U.S. patent application number 09/794596 was filed with the patent office on 2001-10-04 for production method of thin film resistance element formed on printed circuit board, and thin film resistance element employing the method.
Invention is credited to Otsuki, Mitsuru, Segawa, Keiji, Shindoh, Motoshi.
Application Number | 20010026211 09/794596 |
Document ID | / |
Family ID | 18610394 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026211 |
Kind Code |
A1 |
Shindoh, Motoshi ; et
al. |
October 4, 2001 |
Production method of thin film resistance element formed on printed
circuit board, and thin film resistance element employing the
method
Abstract
The invention provides a production method capable of forming a
thin film resistance element having a thickness and a shape
controlled in a high accuracy in a printed circuit board (core
material). The production method of a thin film resistance element
formed on a printed circuit board, has the steps of forming a thin
film resistance layer having a predetermined thickness on the
printed circuit board through an insulation layer by a dry process
used in producing a semiconductor, forming an electrically
conductive layer on the thin resistance layer, and etching the
electrically conductive layer selectively so as to make, at least,
a pair of electrically conductive pads, resulting in the thin film
resistance element having a predetermined value of resistivity
between the pair of electrically conductive pads. Thereby, it is
possible to form the thin film resistance element having a
thickness and a shape controlled in a high accuracy on the printed
circuit board (core material).
Inventors: |
Shindoh, Motoshi;
(Fujisawa-shi, JP) ; Segawa, Keiji;
(Sagamihara-shi, JP) ; Otsuki, Mitsuru;
(Yokohama-shi, JP) |
Correspondence
Address: |
Anderson Kill & Olick, P.C.
1251 Avenue of the Americas
New York
NY
10020-1182
US
|
Family ID: |
18610394 |
Appl. No.: |
09/794596 |
Filed: |
February 27, 2001 |
Current U.S.
Class: |
338/308 ;
338/309 |
Current CPC
Class: |
H05K 2203/0361 20130101;
H05K 1/167 20130101; H05K 2201/0187 20130101; H05K 3/4644 20130101;
Y10T 29/49082 20150115; H05K 2201/09763 20130101; H01C 17/12
20130101; H05K 2201/0179 20130101; H05K 3/388 20130101; H05K 1/0206
20130101; H05K 2201/0175 20130101; H05K 1/165 20130101; H05K
2201/0209 20130101; H05K 2201/09509 20130101; H05K 2201/0317
20130101 |
Class at
Publication: |
338/308 ;
338/309 |
International
Class: |
H01C 001/012 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2000 |
JP |
2000-095497 |
Claims
What is claimed is:
1. A production method of a thin film resistance element formed on
a printed circuit board, comprising the steps of: forming a thin
film resistance layer having a predetermined thickness on the
printed circuit board through an insulation layer by a dry process
used in producing a semiconductor; forming an electrically
conductive layer on the thin resistance layer; and etching the
electrically conductive layer selectively so as to make, at least,
a pair of electrically conductive pads, resulting in the thin film
resistance element having a predetermined value of resistivity
between the pair of electrically conductive pads.
2. The production method as claimed in claim 1, wherein the thin
film resistance layer is formed in a process of fabricating a build
up printed circuit board that has multi layers alternately stacked
with an inner insulation layer and an inner electrically conductive
layer having an inner circuit pattern on a substrate.
3. The production method as claimed in claim 2 further comprising
the step of forming a via hole in the inner insulation layer so as
to electrically connect to the thin film resistance layer to the
inner electrically conductive layer through the via hole.
4. A thin film resistance element formed on a printed circuit board
having a circuit pattern on a substrate and an insulation layer
covering the circuit pattern comprising: a thin film resistance
element formed on the insulation layer of the printed circuit board
by a dry process used in fabricating semiconductors; and at least,
a pair of electrically conductive pads formed on the thin film
resistance layer, the pair of electrically conductive pads being
separated at a predetermined distance to form a thin film
resistance element between the electrically conductive pads.
5. The thin film resistance element as claimed in claim 4 further
comprising an upper insulation layer covering the thin film
resistance element and means for dissipating a heat generated from
the thin film resistance element.
6. The thin film resistance element as claimed in claim 5, wherein
the means for dissipating the heat comprising a recess to expose a
top surface of the pair of electrically conductive pads.
7. The thin film resistance element as claimed in claim 5, wherein
the means for dissipating the heat is a recess to expose a part of
the thin film resistance element.
8. The thin film resistance element as claimed in claim 6, wherein
the means for dissipating the heat further comprising a thermally
conductive layer in the recess, the thermally conductive layer
extending to an outer surface of the upper insulation layer.
9. The thin film resistance element as claimed in claim 6, wherein
the thermally conductive layer is extended to an outer of the upper
insulation layer, and has a fin having a concavity or a convexity
on a surface of the thermally conductive layer.
10. The thin film resistance element as claimed in claim 4, wherein
the printed circuit board is a build-up printed circuit board that
has multi layers alternately stacked with a plurality of inner
insulation layers and a plurality of inner electrically conductive
layers each having an inner circuit pattern on the substrate.
11. The thin film resistance as claimed in claim 10, wherein the
thin film resistance layer is formed so as to electrically connect
to one of the inner electrically conductive layers through a
via-hole provided through the inner insulation layers.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention is related to a production method of a
thin film resistance element formed on or buried in a printed
circuit board, and the thin film resistance element employing the
same method, in particular, the production method capable of
precisely controlling a thickness and a shape of the thin film
resistance element.
[0003] 2. Description of the Related Arts
[0004] Generally, a printed circuited board used in various kinds
of electric facilities is further demanded to be reduced in size
and weight, in particular, how to install electrically resistance
bodies into the printed circuit board is a key not only to reduce
the size and weight of the printed circuit board but also to
maintain an accuracy value of resistivity of the resistance bodies.
As one of examples for forming these resistance bodies in the prior
arts, there is one where a printed circuit pattern is formed on,
for instance, a ceramic substrate (core) and the resistance bodies
are formed by applying an electrical resistance paste on the
printed circuit pattern by using a printing method. This printing
method has been widely used ever since, and the resistance bodies
formed on the printed circuit pattern is referred to as a printed
resistance body.
[0005] FIGS. 10(A) and 10(B) are sectional views for explaining a
production method of a resistance body by a printing method in the
prior arts.
[0006] Next, a description is given of the production method of the
printed resistance body in the prior arts, referring to FIGS. 10(A)
and 10(B).
[0007] In FIGS. 10(A) and 10(B), a character 2 designates a ceramic
substrate (core) with an insulating layer on the surface thereof or
maintaining an electrically insulating state. As shown in FIG.
10(A), on the surface of the ceramic substrate 2, an electrically
conductive paste of Ag--Pd is applied by, for instance, a screen
printing method, resulting in a pair of electrically conductive
pads (referred to as conductive pads) 4, 4 separated at a certain
distance to each other. Then, on the surface of the ceramic
substrate 2, an electrical resistance paste is applied by the
screen printing method, resulting a printed resistance body 6
between the pair of conductive pads 4, 4 separated to each other at
a predetermined distance L as shown in FIG. 10(B).
[0008] The value of resistivity of the printed resistance body 6
depends on the dimensions of the printed resistance body 6, i.e., a
resistance length L, a resistance width W (not shown) and a
thickness t of the printed resistance body 6. Since the value of
resistivity of the printed resistance body 6 is varied according to
the dimensions, there arise problems as follows.
[0009] First, upon applying the electrically conductive paste and
the resistance paste on the ceramic substrate 2 by the screen
printing method, a shift of printing and penetration of these
pastes inevitably occur, resulting in a deviation of value of
resistivity in the printed resistance body 6.
[0010] In particular, a thickness of the resistance paste printed
on the ceramic substrate 2 varies largely because of a difficulty
to control printing conditions such as a squeezing pressure, a
squeezing angle and a viscosity of resistance paste, resulting in
an increase of the deviation of value of resistivity in the printed
resistance body 6.
[0011] The conductive pads 4 made of Cu (copper) give poor ohmic
contact. This causes a generation of an excess value of resistivity
at connecting portions of the conductive pads 4. This fact poses a
difficulty to obtain a designed value of resistivity with the
printed resistance body 6.
[0012] Generally speaking, the deviation of value of resistivity
thereby is as large as about .+-.30%. This fact implies to require
an additional adjustment process such as trimming for correcting
the value of resistivity to a designed value at the final
stage.
SUMMARY OF THE INVENTION
[0013] Accordingly, it is a general object of the present invention
to provide a production method of a thin film resistance element
formed on a printed circuit board (core material), and the thin
film resistance element produced by the same method, in which above
disadvantages have been effectively eliminated.
[0014] More specific object of the present invention is to provide
a production method of a thin film resistance element formed on a
printed circuit board, and the thin film resistance element
produced by the same method, wherein the thin film resistance
element can be formed in such a manner that the dimensions such as
the thickness thereof are controlled in high accuracy.
[0015] Another specific object of the present invention is to
provide a production method of a thin film resistance element
formed on a printed circuit board, comprising the steps of forming
a thin film resistance layer having a predetermined thickness on
the printed circuit board through an insulation layer by a dry
process used in producing a semiconductor; forming an electrically
conductive layer on the thin resistance layer, and etching the
electrically conductive layer selectively so as to make, at least,
a pair of electrically conductive pads, resulting in the thin film
resistance element having a predetermined value of resistivity
between the pair of electrically conductive pads.
[0016] Another more specific object of the present invention is to
provide a thin film resistance element formed on a printed circuit
board having a circuit pattern on a substrate and an insulation
layer covering the circuit pattern having a thin film resistance
element formed on the insulation layer of the printed circuit board
by a dry process used in fabricating semiconductors; and at least,
a pair of electrically conductive pads formed on the thin film
resistance layer, the pair of electrically conductive pads being
separated at a predetermined distance to form a thin film
resistance element between the pair of electrically conductive
pads.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIGS. 1(A) and 1(B) are perspective views for explaining a
thin film resistance element of a first embodiment in the present
invention;
[0018] FIG. 2 is a perspective views for explaining a thin film
resistance element of a second embodiment in the present
invention;
[0019] FIG. 3 is a sectional view for explaining a thin film
resistance element of a third embodiment in the present
invention;
[0020] FIGS. 4(A) to 4(F) are sectional views for explaining a
production method of the thin film resistance element of the
present invention;
[0021] FIGS. 5(A) and 5(B) are sectional views for explaining a
thin film resistance element of a fourth embodiment in the present
invention;
[0022] FIGS. 6(A) and 6(B) are sectional views for explaining a
thin film resistance element of a fifth embodiment in the present
invention;
[0023] FIGS. 7(A) and 7(B) are sectional views for explaining a
thin film resistance element of a sixth embodiment in the present
invention;
[0024] FIG. 8 is a sectional view for explaining a thin film
resistance element of a seventh embodiment in the present
invention;
[0025] FIGS. 9(A) to 9(C) are sectional views for explaining a
production method of a thin film resistance element in a eighth
embodiment in the present invention, wherein the thin film
resistance element is electrically connected to a circuit pattern
formed in an inner layer of a printed circuit board; and
[0026] FIGS. 10(A) and 10(B) are sectional views for explaining a
production method of a resistance body by a printing method in the
prior arts.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0027] Reference will now be made in detail to preferred
embodiments of a thin film resistance element or body (referred as
thin film resistance element hereinafter) in the present invention,
examples of which are illustrated in the accompanying drawings.
[0028] FIGS. 1(A) and 1(B) are perspective views for explaining a
thin film resistance element of a first embodiment in the present
invention.
[0029] In the present invention, a thin film resistance element 10
is formed or buried by using a different method from the screen
printing method in the prior arts.
[0030] Referring to FIG. 1(A), a character 20 represents a printed
circuit board (core material) comprising a core 12 or a substrate
12, for instance, made of resin, a thin cupper plate 24 having a
circuit pattern and an insulation layer 14.
[0031] As shown in FIG. 1(A), the thin film resistance element 10
of a first embodiment in the present invention is formed on the
surface of an insulation layer 14 of the printed circuit board 20.
In this case, the insulation layer 14 is formed on the printed
circuit board (core material) 20. As another example, the
insulation layer 14 may be formed on a top of a plurality of
different type layers accumulated on the printed circuit board
(core material) 20, as mentioned hereinafter.
[0032] The above thin film resistance element 10 formed on the
insulation layer 14 is composed of a thin film resistance layer 16
having, for instance, a rectangular shape as a pattern and a pair
of electrically conductive pads (referred to as conductive pads)
18, 18 made of, for instance, cupper, each formed on an distal end
portion of the rectangular shape. The value of resistivity of the
thin film resistance element 10 depends on a thickness t and
dimensions of the pattern formed in the thin film resistance layer
16, i.e., a resistance width W and a resistance distance L defined
by a distance between the pair of conductive pads 18, 18 separating
to each other.
[0033] The above thin film resistance layer 16 is formed by the dry
process which is widely used for producing semiconductors. The dry
process includes a spattering method, an ion plating, a vapor
deposition and a CVD (Chemical Vapor Deposition) method. The
feature of the dry process for forming the thin film is to easily
control a thickness of the thin film. Thereby, it is possible to
obtain a thin film with a desired thickness in high accuracy
compared with the screen printing method in the prior arts.
Further, in the dry process, a photolithography method is used for
forming a pattern in a thin film. The accuracy of the pattern
obtained thereby is better than that by the screen printing
method.
[0034] In order to form the pair of conductive pads 18, 18, an
electrically conductive layer (referred to as conductive layer)
(not shown) is formed on the whole surface of the insulation layer
14 on which the thin film resistance layer 16 is formed. The
conductive layer is selectively etched in such a manner that a part
of the thin film resistance layer 16 is exposed so as to have a
predetermined shape (a resistance length L and a resistance width
W), remaining the pair of conductive pads 18. As well known, the
value of resistivity of the thin film resistance element 10 is
proportional to a product of the resistance length L and the
resistance width W as mentioned in the foregoing. Thereby, it is
possible to obtain a desired value of resistivity of the thin film
resistance element 16.
[0035] Further, a contact layer (not shown) may be provided on the
insulation layer 14 made of, for instance, resin, so as to enhance
adhesion between the insulation layer 14 and the conductive layer
made of, for instance, Cu, for forming the conductive pads 18, 18.
In this case, the thin film resistance element 16 is formed on the
contact layer before the conductive layer is formed.
[0036] Specifically, as the present applicant stated in the
previous application (the Japanese Patent Application No.
H11-95469/1999), it is difficult to cause the conductive layer to
sufficiently contact with the insulation layer processed by a
conventional surface treatment when a fine pattern is needed. Thus,
the applicant proposed to provide the contact layer between the
insulation layer and the conductive layer by using the dry process.
In this embodiment, the thin film resistance layer 16 is formed on
the contact layer (not shown) by using a patterning method. As the
materials of the thin film resistance layer 16, many kinds of
resistance materials such as Ni, Ni--Cr, and Ni--Cu are
available.
[0037] In FIG. 1(A), there is illustrated a basic model of the thin
film resistance element 10 in the first embodiment of the present
invention, and in FIG. 1(B) a variation 10A of the thin film
resistance element 10 is illustrated, wherein the shapes of the
conductive pads 18, 18 and the thin film resistance layer 16 are
more complicated than those of the thin film resistance element 10
shown in FIG. 1(A). Specifically, the conductive pads 18, 18 along
with the end portions of the thin film resistance layer 16 shown in
FIG. 1(A) have a rectangular shape but the ones (18, 18 and 16)
shown in FIG. 1(B) have a T-letter shape, respectively. This
implies that according to the present invention, it is possible to
form any shape of the thin film resistance element.
[0038] FIG. 2 is a perspective views for explaining a thin film
resistance element of a second embodiment in the present
invention.
[0039] In a thin film resistance element 10B of the second
embodiment shown in FIG. 2, a middle conductive pad 18A is commonly
provided so as to electrically connect the thin film resistance
element 10 shown in FIG. 1(A) and the thin film resistance element
10A shown in FIG. 1(B) in series, wherein the resistance lengths of
the thin film resistance elements 10, 10A are made to be L1 and L2,
respectively, and the resistance widths of the thin film resistance
elements 10, 10A are made to be W and W2, respectively.
[0040] FIG. 3 is a perspective views for explaining a thin film
resistance element of a third embodiment in the present
invention.
[0041] Further, in a thin film resistance element 10C of the third
embodiment shown in FIG. 3, the present invention is applied to a
build-up printed circuit board (containing a build-up multiplayer
printed circuit board).
[0042] In FIG. 3, a character 20 represents a printed circuit board
(core material) comprising a core or substrate (resin) 12, a thin
cupper plate 24 having a circuit pattern 24A attached on the core
or substrate 12 and a lower insulation layer 14A covering the thin
cupper plate 24A. In this embodiment, on the printed circuit board
(core material) 20, a lower thin film resistance element 10C.sub.1
and an upper thin film resistance element 10C are stacked so that
they are electrically connected in parallel.
[0043] Specifically, in the same manner as mentioned in FIGS. 1(A)
and 1(B), the lower thin film resistance layer 16A is formed on the
printed circuit board (core material) 20 through the lower
insulation layer 14A, and a pair of lower conductive pads 18A, 18A
is formed on the lower thin film resistance layer 16A so as to
oppose each other, resulting in the lower thin film resistance
element 10C.sub.1. On the lower thin film resistance element
10C.sub.1, an upper insulation layer 14B is formed. In the upper
insulation layer 14B, a pair of via holes 19, 19 is form to reach
the pair of lower conductive pads 18A, 18A. On the upper insulation
layer 14B, an upper resistance thin film resistance layer 16B is
formed so that it is electrically connected to the pair of lower
conductive pads 18A, 18A through the pair of via holes 19, 19. On
the upper thin film resistance layer 16B, there is formed a pair of
upper conductive pads 18B, 18B separated at a distance L, resulting
in the upper thin film resistance element 10C electrically
connected to the lower thin film resistance element 10C.sub.1 in
parallel.
[0044] Here, the resistance length of the lower thin film
resistance element 10C.sub.1 is made to be L3 defined by the
separated distance between the pair of lower conductive pads 18A,
18A opposing to each other, and the resistance length of the upper
thin resistance element 10C is made to be L4 defined by the
separated distance between the pair of upper conductive pads 18B,
18B opposing to each other.
[0045] FIGS. 4(A) to 4(F) are sectional views for explaining a
production method of the thin film resistance element of the
present invention.
[0046] Next, a description is given to a production method of the
thin film resistance element 16 of the present invention, referring
to FIG. 4(A).
[0047] In FIG. 4(A), a numerical character 20 designates a printed
circuit board (core material) comprising a core or substrate 12
made of, for instance, resin, a cupper plate 24 being attached on
the core 12 and an insulation layer 14 coated on the core 12 and
the cupper plate 24. The cupper plate 24 has an inner circuit
pattern 24A being wet-etched by, for instance, the photolithography
method. The inner circuit pattern 24A is surface-treated by a
blackening or a wet etching. On the surface of the inner circuit
pattern 24A there is formed an insulation layer 14 by a
soft-etching method. Then, the insulation layer 14 is
surface-treated (roughed or activated) through a dry or wet
process.
[0048] Next, as shown in FIG. 4(B), on the insulation layer 14, a
thin film resistance layer 26 having a given thickness, for
instance, of 15 .mu.m is deposited by the dry process like as the
sputtering method by using a resistance material (for instant, Ni:
99.9%). The thin film resistance layer 26 is formed, for instance,
under following conditions.
[0049] Type of a gas to be used: Ar, a pressure of the gas: 0.4 Pa
(3 mTorr), an output of CD power: 400 W, and a temperature: the
room temperature. In this case, it has been confirmed that a
thickness deviation of the thin film resistance layer 26 is about
.+-.5% to the given thickness of 15 .mu.m. This implies that the
accuracy of the film thickness by this method is much better than
that of the printed resistance body by the printing method using
the resistance paste in the prior art, wherein the thickness
deviation of the printed resistance body is about .+-.20%. Further,
a deviation of the dimensions in the pattern of the thin film
resistance layer 26 is about .+-.5%.
[0050] Next, as shown in FIG. 4(C), a conductive layer 28 made of,
for instance, Cu is formed on the thin film resistance layer 26 by
an electric plating method. Further, a pattern as an outer layer is
formed in the conductive layer 28 by the photolithography method.
In particular, in the case of using a resistance material having a
high resistivity, prior to forming the conductive layer 28, a thin
film layer of Cu may be formed on the thin film resistance layer 26
by the spattering method to enhance the electrical conductivity
between the thin film resistance layer 26 and the conductive layer
28. This thin film layer of Cu enables to form an excellent
conductive layer 28 by the electric plating method. In this case,
both the conductive layer 28 and the thin film resistance layer 26
are etched to form a pattern therein. For example, for etching both
the conductive layer 28 made of Cu and the thin film resistance
layer 26 made of Ni at the same time, the solution of cupric
chloride is used. Needless to say, they can be etched separately or
at the same time according to a desired design.
[0051] Next, as shown in FIG. 4(D), as a mask material of a
selecting etching, for instance, a photo-solder resist 30, which is
usually used as a protection layer, is coated on the conductive
layer 28 by the screen printing method. Then, a pattern for making
a thin film resistance element 16 is formed on the photo-solder
resist 30 by exposing and developing the photo-solder resist 30. It
is preferable that the photo-solder resist 30 has excellent
resistance to alkalis to resist the alkali etching solution used in
the next step.
[0052] Next, as shown in FIG. 4(E), the conductive layer 28 is
etched excepting the portion masked with the photo-solder resist
30. Usually, as an etching solution for Cu, an acid system etching
solution may be used. In this embodiment, however, the alkali
system etching solution is used to selectively etch out the
conductive layer 28 made of Cu, remaining the thin film resistance
layer 26 formed under the conductive layer 28. As the etching
solution, for instance, A-process solution (Meltex) is available.
The etching was performed by a spray method for 60 sec under a
temperature of 45.degree. C. As a result, a portion of the
conductive layer 28 of Cu without the photo-solder resist 30 is
perfectly etched out, remaining the masked portion, and the thin
film resistance layer 26 formed under the conductive layer 28 is
exposed.
[0053] The surface of the thin film resistance layer 26 exposed was
evaluated by using the ESCA (Electron Spectroscopy for Chemical
Analysis) (ULVAC.PHI.). As the result of evaluation, a peak value
of Ni and a thickness of the thin film resistance layer (Ni) 26
were no difference between the initial state and the state after
being etched.
[0054] Next, as shown in FIG. 4(F), the photo-solder resist 30 of
the masking portion is removed from the conductive layer 28 by
using a separating solution, resulting in a pair of pads 18, 18. As
the separating solution, Resist Stripper 9296 (Nippon MacDamid Co.
Ltd.) is available.
[0055] As mentioned above, since the patterning shows in FIGS.
4(D), 4(E) and 4(F) is performed by using the photolithography
process, it is possible to obtain the thin film resistance element
16 having the dimensions accuracy of about .+-.5%, which is better
than the dimensions accuracy of about .+-.10% of the one formed
with the resistance paste by the screen printing method in the
prior arts.
[0056] This fact implies that the production method of the thin
film resistance element 16 according to the invention is an
excellent one capable of controlling the dimensions thereof in high
accuracy, accordingly capable of reducing a deviation of value of
resistivity of the thin film resistance element 16 compared with
that in the prior arts.
[0057] FIGS. 5(A) and 5(B) are sectional views for explaining a
thin film resistance element of a fourth embodiment in the present
invention.
[0058] Generally speaking, a thin film resistance element generates
a heat, which raises a temperature of it when a current flows
through the thin film resistance element. It is just the same with
the thin film resistance element 16 mentioned in FIG. 4(F). The
degree of the temperature rise depends on a current density, an
electric resistance material and an installed state of the thin
film resistance element. For instance, the thin film resistance
element formed in an inner layer has a worse heat dissipation
characteristic than that of the one formed on an outer layer
because the thin film resistance element of the inner layer is
sandwiched by lower and upper insulation layers (resin), resulting
in a high temperature rise compared with the one formed on the
outer layer.
[0059] Thus, the description is given to a thin film resistance
element 50A of a fourth embodiment in the present invention,
wherein the heat dissipation of the thin film resistance element
50A is improved.
[0060] Referring to FIG. 5(A), in the thin film resistance element
50A of a fourth embodiment in the present invention, a plurality of
small thin film resistance elements are electrically connected in
series.
[0061] Specifically, on the printed circuit board 20 (core
material) having the insulation layer 14 thereon, a thin film
resistance layer 16 is formed, and a plurality of conductive pads
18 are formed on the thin film resistance layer 16, each separated
at a distance L5. Thus, a real resistance length of the thin film
resistance element 50A is represented as L5.times.n, wherein a
character n designates a number of the small thin film resistance
elements, each formed between the opposite pads 18. Here, the value
of L5.times.n is made to be a resistance length of L5.
[0062] In FIG. 5(B), there is illustrated a thin film resistance
element 50B having a resistance length of L5. When the thin film
resistance element 50A shown in FIG. 5(A) is compared with the thin
film resistance element 50B shown in FIG. 5(B), the thin film
resistance element 50A has a better heat dissipation than that of
the thin film resistance element 50B because a total surface area
of the conductive pads 18 is larger than that of the thin film
resistance element 50B. This fact enables to input a large electric
power to the thin film resistance element 50A compared with the
thin film resistance element 50B.
[0063] FIGS. 6(A) and 6(B) are sectional views for explaining a
thin film resistance element of a fifth embodiment in the present
invention.
[0064] Referring to FIGS. 6(A) and 6(B), the thin film resistance
elements 50A and 50B shown in FIGS. 5(A) and 5(B) are installed in
an inner layer made of an insulation layer (resin) 32,
respectively. In this case, it is preferable to provide recesses 34
such as holes or ditches in the insulation layer 32 to expose top
surfaces of the conductive pads 18 so that the thin film resistance
elements 50A or 50B may effectively dissipates the heat generated
from themselves.
[0065] FIGS. 7(A) and 7(B) are sectional views for explaining a
thin film resistance element of a sixth embodiment in the present
invention.
[0066] As shown in FIGS. 7(A) and 7(B), in the thin film resistance
elements 70A, 70B of a sixth embodiment, the thin film resistance
elements 50A and 50B shown in FIGS. 6(A) and 6(B) are further
provided with thermally conductive layers 36 made of, for instance
an electrically conductive material on inner surfaces of the
recesses 34 to effectively increase the heat dissipation.
[0067] FIG. 8 is a sectional view for explaining a thin film
resistance element of a seventh embodiment in the present
invention.
[0068] As shown in FIG. 8, in the thin film resistance elements 80
of a seventh embodiment, the thin film resistance element 70B shown
in FIG. 7(B) is further provided with fins 38 having a concavity or
a convexity on a surface of the conductive layer 36 extending to a
flat surface of the insulation layer 32, so that a surface area of
the conductive layer 36 is increased. The fins 38 having the
concavity or the convexity can be formed on the conductive layer 36
by using the photolithography method, a laser processing or a
roughing treatment. Thereby, more effective heat dissipation is
expected of the thin film resistance element 80.
[0069] In the production method of the thin film resistance
elements referred to FIGS. 4(A) to 4(F), the description is given
to the embodiment where the thin film resistance elements 16 is
formed on the same plane, however, the present invention is not
limited to the above embodiment, The production method is
applicable to the cases where the thin film resistance element of
the present is connected to another circuit pattern formed in the
same plane (layer) or a different plane (layer) through a via hole
which has a function for electrically connecting one circuit to
another circuit formed in the different layer.
[0070] FIGS. 9(A) to 9(C) are sectional views for explaining a
production method of a thin film resistance element in a eighth
embodiment in the present invention, wherein the thin film
resistance element is electrically connected to a circuit pattern
formed in an inner layer of a printed circuit board.
[0071] Referring to FIG. 9(A), a character 20 designates a printed
circuit board (core material) which comprises a core or substrate
(resin) 12A, an inner circuit pattern 40 and an insulation layer 42
formed to cover the inner circuit pattern 40. In the insulation
layer 42 a pair of via holes 44, 44 is formed to expose desired
parts of the inner circuit pattern 40. A thin film resistance layer
46 is formed on the insulation layer 42, resulting that the thin
film resistance layer 46 is electrically connected to the desired
parts of the inner circuit pattern 40 through the pair of via holes
44, 44. On the thin film resistance layer 46, there is formed a
conductive layer 48, for instance, made of Cu.
[0072] As shown in FIG. 9(B), in order to make a thin film
resistance element 46A (shown in FIG. 9(C)), a pair of portions
stacked with the thin film resistance layer 46 and the conductive
layer 48 is removed by the patterning and etching methods, as
mentioned in FIG. 4(C) in the foregoing. Next, as shown in FIG.
9(C), a part of the conductive layer 48 of Cu is etched to expose
the thin film resistance layer 46, as mentioned in FIGS. 4(E) and
4(F) in the foregoing. Thus, the thin film resistance element 46A
connected to the inner circuit pattern 40 of the printed circuit
board 20 can be obtained.
[0073] According to this method, it is possible to optionally form
the thin film resistance element on the printed circuit board 20
and to electrically connect the thin film resistance element 46A to
the inner circuit pattern 40 of the printed circuit board 20
through the via holes 44.
[0074] As mentioned in the foregoing, according to the thin film
resistance element and the production method thereof, it is
possible to exert excellent effects as follows.
[0075] According to the production method of a thin film resistance
element formed on a printed circuit board (core material) in the
present invention, the method includes the steps of forming a thin
film resistance layer having a predetermined thickness on the
printed circuit board through an insulation layer by a dry process
used in producing a semiconductor; forming an electrically
conductive layer on the thin resistance layer; and etching the
electrically conductive layer selectively so as to make, at least,
a pair of electrically conductive pads, resulting in the thin film
resistance element having a predetermined value of resistivity
between the pair of electrically conductive pads. Thus, it is
possible to form the thin film resistance element having a
thickness and a shape controlled in a high accuracy thereon. For
instance, the electric resistance body formed with the resistance
paste in the prior arts has a deviation of value of resistivity as
large as .+-.30% to a desired value. On the contrary, the thin film
resistance element of the present invention has a deviation of
value of resistivity as small as .+-.10%. As a result, it is
possible to obtain the thin film resistance element having a high
accuracy and an excellent ohmic contact.
[0076] According to a thin film resistance element in the present
invention, it is possible to install means for dissipating a heat
generated from the thin film resistance element thereto, Thereby,
it is possible flow a large current into the thin film resistance
element.
[0077] Further, according to a production method of thin film
resistance element in the present invention, it is possible to
electrically connect the thin film resistance element to an inner
circuit pattern and an inner resistance element formed in an inner
layer through via holes. Thereby, it is possible to compactly
fabricate a multi layer printed circuit board.
[0078] It will be apparent to those skilled in the art that various
modification and variations could be made in the thin film
resistance element in the present invention without departing from
the scope or spirit of the invention.
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