U.S. patent application number 09/866813 was filed with the patent office on 2002-01-24 for wired circuit board.
Invention is credited to Ito, Kenichiro, Yamato, Takeshi.
Application Number | 20020007961 09/866813 |
Document ID | / |
Family ID | 18674500 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020007961 |
Kind Code |
A1 |
Yamato, Takeshi ; et
al. |
January 24, 2002 |
Wired circuit board
Abstract
To provide a wired circuit board capable of surely preventing
occurrence of a short circuit between a metal terminal layer and a
metal supporting layer with a simple construction, to provide
improvement in connection reliability and in voltage proof
property, a wired circuit board comprises a base layer formed on a
supporting board, a conductive layer formed on the base layer, a
surface of the conductive layer being exposed by opening the
supporting board and the base layer, and a metal plated layer
formed on the conductive layer exposed in the openings of the
supporting board and the base layer, wherein a specified space is
defined between a periphery of the metal plated layer and a
periphery of the opening of the supporting board.
Inventors: |
Yamato, Takeshi; (Osaka,
JP) ; Ito, Kenichiro; (Osaka, JP) |
Correspondence
Address: |
KUBOVCIK & KUBOVCIK
SUITE 710
900 17TH STREET NW
WASHINGTON
DC
20006
|
Family ID: |
18674500 |
Appl. No.: |
09/866813 |
Filed: |
May 30, 2001 |
Current U.S.
Class: |
174/250 ;
174/255; 174/262; G9B/5.154 |
Current CPC
Class: |
H05K 3/4092 20130101;
H05K 3/388 20130101; G11B 5/486 20130101; H05K 3/0041 20130101;
H05K 3/44 20130101; H05K 2201/09745 20130101; H05K 2203/0323
20130101; H05K 3/0023 20130101; H05K 3/108 20130101; H05K 1/056
20130101; H05K 3/06 20130101; H05K 2201/0969 20130101 |
Class at
Publication: |
174/250 ;
174/255; 174/262 |
International
Class: |
H05K 001/11; H05K
001/03 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 8, 2000 |
JP |
2000-172034 |
Claims
What is claimed is:
1. A wired circuit board comprising an insulating layer formed on a
metal supporting layer, a conductive layer formed on the insulating
layer, a surface of the conductive layer being exposed by opening
the metal supporting layer and the insulating layer, and a metal
terminal layer formed on the conductive layer exposed in the
openings of the metal supporting layer and the insulating layer,
wherein a specified space is defined between a periphery of the
metal terminal layer and a periphery of the opening of the metal
supporting layer.
2. The wired circuit board according to claim 1, wherein the
conductive layer has a terminal forming portion for forming the
metal terminal layer and the terminal forming portion is hollowed
toward the metal supporting layer with respect to the remaining
portions of the conductive layer.
3. The wired circuit board according to claim 1, which is a
suspension board with circuit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a wired circuit board and,
more particularly, to a wired circuit board suitably used for a
suspension board with circuit.
[0003] 2. Description of the Prior Art
[0004] For example, a suspension board with circuit used for a hard
disk drive comprises a supporting board 1 made of stainless steel
foil, a base layer 2 formed of an insulating material formed on the
supporting board 1, a conductive layer 3 formed on the base layer 2
in the form of a specific circuit pattern, and a cover layer 4,
formed of an insulating material, for covering the conductive layer
3, as shown in FIG. 11(d).
[0005] The suspension board with circuit, prevalent nowadays as the
so-called Flying Lead, is formed to have terminals 5 formed on both
sides of the conductive layer 3, rather than in only either side
thereof, in order to meet the demand of recent years for electronic
equipment to have increasingly higher density and reduced size.
[0006] Conventionally, the terminals 5 of the suspension board with
circuit are formed on the both sides of the conductive layer 3 in
the following manner. First, the cover layer 4 is formed and
simultaneously opened by use of a photo-resist and the like to form
a first opening 7 for forming the terminal 5 in the cover layer 4
and expose a front side of the conductive layer 3, as shown in FIG.
11(a). Then, a second opening 8 for the terminal 5 to be formed in
the supporting board 1 is formed in the supporting board 1 by a
chemical etching and the like, as shown in FIG. 11(b).
Sequentially, with the supporting board 1 as a mask, the base layer
2 exposed in the second opening 8 is opened by a plasma etching and
the like, to form a third opening 9 for the terminal 5 to be formed
in the base layer 2, so that a back side of the conductive layer 3
is exposed, as shown in FIG. 11(c). Thereafter, metal plated layers
6 are formed on the both sides of the conductive layer 3 thus
exposed, as shown in FIG. 11(d).
[0007] The metal plated layer 6 thus formed extends over the whole
area of the conductive layer 3 exposed in the whole area of the
third opening 9 in the base layer 2 formed by using the supporting
board 1 as the mask, without leaving any space between the
periphery of the metal plated layer 6 and the periphery of the
third opening 9 in the base layer 2. As a result of this, the metal
plated layer 6 formed in the second opening 8 also extends in the
thickness direction thereof, without leaving any space between the
periphery of the metal plated layer 6 and the periphery of the
second opening 8 in the supporting board 1. Due to this, depending
on thickness of the metal plated layer 6 formed, the metal plated
layer 6 can contact the periphery of the opening 8 in the
supporting board 1 to cause a short circuit from the contact
between the metal plated layer 6 and the supporting board 1.
[0008] In practice, since the third opening 9 in the base layer 2
is formed, with the second opening 8 of the supporting board 1 as
the mask, the third opening 9 is sometimes made slightly larger
than the second opening 8 in the supporting board 1, as shown in
FIG. 11(d). This makes a more risk of the short circuit being
caused from the contact between the metal plated layer 6 and the
supporting board 1.
[0009] It is the object of the invention to provide a wired circuit
board capable of surely preventing occurrence of a short circuit
between a metal terminal layer and a metal supporting layer with a
simple construction, to provide improvement in connection
reliability and in voltage proof property.
SUMMARY OF THE INVENTION
[0010] The present invention is directed to a novel wired circuit
board comprising an insulating layer formed on a metal supporting
layer, a conductive layer formed on the insulating layer, a surface
of the conductive layer being exposed by opening the metal
supporting layer and the insulating layer, and a metal terminal
layer formed on the conductive layer exposed in the openings of the
metal supporting layer and the insulating layer, wherein a
specified space is defined between a periphery of the metal
terminal layer and a periphery of the opening of the metal
supporting layer.
[0011] With this construction, since the specified space is defined
between the periphery of the metal terminal layer and the periphery
of the opening of the metal supporting layer, the contact between
the periphery of the metal terminal layer and the periphery of the
opening of the metal supporting layer can be surely prevented. This
can surely prevent occurrence of a short circuit caused from the
contact therebetween, thus providing improved connection
reliability and voltage proof property of the suspension board with
circuit.
[0012] It is preferable that the conductive layer has a terminal
forming portion for forming the metal terminal layer and the
terminal forming portion is hollowed toward the metal supporting
layer with respect to the remaining portions of the conductive
layer.
[0013] With this construction, the distance from the front side of
the metal supporting layer to the front side of the metal terminal
layer is shortened to an extent corresponding to the hollowed
portion from the remaining portion and, as a result of this, the
metal terminal layer is placed closer to the outside of the metal
supporting layer to that extent. This can produce the effect that
for example when the connecting terminals of an external circuit
are connected with the metal terminal layers in such a manner that
those connecting terminals are laid over the metal terminal layers
and are bonded to each other via supersonic vibration of a bonding
tool, the pressure bonding can be well ensured, thus providing
further improved connection reliability.
[0014] The wired circuit board of the present invention can be used
as a suspension board with circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] In the drawings:
[0016] FIG. 1 is a perspective view showing a suspension board with
circuit presented in the form of an embodiment of a wired circuit
board of the present invention,
[0017] FIG. 2 is a sectional view taken along a longitudinal
direction of the wiring, showing a magnetic head connecting
terminal and an external connecting terminal of the suspension
board with circuit shown in FIG. 1,
[0018] FIG. 3 illustrates in section the steps of preparing a
supporting board and forming on the supporting board a base layer
with a specified pattern, of the method of producing the suspension
board with circuit presented as an embodiment of the method of a
producing a wired circuit board of the present invention,
[0019] (a) shows the step of preparing a supporting board;
[0020] (b) shows the step of forming a coating a precursor of a
photosensitive polyimide resin on the supporting board;
[0021] (c) shows the step of exposing the coating to light through
a photomask and developing it to form a specified pattern; and
[0022] (d) shows the step of curing the patterned coating to form
the base layer,
[0023] FIG. 4 illustrates in section the steps of forming on the
base layer a conductive layer with a specified circuit pattern,
[0024] (a) shows the step of forming a ground on the supporting
board and the base layer;
[0025] (b) shows the step of forming on the ground a plating resist
of an opposite pattern to the specified circuit pattern;
[0026] (c) shows the step of forming a conductive layer of a
specified circuit pattern on a portion of the base layer in which
no plating resist is formed, by using an electrolysis plating;
[0027] (d) shows the step of removing the plating resist; and
[0028] (e) shows the step of removing the ground,
[0029] FIG. 5 illustrates in section the steps that after a surface
of the conductive layer of the circuit pattern is protected by a
thin metal film, the surface of the conductive layer is covered
with a cover layer,
[0030] (a) shows the step of forming the thin metal film on
surfaces of the conductive layer;
[0031] (b) shows the step of forming a coating of a precursor of a
photosensitive polyimide resin on the base layer and the thin metal
film;
[0032] (c) shows the step of patterning the coating by exposing the
coating to light through a photomask and developing it; and
[0033] (d) shows the step of curing the patterned coating to form
the cover layer,
[0034] FIG. 6 illustrates in section the steps of forming the
magnetic head connecting terminals and the external connecting
terminals in the state of their both sides being exposed,
[0035] (a) shows the step of opening the supporting board at
portions thereof for the magnetic head connecting terminals and the
external connecting terminals to be formed;
[0036] (b) shows the step of peeling the thin metal film formed on
the exposed conductive layer and supporting board;
[0037] (c) shows the step of opening the base layer exposed in the
opening of the supporting board, so as to correspond in position to
the opening;
[0038] (d) shows the step of peeling the ground exposed by opening
the base layer; and
[0039] (e) shows the step of forming a metal plated layer on each
side of the exposed conductive layer,
[0040] FIG. 7 is a schematic plan view of an embodiment of a
photomask used for exposing the coating to light in the step of
FIG. 3(b),
[0041] FIG. 8 is a schematic plan view of another embodiment of the
photomask used for exposing the coating to light in the step of
FIG. 3(b),
[0042] FIG. 9 is a schematic plan view of a further embodiment of a
photomask used for exposing the coating to light in the step of
FIG. 3(b),
[0043] FIG. 10 is a schematic plan view of a yet another embodiment
of a photomask used for exposing the coating to light in the step
of FIG. 3(b),
[0044] FIG. 11 illustrates in section the steps of forming the
terminals in the state of their both sides being exposed in the
producing method of a conventional suspension board with
circuit,
[0045] (a) shows the step of forming an opening for the terminal to
be formed in the cover layer;
[0046] (b) shows the step of forming an opening for the terminal to
be formed in the supporting board;
[0047] (c) shows the step of opening the base layer exposed in the
opening of the supporting board, so as to correspond in position to
the opening; and
[0048] (d) shows the step of forming a metal plated layer on each
side of the exposed conductive layer,
[0049] FIG. 12 is a sectional view taken along a longitudinal
direction of the wiring, showing another embodiment of the magnetic
head connecting terminal and external connecting terminal of the
suspension board with circuit shown in FIG. 1, and
[0050] FIG. 13 is a sectional view taken along a longitudinal
direction of the wiring, showing a further embodiment of the
magnetic head connecting terminal and external connecting terminal
of the suspension board with circuit shown in FIG. 1.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0051] Referring to FIG. 1, there is a perspective view showing a
suspension board with circuit presented in the form of an
embodiment of a wired circuit board of the present invention. The
suspension board with circuit 11 mounts thereon a magnetic head of
a hard disk drive (not shown) and suspends the magnetic head while
holding a minute interval between the magnetic head and a magnetic
disk against airflow generated when the magnetic head and the
magnetic disk run relative to each other. The suspension board with
circuit has the lines of wire 14a, 14b, 14c, 14d, integrally formed
therewith in the form of a specific circuit pattern, for connecting
the magnetic head and a read/write board formed as an external
circuit.
[0052] In FIG. 1, the suspension board with circuit 11 has a base
layer 13 formed as an insulating layer of insulating material. The
base layer 13 is formed on a supporting board 12 extending
longitudinally as a metal supporting layer. The conductive layer 14
is formed on the base layer 13 in the form of a specific circuit
pattern. The circuit pattern is provided in the form of the
plurality of lines of wire 14a, 14b, 14c, 14d arrayed in parallel
with spaced apart at a predetermined interval.
[0053] Gimbals 15 for fitting the magnetic head therein are formed
in the supporting board 12 by cutting out the supporting board 12
at a front end portion thereof. Formed at the front end portion of
the supporting board 12 are magnetic head connecting terminals 16
to connect the magnetic head and the lines of wire 14a, 14b, 14c,
14d. Formed at the rear end portion of the supporting board 12 are
external connecting terminals 17 to connect the read/write board
and the lines of wire 14a, 14b, 14c, 14d. Though not shown in FIG.
1, the conductive layer 14 is actually covered with a cover layer
18 made of insulating material.
[0054] In this suspension board with circuit 11, the cover layer 18
is opened to expose a front side of the conductive layer 14 and
also the supporting board 12 and the base layer 13 are opened to
expose a back side of the conductive layer 14, so as to expose the
both sides of the conductive layer 14, and then the metal plating
layers 19 as metal terminal layers are formed on the both sides of
the exposed conductive layer 14, whereby the magnetic head
connecting terminals 16 and the external connecting terminals 17
are each formed as the terminal with its both sides being exposed,
such as the so-called Flying Lead, as shown in FIG. 2. In FIG. 2, a
ground 20 and a thin metal film 22 as will be mentioned later are
omitted.
[0055] Referring now to FIGS. 3 to 6, a process for manufacturing
the suspension board with circuit 11 will be described. Illustrated
at the right side of FIGS. 3-6 are sectional views, taken along the
longitudinal direction of the lines of wire 14a, 14b, 14c, 14d, of
a part of the suspension board with circuit 11 in which the
magnetic head connecting terminals 16 and the external connecting
terminals 17 are formed. Illustrated at the left side of FIGS. 3-6
are sectional views, taken along a direction orthogonal to the
longitudinal direction of the lines of wire 14a, 14b, 14c, 14d, of
a certain part of the suspension board with circuit 11.
[0056] First, the supporting board 12 is prepared and the base
layer 13 is formed on the supporting board 12 in the form of the
specified pattern, as shown in FIG. 3. A metal foil or a metal
sheet is preferably used as the supporting board 12. For example,
stainless steel, 42 alloy and the like are preferably used. The
supporting board used preferably has thickness of 10-60 .mu.m, or
further preferably 15-30 .mu.m, and width of 50-500 mm, or further
preferably 125-300 mm.
[0057] Insulating material used for forming the base layer 13 is
not limited to any particular insulating material. The insulating
materials that may be used include, for example, synthetic resins
such as polyimide resin, acrylic resin, polyether nitrile resin,
polyether sulfonic resin, polyethylene terephthalate resin,
polyethylene naphthalate resin and polyvinyl chloride resin. Of
these synthetic resins, a photosensitive synthetic resin is
preferably used as the base layer 13. A photosensitive polyimide
resin is further preferably used.
[0058] Then, for example, in the case where the base layer 13 is
formed in the specified pattern on the supporting board 12 by using
photosensitive polyimide resin, liquid solution of precursor of the
photosensitive polyimide resin is, as shown in FIG. 3(b), applied
to the whole area of the supporting board 12 prepared as shown in
FIG. 3(a), first, and then is heated at 60-150.degree. C., or
preferably at 80-120.degree. C., to form a coating 13a of the
precursor of the photosensitive polyimide resin.
[0059] Then, the coating 13a is exposed to light through photomasks
24 and 32, as shown in FIG. 3(c). If required, the exposed part is
heated to a specified temperature. Thereafter, the coating 13a is
developed to form the coating 13a into a specified pattern.
Preferably, radiation irradiated for the exposure has an exposure
wavelength of 300-450 nm, or preferably 350-420 nm. An integrated
quantity of exposure light is preferably of 100-1,000 mJ/cm.sup.2,
or further preferably 200-700 mJ/cm.sup.2. Further, when the
exposed part of the coating 13a irradiated is heated, for example,
at temperature of not less than 130.degree. C. to less than
150.degree. C., it is solubilized (positive type) in the next
processing procedure (development), while on the other hand, when
heated, for example, at temperature of not less than 150.degree. C.
to not more than 180.degree. C., it is irsolubilized (negative
type) in the next processing procedure (development). The
development can be performed by any known method, such as a dipping
process and a spraying process, by using a known developing
solution such as alkaline developer. Preferably, the manufacturing
method uses the negative type to produce the circuit pattern.
Illustrated in FIG. 3 is an embodiment using the negative type of
process steps for patterning the circuit.
[0060] As shown in FIG. 3(d), the coating 13a of the precursor of
the polyimide resin thus patterned is finally heated, for example,
to 250.degree. C. or more to be cured (imidized), whereby the base
layer 13 of polyimide resin is formed in the specified pattern.
[0061] In this method, in the step of forming the base layer 13 on
the supporting board 12 in the specified pattern, an opening
portion 31 of the base layer 13, which is opened in the later stage
to expose the conductive layer 14, is made to have smaller
thickness than the remaining portions of the base layer 13, for
forming the magnetic head connecting terminals 16 and the external
connecting terminals 17.
[0062] The opening portion 31 of the base layer 13 can be made to
have smaller thickness than the remaining portions of the base
layer 13, for example, by use of the photomask 32 formed to have
different transmissivity of irradiated light between the opening
portion 31 of the coating 13a and the remaining portions of the
coating 13a. After this photomask 32 is positioned over the opening
portion 31 of the base layer 13, the coating 13a is exposed to
light through the photomask 32 so that the opening portion 31 and
the remaining portions of the coating 13a can be exposed in
different amount of light exposure, and then is developed and
cured.
[0063] The photomask 32 thus formed can allow the opening portion
31 and the remaining portions of the coating 13a to be exposed in
different amount of light exposure, thus enabling the opening
portion 31 to have smaller thickness than the remaining portions of
the coating 13a in a simple and reliable manner.
[0064] To be more specific, when the coating 13a is patterned with
a negative image, as shown in FIG. 3(c) and 3(d), the photomask 32
may be so structured that the transmissivity of irradiated light in
the opening portion 31 of the coating 13a can be reduced more
(preferably not more than 80% of the remaining portions) than in
the remaining portions of the coating 13a. After this photomask 32
is positioned over the opening portion 31 of the base layer 13, the
coating 13a is exposed to light through the photomask 32, so that
the amount of light exposure in the opening portion 31 of the
coating 13a is reduced more than the amount of light exposure in
the remaining portions of the coating 13a, as shown in FIG. 3(c).
Then, the coating 13a is developed and cured, as mentioned above.
This can produce a smaller thickness for the opening portion 31 of
the base layer 13 than that of the remaining portions of the base
layer 13.
[0065] The photomask 32 may be formed to have difference
transmissivity of irradiated light between the opening portion 31
of the coating 13a and the remaining portions of the coating 13a by
the following manner. For example, an area of the surface of the
photomask 32 corresponding to the opening portion 31 is finely
roughened so that components of irregular reflection on the area of
the photomask 32 can be increased to thereby produce reduced
components of the transmitted light in that area. Or, an irradiated
light absorbing film is stuck on the area of the surface of the
photomask 32 corresponding to the opening portion 31 so that the
components of the transmitted light in that area can be reduced.
Or, a pattern having a light transmitting area and a light
shielding area is formed on the area of the surface of the
photomask 32 corresponding to the opening portion 31 so that the
components of the transmitted light in that area can be
reduced.
[0066] Further, in the case of the photomask 32 of a thin metal
film having a specified pattern is used, a thin metal film smaller
than the thin metal film of the photomask 32 may be formed on the
area of the surface of the photomask 32 corresponding to the
opening portion 31 so that the components of the transmitted light
in that area can be reduced. In other words, this photomask 32 is
formed in the manner that after a photomask 32 having no thin metal
film formed in the area thereof corresponding to the opening
portion 31 (a conventional photomask) is formed, a resist is formed
on that photomask 32 so as to expose only the opening portion 31, a
thin metal film made of e.g. chromium smaller than the
above-mentioned thin metal film is formed by vapor deposition or by
plating and, thereafter, the resist is peeled.
[0067] These photomasks 32 can permit the amount of light exposure
in the opening portion 31 to be surely adjusted by one
exposure.
[0068] Of these photomasks, the photomask having the pattern
including the light transmitting area and the light shielding area
formed on the area of the surface thereof corresponding to the
opening portion 31 is preferably used. Specifically, the photomasks
32a, 32b, 32c, 32d shown in FIGS. 7-10 are preferably used.
[0069] Each of these photomasks 32a, 32b, 32c, 32d shown in FIGS.
7-10 is made of a sheet of glass, such as quartz glass or soda
glass, of thickness of 2-5 mm, and a thin metal film having a
pattern is formed on an area of the glass corresponding to the
opening portion 31, such that the transmissivity in that area can
be reduced more than in the remaining areas. The pattern of the
thin metal film can be formed, for example, by the process that
after a thin metal film made of e.g. chromium is formed on the
whole area of the glass by vapor deposition or by plating, the thin
metal film is patterned by use of laser or electron beam. These
photomasks 32a, 32b, 32c, 32d can permit the light exposure in the
opening portion 31 to be surely controlled with a simple
structure.
[0070] For example, the photomask 32a shown in FIG. 7 has, at its
area corresponding to the opening portion 31, a striped pattern
presented in the form of the light transmitting portions and the
light shielding portions being alternately arranged at a not more
than 6 .mu.m pitch (width of the light transmitting portion and the
light shielding portion) so that the averaged transmissivity of
that area can be about 50% with respect to the remaining areas.
[0071] The photomask 32b shown in FIG. 8 has, at its area
corresponding to the opening portion 31, a lattice pattern
presented in the form of the light transmitting portions and the
light shielding portions being alternately arranged at a not more
than 6 .mu.m pitch (width of the light transmitting portion and the
light shielding portion) so that the averaged transmissivity of
that area can be about 25% with respect to the remaining areas.
[0072] The photomask 32c shown in FIG. 9 has, at its area
corresponding to the opening portion 31, a staggered pattern
presented in the form of round light transmitting portions having a
diameter of not more than 6 .mu.m being arranged in zigzag with
respect to the remaining light shielding portion so that the
averaged transmissivity of that area can be about 25% with respect
to the remaining areas.
[0073] The photomask 32d shown in FIG. 10 has, at its area
corresponding to the opening portion 31, a staggered pattern
presented in the form of round light shielding portions having a
diameter of not more than 6 .mu.m being arranged in zigzag with
respect to the remaining light transmitting portion so that the
averaged transmissivity of that area can be about 70% with respect
to the remaining areas.
[0074] Of the photomasks 32a, 32b, 32c, 32d shown in FIGS. 7-10,
those shown in FIGS. 7-9 of not more than 6 .mu.m in the width
(pitch or diameter) of the striped, latticed or rounded light
transmitting portion are preferable. The light transmitting portion
having the width of not more than 6 .mu.m permits the opening
portion 31 to be uniformly irradiated with the irradiated light of
exposure wavelength of 300-450 nm as mentioned above, and as such
can allow the thickness of the opening portion 31 to be uniformly
reduced. In contrast to this, the light transmitting portion having
the width of more than 6 .mu.m increases the resolving power of
irradiated light, to thereby produce undulations in the opening
portion 31 and, as a result, the opening portion 31 is made uneven
in thickness so that the etching may not be performed in the later
stage. Preferably, the light transmitting portion has the width of
not more than 4 .mu.m, or further preferably not more than 3
.mu.m.
[0075] The averaged transmissivity in the opening portion 31 is
preferably 50% or less, or further preferably 25% or less, with
respect to the remaining portions.
[0076] The photomask 32 may be formed to be integral with the
photomask 24 used for the patterning or may be formed to be
separated therefrom.
[0077] When the coating 13a is patterned with a positive image, the
photomask 32 may be so structured that the transmissivity of
irradiated light in the opening portion 31 can be increased more
than in the remaining portions.
[0078] The opening portion 31 of the base layer 13 can be made
smaller in thickness than the remaining portions of the base layer
13, for example, by using a plurality of photomasks of different
patterns to subject the opening portion 31 to light exposure or
light shielding alternately at least two times, other than by using
the photomask 32 formed to have different transmissivity of
irradiated light between the opening portion 31 and the remaining
portions.
[0079] Further, when the photosensitive resin is not used to form
the base layer 13, for example a resin may be applied or layered in
the form of a dry film on the supporting board 12 in the specified
pattern. The opening 31 of the base layer 13 can then be made
smaller in thickness than the remaining part of the base layer 13,
for example, by layering the resin two or more times and also by
layering the resin in the opening portion 31 a fewer number of
times than in the remaining portions.
[0080] Preferably, the base layer 13 thus formed has thickness of
e.g. 2-30 .mu.m, or preferably 5-20 .mu.m. The base layer 13
usually has thickness of about 10 .mu.m. The thickness of the
opening portion 31 of the base layer 13 is usually 80% or less of
the thickness of the remaining portions. For example, the opening
portion 31 preferably has thickness of not more than 8 .mu.m, or
further preferably not more than 5 .mu.m. Suppose that the opening
portion 31 has thickness of 8 .mu.m or less, when the remaining
portions have a usual thickness of 10 .mu.m, as mentioned above,
the time required for the opening to be formed in the later stage
can be shortened by the extent corresponding to 2 .mu.m.
[0081] The opening portion 31 of the base layer 13 may have a lower
limit of thickness or a minimum thickness to serve as a barrier
layer against the conductive layer 14 when the supporting board 12
is opened. For example, the opening portion 31 can have e.g. 3
.mu.m, or further about 1 .mu.m, as the minimum thickness. For
example, the opening portion 31 of the base layer 13 preferably has
thickness of 0.1-8 .mu.m or further preferably 1.0-5 .mu.m.
[0082] Sequentially, the conductive layer 14 is formed on the base
layer 13 in the form of a specified circuit pattern. The conductive
layer 14 provided in the form of the specified pattern is made of
conductive material. The conductive material may be used without
any particular limitation. The conductive materials that may be
used include, for example, copper, nickel, gold, solder or alloys
thereof. Copper is preferably used. To form the conductive layer 14
in the specified circuit pattern, the conductive layer 14 may be
formed on the base layer 13 in the specified pattern in any known
patterning process, such as a subtracting process, an additive
process and a semi-additive process.
[0083] In the subtracting process, the conductive layer 14 is first
layered on the whole area of the base layer 13, through an adhesive
layer, as required, and then an etching resist is formed on the
conductive layer 14 so as to match with the specified circuit
pattern. With the etching resist as a resist, the conductive layer
14 is etched and thereafter the etching resist is removed from the
conductive layer 14.
[0084] In the additive process, a plating resist is formed on the
base layer 13 in an opposite pattern to the specified circuit
pattern, first. Then, the conductive layer 14 is formed in the form
of the specified circuit pattern by plating on a surface of the
base layer 13 on which the plating resist is not formed.
Thereafter, the plating resist is removed.
[0085] In the semi-additive process, a thin film of conductive
material that is formed as a ground is formed on the base layer 13,
first, and then a plating resist is formed on the ground in an
opposite pattern to the specified circuit pattern. Then, the
conductive layer 14 is formed in the form of a specified circuit
pattern by plating on a surface of the ground on which the plating
resist is not formed. Thereafter, the plating resist and the ground
on which the plating resist is layered are removed.
[0086] Of these patterning processes, the semi-additive process is
preferably used, as shown in FIG. 4. First, a thin film of the
conductive material that comes to be the ground 20 is formed on the
whole area of the supporting board 12 and the base layer 13, as
shown in FIG. 4(a). Preferably, the ground 20 is formed by use of a
vacuum deposition process, or by use of a sputtering deposition
process. Chromium and copper are preferably used as the conductive
material that forms the ground 20. To be more specific, a thin
chrome film and a thin copper film are preferably formed in
sequence on the whole area of the supporting board 12 and the whole
area of the base layer 13 by the sputtering deposition process.
Preferably, the thin chrome film has thickness of 100-600 .ANG. and
the thin copper film has thickness of 500-2,000 .ANG..
[0087] Sequentially, the plating resist 21 having the opposite
pattern to the specified circuit pattern is formed on the ground
20, as shown in FIG. 4(b). The plating resist 21 can be provided by
a known process in the form of a specified resist pattern, for
example, by using a dry film resist. Then, the conductive layer 14
having the specified circuit pattern is formed on a portion of the
ground 20 where the plating resist 21 is not formed, by plating, as
shown in FIG. 4(c). Though either of electrolysis plating and
electroless plating may be used, the electrolysis plating is
preferably used. Among others, the electrolysis copper plating is
preferably used. The circuit pattern is formed in the form of a
pattern formed, for example, by a plurality of lines of wire 14a,
14b, 14c, 14d which are spaced apart in parallel with a given
interval, as shown in FIG. 1. The conductive layer 14 has thickness
of e.g. 2-15 .mu.m, or preferably 5-10 .mu.m. The lines of wire
14a, 14b, 14c, 14d have each width of e.g. 10-500 .mu.m, or
preferably 30-200 .mu.m. The interval between the adjacent lines of
wire 14a, 14b, 14c, 14d is e.g. 10-200 .mu.m, or preferably 30-100
.mu.m.
[0088] Then, the plating resist 21 is removed by a known etching
process, such as a chemical etching process (wet etching), or by
peeling, as shown in FIG. 4(d). Thereafter, the part of the ground
20 on which the plating resist 21 was formed is likewise removed by
a known etching process, such as the chemical etching process, as
shown in FIG. 4(e). Through these process steps the conductive
layer 14 is formed on the base layer 13 in the form of the
specified circuit pattern.
[0089] The base layer 13 is formed to have reduced thickness at the
opening portions 31, so that the conductive layer 14 thus formed
has, at portions thereof corresponding to the opening portions 31
or at terminal forming portions 36 on which a metal plated layer 19
is formed in the later stage, concave portions hollowed toward the
supporting board 12 with respect to the remaining portions of the
conductive layer 14 to an extent corresponding to the reduced
thickness.
[0090] Sequentially, the conductive layer 14 is covered with a thin
metal film 22, first, and then is covered with a cover layer 18 of
insulating material, as shown in FIG. 5. Specifically, the thin
metal film 22 is first formed on both of the surface of the
conductive layer 14 and the surface of the supporting board 12, as
shown in FIG. 5(a). Preferably, the thin metal film 22 is provided
in the form of a rigid nickel thin film by the electroless nickel
plating. The coating 22 is just required to have thickness to
prevent the conductive layer 14 from being bared. For example, it
is enough for the coating 22 to have thickness of about 0.05 to
about 0.1 .mu.m.
[0091] Sequentially, the cover layer 18 for covering the conductive
layer 14 is provided in the form of a specified pattern. The same
insulating material is used as the insulating material for forming
the cover layer 18. Preferably, photosensitive polyimide resin is
used.
[0092] In the case where the cover layer 18 is formed by using the
photosensitive polyimide resin, liquid solution of precursor of the
photosensitive polyimide resin is applied to the whole area of the
base layer 13 and the thin metal film 22, and then is heated at
e.g. 60-150.degree. C., or preferably at 80-120.degree. C., to form
a coating 18a of the precursor of the photosensitive polyimide
resin, as shown in FIG. 5(b). Then, the coating 18a is exposed to
light through the photomask 25, as shown in FIG. 5(c). If required,
the exposed part is heated to a certain temperature. Thereafter,
the coating 18a is developed to be patterned so that the conductive
layer 14 can be covered with the coating 18a.
[0093] When the coating 18a is patterned, openings 33 are formed in
the places in which the magnetic head connecting terminals 16 and
the external connecting terminals 17 are formed so that the thin
metal film 22 formed on terminal forming portions 36 of the
conductive layer 14 can be exposed, as shown in FIG. 5(c) and 5(d).
The openings 33 are formed to correspond in position, size and
shape to the terminal forming portions 36 of the conductive layer
14.
[0094] The coating 18a can be exposed and developed under the same
condition as the condition for exposing and developing the coating
13a to form the base layer 13. The patterning of the coating 18a is
preferably produced with the negative image. Shown in FIG. 5 is an
embodied form in which the coating 18a is patterned with the
negative image.
[0095] As shown in FIG. 5(d), the coating 18a of the precursor of
the polyimide resin thus patterned is finally heated, for example,
to 250.degree. C. or more to be cured (imidized), whereby the cover
layer 18 made of polyimide resin is formed on the conductive layer
14. The cover layer 18 has thickness of e.g. 1-30 .mu.m, or
preferably 2-5 .mu.m.
[0096] Sequentially, the magnetic head connecting terminals 16 and
the external connecting terminals 17 are so formed that their both
sides are exposed or are provided in the form of the so-called
Flying Lead, as shown in FIG. 6.
[0097] The magnetic head connecting terminals 16 and the external
connecting terminals 17 can be provided in the form of their both
sides being exposed by the following process. First, as shown in
FIG. 6(a), openings 34 are formed in the supporting board 12 at
portions thereof where the magnetic head connecting terminals 16
and the external connecting terminals 17 are formed or at portions
thereof opposite to the openings 33 of the cover layer 18, so that
the opening portions 31 of the base layer 13 can be exposed. The
openings 34 can be formed by any known method. For example, after
all area of the supporting board 12 except for the areas
corresponding to the openings 34 are subjected to masking, they are
chemically etched. The openings 34 are formed to be larger than the
opening portions 31, so as to include the opening portions 31 of
the base layer 13.
[0098] At the same time as the forming of the openings 34, gimbals
15 are cut into a predetermined shape by the chemical etching.
[0099] Sequentially, as shown in FIG. 6(b), the thin metal film 22
as was exposed by opening the cover layer 18 is peeled and, at the
same time as this, the thin metal film 22 formed on the supporting
board 12 is also peeled.
[0100] Then, as shown in FIG. 6(c), openings 35 are formed in the
base layer 13 including the opening portions 31 exposed in the
openings 34 of the supporting board 12, so as to expose the ground
20 formed on the back side of the terminal forming portion 36 of
the conductive layer 14. The openings 35 can be formed by any known
method. Preferably, the openings 35 are formed by etching or by
plasma etching, in particular. The etching enables a portion of the
base layer 13 extending from the exposed surface of the base layer
13 to the ground 20 formed in the back side of the terminal forming
portion 36 of the conductive layer 14 to be precisely cut, and as
such can allow the back side of the terminal forming portion 36 to
be surely exposed without damaging it in the later process.
[0101] In the plasma etching, the supporting board 12 can be used
as the mask to etch the entire base layer 13 including the opening
portions 31 exposed in the openings 34 of the supporting board 12.
For example, after the sample is disposed between opposed
electrodes in an atmosphere in which a prescribed gas is filled in
therebetween, high-frequency plasma is produced therebetween. The
prescribed gases that may be used include, for example, He, Ne, Ar,
Xe, Kr, N.sub.2, O.sub.2, CF.sub.4 and NF.sub.3. Of these gases,
Ar, O.sub.2, CF.sub.4 and NF.sub.3 are preferably used. These gases
may be used in mixture in a prescribed proportion. The gas pressure
(degree of vacuum) is, for example, 0.5-200 Pa, or preferably
10-100 Pa. The conditions for producing the high-frequency plasma
require the frequency of e.g. 10 kHz-20 MKz, preferably 10 kHz-100
kHz, and the power for the plasma etching of e.g. 0.5-10
W/cm.sup.2, or preferably 1-5 W/cm.sup.2. The frequency of 10
kHz-100 kHz can make it easy to match with a plasma etching device
(tune for resistances). In these atmospheric conditions, the sample
is disposed on the electrodes whose temperature is controlled to
e.g. 0-120.degree. C., or preferably 10-80.degree. C., and is
etched for a specified time for the base layer 13 to be etched to
have a predetermined thickness.
[0102] Since the openings 35 of the base layer 13 thus formed are
formed by using the supporting board 12 as the mask, they can be
formed in the same size and shape as the openings 34 of the
supporting board 12. Consequently, the openings 35 are formed to be
larger than the terminal forming portions 36 of the conductive
layer 14 and, as a result of this, a certain space is defined with
respect to the thickness direction between the periphery of the
ground 20 formed on the back side of the terminal forming portion
36 exposed in the opening 35 of the base layer 13 and the periphery
of the opening 34 of the supporting board 12.
[0103] Thereafter, as shown in FIG. 6(d), the portions of the
ground 20 exposed in the openings 35 of the base layer 13 are
peeled to expose the back side of the terminal forming portions 36
of the conductive layer 14. Sequentially, as shown in FIG. 6(e),
metal plated layers 19 are simultaneously formed by plating on both
sides of the terminal forming portions 36 of the conductive layer
14 thus exposed. Through these processes, the magnetic head
connecting terminals 16 and the external connecting terminals 17
are formed with their both sides being exposed. The metal plated
layers 19 can be formed by using either the electrolysis plating or
the electroless plating, without any particular limitation. Also,
the plating can be formed by using any known metal, without any
particular limitation. Preferably, the electrolysis nickel plating
and the electrolysis gold plating are sequentially performed to
form a gold plated layer 27 on a nickel plated layer 26.
Preferably, the nickel plated layer 26 and the gold plated layer 27
both have thickness of about 1 .mu.m to about 5 .mu.m.
[0104] The metal plated layer 19 thus formed leaves specified space
between the periphery of the metal plated layer 19 and the
periphery of the opening 35 of the base layer 13 and between the
periphery of the metal plated layer 19 and the periphery of the
opening 34 of the supporting board 12, respectively.
[0105] When the suspension board with circuit 11 is produced by
this method, the opening portions 31 of the base layer 13 to be
opened to expose the terminal forming portions 36 are formed to
have smaller thickness than the remaining portions of the base
layer 13 in the process of forming the base layer 13. Consequently,
when the opening portions 31 are etched in the process of forming
the magnetic head connecting terminals 16 and the external
connecting terminals 17, the time required for the terminal forming
portions 36 of the conductive layer 14 to be exposed can be
shortened to the extent corresponding to the reduced thickness of
the opening portions 31 than the remaining portions. This enables
the terminal forming portions 36 of the conductive layer 14 to be
exposed in a short time, and as such can provide improved
efficiency in forming the magnetic head connecting portions 16 and
the external connecting portions 17 with their both sides being
exposed.
[0106] Thus, this method enables the suspension board with circuit
11 to be produced with improved production efficiency, and as such
can provide the suspension board with circuit 11 at reduced
costs.
[0107] In addition, in this method, since the openings 35 of the
base layer 13 and the openings 34 of the supporting board 12 are
formed to be larger than the terminal forming portions 36 of the
conductive layer 14, the specified space is defined between the
periphery of the metal plated layer 19 and the periphery of the
opening 35 of the base layer 13 and between the periphery of the
metal plated layer 19 and the periphery of the opening 34 of the
supporting board 12, respectively. This can produce the effect that
for example when the metal plated layer 19 is increased in
thickness for improvement in connection reliability, the periphery
of the metal plated layer 19 and the periphery of the opening 34 of
the supporting board 12 can be prevented from contacting with each
other. This can surely prevent occurrence of a short circuit from
the contact between the metal plated layer 19 and the supporting
board 12, thus providing improved connection reliability and
voltage proof property of the suspension board with circuit 11.
[0108] Preferably, the interval between the periphery of the metal
plated layer 19 and the opening 34 of the supporting board 12 (the
interval a in FIG. 2) is at least 1 .mu.m, or preferably about 2
.mu.m to about 40 .mu.m.
[0109] Further, in this method, since the base layer 13 is formed
to have reduced thickness at the opening portions 31, the
conductive layer 14 has, at the terminal forming portions 36 formed
on the opening portions 31, concave portions hollowed toward the
supporting board 12 with respect to the remaining portions of the
conductive layer 14 to an extent corresponding to the reduced
thickness. Due to this, the distance from the front side of the
supporting board 12 to the front side of the metal plated layer 19
is shortened to an extent corresponding to the concave portion and,
as a result of this, the metal plated layers 19 are placed closer
to the outside of the supporting board 12 to that extent. This can
produce the effect that for example when the connecting terminals
of the magnetic head or read/write board are connected with the
metal plated layers 19 in such a manner that those connecting
terminals are laid over the metal plated layers 19 and are bonded
to each other via supersonic vibration of a bonding tool, the
pressure bonding can be well ensured, thus providing further
improved connection reliability.
[0110] Preferably, the widthwise interval between the front side of
the metal plated layers 19 and the interface between the base layer
13 and the supporting board 12 (the interval b shown in FIG. 2) is
.+-.6 .mu.m, or further preferably .+-.2 .mu.m.
[0111] In the suspension board with circuit 11 of the embodiment of
the invention illustrated above, the terminal forming portions 36
of the conductive layer 14 are hollowed with respect to the
remaining portions and also the openings 34 of the supporting board
12 are formed to be larger than the terminal forming portions 36 of
the conductive layer 14, whereby the specified space is formed
between the periphery of the metal plated layer 19 and the
periphery of the opening 34 of the supporting board 12. Depending
on the intended objects and applications, the specified space may
be formed between the periphery of the metal plated layer 19 and
the periphery of the opening 34 of the supporting board 12, without
hollowing the terminal forming portion 36 of the conductive layer
14 with respect to the remaining portions, as shown in FIGS. 12 and
13.
[0112] In the suspension board with circuit 11 of the embodiment
shown in FIG. 12, after the openings 33 of the cover layer 18 are
formed, the openings 34 of the supporting board 12 are formed and
also the openings 35 of the base layer 13 are formed to be smaller
than the openings 34 of the supporting board 12, whereby the metal
plated layers 19 are formed on both sides of the conductive layer
14 thus exposed. The openings 35 of the base layer 13 can be made
smaller than the openings 34 of the supporting board 12 in such a
manner that the openings 35 of the base layer 13 are etched, with
the supporting board 12 as the mask, first, and then the openings
34 of the supporting board 12 are further etched so as to increase
the width of the opening.
[0113] In the suspension board with circuit 11 of the embodiment
shown in FIG. 13, after the openings 33 of the cover layer 18 and
the openings 34 of the supporting board 12 are formed, the openings
35 of the base layer 13 are formed by etching with the supporting
board 12 as the mask. Further, a terminal protecting layer 37 of
insulating material is formed around the periphery of the opening
34 of the supporting board 12 and the periphery of the opening 35
of the base layer 13. Thereafter, the metal plated layers 19 are
formed on both sides of the conductive layer 14 thus exposed.
EXAMPLES
[0114] While in the following, the present invention will be
described in further detail with reference to Examples, the present
invention is not limited to any Examples.
EXAMPLE 1
[0115] Liquid solution of the precursor of the photosensitive
polyimide resin was applied on the stainless steel foil (SUS304
H-TA) having thickness of 25 .mu.m so that after dried, it could
have thickness of 24 .mu.m and then dried at 130.degree. C. to
thereby form a coating of the precursor of the photosensitive
polyimide resin. Sequentially, the coating was exposed to light
(405 nm, 1,500 mJ/cm.sup.2) through the photomask. The exposed part
was heated to 180.degree. C. and then developed by using alkaline
developer, whereby the coating was patterned with the negative
image. Sequentially, the patterned coating of the precursor of the
photosensitive polyimide resin was heated at 350.degree. C. to be
cured (imidized), whereby the base layer made of polyimide resin of
thickness of 10 .mu.m was formed in the specified pattern.
[0116] In the step of forming the base layer, the photomask of
metal film, which has a lattice pattern presented in the form of
the light transmitting portions and the light shielding portions
being alternately arranged at a not more than 6 .mu.m pitch (which
corresponds to the photomask 32b shown in FIG. 8 having the
averaged transmissivity of the opening portion of about 25% with
respect to the remaining portions), was positioned over the opening
portions of the coating to be opened in the later stage so as to
expose the conductive layer in the areas in which the magnetic head
connecting terminals and the external connecting terminals were
formed. Then, the coating was exposed to light through the
photomask, so that the amount of light exposure in the opening
portion of the coating could be reduced more than the amount of
light exposure in the remaining portions of the coating. Then, the
coating was developed and cured. As a result of this, the base
layer having thickness of 2 .mu.m at the opening portion thereof
while thickness of 10 .mu.m at the remaining portions thereof was
obtained.
[0117] Sequentially, as a ground, a thin chrome film of thickness
of 300 .ANG. and a thin copper film having thickness of 700 .ANG.
were formed in sequence on the whole area of the stainless steel
foil and the base layer by the sputtering deposition process.
Thereafter, the plating resist having the opposite pattern to the
specified circuit pattern was formed by use of the dry film resist,
and the conductive layer having the specified circuit pattern was
formed in the part of the base layer where the plating resist was
not formed, by the electrolysis copper plating. As a result of the
base layer being formed to have reduced thickness at the opening
portions, the conductive layer thus formed had, at the terminal
forming portions formed on the opening portions of the conductive
layer, concave portions hollowed toward the stainless steel foil
from the remaining portions of the conductive layer with respect to
the thickness direction by about 8 .mu.m. The conductive layer had
thickness of 20 .mu.m and was formed to have the pattern defined by
four lines of wire each having width of 20 .mu.m being spaced apart
in parallel at interval of 30 .mu.m.
[0118] Thereafter, the plating resist was removed by chemical
etching and then the thin chromium film and the thin copper film on
which the plating resist had been formed were removed by chemical
etching.
[0119] Sequentially, a hard, thin nickel film having thickness of
0.1 .mu.m was formed on the surface of the conductive layer and the
surface of the stainless steel foil by the electroless nickel
plating. Thereafter, liquid solution of the precursor of the
photosensitive polyimide resin was applied on the thin nickel film
and the base layer and then heated at 130 .degree. C. to thereby
form a coating of the precursor of the photosensitive polyimide
resin. Sequentially, the coating was exposed to light (405 nm,
1,500 mJ/cm.sup.2) through the photomask. The exposed part was
heated to 180.degree. C. and then developed by using alkaline
developer, whereby the coating was patterned so that the conductive
layer could be covered with the coating. Sequentially, the
patterned coating of the precursor of photosensitive polyimide
resin was heated at 350.degree. C. to be cured (imidized), whereby
the cover layer formed of polyimide resin of thickness of 3 .mu.m
was formed on the conductive layer.
[0120] It is to be noted that in the step of forming the cover
layer, the openings were formed in the cover layer so that when the
cover layer was patterned, the thin metal film formed on the
terminal forming portions of the conductive layer could be exposed.
The openings were formed to correspond to the terminal forming
portions of the conductive layer in position as well as in size and
shape.
[0121] Sequentially, the magnetic head connecting terminals and the
external connecting terminals were formed with their both sides
being exposed. First, the openings larger than the opening portions
of the base layer were formed in the stainless steel foil at
portions thereof corresponding to the openings of the cover layer
so that the opening portions of the base layer could be exposed.
The openings of the stainless steel foil were formed in the manner
that after all areas of the stainless steel foil except the opening
forming portions were subjected to masking, the stainless foil was
subjected to the chemical etching. At the same time as the forming
of the openings, the gimbals were cut into a predetermined shape by
the chemical etching.
[0122] Sequentially, the thin metal film as was exposed by opening
the cover layer was peeled and, at the same time as this, the thin
metal film formed on the stainless steel foil was peeled.
[0123] Then, the openings were formed in the base layer including
the opening portions exposed in the openings of the stainless steel
foil, so as to expose the ground formed on the back side of the
terminal forming portion of the conductive layer. The openings of
the base layer were formed by the plasma etching. In the plasma
etching, with the stainless steel foil as the mask, the entire base
layer including the opening portions exposed in the openings of the
stainless steel foil was etched for 2 minutes in the conditions of:
the mixed gas of CF.sub.4 and O.sub.2 (CF.sub.4/O.sub.2=20/80) used
as the gas filled; the gas pressure (degree of vacuum) of 25 Pa;
the frequency of 13.5 MKz; and the power required for the plasma
etching of 2,500 W.
[0124] The openings of the base layer thus formed were formed in
the same size and shape as the openings of the stainless steel
foil, so that the space of about 30 .mu.m was defined between the
periphery of the ground exposed in the openings of the base layer
and the periphery of the opening of the base layer and the
periphery of the opening of the stainless steel foil.
[0125] Thereafter, the portions of the ground exposed in the
openings of the base layer are peeled to expose the back side of
the terminal forming portions of the conductive layer.
Sequentially, the metal plated layers were formed by performing the
electrolysis nickel plating and the following electrolysis gold
plating, so that the nickel plated layer having thickness of 2
.mu.m and the gold plated layer having thickness of 1 .mu.m were
formed on the both sides of the terminal forming portions of the
conductive layer thus exposed.
[0126] The metal plated layers on the back side of the terminal
forming portions thus formed have the thicknesswise of .+-.2 .mu.m
between the front side of the metal plated layers and the interface
between the base layer and the stainless steel foil and also have
the interval of 26 .mu.m between the periphery of the metal plated
layer and the periphery of the opening of the base layer and the
periphery of the opening of the stainless steel foil.
EXAMPLE 2
[0127] The suspension board with circuit whose magnetic head
connecting terminals and external connecting terminals were formed
with their both sides being exposed was produced in the same
operation as in Example 1, except that the patterned photomask
having a different structure was used when the precursor of the
photosensitive polyimide resin was exposed to light; a thin metal
film smaller in thickness than the above-mentioned thin metal film
was formed on the surface of the photomask at the areas
corresponding to the opening portions of the base layer so that the
transmissivity in those areas could be about 40% with respect to
the remaining portions.
[0128] When the base layer was formed, the opening portions of the
base layer were formed to be 3 .mu.m in thickness, whereas the
remaining portions of the base layer were formed to be 10 .mu.m in
thickness. This enabled the opening portions to be etched by the
plasma etching for about 3 minutes. Also, the metal plated layer on
the back side of the terminal forming portions of the conductive
layer left the thicknesswise interval of .+-.2 .mu.m between the
front side of the metal plated layer and the interface between the
base layer and the stainless steel foil.
EXAMPLE 3
[0129] The suspension board with circuit whose magnetic head
connecting terminals and external connecting terminals were formed
with their both sides being exposed was produced in the same
operation as in Example 1, except that the precursor of the
photosensitive polyimide resin was exposed to light (405 nm, 600
mJ/cm.sup.2) by using the photomask that does not shield the light
transmitting through its area corresponding to the opening portion
of the base layer, first, and then exposed to light (405 nm, 1,500
mJ/cm.sup.2) by using the photomask that shields the light
transmitting through the area corresponding to the opening portion
of the base layer. In this exposure process, the exposure was
performed twice. Because of this, Example 3 was disadvantageous, as
compared with Examples 1 and 2, in that the second exposure pattern
must be aligned with the first exposure pattern precisely and that
an increased number of works and relatively complex works were
required.
COMPARATIVE EXAMPLE 1
[0130] The suspension board with circuit whose magnetic head
connecting terminals and external connecting terminals were formed
in the state in which their both sides were exposed was produced in
the same operation as in Example 1, except that when the precursor
of the photosensitive polyimide resin was exposed to light, no
photomask was arranged over the area corresponding to the opening
portion of the base layer, so that the base layer was formed to
have even thickness of 10 .mu.m and, thereafter, the metal plated
layers were formed on the whole area of the conductive layer
exposed in whole area of the openings of the base layer opened by
using the supporting board as the mask.
[0131] It took about 10 minutes to etch the base layer by the
plasma etching. Also, the suspension board with circuit thus formed
left no thicknesswise space between the periphery of the metal
plated layer on the back side of the terminal forming portion of
the conductive layer and the periphery of the opening of the base
layer and the periphery of the opening of the supporting board. In
addition, the thicknesswise interval of .+-.2 .mu.m was defined
between the front side of the metal plated layer and the interface
between the base layer and the stainless steel foil.
[0132] While the illustrative embodiments of the present invention
are provided in the above description, such is for illustrative
purpose only and it is not to be construed restrictively.
Modification and variation of the present invention that will be
obvious to those skilled in the art is to be covered by the
following claims.
* * * * *