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The present disclosure provides a cover film, including a conductive
adhesive layer, an electromagnetic shielding layer formed on the
conductive adhesive layer, and an insulating layer formed on the
electromagnetic shielding layer. The electromagnetic shielding layer has
a thickness of from 0.01 to 25 micrometers, such that the cover film can
shield electromagnetic interference through the thinner interposed
electromagnetic shielding layer.
Inventors:
Lin; Chih-Ming; (Zhubei City, TW); Lin; Hui-Feng; (Zhubei City, TW); Lee; Chien-Hui; (Zhubei City, TW)
Applicant:
Name
City
State
Country
Type
ASIA ELECTRONIC MATERIAL CO., LTD.
Hsinchu County
TW
Family ID:
1000001547299
Appl. No.:
14/882753
Filed:
October 14, 2015
Current U.S. Class:
428/40.7 ; 428/216; 428/336; 428/41.3; 428/41.8
Current CPC Class:
H05K 9/0083 20130101; H05K 9/0088 20130101
International Class:
H05K 9/00 20060101 H05K009/00
Foreign Application Data
Date
Code
Application Number
Oct 15, 2014
CN
20141055233.X
Oct 15, 2014
CN
201420596633.9
Claims
1. A cover film, comprising: a conductive adhesive layer; an
electromagnetic shielding layer formed on the conductive adhesive layer
and having a thickness of 0.01 to 25 micrometers; and an insulating layer
formed on the electromagnetic shielding layer, wherein the
electromagnetic shielding layer is sandwiched between the conductive
adhesive layer and the insulating layer.
2. The cover film of claim 1, wherein the electromagnetic shielding layer
has a thickness of from 0.01 to 1.5 micrometers.
3. The cover film of claim 1, wherein the insulating layer has a
thickness of from 3 to 75 micrometers.
4. The cover film of claim 1, wherein the insulating layer comprises a
first polymer and an additive dispersed in the first polymer.
5. The cover film of claim 4, wherein the first polymer is at least one
selected from the group consisting of an epoxy resin, an acrylic resin
and a combination thereof.
6. The cover film of claim 4, wherein a content of the additive is
between 3 wt % to 15 wt % of the insulating layer.
7. The cover film of claim 4, wherein the additive is at least one
selected from the group consisting of carbon powder, titanium dioxide, a
colorant, a pigment and a combination thereof.
8. The cover film of claim 1, wherein the electromagnetic shielding layer
is made of metal or a resin containing metal powder.
9. The cover film of claim 1, wherein the conductive adhesive layer has a
thickness of from 3 to 50 micrometers.
10. The cover film of claim 1, wherein the conductive adhesive layer
comprises a second polymer and at least one conductive powder dispersed
in the second polymer.
11. The cover film of claim 10, wherein the second polymer is at least
one selected from the group consisting of an epoxy resin, a poly-p-xylene
resin, a bismaleimide resin, a polyimide resin, an acrylic resin, a
urethane resin, a silicon rubber-based resin and a combination thereof.
12. The cover film of claim 10, wherein a content of the conductive
powder is between 0.5 wt % to 90 wt % of the conductive adhesive layer.
13. The cover film of claim 10, wherein the at least one conductive
powder is at least one selected from the group consisting of gold powder,
silver powder, copper powder, nickel powder, aluminum powder, silver
coated copper powder, silver coated nickel powder, copper-nickel alloy,
iron powder, iron-based alloy, silver-copper alloy, tin-copper alloy,
gold plated nickel powder, and silver plated copper powder.
14. The cover film of claim 1, further comprising an electromagnetic
absorption layer formed between the electromagnetic shielding layer and
the insulating layer.
15. The cover film of claim 14, wherein the electromagnetic absorption
layer has a thickness of from 0.1 to 25 micrometers.
16. The cover film of claim 14, wherein the electromagnetic absorption
layer comprises a third polymer and at least one magnetic powder
dispersed in the third polymer.
17. The cover film of claim 16, wherein the at least one magnetic powder
is at least one selected from the group consisting of iron oxide,
iron-silicon-aluminum alloy, permalloy (iron-nickel alloy), and
iron-silicon-chrome-nickel alloy.
18. The cover film of claim 1, further comprising a release layer formed
under the conductive adhesive layer, wherein the conductive adhesive
layer is sandwiched between the electromagnetic shielding layer and the
release layer.
19. The cover film of claim 18, wherein the release layer has a thickness
of from 25 to 100 micrometers.
20. The cover film of claim 18, wherein the release layer is a
polyethylene terephthalate (PET) fluorine release film, a PET silicone
oil release film, a PET matte release film or a polyethylene release
film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present disclosure relates to a cover film, and more
particularly, to a cover film with an electromagnetic shielding property.
[0003] 2. Description of Related Art
[0004] Recently, it has become a trend to develop in small consumer
electronics with compact size, light weight as well as degrees of
freedom. Therefore, flexible printed circuit boards (FPCB) are utilized
in smart phone and touch panel due to the characteristics of light
weight, thinness, high degrees of freedom and flexibility.
[0005] In order to properly operate with high speed transmission of
signals, wirings are designed to be more aggregated such that the spacing
between two adjacent wires is smaller. However, the problem of
electromagnetic interference would get worse due to the decreased
spacing, the higher operating frequency, and the unreasonable circuit
arrangement.
[0006] In some designs, an electromagnetic shielding layer is added on a
cover film or a solder resist which is attached on a circuit board by
glue for shielding electromagnetic interference from outside or internal
signal noises. Nevertheless, the process is more complex and
time-consuming, and results in lack of protection for the electromagnetic
shielding layer. Therefore, there is a need to develop a thinner cover
film for shielding electromagnetic interference.
SUMMARY OF THE INVENTION
[0007] The present disclosure provides a cover film, comprising a
conductive adhesive layer, an electromagnetic shielding layer formed on
the conductive adhesive layer, and an insulating layer formed on the
electromagnetic shielding layer, wherein the electromagnetic shielding
layer has a thickness of from 0.01 to 25 micrometers.
[0008] In one preferable embodiment, the thickness of the electromagnetic
shielding layer is from 0.01 to 1.5 micrometers.
[0009] In an embodiment, a thickness of the insulating layer is between 3
to 75 micrometers.
[0010] In an embodiment, the insulating layer comprises a first polymer
and an additive dispersed in the first polymer, wherein a content of the
additive is between 3 wt % to 15 wt % of the insulating layer, and
wherein the first polymer is at least one selected from the group
consisting of an epoxy resin, an acrylic resin and a combination thereof,
and the additive is at least one selected from the group consisting of
carbon powder, titanium dioxide, a colorant, a pigment and a combination
thereof.
[0011] In an embodiment, the electromagnetic shielding layer is made of
metal or a resin containing metal powder. In an embodiment, the
electromagnetic shielding layer is formed on the conductive adhesive
layer by coating, vapor deposition or magnetron sputtering.
[0012] In an embodiment, a thickness of the conductive adhesive layer is
between 3 to 50 micrometers, wherein the conductive adhesive layer
comprises a second polymer and at least one conductive powder dispersed
in the second polymer, and wherein a content of the conductive powder is
between 0.5 wt % to 90 wt % of the conductive adhesive layer. In one
preferred embodiment, the second polymer is at least one selected from
the group consisting of an epoxy resin, a poly-p-xylene resin, a
bismaleimide resin, a polyimide resin, an acrylic resin, a urethane
resin, a silicon rubber-based resin and a combination thereof.
Preferably, the second polymer is an epoxy resin or an acrylic resin.
[0013] In an embodiment, the at least one conductive powder is at least
one selected from the group consisting of gold powder, silver powder,
copper powder, nickel powder, aluminum powder, silver coated copper
powder, silver coated nickel powder, copper-nickel alloy, iron powder,
iron-based alloy, silver-copper alloy, tin-copper alloy, gold plated
nickel powder, and silver plated copper powder.
[0014] In another embodiment, the cover film further comprises an
electromagnetic absorption layer formed between the electromagnetic
shielding layer and the insulating layer, wherein the electromagnetic
absorption layer has a thickness of from 0.1 to 25 micrometers.
[0015] In an embodiment, the electromagnetic absorption layer comprises a
third polymer and at least one magnetic powder dispersed in the third
polymer, wherein a content of the at least one magnetic powder is between
50 wt % to 90 wt % of the electromagnetic absorption layer, and the
electromagnetic absorption layer is formed by filling, laminating or
coating.
[0016] In an embodiment, the at least one magnetic powder is at least one
selected from the group consisting of iron oxide, iron-silicon-aluminum
alloy, permalloy (iron-nickel alloy), and iron-silicon-chrome-nickel
alloy. In one embodiment, the third polymer is selected from the group
consisting of an epoxy resin, a poly-p-xylene resin, a bismaleimide
resin, a polyimide resin, an acrylic resin, a urethane resin and a
silicon rubber-based resin and a combination thereof. Preferably, the
third polymer is an epoxy resin or an acrylic resin.
[0017] In another embodiment, the cover film further comprises a release
layer formed under the conductive adhesive layer such that the conductive
adhesive layer is sandwiched between the electromagnetic shielding layer
and the release layer, wherein the release layer has a thickness of from
25 to 100 micrometers. In a preferred embodiment, the release layer is a
polyethylene terephthalate (PET) fluorine release film, a PET silicone
oil release film, a PET matte release film or a polyethylene release
film.
[0018] According to the present disclosure, an overall thickness of the
FPCB can be reduced through forming the thinner interposed
electromagnetic shielding layer having a thickness of from 0.01 to 25
micrometers. Furthermore, the electromagnetic shielding layer can be
formed by coating, vapor deposition or magnetron sputtering in one single
process such that the process of the cover film is simplified.
[0019] As such, the cover film of the present disclosure has an effect of
preventing not only electromagnetic interference resulting from the
internal signal transmission but also electromagnetic spillover by
forming the electromagnetic absorption layer having a thickness of from
0.1 to 25 micrometers with a limited increased thickness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a cross-sectional schematic view of a cover film
according to a first embodiment of the present disclosure;
[0021] FIG. 2 is a cross-sectional schematic view of a cover film
according to another example of the first embodiment of the present
disclosure;
[0022] FIG. 3 is a cross-sectional schematic view of a cover film
according to a second embodiment of the present disclosure; and
[0023] FIG. 4 is a cross-sectional schematic view of a cover film
according to another example of the second embodiment of the present
disclosure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The detailed description of the present disclosure is illustrated
by the following specific examples. Persons skilled in the art can
conceive the other advantages and effects of the present disclosure based
on the content contained in the specification of the present disclosure.
It should be noted that all the drawings are not intended to limit the
present disclosure. Various modifications and variations can be made
without departing from the spirit of the present disclosure. Further,
terms such as "first," "second," "on," "a," etc. are merely for
illustrative purposes and should not be construed to limit the scope of
the present disclosure.
First Embodiment
[0025] FIG. 1 is a cross-sectional schematic view of a cover film 1 of the
present disclosure, comprising a conductive adhesive layer 11, an
electromagnetic shielding layer 12 formed on the conductive adhesive
layer 11, and an insulating layer 13 formed on the electromagnetic
shielding layer 12, wherein the electromagnetic shielding layer 12 has a
thickness of from 0.01 to 25 micrometers.
[0026] In this embodiment, the insulating layer 13 having a thickness of
from 3 to 75 micrometers is provided. The insulating layer 13 comprises a
first polymer and an additive dispersed in the first polymer, wherein a
content of the additive is between 3 wt % to 15 wt % of the insulating
layer. In a preferred embodiment, the first polymer is at least one
selected from the group consisting of an epoxy resin, an acrylic resin
and a combination thereof.
[0027] Further, the electromagnetic shielding layer 12 having a thickness
of from 0.01 to 25 micrometers is formed on the conductive adhesive layer
11, and the thickness of the electromagnetic shielding layer 12 is
preferably from 0.01 to 1.5 micrometers. The conductive adhesive layer 11
has a thickness of from 3 to 50 micrometers and comprises a second
polymer and at least one conductive powder dispersed in the second
polymer, wherein a content of the conductive powder is between 0.5 wt %
to 90 wt % of the conductive adhesive layer. In a preferred embodiment,
the second polymer is at least one selected from the group consisting of
an epoxy resin, a poly-p-xylene resin, a bismaleimide resin, a polyimide
resin, an acrylic resin, a urethane resin and a silicon rubber-based
resin and a combination thereof. Preferably, the second polymer is an
epoxy resin or an acrylic resin.
[0028] Also, the at least one conductive powder is at least one selected
from the group consisting of gold powder, silver powder, copper powder,
nickel powder, aluminum powder, silver coated copper powder, silver
coated nickel powder, copper-nickel alloy, iron powder, iron-based
alloys, silver-copper alloy, tin-copper alloy, gold plated nickel powder,
and silver plated copper powder.
[0029] Referring to FIG. 2, in order to keep adhesiveness of the
conductive adhesive layer 11, the cover film 2 of the present disclosure
further comprises a release layer 10 formed under the conductive adhesive
layer 11 such that the conductive adhesive layer 11 is sandwiched between
the electromagnetic shielding layer 12 and the release layer 10. When the
cover film 2 is needed to be attached to FPCB, the release layer 10 is
then removed.
Second Embodiment
[0030] As shown in FIG. 3, a cover film 3 according to the present
disclosure further comprises an electromagnetic absorption layer 14
formed between the electromagnetic shielding layer 12 and the insulating
layer 13. In this embodiment, the electromagnetic absorption layer 14 has
a thickness of from 0.1 to 25 micrometers.
[0031] In this embodiment, the electromagnetic absorption layer 14
comprises a third polymer and at least one magnetic powder dispersed in
the third polymer, wherein the at least one magnetic powder is at least
one selected from the group consisting of iron oxide,
iron-silicon-aluminum alloy, permalloy (iron-nickel alloy), and
iron-silicon-chrome-nickel alloy.
[0032] In this embodiment, the third polymer is at least one selected from
the group consisting of an epoxy resin, a poly-p-xylene resin, a
bismaleimide resin, a polyimide resin, an acrylic resin, a urethane
resin, a silicon rubber-based resin and a combination thereof. More
preferably, the third polymer is an epoxy resin or an acrylic resin.
[0033] The structure of the cover film 3 of this embodiment is similar to
that of the cover film 1 of the first embodiment, and the difference is
in that the additional electromagnetic absorption layer 14 having a
thickness of from 0.1 to 25 micrometers is interposed between the
insulating layer 13 and the electromagnetic shielding layer 12.
[0034] Preferably, the electromagnetic shielding layer 12 has a thickness
of from 0.01 to 1.5 micrometers, and the electromagnetic shielding layer
12 is made of metal such as gold, copper, zinc, nickel or aluminum.
[0035] In the embodiment, a conductive adhesive layer 11 is formed under
the electromagnetic shielding layer 12, and a thickness of the conductive
adhesive layer 11 is from 3 to 50 micrometers. The conductive adhesive
layer 11 comprises a second polymer and at least one conductive powder
dispersed in the second polymer, wherein a content of the conductive
powder is between 0.5 wt % to 90 wt % of the conductive adhesive layer.
In a preferred embodiment, the second polymer is at least one selected
from the group consisting of an epoxy resin, a poly-p-xylene resin, a
bismaleimide resin, a polyimide resin, an acrylic resin, a urethane
resin, a silicon rubber-based resin and a combination thereof. More
preferably, the second polymer is an epoxy resin or an acrylic resin. The
at least one conductive powder is at least one selected from the group
consisting of gold powder, silver powder, copper powder, nickel powder,
aluminum powder, silver coated copper powder, silver coated nickel
powder, copper-nickel alloy, iron powder, iron-based alloy, silver-copper
alloy, tin-copper alloy, gold plated nickel powder, and silver plated
copper powder.
[0036] Referring to FIG. 4, in order to keep adhesiveness of the
conductive adhesive layer 11, the cover film 4 of the present disclosure
further comprises a release layer 10 formed under the conductive adhesive
layer 11 such that the conductive adhesive layer 11 is sandwiched between
the electromagnetic shielding layer 12 and the release layer 10. When the
cover film 4 is needed to be attached to FPCB, the release layer 10 is
then removed.
Examples 1 to 2
The Manufacture of the Cover Film of the First Embodiment of the Present
Disclosure
[0037] The cover films of the present disclosure were made according to
the thickness described in Table 1 and the manufacturing method described
below.
[0038] First, an insulating layer comprising an epoxy resin (Dupont;
APLUS-1) and titanium dioxide powder (Dupont; R906) dispersed in the
epoxy resin was provided, wherein a content of the titanium dioxide
powder is 10 wt % of the insulating layer. Then, an acrylic resin (Asia
Electronic Materials Co., Ltd., AEM Co.; RD0351) containing 85 wt % of
silver coated copper powder (AEM Co.; EI-0007) was coated on the
insulating layer. Afterwards, the acrylic resin was baked at a
temperature of 50.degree. C. for 5 minutes to form an electromagnetic
shielding layer having a thickness as shown in Table 1. Subsequently, a
conductive paint was coated on the electromagnetic shielding layer,
wherein the conductive paint was prepared through mixing an epoxy resin
(Dupont; APLUS-1) and a metal powder (Union Chemical Ind. Co. Ltd.; A-3).
The conductive paint was dried to form the conductive adhesive layer
having a content of 60 wt % of the metal powder. The cover film of the
first embodiment of the present disclosure was then obtained.
Examples 3 to 5
The Manufacture of the Cover Film of the First Embodiment of the Present
Disclosure
[0039] The cover films of Examples 3 to 5 were prepared according to the
method described in Examples 1 and 2, except that 10 wt % of titanium
dioxide powder was replaced by 15 wt % of carbon black (CABOT company;
REGAL 400R).
[0040] In addition, a release layer (Mitsubishi; F38) was attached under
the conductive adhesive layer in Examples 4 and 5.
Examples 6 to 7
The Manufacture of the Cover Film of the Second Embodiment of the Present
Disclosure
[0041] First, the cover films of Examples 6 to 7 were prepared according
to the thickness described in Table 1 below and the manufacturing method
previously described, except that an electromagnetic absorption layer was
formed prior to the formation of the electromagnetic shielding layer. The
electromagnetic absorption layer comprising an acrylic resin, and 85 wt %
of iron-silicon-aluminum alloy (Sanyo; HY-008) was formed followed by
applying the resin mixture and baking at a temperature of 50.degree. C.
for 5 minutes. Then, the electromagnetic shielding layer and the
conductive adhesive layer were formed sequentially to obtain the cover
film of the second embodiment.
Examples 8 to 10
The Manufacture of the Cover Film of the Second Embodiment of the Present
Disclosure
[0042] The cover films of Examples 8 to 10 were prepared according to the
method described in Examples 6 and 7, except that 10 wt % of titanium
dioxide powder was replaced by 15 wt % of carbon black (CABOT company;
REGAL 400R).
[0043] In addition, a release layer (Mitsubishi; F38) was attached on the
conductive adhesive layer in Examples 9 and 10.
Comparative Example 1
[0044] The cover film of the Comparative Example 1 was prepared according
to the method described in Example 1 above and the thickness described in
Table 1 below, except that no electromagnetic shielding layer was formed
and the insulating layer was made of polyurethane (Uncore Company;
XC0208BB2500).
TABLE-US-00001
TABLE 1
Thickness (.mu.m)
Electro- Electro-
Conductive magnetic magnetic
adhesive shielding absorption Insulating Release
layer layer layer layer layer
Example 1 3 1 -- 3 --
Example 2 4 2 -- 3 --
Example 3 5 3 -- 4 --
Example 4 6 4 -- 5 50
Example 5 7 5 -- 6 50
Example 6 8 6 5 7 --
Example 7 9 7 6 8 --
Example 8 10 8 7 9 --
Example 9 11 9 8 10 50
Example 10 12 10 9 11 50
Comparative 25 -- -- 20 75
Example 1
Test Example
[0045] The mechanical property and electrical property of the cover films
of Examples 1 to 10 and Comparative example 1 were measured. The test
items include thermal stress, dielectric loss, dielectric constant and
electromagnetic shielding efficiency. The dielectric loss and dielectric
constant were measured by a cavity resonator (Waveguide Resonators)
according to the measurement of ASTM 2520, and the thermal stress and the
electromagnetic shielding efficiency were measured in accordance with the
following conditions.
The Electromagnetic Shielding Efficiency:
[0046] According to the measurement of ASTM D4935-99, a coaxial
transmission line holder and network analyzer (Wiltron 37225B) were used
to measure the electromagnetic shielding efficiency under an operating
frequency of from 30 MHz to 1.5 GHz and 40 MHz to 13.5 GHz.
Test of the Thermal Stress:
[0047] According to the measurement of IPC-TM-650-2.4.13, the sample was
pre-dried in an oven (at 121.degree. C. to 149.degree. C.) for 6 hours,
and the sample was removed from the oven to cool down to room
temperature. Then, the sample was exposed to solder float at 288.degree.
C. for 10 seconds, followed by observation as to whether the exterior
appearance of the sample changes visually. The results were summarized in
Table 2.
TABLE-US-00002
TABLE 2
Electromagnetic
Dielectric Dielectric shielding Thermal
constant loss efficiency stress
(Dk) (Df) (dB) test*
Example 1 2.5 0.025 -50
Example 2 2.6 0.032 -50
Example 3 2.7 0.031 -50
Example 4 2.8 0.037 -50
Example 5 2.9 0.041 -50
Example 6 3.0 0.044 -55
Example 7 3.1 0.056 -55
Example 8 3.2 0.064 -55
Example 9 3.3 0.087 -55
Example 10 3.4 0.089 -55
Comparative 4.5 0.2 -42
Example 1
* : No change
[0048] As illustrated in the result of Table 2, each of the cover films of
Examples 1 to 3 has a lower dielectric constant and dielectric loss in
comparison with the cover film of Comparative Example 1. Although the
thickness of each of the cover films of Examples 6 to 10 is higher and an
additional electromagnetic absorption layer is attached, the cover films
of Examples 6 to 10 show a limited increasing trend in dielectric
constant and dielectric loss. In addition, the cover films of Examples 6
to 10 show a superior characteristic of electromagnetic shielding.
[0049] The above-described descriptions of the specific embodiments are
intended to illustrate the preferred implementation according to the
present disclosure but are not intended to limit the scope of the present
disclosure. Accordingly, all modifications and variations completed by
those with ordinary skill in the art should fall within the scope of
present disclosure defined by the appended claims.