layer 31, the second signal line layer 41,
the two insulating layers 50, the third copper layer 60, and the
fourth copper layer 70 are electrically interconnected by at least
one conductive via 82 formed therethrough.
[0066] A cover film 90 is formed on a surface of each of the first
ground layer 61 and the second ground layer 71, thereby completing
formation of the flexible circuit board 100.
[0067] The embodiments shown and described above are only examples.
Even though numerous characteristics and advantages of the present
technology have been set forth in the foregoing description,
together with details of the structure and function of the present
disclosure, the disclosure is illustrative only, and changes may be
made in the detail, including in matters of shape, size and
arrangement of the parts within the principles of the present
disclosure up to, and including, the full extent established by the
broad general meaning of the terms used in the claims.
* * * * *