U.S. patent application number 12/222177 was filed with the patent office on 2009-12-10 for printed circuit board and method of manufacturing the same.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Eung Suek Lee, Jee Soo Mok, Chang Sup Ryu, Je Gwang Yoo.
Application Number | 20090301767 12/222177 |
Document ID | / |
Family ID | 41399250 |
Filed Date | 2009-12-10 |
United States Patent
Application |
20090301767 |
Kind Code |
A1 |
Mok; Jee Soo ; et
al. |
December 10, 2009 |
Printed circuit board and method of manufacturing the same
Abstract
Disclosed is a printed circuit board including bumps formed
using a conductive paste including carbon nanotubes and a
photosensitive binder. A method of manufacturing the printed
circuit board is also provided. The printed circuit board includes
bumps formed using the conductive paste having carbon nanotubes,
and can realize good electrical connection with electronic parts
mounted thereon. The bumps can be formed at a fine pitch, thus
realizing a circuit layer having a high density.
Inventors: |
Mok; Jee Soo; (Gyunggi-do,
KR) ; Yoo; Je Gwang; (Gyunggi-do, KR) ; Lee;
Eung Suek; (Gyunggi-do, KR) ; Ryu; Chang Sup;
(Gyunggi-do, KR) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700, 1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
SAMSUNG ELECTRO-MECHANICS CO.,
LTD.
Suwon
KR
|
Family ID: |
41399250 |
Appl. No.: |
12/222177 |
Filed: |
August 4, 2008 |
Current U.S.
Class: |
174/255 ; 29/846;
977/932 |
Current CPC
Class: |
H05K 1/095 20130101;
H05K 2203/0514 20130101; B82Y 10/00 20130101; Y10T 29/49155
20150115; H05K 3/4007 20130101; H05K 2201/026 20130101; H05K
2201/0367 20130101 |
Class at
Publication: |
174/255 ; 29/846;
977/932 |
International
Class: |
H05K 3/10 20060101
H05K003/10; H05K 1/00 20060101 H05K001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2008 |
KR |
10-2008-0053667 |
Claims
1. A printed circuit board, comprising: a circuit substrate having
a circuit layer for transferring electrical signals; and bumps
electrically connected to the circuit layer and formed of a
conductive paste including carbon nanotubes and a photosensitive
binder.
2. The printed circuit board as set forth in claim 1, wherein the
circuit substrate further comprises external connection terminals
exposed in an outermost circuit layer thereof, and the bumps are
formed on the external connection terminals.
3. The printed circuit board as set forth in claim 1, wherein the
bumps have a stepped cylindrical shape.
4. The printed circuit board as set forth in claim 1, wherein the
conductive paste further comprises metal powder.
5. The printed circuit board as set forth in claim 1, wherein the
photosensitive binder is any one selected from among acrylic resin,
styrene resin, novolac epoxy resin, and polyester resin.
6. A method of manufacturing a printed circuit board, comprising:
applying a conductive paste including carbon nanotubes and a
photosensitive binder on a bump-forming area of a circuit substrate
having a circuit layer for transferring electrical signals; and
patterning the conductive paste, thus forming bumps.
7. The method as set forth in claim 6, wherein the conductive paste
further comprises metal powder.
8. The method as set forth in claim 6, wherein the circuit
substrate further comprises external connection terminals exposed
in an outermost circuit layer thereof, and the bump-forming area
comprises an area in which the external connection terminals are
exposed.
9. The method as set forth in claim 6, wherein the forming the
bumps comprises: disposing a mask having light-blocking patterns
for forming the bumps on the conductive paste; and radiating light
onto the mask, thus selectively exposing the conductive paste to
light, and then developing the conductive paste.
10. The method as set forth in claim 9, wherein the forming the
bumps further comprises drying the bumps, after the radiating
light.
11. The method as set forth in claim 9, wherein the mask is a glass
mask.
12. The method as set forth in claim 9, wherein the developing in
the radiating light is conducted using any one developer selected
from among Na2CO3, KCO3, and KOH.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2008-0053667, filed Jun. 9, 2008, entitled "A
printed circuit board and a method for manufacturing the same",
which is hereby incorporated by reference in its entirety into this
application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a printed circuit board
(PCB) and a method of manufacturing the same, and more
particularly, to a PCB, which includes bumps formed using a
conductive paste including carbon nanotubes and a photosensitive
binder, and to a method of manufacturing the same.
[0004] 2. Description of the Related Art
[0005] Conventionally, the formation of solder bumps on a substrate
includes a method of printing solder paste on a substrate or a
wafer and performing a reflow process (FIGS. 1A to 1E), an
electroless plating method, or an electroplating method.
[0006] With reference to FIG. 1A, a solder resist 15 is formed on a
substrate 11 having pads 13. The solder resist 15 is formed between
the pads 13, and functions to prevent the downward flow of solder
paste 19 in the subsequent course of forming bumps 23.
[0007] As shown in FIG. 1B, a printing mask 17 is located on the
solder resist 15. The printing mask 17 functions such that the
solder paste is applied to a predetermined height on the pads 13
while preventing the application of the solder paste on the solder
resist 15 in the subsequent course of printing the solder paste. As
shown in FIG. 1C, the solder paste 19 is printed on the pads 13
using a squeegee blade 21. The solder paste 19 fills recesses
defined by the solder resist 15 and the printing mask 17, as shown
in FIG. 1C.
[0008] As shown in FIG. 1D, the printing mask 17 located on the
solder resist 15 is removed, and a reflow process is performed,
thereby completing a PCB including bumps 23, as shown in FIG.
1E.
[0009] However, the method of forming the bumps of the PCB using
printing is problematic in that bumps having a fine pitch of 120
.mu.m or less are difficult to realize. Thus, the method of forming
the bumps using printing cannot be applied when it is intended to
form fine bumps. Even if such bumps are formed, the volume thereof
becomes very small.
[0010] Presently, the size of a PCB, which enables the formation of
bumps through printing, approximates a quarter size or a half size.
Hence, it is impossible to perform a panel-size bumping
process.
SUMMARY OF THE INVENTION
[0011] Therefore, the present invention has been made keeping in
mind the above problems encountered in the related art, and
provides a PCB having a fine pitch using a conductive paste
including carbon nanotubes and a photosensitive binder, and a
method of manufacturing the PCB, which enables the bumping on a
panel-size substrate.
[0012] According to the present invention, a PCB may comprise a
circuit substrate having a circuit layer for transferring
electrical signals; and bumps electrically connected to the circuit
layer and formed of a conductive paste including carbon nanotubes
and a photosensitive binder.
[0013] According to a preferred feature of the present invention,
the circuit substrate may further comprise external connection
terminals exposed in the outermost circuit layer thereof, and the
bumps may be formed on the external connection terminals.
[0014] According to another preferred feature of the present
invention, the bumps may have a stepped cylindrical shape.
[0015] According to a further preferred feature of the present
invention, the conductive paste may further comprise metal
powder.
[0016] According to still a further preferred feature of the
present invention, the photosensitive binder may be any one
selected from among acrylic resin, styrene resin, novolac epoxy
resin, and polyester resin.
[0017] In addition, according to the present invention, a method of
manufacturing a PCB may comprise (A) applying a conductive paste
including carbon nanotubes and a photosensitive binder on the
bump-forming area of a circuit substrate having a circuit layer for
transferring electrical signals; and (B) patterning the conductive
paste, thus forming bumps.
[0018] According to a preferred feature of the present invention,
the conductive paste may further comprise metal powder.
[0019] According to another preferred feature of the present
invention, the circuit substrate may further comprise external
connection terminals exposed in the outermost circuit layer
thereof, and the bump-forming area may comprise an area in which
the external connection terminals are exposed.
[0020] According to a further preferred feature of the present
invention, forming the bumps may comprise (i) disposing a mask
having light-blocking patterns for forming the bumps on the
conductive paste; and (ii) radiating light onto the mask, thus
selectively exposing the conductive paste to light, and then
developing the conductive paste.
[0021] According to still a further preferred feature of the
present invention, forming the bumps may further comprise drying
the bumps, after (ii) radiating light.
[0022] According to yet another preferred feature of the present
invention, the mask may be a glass mask.
[0023] According to still another preferred feature of the present
invention, developing in (ii) radiating light may be conducted
using any one developer selected from among Na.sub.2CO.sub.3,
KCO.sub.3, and KOH.
[0024] The features and advantages of the present invention will be
more clearly understood from the following detailed description
taken in conjunction with the accompanying drawings.
[0025] Further, the terms and words used in the present
specification and claims should not be interpreted as being limited
to typical meanings or dictionary definitions, but should be
interpreted as having meanings and concepts relevant to the
technical scope of the present invention based on the rule
according to which an inventor can appropriately define the concept
of the term to describe the best method he or she knows for
carrying out the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIGS. 1A to 1E are schematic views sequentially showing a
conventional process of manufacturing a PCB by printing a solder
paste and then performing reflow;
[0027] FIG. 2 is a cross-sectional view illustrating a PCB having
bumps formed using a conductive paste including carbon nanotubes
and a photosensitive binder, according to the present invention;
and
[0028] FIGS. 3 to 6 are schematic views sequentially showing a
process of manufacturing the PCB having bumps formed using the
conductive paste including carbon nanotubes and a photosensitive
binder, according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] Hereinafter, a detailed description will be given of a PCB
and a method of manufacturing the same according to the present
invention, with reference to the appended drawings. Throughout the
drawings, like reference numerals refer to like elements, and
redundant descriptions are omitted. In the description, the terms
"first", "second" and so on are used to distinguish one element
from another element, but are not to be construed to limit the
elements.
[0030] FIG. 2 is a cross-sectional view showing the PCB according
to the present invention. As shown in FIG. 2, the PCB according to
the present invention includes a circuit substrate 10 having a
circuit layer for transferring electrical signals, and bumps 35
electrically connected to the circuit layer and formed using a
conductive paste 30 including carbon nanotubes and a photosensitive
binder.
[0031] The circuit substrate 10 is used to mount electronic parts
and for wiring, and is typically a PCB obtained by etching a metal
layer along a circuit pattern (the portion of the metal layer other
than circuit lines is removed through etching), thus forming a
necessary circuit layer, and forming bumps 35 and holes for
attaching and mounting electronic parts on the outermost circuit
layer. The circuit substrate 10 may be a single-sided PCB, in which
a circuit layer is formed on only one surface of an insulating
substrate, a double-sided PCB, in which a circuit layer is formed
on both surfaces of an insulating substrate, or a multilayered
board (MLB) having multiple circuit layers.
[0032] The circuit layer is composed of circuit patterns for
transferring electrical signals along a designed pattern. The
circuit pattern is a conductive line formed on the insulating
substrate using highly conductive metal, such as copper or nickel.
In particular, the circuit layer, which is disposed on the
outermost surface of the circuit substrate 10, is referred to as an
outermost circuit layer. The outermost circuit layer is provided
with external connection terminals 15 to connect the substrate to
electronic parts. The external connection terminal 15 may further
include a nickel layer or a gold layer as a surface treatment layer
in addition to the metal for the circuit layer. Furthermore, in
order to prevent the corrosion and etching of the outermost circuit
layer, the portion of the outermost circuit layer other than the
external connection terminals 15 is covered with the solder resist
layer 13 and is thus protected.
[0033] The bumps 35 are a conductive member formed on the external
connection terminals 15 to electrically interconnect the layers of
the MLB or to electrically physically connect the electronic parts
and the PCB. In the present invention, the bumps for connecting the
electronic parts and the PCB are depicted and described.
[0034] As shown in FIG. 2, the bumps 35 of the PCB according to the
present invention may be formed in a stepped cylindrical shape,
using a conductive paste 30 including carbon nanotubes and a
photosensitive binder. In addition, the conductive paste 30 used in
the present invention may further include metal powder, a curing
agent, and a thixotrophic agent. Specific components of the
conductive paste 30 used in the present invention are shown in
Table 1 below. The components of Table 1 are illustrative, and the
present invention is not limited thereto.
TABLE-US-00001 TABLE 1 Components of Conductive Paste Amount
Components (wt %) Note Carbon Nanotubes 50~90 Use of SWNT or MWNT
(CNT) Metal Powder 10~30 Ag, Cu, Sn, Bi, Sn/Ag, Sn/Bi, Ag/Cu/Sn,
(size: 1 .mu.m or less) Mixing of Sn and other metal at a ratio of
7:3 Photosensitive 5~20 Photosensitive Resin Binder (epoxy) Binder
Additive 0.5~5.0 Curing Agent, Thixotrophic Agent Solvent 5~10
--
[0035] Compared to other material (e.g., copper), carbon nanotubes
exhibit superior electrical properties. For example, Table 2 below
shows the properties of carbon nanotubes and other material.
TABLE-US-00002 TABLE 2 Properties of Carbon Nanotubes and
Comparative Material Physical Properties Carbon Nanotubes
Comparative Material Density 1.33~1.40 g/cm.sup.3 2.7 g/cm.sup.3
Current Density 1 .times. 10.sup.9 A/cm.sup.2 1 .times. 10.sup.6
A/cm.sup.2 (copper cable) Thermal 6000 W/mK 400 W/mK (copper)
Conductivity Resistivity 1 .times. 10.sup.-10 .OMEGA.cm 1 .times.
10.sup.-10 .OMEGA.cm (copper)
[0036] As is apparent from the table, the carbon nanotubes have
electrical properties superior to those of metal material, such as
aluminum or copper, which have good properties in terms of
electrical conductivity and resistivity. Thus, the PCB according to
the present invention has the bumps 35 formed using a composition
including carbon nanotubes, and thereby exhibits better electrical
connection with electronic parts mounted thereon, compared to
conventional PCBs having bumps 35 formed of other material.
[0037] In the present invention, the photosensitive binder may be
any one selected from among acrylic resin, styrene resin, novolac
epoxy resin, and polyester resin.
[0038] In this way, because the PCB according to the present
invention has the bumps formed using the conductive paste including
carbon nanotubes, it can realize good electrical connection with
electronic parts mounted thereon.
[0039] Below, the method of manufacturing the PCB according to the
present invention is described. FIGS. 3 to 6 sequentially show the
process of manufacturing the PCB according to the present
invention.
[0040] As shown in FIG. 3, the circuit substrate 10 having the
circuit layer for transferring electrical signals is provided. The
circuit substrate 10 may be a single-sided PCB, a double-sided PCB
in which a circuit layer is formed on both surfaces of an
insulating substrate, or an MLB having multiple circuit layers, and
includes external connection terminals 15 exposed in the outermost
circuit layer.
[0041] The external connection terminals 15 may be uniformly
distributed over the entire area of the outermost circuit layer of
the circuit substrate 10. Specifically, as shown in FIG. 3, the
external connection terminals are mainly formed on a predetermined
area of the outermost layer, that is, the area on which electronic
parts are mounted. For convenience, the area on which the external
connection terminals 15 are mainly present is referred to as a
bump-forming area 17. In an exemplary embodiment, the circuit
substrate 10 has a bump-forming area 17 in which twelve external
connection terminals 15 are exposed in the center of the outermost
circuit layer.
[0042] Next, as shown in FIG. 4, the conductive paste 30, including
carbon nanotubes and a photosensitive binder, is applied on the
bump-forming area 17. The specific components of the conductive
paste 30 are mentioned as above. In the present invention, using a
metal mask having openings corresponding to the bump-forming area
17, the conductive paste is applied through printing. However, the
process of applying the conductive paste is not limited thereto,
and it is noted that the conductive paste may be applied over the
entire area of the outermost layer of the circuit substrate.
[0043] The photosensitive binder included in the conductive paste
30 may be a negative type or a positive type. In an exemplary
embodiment, useful is a positive type photosensitive binder, that
is, a photosensitive binder by which a portion not irradiated with
light is cured, as will be described later.
[0044] After the application of the conductive paste 30 is
completed, the conductive paste 30 is patterned through exposure
and development, thus forming the bumps 35. The patterning of the
conductive paste 30 through exposure and development enables more
accurate control than when using a printing process, and is thus
applied to a panel-size substrate.
[0045] As shown in FIG. 5, a glass mask 50 having light-blocking
patterns 55 at positions at which the bumps 35 are to be formed is
disposed on the conductive paste 30, and UV light is radiated via
the glass mask 50, thus curing the portions of the conductive paste
30 corresponding to the bumps 35. As mentioned above, because the
conductive paste 30 includes a positive type photosensitive binder,
the portions of the outermost circuit layer onto which light is not
radiated, namely bumps 35, are cured.
[0046] In the present invention, the use of the glass mask 50 is
mentioned, but the present invention is not limited thereto.
Alternatively, another kind of mask, such as an art work film, may
be used. However, in order to form the bumps 35 at a fine pitch, it
is preferred that the glass mask 50 be used.
[0047] Next, as shown in FIG. 6, the conductive paste 30 which is
not cured is removed through development. As such, the development
is conducted using a developer, which is any one selected from
among Na.sub.2CO.sub.3, KCO.sub.3, and KOH. Thereafter, a drying
process is conducted, thus completing the bumps 35 having a stepped
cylindrical shape as shown in FIG. 2. The drying process is
typically performed at 160.about.180.degree. C. for 30.about.90
min.
[0048] In the method of manufacturing the PCB according to the
present invention, because the conductive paste 30 including carbon
nanotubes and a photosensitive binder is used, a bumping process
can be conducted even on a panel-size substrate, and the bumps 35
having a fine pitch can be formed.
[0049] As described hereinbefore, the present invention provides a
PCB and a method of manufacturing the same. The PCB according to
the present invention includes bumps formed using a conductive
paste having carbon nanotubes, and thus can realize good electrical
connection with electronic parts mounted thereon. Further, the
bumps are formed at a fine pitch, thus forming a circuit layer
having a high density.
[0050] In the method of manufacturing the PCB according to the
present invention, because the conductive paste including carbon
nanotubes and a photosensitive binder is used, a bumping process
can be realized even on a panel-size substrate, and bumps having a
fine pitch can be formed.
[0051] Although the preferred embodiments of the present invention
have been disclosed for illustrative purposes, those skilled in the
art will appreciate that various modifications, additions and
substitutions are possible within the technical scope of the
invention.
* * * * *