U.S. patent application number 12/466770 was filed with the patent office on 2009-09-10 for method for manufacturing a printed circuit board with a thin film capacitor embedded therein having a dielectric film by using laser lift-off, and printed circuit board with a thin film capacitor embedded therein manufactured thereby.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Yul Kyo Chung, In Hyung Lee, Jung Won Lee.
Application Number | 20090223045 12/466770 |
Document ID | / |
Family ID | 39028949 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090223045 |
Kind Code |
A1 |
Lee; Jung Won ; et
al. |
September 10, 2009 |
METHOD FOR MANUFACTURING A PRINTED CIRCUIT BOARD WITH A THIN FILM
CAPACITOR EMBEDDED THEREIN HAVING A DIELECTRIC FILM BY USING LASER
LIFT-OFF, AND PRINTED CIRCUIT BOARD WITH A THIN FILM CAPACITOR
EMBEDDED THEREIN MANUFACTURED THEREBY
Abstract
A method for manufacturing a printed circuit board with a
capacitor embedded therein which has a dielectric film using laser
lift off, and a capacitor manufactured thereby. In the method, a
dielectric film is formed on a transparent substrate and
heat-treated. A first conductive layer is formed on the
heat-treated dielectric film. A laser beam is irradiated onto a
stack formed, from below the transparent substrate, to separate the
transparent substrate from the stack. After the transparent
substrate is separated from the stack, a second conductive layer is
formed with a predetermined pattern on the dielectric film. Also,
an insulating layer and a third conductive layer are formed on the
first and second conductive layers to alternate with each other in
a predetermined number.
Inventors: |
Lee; Jung Won; (Seoul,
KR) ; Chung; Yul Kyo; (Yongin, KR) ; Lee; In
Hyung; (Seoul, KR) |
Correspondence
Address: |
MCDERMOTT WILL & EMERY LLP
600 13TH STREET, N.W.
WASHINGTON
DC
20005-3096
US
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
Gyunggi-Do
KR
|
Family ID: |
39028949 |
Appl. No.: |
12/466770 |
Filed: |
May 15, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11808298 |
Jun 8, 2007 |
|
|
|
12466770 |
|
|
|
|
Current U.S.
Class: |
29/846 |
Current CPC
Class: |
H01L 2924/0002 20130101;
H05K 1/162 20130101; H05K 2203/016 20130101; H05K 2203/107
20130101; Y10T 29/49165 20150115; H01G 4/33 20130101; Y10T 29/49155
20150115; H01L 23/50 20130101; H05K 2201/0175 20130101; H05K
2201/0179 20130101; H05K 2201/0108 20130101; Y10T 29/43 20150115;
H01L 21/4857 20130101; H01G 13/00 20130101; H01L 2924/0002
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
29/846 |
International
Class: |
H05K 3/02 20060101
H05K003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 2006 |
KR |
2006-67188 |
Claims
1-13. (canceled)
14. A method for manufacturing a printed circuit board with a thin
film capacitor embedded therein, the method comprising: forming a
dielectric film on a transparent substrate and heat-treating the
dielectric film; forming a first conductive layer on the
heat-treated dielectric film; forming an insulating layer on the
conductive layer and stacking a copper clad laminate on the
insulating layer; irradiating a laser beam onto a stack formed,
from below the transparent substrate, to separate the transparent
substrate from the stack; and after transparent substrate is
separated from the stack, forming a second conductive layer with a
predetermined pattern on the dielectric film.
15. The method according to claim 14, wherein the transparent
substrate comprises one selected from a group consisting of
sapphire, quartz, glass, MgO, lanthanum aluminate, fused silica,
and zirconia.
16. The method according to claim 16, wherein the dielectric film
comprises one dielectric composition selected from a group
consisting of lead zirconium titanate, barium titanate, strontium
bismuth tantalate, bismuth lanthanum titanate, lead magnesium
niobate-lead titanate, and lead zinc niobate-lead titanate.
17. The method according to claim 16, wherein the dielectric film
further comprises a dopant added to the dielectric composition.
18. The method according to claim 14, wherein at least one of the
first and second conductive layer comprises one selected from a
group consisting of Au, Ag, Ni, Cu, Al, Pt, Ti, Ir, IrO.sub.2, Ru,
and RuO.sub.2.
19. The method according to claim 14, wherein at least one of the
first and second conductive layer is formed by a process selected
from a group consisting of PVD, CVD, ALD, screen printing, plating
and inkjet printing.
20. The method according to claim 20, wherein at least one of the
first and second conductive layer is formed by the PVD using
sputtering or e-beam.
21. The method according to claim 14, wherein at least one of the
first and second conductive layer is formed by forming a metal seed
layer by PVD and electrolytically plating the metal seed layer.
22. The method according to claim 14, wherein the transparent
substrate is separated from the stack by an excimer laser or an Nd
YAG laser.
23. The method according to claim 22, further comprising: after
separating the transparent substrate, removing an amorphous damaged
layer formed on a top surface of the dielectric film, which is
caused by heat of the laser.
24. The method according to claim 14, wherein the transparent
substrate is separated from the stack by a Femto laser.
25. The method according to claim 14, further comprising: after
forming the dielectric film, forming a bonding layer or a barrier
layer on the dielectric film.
26. The method according to claim 25, wherein the step of forming
the bonding layer or the barrier layer comprises sputtering Ti or
Cr.
27-39. (canceled)
40. A printed circuit board with a thin film capacitor embedded
therein manufactured as described in claim 14.
Description
CLAIM OF PRIORITY
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/808,298, filed Jun. 8, 2007, claims the benefit of
Korean Patent Application No. 2006-67188 filed on Jul. 19, 2006 in
the Korean Intellectual Property Office, the disclosure of each of
which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a method for manufacturing
a printed circuit board with a thin film capacitor embedded therein
using laser lift-off, and more particularly, to a method for
manufacturing a printed circuit board with a thin film capacitor
embedded therein which has a dielectric film using laser lift off,
and a printed circuit board with a thin film capacitor embedded
therein manufactured thereby.
[0004] 2. Description of the Related Art
[0005] With a smaller, lighter, higher-speed and higher-frequency
trend of electronic devices, the electronic devices are
increasingly required to possess higher-density. In reality,
vigorous studies have been conducted on technologies to integrate
passive and/or active devices into a substrate. Also, in ongoing
researches to reduce size of the electronic devices, many passive
devices such as a resistor, a capacitor and an inductor are
embedded in a printed circuit board (PCB) instead of being
installed thereon. Out of these passive devices, the capacitor
accounts for a considerable proportion of about 60%. Thus, much
attention is drawn on an embedded capacitor. As described above,
the capacitor is embedded in the PCB instead of being installed
thereon. This downscales size of the passive device by 40% and
assures better electrical properties at a higher frequency due to
low impedance (<10 pH).
[0006] The conventional embedded capacitor is disclosed in U.S.
Pat. No. 5,261,153. The document teaches a method for manufacturing
a printed circuit board with a capacitor embedded therein by
lamination of conductive foils and uncured dielectric sheets
alternating therewith. Moreover, U.S. Pat. No. 6,541,137 discloses
a high temperature thin film embedded capacitor using dielectrics.
Specifically, the document proposes a barrier layer for preventing
the conductive layer from oxidizing from high temperature heat
treatment of 400.degree. C. to 800.degree. C.
[0007] However, in this embedded capacitor, a dielectric film is
necessarily made of a dielectric material having a high dielectric
constant selected from a group consisting of barium strontium
titanate (BSTO), barium titanate (BT), lead zirconium titanate
(PZT), barium zirconium titanate (BZTO), and tantalum titanate
(TTO). This dielectric material should be excellent in
crystallinity to exhibit high dielectric constant. To this end, the
dielectric material should be heat-treated at a temperature of
500.degree. C. or more.
[0008] But in the conventional embedded capacitor, a thin film is
formed on an electrode as an RCC type and crystallized through heat
treatment to impart a certain dielectric constant to a capacitor
product. Then these materials are employed in a PCB process.
However, the materials need heat-treating at a high temperature of
400.degree. C. to 800.degree. C., and are hardly configured on a
resin-containing PCB.
[0009] Dielectric properties of the thin film capacitor are greatly
affected by the type of the substrate, as is apparent from FIG. 1.
FIG. 1 demonstrates capacitance of a Pb-based dielectric film
deposited on two types of substrates with respect to a voltage
applied. A copper foil and a Pt/Ti/SiO.sub.2/Si substrate are
adopted for the substrates, and heat treated in the air at
650.degree. C. for 30 minutes. The dielectric film is deposited to
a thickness of 0.6 micrometer. The dielectric film on the cooper
foil exhibits capacitance of 0.2 .mu.F/cm.sup.2, much lower than
the dielectric film on the Pt/Ti/SiO.sub.2/Si substrate whose
capacitance is 2.5 .mu.F/cm.sup.2. The dielectric film deposited on
the copper foil is affected by an oxidized interface resulting from
oxidation of the copper foil which is heat-treated along with the
substrate. This prevents the dielectric film on the copper foil
from manifesting properties peculiar to the dielectric
material.
[0010] Therefore, studies have been conducted unceasingly to
prevent the copper foil from oxidization in two methods. That is, a
heat-treatment atmosphere has been regulated or a strong
oxidation-resistant nickel layer has been formed on the copper foil
to deposit and heat-treat the dielectric film. These methods
however entail a problem of decreased capacitance of the capacitor
manufactured.
[0011] As a result, there has arisen a demand for developing a
method for manufacturing a capacitor with a printed circuit board
embedded therein having a dielectric film that needs heat-treating
at a high-temperature through a general PCB manufacturing
process.
SUMMARY OF THE INVENTION
[0012] The present invention has been made to solve the foregoing
problems of the prior art and therefore an aspect of the present
invention is to provide a method for manufacturing a printed
circuit board with a capacitor embedded therein having a dielectric
film using laser lift-off, and a printed circuit board with a thin
film capacitor embedded therein manufactured thereby.
[0013] According to an aspect of the invention, the invention
provides a method for manufacturing a printed circuit board with a
thin film capacitor embedded therein, the method including:
[0014] forming a dielectric film on a transparent substrate and
heat-treating the dielectric film;
[0015] forming a first conductive layer on the heat-treated
dielectric film;
[0016] irradiating a laser beam onto a stack formed, from below the
transparent substrate, to separate the transparent substrate from
the stack;
[0017] after the transparent substrate is separated from the stack,
forming a second conductive layer with a predetermined pattern on
the dielectric film; and
[0018] forming an insulating layer and a third conductive layer on
the first and second conductive layers to alternate with each other
in a predetermined number.
[0019] According to another aspect of the invention, the invention
provides a method for manufacturing a printed circuit board with a
thin film capacitor embedded therein, the method including:
[0020] forming a dielectric film on a transparent substrate and
heat-treating the dielectric film;
[0021] forming a first conductive layer on the heat-treated
dielectric film;
[0022] forming an insulating layer on the conductive layer and
stacking a copper clad laminate on the insulating layer;
[0023] irradiating a laser beam onto a stack formed, from below the
transparent substrate, to separate the transparent substrate from
the stack; and
[0024] after transparent substrate is separated from the stack,
forming a second conductive layer with a predetermined pattern on
the dielectric film.
[0025] According to further another aspect of the invention, the
invention provides a method for manufacturing a printed circuit
board with a thin film capacitor embedded therein, the method
including:
[0026] forming a dielectric film on a transparent substrate and
heat-treating the dielectric film;
[0027] forming a first conductive layer on the heat-treated
dielectric film;
[0028] stacking a resin coated copper on the conductive layer;
[0029] irradiating a laser beam onto a stack formed, from below the
transparent substrate, to separate the transparent substrate from
the stack;
[0030] after the transparent substrate is separated from the stack,
forming a second conductive layer with a predetermined pattern on
the dielectric film; and
[0031] forming an insulating layer and a third conductive layer on
the RCC film and the second conductive layer to alternate with each
other in a predetermined number.
[0032] According to further another aspect of the invention, the
invention provides a printed circuit board with a thin film
capacitor embedded therein manufactured as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The above and other objects, 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:
[0034] FIG. 1 is a graph illustrating capacitance of a Pb-based
dielectric film formed on a copper foil coated with a nickel
oxidation prevention layer and a dielectric film formed on a
Pt/Ti/SiO.sub.2/Si substrate, respectively;
[0035] FIG. 2 is a view illustrating a method for manufacturing a
printed circuit board with a thin film capacitor embedded therein
according to an embodiment of the invention;
[0036] FIG. 3 is a view illustrating a method for manufacturing a
printed circuit board with a thin film capacitor embedded therein
according to another embodiment of the invention;
[0037] FIG. 4 is a view illustrating a method for manufacturing a
printed circuit substrate with a thin film capacitor embedded
therein according to further another embodiment of the
invention;
[0038] FIG. 5 is a graph illustrating dielectric properties of a
PZT film transferred onto a PCB by excimer laser lift-off;
[0039] FIG. 6 is a graph illustrating a X-ray diffraction analysis
of a dielectric film deposited on a copper foil, a dielectric film
deposited on a sapphire, and a PZT thin film transferred onto a
polymer/CCL material by excimer laser lift-off, respectively;
[0040] FIG. 7 is a TEM picture illustrating a cross-section of a
PZT thin film transferred onto a polymer/CCL material by excimer
laser lift-off, which has a laser-induced amorphous layer and a
dielectric layer formed thereon;
[0041] FIG. 8 is a TEM picture illustrating a cross-section of a
PZT thin film transferred onto a polymer/CCL material by Femto
laser lift-off, in which the PZT film maintains a tetragonal
crystal structure even after laser irradiation; and
[0042] FIG. 9 is a graph illustrating dielectric properties of a
PZT thin film transferred onto a PCB by Femto laser lift-off.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0043] Exemplary embodiments of the present invention will now be
described in detail with reference to the accompanying
drawings.
[0044] FIG. 2 is a schematic view illustrating a method for
manufacturing a printed circuit board with a thin film capacitor
embedded therein according to an embodiment of the invention.
[0045] As shown in FIG. 2(a), according to the invention, first, a
laser-transmissible transparent substrate 11 is prepared, and then
a dielectric film 13 is formed thereon. In this invention, a
material for the transparent substrate 11 is not limited to a
specific type. But the transparent substrate 11 is made of
preferably one selected from a group consisting of sapphire,
quartz, glass, MgO, lanthanum aluminate (LaAlO.sub.3), fused
silica, and zirconia (YSZ).
[0046] Also, according to the invention, the dielectric film 13 may
be formed by a general sol-gel process using a metal organic
precursor exhibiting superior dielectric properties by
high-temperature heat treatment. Meanwhile, according to the
invention, the dielectric film 13 has various dielectric
compositions exhibiting superior dielectric properties through
high-temperature heat treatment. However, the dielectric film 13 is
not limited to a specific composition and type. For example, the
dielectric film 13 can be made of a dielectric material containing
volatile elements of e.g., Bi or Pb which is selected from a group
consisting of lead zirconium titanate (PZT), barium titanate (BT),
strontium bismuth tantalate (SBT), bismuth lanthanum titanate
(BLT), lead magnesium niobate-lead titanate (PMN-PT), and lead zinc
niobate-lead titanate (PZN-PT), or a dielectric material having a
dopant added thereto.
[0047] Next, according to the invention, the dielectric film 13 is
heat treated. The heat-treatment improves crystallinity of the thin
film and assures superior dielectric properties thereof.
Preferably, the dielectric film 13 is heat treated at a temperature
of 400.degree. C. or more, and more preferably, at a temperature
ranging from 500.degree. C. to 700.degree. C.
[0048] Thereafter, according to the invention, as shown in FIG.
2(b), a first metal conductive layer 15 is formed on the
heat-treated dielectric film 13 to serve as an electrode of the
thin film capacitor. The conductive layer 15 may be composed of
various conductive metals or oxidants. Preferably, the conductive
layer 15 is made of one selected from a group consisting of, for
example, Au, Ag, Ni, Cu, Al, Pt, Ti, Ir, IrO.sub.2, Ru and
RuO.sub.2. Moreover, the first conductive layer 15 can be formed by
a general process selected from a group consisting of PVD, CVD,
ALD, screen printing, plating and inkjet printing. Preferably, the
first conductive layer 15 is formed by the PVD using sputtering or
e-beam. More preferably, the first conductive layer 15 is formed by
sputtering. Alternatively, the first conductive layer 15 may be
formed by forming a metal seed layer by PVD and electrolytically
plating the metal seed layer.
[0049] According to the invention, optionally, the first conductive
layer 15 may have a predetermined pattern. In order to form this
pattern, the first conductive layer 15 is formed via a mask by a
process selected from PVD, CVD, ALD, screen printing, plating and
inkjet printing. Alternatively, a sensitive film is applied on the
first conductive layer by a predetermined process, and then the
pattern is attained by a general process of exposure and
development.
[0050] Furthermore, according to the invention, a bonding layer or
a barrier layer may be disposed between the dielectric film 13 and
the first conductive layer 15. This ensures the dielectric film 13
and the first conductive layer 15 to be more bonded together or
prevents the first metal conductive layer 15 from diffusion and
oxidization. Such a bonding layer or barrier layer can be formed by
sputtering Ti or Cr.
[0051] Also, according to the invention, as shown in FIG. 2(c), a
laser beam is irradiated onto a stack formed, from below the
transparent substrate 11, to separate the transparent substrate 11
from the stack. That is, the laser beam irradiated from below the
transparent substrate 11 locally increases temperature of an
interface between the substrate 11 and the dielectric film 13. This
renders some portions of the dielectric film elements volatile,
thus allowing the substrate 11 to be effectively separated from the
dielectric film 13. For example, in a case where a dielectric film
having a composition of Pb-based PbZrTiO.sub.3 (110/52/48) is
deposited on the sapphire substrate, an excimer laser beam (248 nm)
may be irradiated onto an interface between the PZT thin film and
the sapphire substrate at an intensity of 400 mJ/cm.sup.2. This
increases temperature of the interface between the substrate and
the dielectric film to at least 1350.degree. C., which is higher
than a melting point of PZT. Thus volatile PbO elements are formed
at the interface between the substrate and the dielectric film,
leading to separation of the transparent substrate 11 from the
dielectric film 13.
[0052] This invention is not limited to a specific type of the
laser and an irradiation method. For example, an excimer laser (126
nm, 146 nm, 157 nm, 172 nm, 175 nm, 193 nm, 248 nm, 282 nm, 308 nm,
351 nm, 222 nm, and 259 nm) can bead opted to separate the
substrate 11 as described above. Alternatively, an Nd YAG laser
(266 nm, 355 nm) may be employed. The Nd YAG laser has a wavelength
corresponding to the energy band gap between a dielectric film and
a transparent substrate. That is, various types of lasers can be
utilized to separate the substrate as long as the laser energy that
passed the transparent substrate is absorbed in the dielectric film
to increase temperature of the interface between the dielectric
film and the substrate to at least a melting point of the
dielectric film. A laser beam used at this time can be modified
into various beam profiles such as spot, square and line.
[0053] Meanwhile, when the substrate 11 is separated by an excimer
laser or an Nd YAG laser, a portion of the dielectric film 13
adjacent to the substrate 11, which is exposed to heat of the
laser, may have a transformation from a crystalline into an
amorphous structure to a small thickness (about 108 nm), thus
producing a damaged layer. This damaged layer may degrade
dielectric properties of the dielectric film. For example, the PZT
film transferred onto a PCB may have a dielectric constant ranging
from 1 MHz to 600 MHz. However, the PZT film with this damaged
layer can provide a higher capacitance than the PZT film formed on
the copper foil, and thus be suitably applied.
[0054] But to ensure much better dielectric properties, preferably,
the damaged layer should be removed. The damaged layer can be
removed by various processes such as wet etching and ion beam
milling, without being limited to a specific process.
[0055] To preclude a possibility of the damaged layer, preferably a
Femto laser beam is irradiated onto the stack, from below the
substrate, to separate the transparent substrate 11 from the stack.
For example, the Femto laser beam (800 nm, 300 fs), when employed
to separate the substrate 11, can effectively prevent formation of
the damaged layer caused by laser irradiation. In consequence, the
PZT film transferred onto the PCB manufactured as described above
maintains a tetragonal crystal structure, thereby exhibiting a
superior dielectric constant ranging from 1 MHz to 1600 MHz.
[0056] Next, as shown in FIG. 2(d), after the transparent substrate
11 is separated from the stack, a second metal conductive layer 17
with a predetermined pattern is formed on the dielectric film 13 to
serve as another electrode. This second conductive layer 17 may be
made of various conductive metals or oxidants. Preferably, the
second conductive layer 17 is made of one selected from a group
consisting of Au, Ag, Ni, Cu, Al, Pt, Ti, Ir, IrO.sub.2, Ru, and
RuO.sub.2. Also, the second conductive layer 17 is formed by a
general process selected from a group consisting of PVD, CVD, ALD,
screen printing, plating and inkjet printing. Preferably, the
second conductive layer 17 is formed by the PVD using sputtering or
e-beam, and more preferably, sputtering. Alternatively, the second
conductive layer 17 is formed by forming a metal seed layer by the
PVD and electrolytically plating the metal seed layer.
[0057] The second metal conductive layer 17 may be formed to have a
predetermined pattern via a mask using the PVD. Alternatively, a
sensitive film is applied on the first conductive layer by a
predetermined process, and then the pattern is attained by a
general process of exposure and development.
[0058] Subsequently, according to the invention, an insulating
layer and a third conductive layer are formed on the first and
second conductive layers to alternate with each other in a
predetermined number by adopting a typical manufacturing method of
a printed circuit board. This produces a printed circuit board with
a dielectric thin fin film capacitor embedded therein.
[0059] FIG. 3 is a schematic view illustrating a method for
manufacturing a printed circuit board with a thin film capacitor
embedded therein according to another embodiment of the
invention.
[0060] As shown in FIG. 3(a), according to the invention, a
dielectric film 23 is formed on a transparent substrate 21 and
heat-treated. As shown in FIG. 3(b), a first metal conductive layer
25 is formed on the heat-treated dielectric film 23 to serve as an
electrode of the capacitor. Optionally, this first conductive layer
25 has a predetermined pattern. The composition, forming method and
patterning of the first conductive layer 25 have been described
above and thus will be explained in no more detail.
[0061] Also, as described above, a bonding layer or a barrier layer
may be formed between the dielectric film 23 and the first
conductive layer 25 to improve bonding therebetween and prevent the
first metal conductive layer 25 from diffusion or oxidization.
[0062] Afterwards, according to the invention, as shown in FIG.
3(c), an insulating layer 26 is stacked on the conductive layer 25.
The insulating layer is typically composed of a polymer resin but
can be made of various insulating materials used in a PCB
manufacturing process.
[0063] Moreover, according to the invention, a copper clad laminate
(CCL) 27 is stacked on the insulating layer 26. The CCL 27 has an
insulating member 27b attached with copper foils 27a at both
surfaces thereof.
[0064] Next, as shown in FIG. 3(d), a laser beam is irradiated onto
a stack formed, from below the transparent substrate 21, to
separate the transparent substrate 21 from the stack. An
explanation has been given previously about a process for
separating the transparent substrate through a laser beam, and type
of the laser and subsequent operations, which thus will be
explained in no more detail.
[0065] Moreover, as shown in FIG. 3(e), after the transparent
substrate 21 is separated from the stack, a second conductive layer
29 with a predetermined pattern is formed on the dielectric film 23
under the same conditions as described above. This second metal
conductive layer 29 serves as an electrode of the thin film
capacitor. Here, the composition and forming method of the metal
conductive layer 29 have been described above and thus will not be
explained further.
[0066] Thereafter, according to the invention, an insulating layer
and a third conductive layer are formed on the CCL 27 and the
conductive layer 29 to alternate with each other in a predetermined
number by adopting a general manufacturing method of a printed
circuit board.
[0067] Meanwhile, FIG. 4 is a schematic view illustrating a method
for manufacturing a printed circuit board with a thin film
capacitor embedded therein according to further another embodiment
of the invention.
[0068] As shown in FIG. 4(a), a dielectric film 33 is formed on a
transparent substrate 31 and heat-treated. Then as shown in FIG.
4(b), a first metal conductive layer 35 is formed on the
heat-treated dielectric film 33 to serve as an electrode of the
capacitor. Optionally, the first conductive layer 35 has a
predetermined pattern. The composition and forming method of the
conductive layer 35 have been described above and thus will be
explained in no more detail.
[0069] Furthermore, as described above, a bonding layer or a
barrier layer may be formed between the dielectric film 33 and the
first conductive layer 35 to improve bonding therebetween and
prevent the first metal conductive layer 35 from diffusion and
oxidization.
[0070] According to the invention, as shown in FIG. 4(c), a resin
coated copper (RCC) 37 is stacked on the first conductive layer 35.
The RCC has a copper foil 37a attached with a resin 37b.
[0071] Then, as shown in FIG. 4(d), a laser beam is irradiated onto
a stack formed, from below the transparent substrate 31, to
separate the transparent substrate 31 from the stack. An
explanation has been given previously about a process of separating
the transparent substrate by a laser beam, and type of the laser
and subsequent operations, which thus will not be explained
further.
[0072] Also, as shown in FIG. 4(e), after the transparent substrate
31 is separated from the stack, a second conductive layer 39 with a
predetermined pattern is formed on the dielectric film 33 under the
same conditions as described above.
[0073] Thereafter, according to the invention, an insulating layer
and a conductive layer are formed on the RCC 37 and the second
conductive layer 39 to alternate with each other in a predetermined
number by a general manufacturing method of a printed circuit
board. This produces a printed circuit board with a dielectric film
capacitor embedded therein.
[0074] As described above, the printed circuit board with a thin
film capacitor embedded therein has a dielectric film using laser
lift-off and can be manufactured effectively in a general PCB
manufacturing process.
[0075] The invention will be explained in detail by way of
example.
EXAMPLE
[0076] A dielectric material of PbZrTiO.sub.3 (Zr/Ti=52/48, 10% Pb
excess) was spin coated on a sapphire transparent substrate at a
thickness of 0.4 micrometer by general sol-gel, and heat-treated in
the air at a temperature of 650.degree. C. This produced a
crystallized PZT dielectric film on the transparent sapphire
substrate. Then, a first Au metal layer was formed on the
dielectric film by sputtering and an insulating layer made of an
epoxy resin was formed on the conductive layer.
[0077] Thereafter, a copper clad laminate was disposed on the
insulating layer and lamination was performed. Then, an excimer
laser beam (308 nm) was irradiated onto a stack formed, from below
the transparent sapphire substrate, to separate the transparent
substrate from the stack. Here, the excimer laser beam was shaped
as a line and had an energy of 400 mJ/cm.sup.2 (308 nm). The laser
beam had a size of 370 mm.times.40M, and was irradiated at a
repetition rate of 10 Hz and for a pulse duration of 30 nsec. Also,
after the transparent substrate was separated from the stack, a
second Au conductive layer was formed by sputtering on the PZT
dielectric film. This produced a capacitor with a structure of
metal conductive layer/dielectric film/metal conductive layer.
[0078] FIG. 5 is a graph illustrating change in dielectric constant
of a thin film capacitor embedded in the PCB substrate manufactured
as above with respect to a frequency. As shown in FIG. 5, the PZT
film transferred onto the PCB exhibits a dielectric constant
ranging from 1 MHz to 600 MHz. Also, the PZT film assures a high
capacitance of 1.3 .mu.F/cm.sup.2 (film thickness 0.4 micrometer),
much higher than 0.2 .mu.F/cm.sup.2 to 0.3 .mu.F/cm.sup.2 (FIG. 1)
which is obtained from a ferroelectric film on a copper foil.
[0079] FIG. 6 is a graph illustrating an x-ray diffraction pattern
of a PZT dielectric film (0.6 micrometer). In FIG. 6, A indicates
XRD of a PZT film on a copper foil, B indicates XRD of a PZT film
deposited on a sapphire substrate, and C indicates XRD of a PZT
film on a sapphire substrate transferred onto ABF/CCL by laser
lift-off. Here, heat-treatment was performed in the air at a
temperature of 650.degree. C. and for 30 minutes.
[0080] As noted from FIG. 6, the PZT film on the copper foil is
degraded in crystallinity due to decline in interface properties
resulting from oxidation of the copper foil. In contrast, the PZT
film on the sapphire substrate exhibits very good crystallinity.
Also, the PZT film transferred by laser lift off shows a similar
XRD pattern, maintaining good crystallinity.
[0081] To determine changes in the PZT films irradiated with laser
beam, cross-sections of the PZT films that underwent laser lift-off
were observed with a transmission electron microscope (TEM), whose
results are illustrated in FIG. 7. As shown in FIG. 7, a PZT film
is constructed of two layers (layer 1 and layer 2) after being
irradiated with laser beam. The layer 1 is a laser-damaged layer
with a thickness of about 108 nm. The layer 1 features a diffused
ring, which is characteristic of an amorphous phase, in the
electron diffraction pattern. The layer 1 was observed to be
amorphous in the high resolution TEM image. Meanwhile, the layer 2
inside the PZT film was observed to have an electron diffraction
pattern indicative of a tetragonal crystal structure. The layer 2
also exhibited a tetragonal crystal structure in the high
resolution TEM image.
[0082] Due to presence of this amorphous layer, as shown in FIG. 7,
the PZT thin film transferred onto the PCB according to the
invention showed a dielectric constant ranging from 1 MHz to 600
MHz, lower than that (1600 to 1700) of a general PZT film. Here,
the PZT thin film was amorphous.
[0083] However, in this invention, this amorphous damaged layer is
removed by various methods such as wet etching and ion beam
milling, thereby elevating its dielectric constant to from 1600 to
1700.
[0084] Meanwhile, a capacitor with a structure of a metal
conductive layer/dielectric layer/metal conductive layer was formed
under the same conditions as described above except that the
sapphire substrate was separated by a Femto laser (800 nm, 300 fs).
Moreover, to determine changes in the PZT films irradiated with
laser beam, cross-sections of the PZT films that underwent laser
lift-off were observed with a transmission electron microscope
(TEM), the pictures of which are shown in FIG. 8. As seen from FIG.
8, in a case where the sapphire substrate was separated by a Femto
laser, the PZT films obtained had tetragonal crystal structures,
thereby maintaining crystallinity of the PZT material.
[0085] FIG. 9 is a graph illustrating a dielectric constant of a
PZT film transferred onto a PCB substrate using a Femto laser with
respect to a frequency. The PZT film exhibits a superior dielectric
constant ranging from 1 MHz to 1600 MHz.
[0086] As set forth above, according to exemplary embodiments of
the invention, a printed circuit board with a thin film capacitor
embedded therein has a dielectric film using laser lift off without
obstructing a general PCB process. In addition, the invention
overcomes a conventional problem of oxidation of a copper foil.
[0087] While the present invention has been shown and described in
connection with the preferred 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 invention
as defined by the appended claims.
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