Title: Wired circuit board
Abstract: A wired circuit board having a terminal portion formed as a flying lead that can provide enhanced strength of the conductive pattern, both sides of which are exposed, by simple construction to effectively prevent disconnection of the conductive pattern. The wired circuit board having the terminal portion formed as the flying lead in which the both sides of the conductive pattern are exposed includes, in crossing areas where ends of a cover-side opening and ends of a base-side opening and the conductive pattern are crossed each other, (i) the widened portions formed in the conductive pattern or (ii) cover-side projections and base-side projections formed in the cover layer and the base layer, respectively.
Patent Number: 6,841,737 Issued on 01/11/2005 to Komatsubara, et al.
| Inventors:
|
Komatsubara; Makoto (Osaka, JP);
Morita; Shigenori (Osaka, JP);
Ookawa; Tadao (Osaka, JP);
Shintani; Toshio (Osaka, JP)
|
| Assignee:
|
Nitto Denko Corporation (Osaka, JP)
|
| Appl. No.:
|
195392 |
| Filed:
|
July 16, 2002 |
Foreign Application Priority Data
| Jul 17, 2001[JP] | 2001-216812 |
| Current U.S. Class: |
174/250; 174/255; 174/257; 174/258 |
| Intern'l Class: |
H05K 007/06 |
| Field of Search: |
361/749-751
174/254,250,255-258,261
|
References Cited [Referenced By]
U.S. Patent Documents
| 3711626 | Jan., 1973 | Kilby et al. | 174/251.
|
| 5446245 | Aug., 1995 | Iwayama et al. | 174/261.
|
| 6388201 | May., 2002 | Yamato et al. | 174/255.
|
| 6399899 | Jun., 2002 | Ohkawa et al. | 174/261.
|
Primary Examiner: Vigushin; John B.
Attorney, Agent or Firm: Edwards, Esq.; Jean C.
Dickinson Wright PLLC
Claims
What is claimed is:
1. A wired circuit board comprising a metal supporting layer, a first
insulating layer formed on the metal supporting layer, a conductive
pattern formed on the first insulating layer, a second insulating layer
formed on the conductive pattern, and an opening, formed at the same
position of the conductive pattern, for allowing the metal supporting
layer and the first insulating layer, and the second insulating layer to
open, so as to form a terminal portion in which front and back sides of
the conductive pattern are exposed,
wherein at least any one of the first insulating layer, the second
insulating layer and the conductive pattern has reinforcing portions for
reinforcing the conductive pattern formed at the ends of the opening in
crossing areas where ends of the opening and the conductive pattern cross
each other.
2. The wired circuit board according to claim 1, wherein the wired circuit
board is a suspension board with circuit.
3. A wired circuit board comprising a first insulating layer, a conductive
pattern formed on the first insulating layer, a second insulating layer
formed on the conductive pattern, and an opening, formed at the same
position of the conductive pattern, for allowing the first insulating
layer and the second insulating layer to open, so as to form a terminal
portion in which front and back sides of the conductive pattern are
exposed,
wherein the conductive pattern has widened portions formed to extend in a
widthwise direction substantially orthogonal to an extending direction of
the conductive pattern in crossing areas where ends of the opening and the
conductive pattern cross each other.
4. A wired circuit board comprising a metal supporting layer, a first
insulating layer formed on the metal supporting layer, a conductive
pattern formed on the first insulating layer, a second insulating layer
formed on the conductive pattern, and an opening, formed at the same
position of the conductive pattern, for allowing the metal supporting
layer and the first insulating layer, and the second insulating layer to
open, so as to form a terminal portion in which front and back sides of
the conductive pattern are exposed,
wherein the conductive pattern has widened portions formed to extend in
widthwise direction substantially orthogonal to an extending direction of
the conductive pattern in crossing areas where ends of the opening and the
conductive pattern cross each other.
5. The wired circuit board according to claim 4, wherein the wired circuit
board is a suspension board with circuit.
6. A wired circuit board comprising a metal supporting layer, a first
insulating layer formed on the metal supporting layer, a conductive
pattern formed on the first insulating layer, a second insulating layer
formed on the conductive pattern, and an opening, formed at the same
position of the conductive pattern, for allowing the metal supporting
layer and the first insulating layer, and the second insulating layer to
open, so as to form a terminal portion in which front and back sides of
the conductive pattern are exposed,
wherein at least one of the first insulating layer and the second
insulating layer have projections projecting from ends of the opening onto
the conductive pattern in the opening in the crossing areas where the ends
of the opening and the conductive pattern cross each other.
7. The wired circuit board according to claim 6, wherein the red circuit
board is a suspension board with circuit.
Description
The present invention claims priority from Japanese Patent Application
Serial No. 2001-21812 filed Jul. 17, 2001, which is herein incorporated by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
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.
2. Description of the Prior Art
The wired circuit boards used for electronic/electric equipment are usually
provided with terminal portions to connect with external connecting
terminals.
In recent years, the so-called "flying lead" in which the terminal portions
are formed on both sides of the conductive pattern, rather than in only
either side thereof, is in widespread use in order to meet the demand for
electronic/electric equipment to have increasingly higher density and
reduced size. It is known, for example, in a suspension board with circuit
used for a hard disk drive that the terminals are provided in the form of
flying lead.
To be more specific, the suspension board with circuit comprises a
supporting board 1 of stainless steel foil, a base layer 2 of an
insulating material formed on the supporting board 1, a conductive pattern
3 formed on the base layer 2 in the form of a specified circuit pattern,
and a cover layer 4 of an insulating material, for covering the conductive
pattern 3, as shown in FIG. 21. The terminal portions 5 provided in the
form of the flying lead are formed on both sides of the conductive pattern
3 in the following manner. The cover layer 4 is opened to expose a front
side of the conductive pattern 3, while also the supporting board 1 and
the base layer 2 are opened to expose a back side of the conductive
pattern 3. If necessary, metal plated layers 6 are formed on the both
sides of the thus exposed conductive pattern 3 by nickel/gold plating and
the like.
Thereafter, these terminal portions formed as the flying lead are bonded to
external connecting terminals by applying supersonic vibration thereto by
use of a bonding tool and the like.
In this terminal portion formed as the flying lead, since the both sides of
the conductive pattern are exposed, the supersonic vibration is easily
transmitted to the terminals. This is suitable for the bonding using the
supersonic vibration: on the other hand, this provides the disadvantage
that the conductive pattern exposed at both sides thereof is weak in
physical strength and is subject to stress concentration at edge portions
of the openings in the base layer and cover layer, to cause easy
disconnection of the conductive pattern.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a new wired circuit board
having a terminal portion formed as a flying lead in which both sides of a
conductive pattern are exposed that can provide enhanced strength of the
conductive pattern by simple construction to effectively prevent the
occurrence of disconnection of the conductive pattern.
The present invention provides a wired circuit board comprising a first
insulating layer, a conductive pattern formed on the first insulating
layer, a second insulating layer formed on the conductive pattern, and an
opening, formed at the same position of the conductive pattern, for
allowing the first insulating layer and the second insulating layer to
open, so as to form a terminal portion in which front and back sides of
the conductive pattern are exposed, wherein at least any one of the first
insulating layer, the second insulating layer and the conductive pattern
has reinforcing portions for reinforcing the conductive pattern formed at
ends of the opening in crossing areas where ends of the opening and the
conductive pattern cross each other.
Also, the present invention provides a wired circuit board comprising a
metal supporting layer, a first insulating layer formed on the metal
supporting layer, a conductive pattern formed on the first insulating
layer, a second insulating layer formed on the conductive pattern, and an
opening, formed at the same position of the conductive pattern, for
allowing the metal supporting layer and the first insulating layer, and
the second insulating layer to open, so as to form a terminal portion in
which front and back sides of the conductive pattern are exposed, wherein
at least any one of the first insulating layer, the second insulating
layer and the conductive pattern has reinforcing portions for reinforcing
the conductive pattern formed at ends of the opening in crossing areas
where ends of the opening and the conductive pattern cross each other.
In the wired circuit boards mentioned above, since at least any one of the
first insulating layer, the second insulating layer and the conductive
pattern has the reinforcing portions for reinforcing the conductive
pattern formed at the ends of the opening in the crossing areas where the
ends of the opening and the conductive pattern cross each other, the
physical strength of the conductive pattern at the ends of the opening can
be reinforced. This can produce the effect that for example, when the
conductive pattern, both sides of which are exposed, is subject to stress
concentration at the end portions of the opening in the process of bonding
the terminal portion and the external connecting terminal by applying
supersonic vibration of a bonding tool, the disconnection of the
conductive pattern can be effectively prevented, thus providing improved
bonding reliability.
In addition, the present invention provides a wired circuit board
comprising a first insulating layer, a conductive pattern formed on the
first insulating layer, a second insulating layer formed on the conductive
pattern, and an opening, formed at the same position of the conductive
pattern, for allowing the first insulating layer and the second insulating
layer to open, so as to form a terminal portion in which front and back
sides of the conductive pattern are exposed, wherein the conductive
pattern has widened portions formed to extend in a widthwise direction
substantially orthogonal to an extending direction of the conductive
pattern in crossing areas where ends of the opening and the conductive
pattern cross each other.
Also, the present invention provides a wired circuit board comprising a
metal supporting layer, a first insulating layer formed on the metal
supporting layer, a conductive pattern formed on the first insulating
layer, a second insulating layer formed on the conductive pattern, and an
opening, formed at the same position of the conductive pattern, for
allowing the metal supporting layer and the first insulating layer, and
the second insulating layer to open, so as to form a terminal portion in
which front and back sides of the conductive pattern are exposed, wherein
the conductive pattern has widened portions formed to extend in a
widthwise direction substantially orthogonal to an extending direction of
the conductive pattern in crossing areas where ends of the opening and the
conductive pattern cross each other.
In the wired circuit boards mentioned above, since the conductive pattern
has widened portions formed to extend in a widthwise direction
substantially orthogonal to the extending direction of the conductive
pattern in the crossing areas where the ends of the opening and the
conductive pattern cross each other, the physical strength of the
conductive pattern at the ends of the opening can be reinforced. This can
produce the effect that for example when the conductive pattern both sides
of which are exposed is subject to stress concentration at the end
portions of the opening in the process of bonding the terminal portion and
the external connecting terminal by applying supersonic vibration of the
bonding tool, the disconnection of the conductive pattern can be
effectively prevented, thus providing improved bonding reliability.
Further, the present invention provides a wired circuit board comprising a
first insulating layer, a conductive pattern formed on the first
insulating layer, a second insulating layer formed on the conductive
pattern, and an opening, formed at the same position of the conductive
pattern, for allowing the first insulating layer and the second insulating
layer to open, so as to form a terminal portion in which front and back
sides of the conductive pattern are exposed, wherein the first insulating
layer and/or the second insulating layer have projections projecting from
ends of the opening onto the conductive pattern in the opening in the
crossing areas where the ends of the opening and the conductive pattern
cross each other.
Also, the present invention provides a wired circuit board comprising a
metal supporting layer, a first insulating layer formed on the metal
supporting layer, a conductive pattern formed on the first insulating
layer, a second insulating layer formed on the conductive pattern, and an
opening, formed at the same position of the conductive pattern, for
allowing the metal supporting layer and the first insulating layer, and
the second insulating layer to open, so as to form a terminal portion in
which front and back sides of the conductive pattern are exposed, wherein
the first insulating layer and/or the second insulating layer have
projections projecting from ends of the opening onto the conductive
pattern in the opening in the crossing areas where the ends of the opening
and the conductive pattern cross each other.
In the wired circuit boards mentioned above, since the first insulating
layer and/or the second insulating layer have projections projecting from
the ends of the opening onto the conductive pattern in the opening in the
crossing areas where the ends of the opening and the conductive pattern
cross each other, the physical strength of the conductive pattern at the
ends of the opening can be reinforced. This can produce the effect that
for example when the conductive pattern both sides of which are exposed is
subject to stress concentration at the end portions of the opening in the
process of bonding the terminal portion and the external connecting
terminal by applying supersonic vibration of the bonding tool, the
disconnection of the conductive pattern can be effectively prevented, thus
providing improved bonding reliability.
The wired circuit board of the present invention can provide high bonding
reliability so that the wired circuit board can be used as the suspension
board with circuit, even when formed as the flying lead in which both
sides of the conductive pattern are exposed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the drawings:
FIG. 1 shows an embodiment of a wired circuit board (wherein a widened
portion is formed) of the present invention: (a) is a sectional view of a
principal portion of a terminal portion of the wired circuit board; and
(b) is a plan view of the terminal portion of the same.
FIG. 2 is an enlarged plan view of FIG. 1(b).
FIG. 3 illustrates the production processes of a wired circuit board shown
in FIG. 1:
(a) shows the step of forming a conductive pattern on a base layer;
(b) shows the step of forming a base layer on the conductive pattern;
(c) shows the step of forming a cover-side opening on the cover layer at a
portion thereof at which terminals are to be formed;
(d) shows the step of forming a base-side opening on the base layer at a
portion thereof at which terminals are to be formed; and
(e) shows the step of forming a metal plated layer on each of front and
back sides of the conductive pattern exposed in the cover-side opening and
the base-side opening.
FIG. 4 shows another embodiment of the wired circuit board (wherein a
cover-side projection and a base-side projection are formed) of the
present invention: (a) is a sectional view of a principal portion of a
terminal portion of the wired circuit board; and (b) is a plan view of the
terminal portion of the same.
FIG. 5 is an enlarged view of the plan view shown in FIG. 4(b).
FIG. 6 is an enlarged view of the plane view of another embodiment shown in
FIG. 4(b).
FIG. 7 shows in section a principal portion of another embodiment (only the
cover-side projection is formed) of the wired circuit board shown in FIG.
4(a).
FIG. 8 shows in section a principal portion of still another embodiment
(only the base-side projection is formed) of the wired circuit board shown
in FIG. 4(a).
FIG. 9 is a plan view of a suspension board with circuit presented as one
embodiment of the wired circuit board of the present invention.
FIG. 10 illustrates the production processes of the suspension board with
circuit shown in FIG. 9:
(a) shows the step of forming a coating of a precursor of a photosensitive
polyimide resin on a supporting board;
(b) shows the step of exposing the coating to light through a photomask;
(c) shows the step of developing the coating to form it into a
predetermined pattern;
(d) shows the step of curing the patterned coating to form the base layer,
(e) shows the step of forming a conductive pattern on the base layer;
(f) shows the step of forming a coating of a precursor of a photosensitive
polyimide resin on the conductive pattern;
(g) shows the step of exposing the coating to light through a photomask;
(h) shows the step of developing the coating to form it into a
predetermined pattern;
(i) shows the step of curing the patterned coating to form the cover layer;
(j) shows the step of opening the supporting board at portions thereof at
which the external-side connecting terminals are formed;
(k) shows the step of opening the base layer at portions thereof at which
the external-side connecting terminals are formed; and
(l) shows the step of forming a metal plated layer on each side of the
exposed conductive pattern.
FIG. 11 shows an embodiment of a suspension board with circuit shown in
FIG. 9 (wherein a widened portion is formed) of the present invention: (a)
is a sectional view of a principal portion of an external-side connecting
terminal of the suspension board with circuit; and (b) is a plan view of
the external-side connecting terminal of the same.
FIG. 12 shows an embodiment of a suspension board with circuit shown in
FIG. 9 (wherein a cover-side projection and a base-side projection are
formed): (a) is a sectional view of a principal portion of an
external-side connecting terminal of the suspension board with circuit;
and (b) is a plan view of the external-side connecting terminal of the
same.
FIG. 13 shows in section a principal portion of another embodiment (only
the cover-side projection is formed) of the suspension board with circuit
shown in FIG. 12(a).
FIG. 14 shows in section a principal portion of still another embodiment
(only the base-side projection is formed) of the suspension board with
circuit shown in FIG. 12(a).
FIG. 15 shows an embodiment of a suspension board with circuit shown in
FIG. 9 (wherein the conductive pattern has a concave form and a widened
portion is formed): (a) is a sectional view of a principal portion of an
external-side connecting terminal of the suspension board with circuit;
and (b) is a plan view of the external-side connecting terminal of the
same.
FIG. 16 illustrates the production processes of the suspension board with
circuit shown in FIG. 15:
(a) shows the step of forming a coating of a precursor of a photosensitive
polyimide resin on a supporting board;
(b) shows the step of exposing the coating to light through a photomask;
(c) shows the step of developing the coating to form it into a
predetermined pattern;
(d) shows the step of curing the patterned coating to form the base layer,
(e) shows the step of forming a conductive pattern on the base layer;
(f) shows the step of forming a coating of a precursor of a photosensitive
polyimide resin on the conductive pattern;
(g) shows the step of exposing the coating to light through a photomask;
(h) shows the step of developing the coating to form it into a
predetermined pattern;
(i) shows the step of curing the patterned coating to form the cover layer;
(j) shows the step of opening the supporting board at portions thereof at
which the external-side connecting terminals are formed;
(k) shows the step of opening the base layer at portions thereof at which
the external-side connecting terminals are formed; and
(l) shows the step of forming a metal plated layer on each side of the
exposed conductive pattern.
FIG. 17 is a schematic plan view of an embodiment of a photomask used for
exposing the coating to light in the step of FIG. 16(b):
(a) shows a semi-translucent striped pattern having an average transmission
ratio of about 50%;
(b) shows a semi-translucent latticed pattern having an average
transmission ratio of about 25%;
(c) shows a semi-translucent circular staggered pattern having an average
transmission ratio of about 25%; and
(d) shows a semi-translucent circular staggered pattern having an average
transmission ratio of about 70%.
FIG. 18 shows an embodiment of a suspension board with circuit shown in
FIG. 9 (wherein the conductive pattern has a concave form and a cover-side
projection and a base-side projection are formed): (a) is a sectional view
of a principal portion of an external-side connecting terminal of the
suspension board with circuit; and (b) is a plan view of the external-side
connecting terminal of the same.
FIG. 19 shows in section a principal part of another embodiment of a
suspension board with circuit shown in FIG. 18(a) (wherein only the
cover-side projection is formed).
FIG. 20 shows in section a principal part of still another embodiment of a
suspension board with circuit shown in FIG. 18(a) (wherein only the
base-side projection is formed).
FIG. 21 shows a conventional suspension board with circuit: (a) is a
sectional view of a principal portion of a terminal of the suspension
board with circuit; and (b) is a plan view of the terminal of the same.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to FIG. 1, there is shown an embodiment of a wired circuit board
of the present invention. FIG. 1(a) is a sectional view of a principal
portion of a terminal portion of the wired circuit board; and FIG. 1(b) is
a plan view of the terminal portion of the same. In FIG. 1(a), the wired
circuit board 11 comprises a base layer 12 formed as a first insulating
layer of insulating material, a conductive pattern 13 formed on the base
layer 12 in the form of a specified wired circuit pattern, and a cover
layer 14 formed as a second insulating layer of insulating material on the
conductive pattern 13. The conductive pattern 13 is provided in the form
of a plurality of lines of wires 13a, 13b, 13c and 13d arrayed in parallel
with each other with spaced at a predetermined interval, as shown in FIG.
1(b).
The insulating materials of the base layer 12 and the cover layer 14 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. Polyimide resin is preferably used.
The base layer 12 and the cover layer 14 usually have thickness of 1-30
.mu.m, or preferably 2-20 .mu.m.
The conductive materials used for the conductive pattern 13 include, for
example, copper, nickel, gold, solder or alloys thereof. Copper is
preferably used. The conductive pattern 13 usually has thickness of 2-30
.mu.m, or preferably 5-20 .mu.m.
This wired circuit board 11 is formed in the following way. First, as shown
in FIG. 3(a), the conductive pattern 13 is formed on the base layer 12
formed in a film-like form, in the form of the specified wired circuit
pattern by a known patterning process, such as a subtracting process, an
additive process and a semi-additive process. Then, as shown in FIG. 3(b),
the base layer 12 is covered with the cover layer 14 in a known method,
for example, by adhesive bonding a film-like resin to the conductive
pattern 13 or by applying a photosensitive resin to the conductive pattern
13 and then curing that resin.
In the wired circuit board 11 thus formed, as shown in FIG. 1(a), the cover
layer 14 is opened to expose a front side of the conductive pattern 13 and
also the base layer 12 is opened to expose a back side of the conductive
pattern 13 in such a manner that the exposed front side of the conductive
pattern 13 and the exposed back side of the same correspond in position to
each other so as to expose the both sides of the conductive pattern 13.
Then, on the both sides of the exposed conductive pattern 13, metal
plating layers 15 are formed thereby forming the terminal portion 16 in
the form of the flying lead.
This terminal portion 16 is formed in the following manner. First, a
cover-side opening 17 is formed in the cover layer 14 in a portion thereof
in which the terminal portion 16 is to be formed, in a known method, such
as drilling, laser machining, etching and patterning of photosensitive
resin, as shown in FIG. 3(c). Likewise, a base-side opening 18 is formed
in the base layer 12 in a portion thereof corresponding to the cover-side
opening 17, in a known method, such as drilling, laser machining, etching
and patterning of photosensitive resin, as shown in FIG. 3(d). The
cover-side opening 17 and the base-side opening 18 are opened into a
rectangular shape to cover all the lines of wire 13a, 13b, 13c and 13d.
As shown in FIG. 3(e), the metal plating layers 15 are formed by plating on
both sides of the conductive pattern 13 exposed in the cover-side opening
17 and the base-side opening 18.
No particular limitation is imposed on the plating method used for forming
the metal plated layer 15. The metal plating layer 15 may be formed by
either of electrolysis plating and electroless plating. Also, no
particular limitation is imposed on the metals used for the plating. Known
metals may be used for the plating. It is preferable that the electrolysis
nickel plating and the electrolysis gold plating are performed in sequence
so that a gold plated layer 20 is formed on a nickel plated layer 19. The
nickel plated layer 19 and the gold plated layer 20 each have thickness of
the order of 1-5 .mu.m.
The wired circuit board 11 has the terminal portion 16 in the form of the
flying lead. In the terminal portion 16, widened portions 22 as
reinforcing portions which extend in a widthwise direction substantially
orthogonal to an extending direction of the conductive pattern 13 are
provided in the conductive pattern 13 in crossing areas 21 where the ends
of the cover-side opening 17/base-side opening 18 and the conductive
patterns 13 cross each other, as shown in FIG. 1(b).
To be more specific, the widened portions 22 are formed in the respective
lines of wire 13a, 13b, 13c and 13d at positions thereof which correspond
to the crossing areas 21 (two areas per each line of wire) and arranged
with space from each other along the longitudinal direction of the lines
of wire 13a, 13b, 13c and 13d. The widened portions 22 are formed in such
a generally round shape as to protrude widthwise from the lines of wire
13a, 13b, 13c and 13d.
As shown in FIG. 2, each widened portion 22 is arranged, with its generally
outer half portion embedded in the cover layer 14/base layer 12 and its
generally inner half portion exposed in the cover-side opening
17/base-side opening 18, when a maximum widthwise length 23 between the
adjacent lines of wire is defined as a boundary between the outer half
portion and the inner half portion. Thus, the terminals 16 are formed in
such a dumbbell shape that the lines of wire 13a, 13b, 13c and 13d are
protruded widthwise at both ends thereof in the cover-side opening 17/the
base-side opening 18.
Each widened portion 22 is so formed that the maximum widthwise length 23
is 1.1-4 times, or preferably 2-3 times, as longer as a usual line width
24 of the lines of wire 13a, 13b, 13c and 13d exposed outside in the
cover-side opening 17/base-side opening 18. To be more specific, a
widthwise part of widened portion 22 at the maximum widthwise length 23 is
20-1,000 .mu.m in length and a lengthwise part of the widened portion 22
extending in a longitudinal direction of the lines of wire 13a, 13b, 13c
and 13d is 50-500 .mu.m in length.
The widened portions 22 may be formed in any shape other than the generally
round shape, as long as they are shaped to protrude widthwise and have
widths larger than the usual width. For example, the widened portion 22
may be formed in rectangle.
The terminal portion 16 having this widened portion 22 can be formed in the
processes given below. The widened portions 22 are formed with the
patterning of the wired circuit pattern in the process of forming the
conductive pattern 13. Then, in the processes of FIGS. 3(c) and (d), the
cover layer 14 and the base layer 12 are each opened so that the maximum
widthwise length 23 of the widened portion 22 can be within the crossing
areas 21 and thereby the cover-side opening 17 and the base-side opening
18 are formed. Thereafter, in the process shown in FIG. 3(e), the metal
plated layer 15 is formed on each side of the conductive pattern 13
exposed in the cover-side opening 17 and the base-side opening 18.
In this formation of the wired circuit board 11, since the widened portions
22 widened in the widthwise direction of the conductive pattern 13 are
formed in the conductive pattern 13 in the crossing areas 21 where the
ends of the cover-side opening 17/the base-side opening 18 and the
conductive pattern 13 are crossed each other, the physical strength of the
conductive pattern 13 at the ends of the cover-side opening 17 and at the
ends of the base-side opening 18 can be reinforced. This can produce the
effect that for example when the conductive pattern 13 is subject to
stress concentration at exposed portions thereof at ends of the cover-side
opening 17 and base-side opening 18 in the process of bonding the terminal
portions 16 and the external connecting terminals by applying supersonic
vibration of a bonding tool, the disconnection of the conductive pattern
13 can be effectively prevented, thus providing improved connection
reliability.
In addition, the wired circuit board 11 may be formed so that the terminal
portion 16 presented in the form of this flying lead can have cover-side
projections 25 formed as the reinforcing portions and base-side
projections 26 formed as the reinforcing portions, as shown in FIG. 4.
Specifically, the cover-side projections 25 are formed to project from the
ends of the cover-side opening 17 onto the conductive pattern 13 in the
cover-side opening 17 in the cover layer 14 in the crossing areas 21 where
the ends of the cover-side opening 17/the base-side opening 18 and the
conductive patterns 13 are crossed each other. The base-side projections
26 are formed to project from the ends of the base-side opening 18 onto
the conductive pattern 13 in the base-side opening 18 in the base layer 12
in the crossing areas 21.
To be more specific, the cover-side projections 25 and the base-side
projections 26 are formed in the respective lines of wire 13a, 13b, 13c
and 13d at positions thereof which correspond to the crossing areas 21
(two areas per each line of wire) and arranged with space from each other
along the longitudinal direction of the lines of wire 13a, 13b, 13c and
13d, as shown in FIG. 4(b). These projections 25, 26 are formed in a
convex shape projecting inwardly from the ends of the cover-side opening
17 and the base-side opening 18 along the extending direction of the lines
of wire 13a, 13b, 13c and 13d, respectively.
The cover-side projections 25 and the base-side projections 26 are
overlapped with the lines of wire 13a, 13b, 13c and 13d and are so tapered
(shaped generally in triangle as viewed from the top) that the overlap can
gradually reduce toward the inside of the cover-side opening 17/base-side
opening 18, respectively. As a result of this, the terminal portions 16
are so formed that the lines of wire 13a, 13b, 13c and 13d can be covered
with the cover-side projections 25 and the base-side projections 26 at
opposite ends thereof in the cover-side opening 17 and the base-side
opening 18.
The cover-side projections 25 and the base-side projections 26 are formed
to project at projection length 27 of one-fourth to one-thirtieth, or
preferably one-fifth to one-twentieth, to a line length 29 of each of the
lines of wire 13a, 13b, 13c and 13d exposed in the cover-side opening 17
and the base-side opening 18, as shown in FIG. 5. To be more specific,
each of the cover-side projections 25 and the base-side projections 26 has
a basal width 28 of 5-20 .mu.m slightly smaller than a line width 24 of
lines of wire 13a, 13b, 13c and 13d at the ends of the cover-side opening
17/the base-side opening 18. The cover-side projections 25 and the
base-side projections 26 are projected inwardly in a taped manner at a
projection length 27 of 5-250 .mu.m and are formed in a generally triangle
whose top is located at a widthwise center of lines of wire 13a, 13b, 13c
and 13d.
The shape of the cover-side projections 25 and the base-side projections 26
is not limited to the one shown in FIG. 5, as long as those projections
have such a shape as to overlap with the lines of wire 13a, 13b, 13c and
13d along the longitudinal direction of the lines of wire 13a, 13b, 13c
and 13d. For example, as shown in FIG. 6, the cover-side projections 25
and the base-side projections 26 may be formed to project toward the
inside thereof in a tapered manner from the ends of the cover-side opening
17/the base-side opening 18, with the basal width 28 slightly larger than
the line width 24 of the lines of wire 13a, 13b, 13c and 13d. Further,
those projections 25, 26 may be formed in such a rectangular shape as to
overlap with the lines of wire 13a, 13b, 13c and 13d along the
longitudinal direction of the lines of wire 13a, 13b, 13c and 13d, without
limiting to the generally triangle shape.
The terminal portions 16 having these cover-side projections 25 and the
base-side projections 26 are formed as follows. In the process of FIG.
3(c), the cover layer 14 is opened in such a manner as to form the
cover-side projections 25 to thereby produce the cover-side opening 17. In
the process of FIG. 3(d), the base layer 12 is opened in such a manner as
to form the base-side projections 26 to thereby produce the base-side
opening 18. Thereafter, in the process of FIG. 3(e), the metal plated
layer 15 is formed on each side of the conductive pattern 13 exposed in
the cover-side opening 17 and the base-side opening 18.
In this formation of the wired circuit board 11, since the cover-side
projections 25 and the base-side projections 26 are formed in the cover
layer 14 and the base layer 12 in the crossing areas 21 where the ends of
the cover-side opening 17/the base-side opening 18 and the conductive
patterns 13 are crossed each other, so as to project from the ends of the
cover-side opening 17/the base-side opening 18 onto the conductive pattern
13 in the cover-side opening 17 and the base-side opening 18,
respectively, the physical strength of the conductive pattern 13 at the
ends of the cover-side opening 17 and at the ends of the base-side opening
18 can be reinforced. This can produce the effect that for example when
the conductive pattern 13 are subject to stress concentration at exposed
portions thereof at ends of the cover-side opening 17 and base-side
opening 18 in the process of bonding the terminal portions 16 and the
external connecting terminals by applying supersonic vibration of the
bonding tool, the disconnection of the conductive pattern 13 can be
effectively prevented, thus providing improved connection reliability.
It is to be noted that in the wired circuit board 11, both of cover-side
projections 25 and the base-side projections 26 are not necessarily
required. For example, only the cover-side projections 25 may be formed,
as shown in FIG. 7. Alternatively, only the base-side projections 26 may
be formed, as shown in FIG. 8.
Further, modification may be made of the invention by forming the widened
portions 22 in the conductive pattern 13 and also forming the cover-side
projections 25 in the cover layer 14 and/or forming the base-side
projections 26 in the base layer 12, though not shown.
The wired circuit board 11 having these terminal portions 16 is
particularly preferably applicable to a suspension board with circuit.
Referring to FIG. 9, there is shown a perspective view of a suspension
board with circuit presented as an embodiment of the wired circuit board
of the present invention. The suspension board with circuit 31 mounts
thereon a magnetic head of a hard disk driver (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 34a, 34b, 34c, 34d, integrally formed in the
form of a specified wired circuit pattern, for connecting the magnetic
head and a read/write board 39 formed as an external circuit.
In FIG. 9, the suspension board with circuit 31 has a base layer 33, as a
first insulating layer of insulating material, which is formed on a
supporting board 32 extending longitudinally as a metal supporting layer.
A conductive pattern 34 is formed on the base layer 33 in the form of a
specified wired circuit pattern, and a cover layer 35 (see FIG. 10) is
formed on the conductive pattern 34 as a second insulating layer of
insulating material. The conductive pattern 34 is provided in the form of
the plurality of lines of wire 34a, 34b, 34c and 34d arrayed in parallel
with spaced at a predetermined interval.
Gimbals 36 for fitting the magnetic head therein are formed in the
supporting board 32 by cutting out the supporting board 32 at a front end
portion thereof At the front end portion of the supporting board 32,
magnetic head connecting terminals 37 are formed to connect between the
magnetic head and the lines of wire 34a, 34b, 34c and 34d. At the rear end
portion of the supporting board 32, external-side connecting terminals 38
as the terminals are formed to connect between the read/write board 39 and
the lines of wire 34a, 34b, 34c and 34d. The external-side connecting
terminals 38 are formed in the ends of the lines of wire 34a, 34b, 34c and
34d, to correspond to each of the read/write terminals 54.
This suspension board with circuit 31 can be formed in the following
processes. First, the supporting board 32 is prepared and the base layer
33 is formed on the supporting board 32 in the form of the specified
pattern, as shown in FIGS. 10(a)-(d). A metal foil or a metal sheet is
preferably used as the supporting board 32. For example, stainless steel,
42 alloy and the like are preferably used. The supporting board 32 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.
Insulating material used for forming the base layer 33 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
resin is preferably used as the base layer. A photosensitive polyimide
resin is further preferably used.
Then, for example when the base layer 33 is formed in the specified pattern
on the supporting board 32 by using photosensitive polyimide resin, liquid
solution of precursor of the photosensitive polyimide resin is applied to
the whole area of the supporting board 32 prepared first, and then is
dried, for example, at 60-150.degree. C., to form a coating 33p of the
precursor of the photosensitive polyimide resin, as shown in FIG. 10(a).
Then, the coating 33p is exposed to light through a photomask 40, as shown
in FIG. 10(b). If required, the exposed part is heated to a specified
temperature. Thereafter, the coating 33p is developed to form the coating
33p into a specified pattern, as shown in FIG. 10(c). Preferably,
radiation irradiated for the exposure has an exposure wavelength in the
range of 300-450 nm, or preferably 350-420 nm. An integrated quantity of
exposure light is preferably in the range 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 33p irradiated is heated, for example, at a temperature in the
range of not less than 130.degree. C. to less than 150.degree. C., it is
solubilized (positive type) for the next processing procedure
(development), while on the other hand, when heated, for example, at a
temperature in the range of not less than 150.degree. C. to not more than
180.degree. C., it is non-solubilized (negative type) for 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. 10 is an embodiment using the process steps
of negative type for patterning the circuit.
As shown in FIG. 10(d), the coating 33p 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 33 of polyimide resin
is formed in the specified pattern. The base layer 33 thus formed have a
thickness in the range of e.g. 2-30 .mu.m, or preferably 5-20 .mu.m.
Sequentially, the conductive pattern 34 is formed on the base layer 33 in
the form of a specified wired circuit pattern, as shown in FIG. 10(e). The
conductive materials that may be used for forming the conductive pattern
34 include metals, such as copper, nickel, gold, solder or alloys thereof.
Copper is preferably used. To form the conductive pattern 34 in the
specified wired circuit pattern, the conductive pattern 34 may be formed
on the base layer 33 in the specified wired circuit pattern in any known
patterning process, such as the subtracting process, the additive process
and the semi-additive process. In this method, the semi-additive process
is preferably used.
The conductive pattern 34 thus formed is in the form of a pattern formed by
the plurality of lines of wire 34a, 34b, 34c and 34d which are spaced from
each other in parallel with a given interval, as mentioned above. The
conductive pattern 34 has a thickness in the range of e.g. 2-30 .mu.m, or
preferably 5-20 .mu.m. The lines of wire 34a, 34b, 34c and 34d have a line
width in the range of e.g. 10-500 .mu.m, or preferably 30-200 .mu.m. The
interval (space width) between the adjacent lines of wire 34a, 34b, 34c
and 34d is in the range of e.g. 10-500 .mu.m, or preferably 30-200 .mu.m.
Sequentially, the conductive pattern 34 is covered with the cover layer 35
of insulating material, as shown in FIGS. 10(f)-(i). The same insulating
material as the insulating material of the base layer 33 is used for
forming the cover layer 35. Preferably, photosensitive polyimide resin is
used therefor.
For example when the cover layer 35 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 supporting board 32
and the base layer 33, first, and then is dried at a temperature in the
range of e.g. 60-150.degree. C., in the same manner as in the patterning
of the base layer 33, to form a coating 35p of the precursor of the
photosensitive polyimide resin, as shown in FIG. 10(f). Then, the coating
35p is exposed to light through the photomask 41, as shown in FIG. 10(g).
If required, the exposed part is heated to a certain temperature.
Thereafter, the coating 35p is developed to be patterned so that the
conductive pattern 34 can be covered with the coating 35p, as shown in
FIG. 10(h).
In the patterning of the coating 35p, the photomasks 41 are placed to
confront the areas where the external-side connecting terminals 38 are
formed, so that the front side of the conductive pattern 34 can be exposed
from the coating 35p to form the cover-side opening 42. To be more
specific, the coating 35p is opened so that the cover-side opening 42 can
be formed in such a rectangle shape as to include the lines of wire 34a,
34b, 34c and 34d, so as to provide the external-side connecting terminals
38 in the form of the flying lead, as mentioned later.
The coating 35p can be exposed to light and developed under the same
condition as the condition for exposing and developing the base layer 33.
Shown in FIG. 10 is the patterning in which the coating 35p is patterned
in the negative type in the same manner as in the case of the base layer
33.
As shown in FIG. 10(i), the coating 35p 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 35 made of polyimide
resin is formed on the conductive pattern 34. The cover layer 35 has a
thickness in the range of e.g. 1-30 .mu.m, or preferably 2-5 .mu.m.
Before the cover layer 35 is formed on the conductive pattern 34, the
conductive pattern 34 may be protected by a thin film of rigid nickel by
nickel plating.
In the suspension board with circuit 31 thus formed, the external-side
connecting terminals 38 are presented in the form of the flying lead
exposed at both sides of the conductive pattern 34, as shown in FIGS.
10(j)-(l).
The external-side connecting terminals 38 are presented in the form of the
terminals exposed at both sides of the conductive pattern 34 in the
following processes. First, as shown in FIG. 10(j), supporting-board-side
openings 43 are formed in the supporting board 32 at portions thereof
where the external-side connecting terminals 38 are formed or at portions
thereof corresponding to the cover-side openings 42 of the cover layer 35,
so that the base layer 33 can be exposed. The supporting-board-side
openings 43 can be formed by any known method. For example, after all area
of the supporting board 32 but the areas of the same corresponding to the
supporting-board-side openings 43 are subjected to masking, they are
chemically etched.
Sequentially, as shown in FIG. 10(k), base-side openings 44 are formed in
the base layer 33 exposed in the supporting-board-side openings 43 of the
supporting board 32, so as to expose the conductive pattern 34. Though the
base-side openings 44 can be formed by a known method, the base-side
openings 44 are preferably formed by etching or by plasma etching, in
particular. The etching enables a portion of the base layer 33 to be
precisely cut from the exposed surface of the base layer 33 to the back
side of the conductive pattern 34.
In the plasma etching, the supporting board 32 can be used as the mask to
etch the entire base layer 33 exposed in the supporting-board-side
openings 43 of the supporting board 32. 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 in the range of 0.5-200 Pa, or preferably 10-100 Pa.
Cited as the conditions required for producing the high-frequency plasma
are the frequency in the range of e.g. 10 kHz-20 MKz, or preferably 10
kHz-100 kHz, and the power required for the plasma etching in the range of
e.g. 0.5-10 W/cm.sup.2, or preferably 1-5 W/cm.sup.2. The frequency in the
range 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 the
time required for the base layer 33 to be etched to a predetermined
thickness.
Since the base-side openings 44 of the base layer 33 thus formed are formed
by using the supporting board 32 as the mask, they can be formed in the
same size and shape as the supporting-board-side openings 43 of the
supporting board 32.
Thereafter, as shown in FIG. 10(l), metal plated layers 45 are
simultaneously formed by plating on both sides of the conductive pattern
34 thus exposed. The metal plated layers 45 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 47 on a nickel plated layer 46.
Preferably, the nickel plated layer 46 and the gold plated layer 47 both
have a thickness in the range of about 1-5 .mu.m. As a result of this, the
external-side connecting terminals 38 are formed with the conductive
pattern exposed at both sides thereof.
As shown in FIG. 11, in the external-side connecting terminals 38 of the
suspension board with circuit 31, widened portions 49 as reinforcing
portions extending in a widthwise direction substantially orthogonal to an
extending direction of the conductive pattern 34 are provided in the
conductive pattern 34 in the crossing areas 48 where the ends of the
cover-side opening 42/the base-side opening 44 and the conductive patterns
34 cross each other, as is the case with the wired circuit board 11.
To be more specific, the widened portions 49 are formed in the respective
lines of wire 34a, 34b, 34c and 34d at positions thereof which correspond
to the crossing areas 48 (two areas per each line of wire) and arranged
with space from each other along the longitudinal directions of the lines
of wire 34a, 34b, 34c and 34d. The widened portions 49 are formed in such
a generally round shape as to protrude widthwise from the lines of wire
34a, 34b, 34c and 34d, as shown in FIG. 11(b). Each widened portion 49 is
arranged, with its generally outer half portion embedded in the cover
layer 35/base layer 33 and its generally inner half portion exposed in the
cover-side opening 42, the base-side opening 44 and the
supporting-board-side opening 43, when a maximum widthwise length between
the adjacent lines of wire is defined as a boundary between the outer half
portion and the inner half portion, as is the case with widened portions
22 of the wired circuit board 11. Thus, the external-side connecting
terminals 38 are formed in such a dumbbell shape that the lines of wire
34a, 34b, 34c and 34d are protruded widthwise at both ends thereof in the
cover-side opening 42, the base-side opening 44 and the
supporting-board-side opening 43.
The widened portions 49 may be made identical in the maximum widthwise
length and the longitudinal length extending along the extending direction
of the conductive pattern 34 with the widened portions 22 of the wired
circuit board 11 mentioned above. Also, the widened portions 49 may be
formed in any shape other than the generally round shape, as long as they
are shaped to protrude widthwise and have widths larger than the usual
width. For example, the widened portion 49 may be formed in rectangle.
The external-side connecting terminals 38 having these widened portions 49
can be formed in the processes given below. The widened portions 49 are
formed with the patterning of the wired circuit pattern in the process of
forming the conductive pattern 34. Then, in the processes of FIGS. 10(h)
and (k), the cover layer 35, the supporting board 32 and the base layer 33
are each opened so that the maximum widthwise length of the widened
portion 49 can be within the crossing areas 48 and thereby the cover-side
opening 42, the supporting-board-side opening 43 and the base-side opening
44 are formed. Thereafter, in the process shown in FIG. 10(i), the metal
plated layer 45 is formed on each side of the conductive pattern 34
exposed in the cover-side opening 42 and the base-side opening
44/supporting-board-side opening 43.
In this formation of the suspension board with circuit 31, since the
widened portions 49 widened in the widthwise direction of the conductive
pattern 34 are formed in the conductive pattern 34 in the crossing areas
48 where the ends of the cover-side opening 42/base-side opening 44 and
the conductive pattern 34 are crossed each other, the physical strength of
the conductive pattern 34 at the ends of the cover-side opening 42 and at
the ends of the base-side opening 44 can be reinforced. This can produce
the effect that for example when the conductive pattern 34 are subject to
stress concentration at exposed portions thereof at ends of the cover-side
opening 42 and base-side opening 44 in the process of bonding the
external-side connecting terminals 38 and the read/write terminals 54 by
applying supersonic vibration of the bonding tool, the disconnection of
the conductive pattern 34 can be effectively prevented, thus providing
further improved connection reliability.
In addition, the suspension board with circuit 31 may be formed so that the
external-side connecting terminals 38 presen
