U.S. patent application number 11/976760 was filed with the patent office on 2008-05-15 for printed circuit board having embedded resistors and method of manufacturing the same.
This patent application is currently assigned to SAMSUNG ELECTRO-MECHANICS CO., LTD.. Invention is credited to Sang Jin Baek, Jong Kuk Hong, Jin Soo Jeong, Hong Won Kim, Tae Eui Kim, Hwa Sun Park.
Application Number | 20080110669 11/976760 |
Document ID | / |
Family ID | 39148202 |
Filed Date | 2008-05-15 |
United States Patent
Application |
20080110669 |
Kind Code |
A1 |
Park; Hwa Sun ; et
al. |
May 15, 2008 |
Printed circuit board having embedded resistors and method of
manufacturing the same
Abstract
Disclosed herein is a Printed Circuit Board (PCB) having
embedded resistors and a method of manufacturing the same, in which
contact pads are formed by filling via holes formed on electrode
pads with oxidation-resistant conductive material, and resistors
are formed on the contact pads. Accordingly, erosion that occurs
between the electrode pads and the resistors can be prevented using
the contact pads made of oxidation-resistant conductive material,
and connections between circuits also can be realized. Furthermore,
resistors are formed on a flat plane without any difference in
height, attributable to the electrode pads, and thus differences
between the resistance values of the built-in resistors can be
greatly reduced.
Inventors: |
Park; Hwa Sun; (Gyunggi-do,
KR) ; Kim; Tae Eui; (Seoul, KR) ; Hong; Jong
Kuk; (Chungcheongnam-do, KR) ; Baek; Sang Jin;
(Chungcheongbuk-do, KR) ; Kim; Hong Won;
(Gyunggi-do, KR) ; Jeong; Jin Soo; (Seoul,
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: |
39148202 |
Appl. No.: |
11/976760 |
Filed: |
October 26, 2007 |
Current U.S.
Class: |
174/260 ;
29/832 |
Current CPC
Class: |
H05K 1/095 20130101;
Y10T 29/435 20150115; Y10T 29/49128 20150115; Y10T 29/49156
20150115; H05K 3/4069 20130101; Y10T 29/49165 20150115; H05K 3/4644
20130101; H05K 2201/09481 20130101; Y10T 29/49155 20150115; H05K
1/167 20130101; Y10T 29/4913 20150115 |
Class at
Publication: |
174/260 ;
29/832 |
International
Class: |
H05K 1/16 20060101
H05K001/16; H05K 3/30 20060101 H05K003/30 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 13, 2006 |
KR |
10-2006-0111733 |
Claims
1. A Printed Circuit Board (PCB) having embedded resistors,
comprising: (a) a plurality of circuit layers comprising circuit
patterns including electrode pads formed on an internal circuit
layer; (b) a plurality of insulating layers located between
respective circuit layers; (c) a plurality of via holes formed in
the insulating layers to enable interlayer electrical connections;
(d) contact pads formed by filling the via holes, which are formed
on the electrode pads, with oxidation-resistant conductive
material; and (e) resistors connected with the electrode pads, and
formed such that ends of each resistor are connected to two
respective contact pads, which are spaced apart from each other, at
surfaces of the contact pads, which are on an opposite side from
surfaces of the contact pads that are in contact with the electrode
pads, and thus connected in an identical plane.
2. The PCB as set forth in claim 1, wherein the oxidation-resistant
conductive material is Ag paste.
3. The PCB as set forth in claim 1, wherein the resistors are
formed through screen printing of resistor material.
4. The PCB as set forth in claim 3, wherein the resistor material
is carbon-based paste.
5. A method of manufacturing a PCB having embedded resistors, the
method comprising: (a) providing a PCB on which internal layer
circuit patterns, including electrode pads, are formed; (b)
layering insulating layers on the PCB; (c) forming first via holes
on the electrode pads and simultaneously forming second via holes
at predetermined locations on the internal layer circuit patterns;
(d) forming contact pads for connecting the electrode pads with
resistors by filling the first via holes with oxidation-resistant
conductive material and flattening the oxidation-resistant
conductive material; (e) forming the resistors so that ends of each
resistor are connected to two respective contact pads, which are
spaced apart from each other; (f) forming circuit patterns on the
PCB, in which the second via holes are formed; and (g) layering
insulting layers on the PCB obtained at step (f), and forming
external layer circuit patterns.
6. The method as set forth in claim 5, wherein the
oxidation-resistant conductive material is Ag paste.
7. The method as set forth in claim 5, wherein the filling of the
oxidation-resistant conductive material is performed using screen
printing.
8. The method as set forth in claim 5, wherein the flattening is
performed through a mechanical polishing process, a chemical
polishing process, or a chemical mechanical polishing process.
9. The method as set forth in claim 5, wherein the forming the
resistors is performed through screen printing of resistor
material.
10. The method as set forth in claim 9, wherein the resistor
material is carbon-based paste.
11. The method as set forth in claim 5, further comprising
performing laser trimming using the circuit patterns, formed at
step (f), as pads.
12. A method of manufacturing a printed circuit board having
embedded resistors, the method comprising: (a) providing a PCB on
which internal layer circuit patterns, including electrode pads,
are formed; (b) layering insulating layers on the PCB; (c) forming
first via holes on the electrode pads; (d) forming contact pads for
connecting the electrode pads with resistors by filling the first
via holes with oxidation-resistant conductive material and
flattening the oxidation-resistant conductive material; (e) forming
the resistors so that ends of each resistor are connected to two
respective contact pads, which are spaced apart from each other;
(f) forming second via holes at predetermined locations on the
internal layer circuit patterns; (g) forming circuit patterns on
the PCB, in which the second via holes are formed; and (h) layering
insulting layers on the PCB obtained at step (g), and forming
external layer circuit patterns.
13. The method as set forth in claim 12, wherein the
oxidation-resistant conductive material is Ag paste.
14. The method as set forth in claim 12, wherein the filling of the
oxidation-resistant conductive material is performed using screen
printing.
15. The method as set forth in claim 12, wherein the flattening is
performed through a mechanical polishing process, a chemical
polishing process, or a chemical mechanical polishing process.
16. The method as set forth in claim 12, wherein the forming the
resistors is performed through screen printing of resistor
material.
17. The method as set forth in claim 16, wherein the resistor
material is carbon-based paste.
18. The method as set forth in claim 12, further comprising
performing laser trimming using the circuit patterns, formed at
step (g), as pads.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of Korean Patent
Application No. 10-2006-0111733, filed on Nov. 13, 2006, entitled
"Printed Circuit Board Having Embedded Resistor and Method of
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 generally to a printed circuit
board having embedded resistors and a method of manufacturing the
same. More particularly, the present invention relates to a printed
circuit board having embedded resistors and a method of
manufacturing the same, in which contact pads are formed by filling
via holes formed on electrode pads with oxidation-resistant
conductive material, and resistors are formed on the contact pads,
thus not only reducing the differences between the resistance
values of the embedded resistors, but also preventing erosion from
occurring between the electrode pads and the resistors.
[0004] 2. Description of the Related Art
[0005] In electronic products including recent portable electronic
devices, various demands from consumers are increasing. In
particular, consumers' desires for multiple functions, a small size
and light weight, a high speed, a low price, increased convenience
of movement, real-time wireless connection with the Internet,
refined design and the like cause developers, designers and
manufacturers to feel greatly burdened in the manufacturing of
high-quality products. Such increased competition leads rival
manufacturers to market new models on a daily basis. This increases
again the burden on all persons concerned.
[0006] As the functions of products becomes diverse in this manner,
the number of passive elements increases relative to the increase
in the number of Integrated Circuits (ICs), and thus the size of
portable terminals also increases. Generally, in an electronic
device, a plurality of active elements and a plurality of passive
elements are mounted on the surfaces of a circuit board. In order
to facilitate the transmission of signals between the active
elements, a large number of passive elements are surface-mounted in
the form of discrete chip resistors.
[0007] As a part of an effort to realize high density mounting for
an electronic system, development for embedded Printed Circuit
Boards (PCBs) is being conducted by the large number of
manufacturers concerned. Passive elements embedded in such a board
are classified into Resistors R, inductors L and capacitors C
according to type, and embedded elements are classified into
existing thin passive elements, film elements formed using printing
or sputtering, and plating-type elements based on plating according
to size and form. However, discrete chip resistors, that is,
passive elements have a limitation in the ability to satisfy the
trend of making electronic products light, thin, short and small
using only, have a problem with the use of space, and have a
disadvantage in that the cost is increased.
[0008] Accordingly, various attempts to embed film-type resistors
having a thickness of 15.about.25 .mu.m, which belong to passive
elements, in a board have been made. In order to embed such
film-type resistors in a board, methods such as screen printing,
sputtering and plating are employed. In particular, screen printing
is advantageous in that the number of element mounting processes
can be reduced and the cost can be reduced. Furthermore, screen
printing is advantageous in that the reliability of contact can be
improved, light weight can be realized, and environmental loads can
be reduced, because the number of solder joints is reduced.
[0009] Technology for embedding resistors in a PCB using an
existing printing technique includes various forms and processes.
According to an embodiment of a prior art, as shown in FIGS. 2A and
2B, resistors 5 are formed by forming electrode pads 1 and 2 on an
insulating board 6, and printing resistor paste between the
electrode pads 1 and 2, which are spaced apart from each other,
using a photoresist film 3 as a resist. However, the prior art is
problematic in that poor printability of the resistors 5 results
due to the differences in height between the electrode pads 1 and 2
and the insulating board 6, so that the formed shapes thereof
become irregular, thereby resulting in increased differences
between the resistance values. When the resistance values are
measured after the resistor paste has been formed through printing
as described above, a problem occurs when performing laser trimming
if the resistance values are greater or much smaller than a target
resistance value. The trimming cannot be performed when the
resistance values of the printed resistors are large, and a problem
with the reliability thereof may be caused when the resistance
values of the printed resistors are very small. Such error results
in decreased yield with increased incidence of defects and
ultimately degrades the performance of products, and therefore it
is considered to be the factor most urgently requiring
improvement.
SUMMARY OF THE INVENTION
[0010] Accordingly, in order to solve the above-described problems,
extensive research has been continuously conducted. As a result
thereof, contact pads are formed by filling via holes formed on
electrode pads with oxidation-resistant conductive material, and
resistors are formed on the contact pads, and therefore embedded
resistors having a desired size can be manufactured with high
reliability without error or great variation. Based on this, the
present invention was completed.
[0011] Accordingly, an aspect of the present invention is to
provide a PCB having embedded resistors and a method of
manufacturing the same, in which resistors are formed without any
difference in the height thereof attributable to electrode pads,
thus reducing the differences between the resistance values of the
embedded resistors.
[0012] Another aspect of the present invention is to provide a PCB
having embedded resistors and a method of manufacturing the same,
which can not only prevent erosion from occurring between the
electrode pads and the resistors, but also realize a desired
resistance value with high accuracy and high reliability.
[0013] In order to accomplish the above objects, the present
invention provides a PCB having embedded resistors, including (a) a
plurality of circuit layers comprising circuit patterns including
electrode pads formed on an internal circuit layer; (b) a plurality
of insulating layers located between respective circuit layers; (c)
a plurality of via holes formed in the insulating layers to enable
interlayer electrical connections; (d) contact pads formed by
filling the via holes, which are formed on the electrode pads, with
oxidation-resistant conductive material; and (e) resistors
connected with the electrode pads, and formed such that the ends of
each resistor are connected to two respective contact pads, which
are spaced apart from each other, at the surfaces of the contact
pads, which are on the opposite side from the surfaces of the
contact pads that are in contact with the electrode pads, and thus
connected in the same plane.
[0014] The oxidation-resistant conductive material may be Ag
paste.
[0015] It is preferred that the resistors be formed through screen
printing of resistor material, and the resistor material is,
preferably, carbon-based paste.
[0016] In addition, the present invention provides a method of
manufacturing a PCB having embedded resistors, the method including
(a) providing a PCB on which internal layer circuit patterns,
including electrode pads, are formed; (b) layering insulating
layers on the PCB; (c) forming first via holes on the electrode
pads and simultaneously forming second via holes at predetermined
locations on the internal layer circuit patterns; (d) forming
contact pads for connecting the electrode pads with resistors by
filling the first via holes with oxidation-resistant conductive
material and flattening the oxidation-resistant conductive
material; (e) forming the resistors so that the ends of each
resistor are connected to two respective contact pads, which are
spaced apart from each other; (f) forming circuit patterns on the
PCB, in which the second via holes are formed; and (g) layering
insulting layers on the PCB obtained at step (f), and forming
external layer circuit patterns.
[0017] In addition, the present invention provides a method of
manufacturing a printed circuit board having embedded resistors,
the method including (a) providing a PCB on which internal layer
circuit patterns, including electrode pads, are formed; (b)
layering insulating layers on the PCB; (c) forming first via holes
on the electrode pads; (d) forming contact pads for connecting the
electrode pads with resistors by filling the first via holes with
oxidation-resistant conductive material and flattening the
oxidation-resistant conductive material; (e) forming the resistors
so that the ends of each resistor are connected to two respective
contact pads, which are spaced apart from each other; (f) forming
second via holes at predetermined locations on the internal layer
circuit patterns; (g) forming circuit patterns on the PCB, in which
the second via holes are formed; and (h) layering insulting layers
on the PCB obtained at step (g), and forming external layer circuit
patterns.
[0018] Preferably, the filling of the oxidation-resistant
conductive material is performed using screen printing.
[0019] The flattening may be performed through a mechanical
polishing process, a chemical polishing process, or a chemical
mechanical polishing process.
[0020] Performing laser trimming using the circuit patterns, formed
at step (f) of the first method or formed at step (g) of the second
method, as pads may be further included.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The above and other objects, features and advantages of the
present invention will be more clearly understood from the
following detailed description taken in conjunction with the
accompanying drawings, in which:
[0022] FIGS. 1A to 1H are sectional views schematically showing a
process of manufacturing a PCB having embedded resistors according
to a preferred embodiment of the present invention; and
[0023] FIGS. 2A and 2B are sectional views schematically showing a
process of manufacturing a board having embedded resistors
according to an embodiment of a prior art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The present invention is described in detail with reference
to the accompanying drawings below.
[0025] FIGS. 1A to 1H schematically show a process of manufacturing
a PCB having embedded resistors according to a preferred embodiment
of the present invention.
[0026] First, a resin board 101, which is generally used in the art
and has conductive metal layers 102 layered on both surfaces
thereof, is prepared (refer to FIG. 1A). Although, in the present
drawing, the conductive metal layers 102 are shown as being layered
on both surfaces of the PCB, a selective layering process may also
be performed on either of the two surfaces of the PCB as needed.
Although the conductive metal layers 102 are limited to any
specific material as long as they are well known in the art, copper
Cu is typically used for the conductive metal layers 102. All of
resin boards, as long as they are well known in the art, may be
used as the resin board 101, that is, the resin board 101 is not
limited to any specific board.
[0027] Thereafter, the conductive metal layers 102 are patterned
using a circuit forming process, for example, using
exposure/development and etching methods, which are well known in
the art, and thus internal layer circuit patterns 104 including
electrode pads 103 are formed (refer to FIG. 1B).
[0028] Subsequently, insulating layers 105 are layered on the PCB
on which the internal layer patterns 104 are formed (refer to FIG.
1C). All of insulating layers, as long as they are well known in
the art, may be used as the insulating layers 105, that is, the
insulating layers 105 are not limited to any specific insulating
layer. In particular, it is advantageous to use resin material,
such as ABF, which has an excellent degree of flatness and enables
the shape thereof to be kept uniform by minimizing the flow of
resistor material, thus enabling the design size of resistors to
predict the actual resultant resistors with great accuracy in a
subsequent process.
[0029] Thereafter, the insulating layers 105 on the electrode pads
103 are processed through a general via forming process, and thus
first via holes 106 are formed (refer to FIG. 1D). In this case,
second via holes 109 may be formed at predetermined locations on
the circuit patterns 103 and 104 at the same time as the first via
holes 106, but the case where only the second via holes 109 are
formed through a subsequent process is shown in the present
drawing.
[0030] The first via holes 106 are filled with Oxidation-resistant
conductive material, preferably, Ag paste, using screen printing
(refer to FIG. 1E). In this case, the conductive material, which is
printed to protrude outside the via-holes 106, is flattened through
a mechanical polishing process, a chemical polishing process or a
chemical mechanical polishing process, such as buffing, which is
well known in the art, and thus contact pads 107 for connecting the
electrode pads 103 with resistors 108 are formed. The contact pad
107, formed as described above, functions not only to merely
connect the electrode pads 103 with the resistors 108, but also to
prevent erosion from occurring between the electrode pads 103 and
the resistors 108.
[0031] Subsequently, the resistors 108 are formed to a desired size
such that the ends of each resistor are connected with two
respective contact pads 107, which are formed as described above
and are spaced apart from each other, (refer to FIG. 1F). In this
case, it is preferred that the resistors 108 be formed to have a
predetermined size through screen printing of resistor material,
such as carbon-based paste, in the interests of economic
efficiency, process efficiency and reliability, but the present
invention is not limited only thereto. Accordingly, the prior art
has a disadvantage in that the differences in height occur between
pads and thus greatly affect the differences between resistance
values, but the present invention can prevent the differences
between resistance values from occurring because no such
differences in height occur at all.
[0032] Thereafter, second via holes 109 for enabling interlayer
electrical connections are formed by processing the insulating
layers 105 at predetermined locations on the circuit patterns 103
and 104 (refer to FIG. 1F) and, thereafter, circuit patterns 110
and 111 are formed through general conductive metal
plating/patterning processes (refer to FIG. 1G). As needed, a
general laser trimming process may be further performed using the
circuit patterns 110, which are formed in this process, as
pads.
[0033] Thereafter, a final PCB having embedded resistors is
manufactured by forming external layer circuit patterns 113 through
a general process of layering insulating layers 112 and a general
circuit forming process.
[0034] As needed, the number of circuit layers formed in an
internal layer and on an external layer may be changed.
[0035] In this manner, the present invention uses a method of
filling via holes formed on electrode pads with oxidation-resistant
conductive material, forming the contact pads, and forming
resistors on the contact pads, so that it can not only realize
connections between circuits but also prevent erosion from
occurring between the electrode pads and the resistors using the
contact pads made of oxidation-resistant conductive material. In
particular, the resistors are formed such that the ends of each
resistor are connected to two respective contact pads, which are
spaced apart from each other, at the surfaces of the contact pads,
which are on the opposite side from the surfaces of the contact
pads that are in contact with the electrode pads, and thus
connected in the same plane without any difference in height, so
that irregular resistance that occurs generally due to the
difference in height can be eliminated, thereby achieving a great
effect of reducing the differences between the resistance values of
the embedded resistors.
[0036] Although the present invention has been described in detail
with reference to the preferred embodiment as described above, this
is only an exemplary embodiment for the purpose of describing the
present invention in detail, and the PCB having embedded resistors
and the method of manufacturing the same according to the present
invention are not limited thereto. It will be apparent that various
variations and modifications can be made within the technical
spirit of the present invention by a person having ordinary
knowledge in the art.
[0037] As described above, in accordance with the present
invention, the contact pads are formed by filling the via holes
formed on the electrode pad with oxidation-resistant conductive
material, and the resistors are formed on the contact pads, so that
the width and size of the designed resistors can be predicted
because there is no difference in height between the pads.
Furthermore, an electroless plating process, which is generally
used to make the conductive material, such as Ag paste, can be
omitted, and thus an advantage of reducing the cost can be
achieved.
[0038] 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, without departing from the scope and
spirit of the invention as disclosed in the accompanying
claims.
* * * * *