U.S. patent application number 13/946431 was filed with the patent office on 2013-11-21 for printed wiring board and method for manufacturing printed wiring board.
This patent application is currently assigned to IBIDEN CO., LTD.. The applicant listed for this patent is IBIDEN CO., LTD.. Invention is credited to Tomohiko MURATA, Fusaji NAGAYA, Hiroyuki SATO.
Application Number | 20130305531 13/946431 |
Document ID | / |
Family ID | 44655061 |
Filed Date | 2013-11-21 |
United States Patent
Application |
20130305531 |
Kind Code |
A1 |
SATO; Hiroyuki ; et
al. |
November 21, 2013 |
PRINTED WIRING BOARD AND METHOD FOR MANUFACTURING PRINTED WIRING
BOARD
Abstract
A printed wiring board includes a core substrate having a
penetrating hole penetrating through the core substrate and having
a first insulation layer, a second insulation layer and an
insulative substrate interposed between the first and second
layers, a first circuit formed on a surface of the core, a second
circuit formed on opposite surface of the core, and a through-hole
conductor formed in the penetrating hole of the core and connecting
the first and second circuits. The penetrating hole has first and
second opening portions, the first opening portion becomes thinner
from the first surface toward the second surface, the second
opening portion becomes thinner from the second surface toward the
first surface, and the first and second insulation layers are
comprised of resin materials easier to be processed by laser than
resin material of the insulative substrate under same conditions of
the laser.
Inventors: |
SATO; Hiroyuki; (Ogaki-shi,
JP) ; MURATA; Tomohiko; (Ogaki-shi, JP) ;
NAGAYA; Fusaji; (Ogaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
IBIDEN CO., LTD. |
Ogaki-shi |
|
JP |
|
|
Assignee: |
IBIDEN CO., LTD.
Ogaki-shi
JP
|
Family ID: |
44655061 |
Appl. No.: |
13/946431 |
Filed: |
July 19, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13618427 |
Sep 14, 2012 |
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13946431 |
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12954052 |
Nov 24, 2010 |
8304657 |
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13618427 |
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61317408 |
Mar 25, 2010 |
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Current U.S.
Class: |
29/852 |
Current CPC
Class: |
Y10T 29/49165 20150115;
H05K 3/4661 20130101; H05K 2201/0959 20130101; H05K 3/0032
20130101; H05K 2201/09827 20130101; H05K 3/426 20130101; H05K 3/42
20130101; H05K 2203/1572 20130101; H05K 2201/09845 20130101 |
Class at
Publication: |
29/852 |
International
Class: |
H05K 3/42 20060101
H05K003/42 |
Claims
1-14. (canceled)
15. A method for manufacturing a printed wiring board, comprising:
preparing a core substrate having a first surface and a second
surface on an opposite side of the first surface and comprising a
first insulation layer, a second insulation layer and an insulative
substrate interposed between the first insulation layer and the
second insulation layer; forming a penetrating hole having a first
opening portion and a second opening portion in the core substrate
such that the first opening portion becomes thinner from the first
surface of the core substrate toward the second surface and that
the second opening portion becomes thinner from the second surface
of the core substrate toward the first surface; forming a first
circuit on the first surface of the core substrate; forming a
second circuit on the second surface of the core substrate; and
forming a plated film in the penetrating hole such that a
through-hole conductor connecting the first circuit and the second
circuit is formed, wherein the first insulation layer comprises a
resin material which is easier to be processed by a laser than a
resin material of the insulative substrate when the first opening
portion is formed under same conditions of the laser for the first
insulation layer and the insulative substrate, and the second
insulation layer comprises a resin material which is easier to be
processed by a laser than the material of the insulative substrate
when the second opening portion is formed under same conditions of
the laser for the second insulation layer and the insulative
substrate.
16. The method for manufacturing a printed wiring board according
to claim 15, wherein the preparing of the core substrate comprises
providing the insulative substrate having a main surface and a
secondary surface on an opposite side of the main surface,
laminating the first insulation layer such that the first
insulation layer faces the main surface of the insulative
substrate, and laminating the second insulation layer such that the
second insulation layer faces the secondary surface of the
insulative substrate.
17. The method for manufacturing a printed wiring board according
to claim 15, wherein the forming of the penetrating hole comprises
forming the first opening portion by irradiating a laser on the
first surface of the core substrate and forming the second opening
portion by irradiating a laser on the second surface of the core
substrate.
18. The method for manufacturing a printed wiring board according
to claim 15, wherein the insulative substrate includes a
reinforcing material.
19. The method for manufacturing a printed wiring board according
to claim 15, wherein the first insulation layer includes an
inorganic filler, and the second insulation layer includes an
inorganic filler.
20. The method for manufacturing a printed wiring board according
to claim 15, wherein the insulative substrate includes a
reinforcing material, the first insulation layer includes an
inorganic filler, the second insulation layer includes an inorganic
filler, and the first insulation layer and the second insulation
layer do not include a reinforcing material.
21. The method for manufacturing a printed wiring board according
to claim 15, wherein the first opening portion is formed by
irradiating a CO.sub.2 gas laser on the first surface of the core
substrate, and the second opening portion is formed by irradiating
a CO.sub.2 gas laser on the second surface of the core
substrate.
22. The method for manufacturing a printed wiring board according
to claim 16, wherein the insulative substrate includes a
reinforcing material.
23. The method for manufacturing a printed wiring board according
to claim 22, wherein the first insulation layer includes an
inorganic filler, and the second insulation layer includes an
inorganic filler.
24. The method for manufacturing a printed wiring board according
to claim 23, wherein the first insulation layer and the second
insulation layer do not include a reinforcing material.
25. The method for manufacturing a printed wiring board according
to claim 22, wherein the reinforcing material is a glass cloth.
26. The method for manufacturing a printed wiring board according
to claim 15, wherein a straight line passing through the gravity
center of the first opening and perpendicular to the first surface
of the core substrate is not aligned with a straight line passing
through the gravity center of the second opening and perpendicular
to the first surface of the core substrate.
27. The method for manufacturing a printed wiring board according
to claim 15, wherein the forming of the plated film in the
penetrating hole comprises filling the penetrating hole with a
plating material such that the through-hole conductor made of the
plated film filling the penetrating hole is formed.
28. The method for manufacturing a printed wiring board according
to claim 22, wherein the reinforcing material is an aramid fiber
material.
29. The method for manufacturing a printed wiring board according
to claim 15, wherein the first insulation layer and the second
insulation layer do not include a reinforcing material.
30. The method for manufacturing a printed wiring board according
to claim 15, wherein the first insulation layer includes an
inorganic filler comprising at least one of silica and alumina, and
the second insulation layer includes an inorganic filler comprising
at least one of silica and alumina.
31. The method for manufacturing a printed wiring board according
to claim 15, wherein the first opening portion is formed by
irradiating a CO.sub.2 gas laser on the first surface of the core
substrate, and the second opening portion is formed by irradiating
a CO.sub.2 gas laser on the second surface of the core substrate,
and a straight line passing through the gravity center of the first
opening and perpendicular to the first surface of the core
substrate is not aligned with a straight line passing through the
gravity center of the second opening and perpendicular to the first
surface of the core substrate.
32. The method for manufacturing a printed wiring board according
to claim 15, wherein the forming of the penetrating hole comprises
forming the first opening portion by irradiating a laser on the
first surface of the core substrate and forming the second opening
portion by irradiating a laser on the second surface of the core
substrate, and a straight line passing through the gravity center
of the first opening and perpendicular to the first surface of the
core substrate is not aligned with a straight line passing through
the gravity center of the second opening and perpendicular to the
first surface of the core substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional application of and
claims the benefit of priority to U.S. application Ser. No.
13/618,427, filed Sep. 14, 2012, which is a continuation
application of U.S. application Ser. No. 12/954,052, filed Nov. 24,
2010, Now U.S. Pat. No. 8,304,657, granted Nov. 6, 2012, which is
based upon and claims the benefit of priority to U.S. Application
No. 61/317,408, filed Mar. 25, 2010. The entire contents of these
applications are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a printed wiring board and
its manufacturing method. A printed wiring board of the present
invention includes a core substrate having a penetrating hole made
up of a first opening portion and a second opening portion, first
circuit and second circuits formed on the core substrate, and a
through-hole conductor formed in the penetrating hole and
connecting the first and second circuits.
[0004] 2. Discussion of the Background
[0005] Japanese Laid-Open Patent Publication 2006-41463 describes
forming a penetrating hole made up of a first blind hole and a
second blind hole in a dielectric layer. The penetrating hole in
Japanese Laid-Open Patent Publication 2006-41463 is formed as an
hourglass and is filled with conductive material. The contents of
this publication are incorporated herein by reference in their
entirety.
SUMMARY OF THE INVENTION
[0006] According to one aspect of the present invention, a printed
wiring board includes a core substrate having a first surface and a
second surface on the opposite side of the first surface, the core
substrate having a penetrating hole penetrating through the core
substrate between the first surface and the second surface, a first
circuit formed on the first surface of the core substrate, a second
circuit formed on the second surface of the core substrate, and a
through-hole conductor formed in the penetrating hole of the core
substrate and connecting the first circuit and the second circuit.
The penetrating hole has a first opening portion and a second
opening portion. The first opening portion of the penetrating hole
becomes thinner from the first surface toward the second surface.
The second opening portion of the penetrating hole becomes thinner
from the second surface toward the first surface. The first opening
portion has a first opening on the first surface of the core
substrate and has a first portion including the first opening and a
second portion contiguous to the first portion of the first opening
portion. The second opening portion has a second opening on the
second surface of the core substrate and has a first portion
including the second opening and a second portion contiguous to the
first portion of the second opening portion. The first portion and
second portion of the first opening portion form inner walls of the
first opening portion which bend inward with respect to the
periphery of the penetrating hole at the boundary between the first
portion and second portion of the first opening portion. The first
portion and second portion of the second opening portion form inner
walls of the second opening portion which bend inward with respect
to the periphery of the penetrating hole at the boundary between
the first portion and second portion of the second opening
portion.
[0007] According to another aspect of the present invention, a
method for manufacturing a printed wiring board includes preparing
a core substrate having a first surface and a second surface on the
opposite side of the first surface, forming a penetrating hole
having a first opening portion and a second opening portion in the
core substrate such that the first opening portion becomes thinner
from the first surface of the core substrate toward the second
surface and that the second opening portion becomes thinner from
the second surface of the core substrate toward the first surface,
forming a first circuit on the first surface of the core substrate,
forming a second circuit on the second surface of the core
substrate, and forming a plated film in the penetrating hole such
that a through-hole conductor connecting the first circuit and the
second circuit is formed. The first opening portion has a first
opening on the first surface of the core substrate and has a first
portion including the first opening and a second portion contiguous
to the first portion of the first opening portion. The second
opening portion has a second opening on the second surface of the
core substrate and has a first portion including the second opening
and a second portion contiguous to the first portion of the second
opening portion. The first portion and second portion of the first
opening portion form inner walls of the first opening portion which
bend inward with respect to the periphery of the penetrating hole
at the boundary between the first portion and second portion of the
first opening portion. The first portion and second portion of the
second opening portion form inner walls of the second opening
portion which bend inward with respect to the periphery of the
penetrating hole at the boundary between the first portion and
second portion of the second opening portion.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0009] FIGS. 1(A) through 1(E) are views showing the steps of a
method for manufacturing a multilayer printed wiring board
according to the first embodiment;
[0010] FIGS. 2(A) through 2(C) are views showing the steps of a
method for manufacturing a multilayer printed wiring board
according to the first embodiment;
[0011] FIGS. 3(A) through 3(D) are views showing the steps of a
method for manufacturing a multilayer printed wiring board
according to the first embodiment;
[0012] FIGS. 4(A) through 4(D) are views showing the steps of a
method for manufacturing a multilayer printed wiring board
according to the first embodiment;
[0013] FIGS. 5 (A) through 5(C) are views showing the steps of a
method for manufacturing a multilayer printed wiring board
according to the first embodiment;
[0014] FIG. 6 is a cross-sectional view of a multilayer printed
wiring board according to the first embodiment;
[0015] FIG. 7 is a view showing angles between a first surface of a
core substrate and inner walls of a penetrating hole;
[0016] FIG. 8 are views showing cross sections of penetrating holes
in a reference example and in the first embodiment;
[0017] FIG. 9 are views showing inner diameters of a penetrating
hole in the first embodiment;
[0018] FIGS. 10(A) and 10(C) show a through-hole conductor in a
reference example, and FIGS. 10(B), 10(D), 10(E) and 10(F) show
through-hole conductors in the first embodiment;
[0019] FIGS. 11(A), 11(B), 11(C) and 11(D) show penetrating holes
in the first embodiment, (A-1) is a plan view showing a first
surface of a core substrate in the first embodiment, and (A-2) is a
plan view showing a second surface of the core substrate in the
first embodiment;
[0020] FIGS. 12(A) and 12(B) are views schematically showing energy
intensity of a laser, and FIG. 12(C) is a view showing an example
where a penetrating hole is bent in a reinforcing material;
[0021] FIG. 13 are views showing other steps for manufacturing a
printed wiring board of the first embodiment;
[0022] FIG. 14 are cross-sectional views showing penetrating holes
in the first embodiment;
[0023] FIG. 15 are views to illustrate the positions to irradiate
laser beams; and
[0024] FIG. 16 is a cross-sectional view showing a multilayer
printed wiring board according to the second embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0025] The embodiments will now be described with reference to the
accompanying drawings, wherein like reference numerals designate
corresponding or identical elements throughout the various
drawings.
First Embodiment
[0026] Multilayer printed wiring board 10 of the first embodiment
is described with reference to FIG. 6. FIG. 6 shows a
cross-sectional view of multilayer printed wiring board 10. In
multilayer printed wiring board 10, first circuit (34A) is formed
on a first surface of core substrate 30, and second circuit (34B)
is formed on a second surface. First circuit (34A) has first
conductive circuit (34AC) and first land (34AL), and second circuit
(34B) has second conductive circuit (34BC) and second land (34BL).
The first conductive circuit and the second conductive circuit are
connected by through-hole conductor 36. The first land and the
second land are connected by through-hole conductor 36. Upper-layer
first interlayer resin insulation layer (50A) is formed on the
first surface of core substrate 30 and on the first circuit.
Upper-layer first interlayer resin insulation layer (50A) has a
first surface and a second surface opposite the first surface. The
second surface of upper-layer first interlayer resin insulation
layer (50A) faces the first surface of the core substrate.
Conductive circuit (58A) is formed on the first surface of
upper-layer first interlayer resin insulation layer (50A).
Conductive circuit (58A) on upper-layer first interlayer resin
insulation layer (50A) and the first circuit or the through-hole
conductor are connected by via conductor (60A), which penetrates
through upper-layer first interlayer resin insulation layer
(50A).
[0027] Lower-layer first interlayer resin insulation layer (50B) is
formed on the second surface of core substrate 30 and on the second
circuit. Lower-layer first interlayer resin insulation layer (50B)
has a first surface and a second surface opposite the first
surface. The second surface of lower-layer first interlayer resin
insulation layer (50B) faces the second surface of the core
substrate. Conductive circuit (58B) is formed on the first surface
of lower-layer first interlayer resin insulation layer (50B).
Conductive circuit (58B) on lower-layer first interlayer resin
insulation layer (50B) and the second circuit or the through-hole
conductor are connected by via conductor (60B), which penetrates
through lower-layer first interlayer resin insulation layer
(50B).
[0028] Upper-layer solder-resist layer (70A) is formed on the first
surface of upper-layer first interlayer resin insulation layer
(50A), and lower-layer solder-resist layer (70B) is formed on the
first surface of lower-layer first interlayer resin insulation
layer (50B). Upper and lower solder-resist layers (70A, 70B) have
openings (71A, 71B) that expose via conductors (60A, 60B) and
conductive circuits (58A, 58B). Top surfaces of the via conductors
and the conductive circuits exposed through openings (71A, 71B)
function as solder pads (72A, 72B). Solder bumps (78A, 78B) are
formed on solder pads (72A, 72B).
[0029] A magnified view of through-hole conductor 36 formed in core
substrate 30 in FIG. 6 is shown in FIG. 10(B).
[0030] Core substrate 30 has insulative substrate 31 having main
surface (31A) and secondary surface (31B) opposite the main
surface, first resin insulation layer (32A) formed on the main
surface of insulative substrate 31, and second resin insulation
layer (32B) formed under the secondary surface. Core substrate 30
has penetrating hole 33 which penetrates through the core
substrate. First resin insulation layer (32A) has a front surface
and a back surface opposite the front surface, and the back surface
faces the main surface. Second resin insulation layer (32B) has an
upper surface and a lower surface opposite the upper surface, and
the upper surface faces the secondary surface. The core substrate
has a first surface and a second surface opposite the first
surface; and the first surface corresponds to the front surface and
the second surface corresponds to the lower surface. Insulative
substrate 31 is preferred to contain a reinforcing material, but
the first resin insulation layer (32A) and second resin insulation
layer (32B) are preferred not to contain a reinforcing material. As
for a reinforcing material, glass cloth, aramid fiber or the like
may be used. First and second resin insulation layers (32A, 32B)
may contain inorganic fillers such as silica and alumina.
Through-hole conductor 36 is made of the plated metal filled in
penetrating hole 33. FIG. 11 show penetrating hole 33 for a
through-hole conductor. Penetrating hole 33 has first opening
portion (33A) formed by irradiating a laser from first surface
(30A) of core substrate 30, and second opening portion (33B) formed
by irradiating a laser from second surface (30B) of the core
substrate. FIG. 11(A-1) is a plan view of the first surface of the
core substrate, and FIG. 11(A-2) is a plan view of the second
surface of the core substrate. First opening portion (33A) has
first opening (33A-A) on the first surface of the core substrate,
and second opening portion (33B) has second opening (33B-B) on the
second surface of the core substrate. First opening portion (33A)
and second opening portion (33B) are joined inside insulative
substrate 31. First opening portion (33A) becomes thinner from the
first surface of the core substrate toward the second surface; and
second opening portion (33B) becomes thinner from the second
surface of the core substrate toward the first surface. FIG. 11 are
cross-sectional views obtained by slicing penetrating hole 33 with
a plane which passes through the gravity center of the first
opening and includes a straight line (first gravity line) (G1)
perpendicular to the first surface of the core substrate. As shown
in FIG. 11, the inner walls of the first opening portion bend
inward at the interface of the first resin insulation layer and the
insulative substrate; and the inner walls of the second opening
portion bend inward at the interface of the second resin insulation
layer and the insulative substrate. Such bending directions
indicate directions toward the first gravity line.
[0031] A straight line passing through the gravity center of the
first opening and perpendicular to the first surface of the core
substrate may be offset from a straight line (second gravity line)
(G2) passing through the gravity center of the second opening and
perpendicular to the first surface of the core substrate (FIG.
11(B)). The first gravity line and the second gravity line are not
required to overlap. In such a case, it is easier to fill a
penetrating hole with plating. The area where a first opening
portion and a second opening portion are connected increases, and
the connection reliability of the through-hole conductor is
enhanced.
[0032] The first opening portion has a third opening at the
junction of the (first-1) opening portion and the (first-2) opening
portion. The second opening portion has a fourth opening at the
junction of the (second-1) opening portion and the (second-2)
opening portion. A straight line (the third gravity line) (G3)
passing through the gravity center of the third opening and
perpendicular to the first surface of the core substrate may be
offset from the first gravity line. The first gravity line and the
third gravity line are not required to overlap. A straight line
(fourth gravity line) (G4) passing through the gravity center of
the fourth opening and perpendicular to the first surface of the
core substrate may be offset from the second gravity line. The
second gravity line and the fourth gravity line are not required to
overlap. Penetrating hole 33 tends to fill with plating film, and
voids are less likely to occur in the through-hole conductor. The
reliability of the through-hole conductor increases. FIG. 7 shows a
cross-sectional view of a penetrating hole obtained in a case where
the first gravity line and the third gravity line are offset. Inner
walls (X, Y) facing each other in a penetrating hole make different
angles (.theta.1, .theta.2) to the first surface of the core
substrate. When a penetrating hole is filled with plated film, the
penetrating hole is gradually filled with plated film starting from
inner wall X and inner wall Y. If angle (.theta.1) formed between
inner wall X and the first surface of the core substrate is
different from angle (.theta.2) formed between inner wall Y and the
first surface of the core substrate, it is thought that the plating
solution supplied into the penetrating hole along the plated film
on inner wall X and the plating solution supplied into the
penetrating hole along the plated film on inner wall Y enters the
penetrating hole from different directions. Also, it is thought
that the plating solution is supplied into the penetrating hole
from different directions. The plating solution in the penetrating
hole tends to circulate, and the penetrating hole tends to be
filled with plating. When a penetrating hole is filled with
electrolytic plated film, since deposition speed is fast in
electrolytic plating, voids tend to occur in the electrolytic
plated film. However, when the first gravity line and the third
gravity line are offset, since the plating solution in the opening
portion tends to circulate, the first opening portion tends to fill
with plated film. In the same manner, when the second gravity line
and the fourth gravity line are offset, the second opening portion
tends to fill with plated film.
[0033] The first, second, third and fourth gravity lines may all be
offset from each other. It is not required that the first, second,
third and fourth gravity lines all overlap. The same effects are
achieved as above.
[0034] When a core substrate is formed with an insulative substrate
and with a first resin insulation layer and a second resin
insulation layer sandwiching the insulative substrate, the third
opening tends to be formed on the interface of the insulative
substrate and the first resin insulation layer, and the fourth
opening tends to be formed on the interface of the insulative
substrate and the second resin insulation layer.
[0035] A first opening portion is made up of (first-1) opening
portion (33A-1) and (first-2) opening portion (33A-2). When the
degree at which the (first-1) opening portion becomes thinner from
the first surface of the core substrate toward the second surface
is (.DELTA.W1), and the degree at which the (first-2) opening
portion becomes thinner from the first surface of the core
substrate toward the second surface is (.DELTA.W2), (.DELTA.W1) is
set smaller than (.DELTA.W2). Also, a second opening portion is
made up of (second-1) opening portion (33B-1) and (second-2)
opening portion (33B-2). When the degree at which (second-1)
opening portion (33B-1) becomes thinner from the second surface of
the core substrate toward the first surface is (.DELTA.W3), and the
degree at which the (second-2) opening portion becomes thinner from
the second surface of the core substrate toward the first surface
is (.DELTA.W4), (.DELTA.W3) is set smaller than (.DELTA.W4).
[0036] When a core substrate is formed with an insulative substrate
and with a first resin insulation layer and a second resin
insulation layer sandwiching the insulative substrate, a (first-1)
opening portion is likely formed in the first resin insulation
layer, a (first-2) opening portion and a (second-2) opening portion
is likely formed in the insulative substrate, and a (second-1)
opening portion is likely formed in the second resin insulation
layer. In such situations, (.DELTA.W1) is the degree at which the
(first-1) opening portion becomes thinner from the front surface of
the first resin insulation layer toward the back surface;
(.DELTA.W2) is the degree at which the (first-2) opening portion
becomes thinner from the main surface of the insulative substrate
toward the secondary surface; (.DELTA.W4) is the degree at which
the (second-2) opening portion becomes thinner from the secondary
surface of the insulative substrate toward the main surface; and
(.DELTA.W3) is the degree at which the (second-1) opening portion
becomes thinner from the lower surface of the second resin
insulation layer toward the upper surface.
[0037] Accordingly, diameter (Wmin) tends to be enlarged at portion
(junction) (33c) where the first opening portion joins the second
opening portion. In addition, diameters of first opening (33A-A)
and second opening (33B-B) may be set smaller. Diameter (Wmin)
indicates the minimum diameter of a penetrating hole, corresponding
to "Wmin" in FIG. 11. "Wmin" in FIG. 11 is the distance between the
portions where the first opening portion intersects the second
opening portion. Since the minimum diameter of a penetrating hole
is enlarged in the first embodiment, cracks seldom occur at
junction (33c) in the through-hole conductor. In addition, the
diameter of the first opening and the diameter of the second
opening may be set smaller. The greater of the diameter of the
first opening and the diameter of the second opening is set as the
diameter of the penetrating hole. While preventing a decrease in
the reliability of through-hole conductors when their diameters
become smaller, through-hole conductors are arranged at high
density.
[0038] FIG. 8(A) shows a penetrating hole of a reference example.
In the reference example, the inner walls of first opening portion
(333A) change in a straight line. The inner walls of second opening
portion (333B) change in a straight line as well. In FIG. 8(B), a
penetrating hole of the first embodiment overlaps a penetrating
hole of the reference example. The inner walls of the reference
example are drawn using a solid line, and parts of the inner walls
of the first embodiment are drawn using a broken line. In the first
embodiment, a first opening portion is made up of a (first-1)
opening portion and a (first-2) opening portion, and the inner
walls of the first opening portion bend at predetermined spots (a,
b). The inner walls of the (first-1) opening portion range from the
first surface of the core substrate to bent portions (a, b). The
inner walls of the (first-1) opening portion are drawn using broken
line "Z." The inner walls of the (first-2) opening portion range
from bent portions (a, b) to bent portions (c, d). The inner walls
of the reference example overlap the inner walls of the (first-2)
opening portion in the first embodiment (see FIG. 8(B)). The first
opening portion bends toward the inside of the penetrating hole at
the boundary between the (first-1) opening portion and the
(first-2) opening portion. The inner walls of a second opening
portion bend at predetermined spots (e, f). The inner walls of the
(second-1) opening portion range from the second surface of the
core substrate to bent portions (e, f). The inner walls of the
(second-1) opening portion are drawn using broken line "V." The
inner walls of the (second-2) opening portion range from bent
portions (e, f) to bent portions (c, d). The inner walls of the
reference example overlap the inner walls of the (second-2) opening
portion in the first embodiment (see FIG. 8(B)). The second opening
portion bends toward the inside of the penetrating hole at the
boundary between the (second-1) opening portion and the (second-2)
opening portion.
[0039] As shown in FIG. 8(B), if the minimum diameter (Wmin) of a
penetrating hole is the same in the reference example and in the
first embodiment, diameter (W2) of first opening (33A-A) in the
first embodiment is set smaller than diameter (W1) of the first
opening in the reference example; and diameter (W3) of second
opening (33B-B) in the first embodiment is set smaller than
diameter (W4) of the second opening in the reference example. Even
if the minimum diameter of a penetrating hole in the reference
example is the same as the minimum diameter of a penetrating hole
in the first embodiment, diameter (WW) of a penetrating hole in the
first embodiment is set smaller than the diameter of a penetrating
hole in the reference example. The greater of W2 and W3 is set as
diameter (WW) of the penetrating hole. Therefore, in the first
embodiment, the diameter of a through-hole conductor (the diameter
of a penetrating hole) may be set smaller than that of the
reference example. Through-hole conductors may be set at a smaller
pitch in the first embodiment than those in the reference example.
The core substrate may be formed smaller in the first embodiment.
The reliability of through-hole conductors in the first embodiment
is better than the reliability of through-hole conductors in the
reference example.
[0040] When the first embodiment and the reference example are
compared, since the ratio of diameter (WW) of penetrating hole 33
to minimum diameter (Wmin) (Wmin/WW) is greater in the first
embodiment, the reliability of a through-hole conductor is enhanced
against core substrate warping or the like that is caused by
thermal contraction.
[0041] In FIG. 8(C), a penetrating hole of the first embodiment
overlaps a penetrating hole of the reference example. The inner
walls in the reference example are drawn using a broken line, and
the inner walls of the first embodiment are drawn using a solid
line. First opening portion (33A) of the first embodiment is made
up of the (first-1) opening portion and the (first-2) opening
portion, and the inner walls of the first opening portion bend at
predetermined spots. The inner walls of the (first-1) opening
portion are drawn using solid line "Z'." The inner walls of second
opening portion (33B) bend at predetermined spots. The inner walls
of the (second-1) opening portion are drawn using solid line "V'."
As shown in FIG. 8(C), if diameter (W1) of the first opening of a
penetrating hole is the same in the reference example and the first
embodiment, minimum diameter (D1) of a penetrating hole in the
first embodiment is greater than minimum diameter (D2) of a
penetrating hole in the reference example. Namely, in the first
embodiment, since the minimum diameter of a penetrating hole is
enlarged relative to the diameter of the first opening, the first
opening portion and the second opening portion is joined highly
accurately. In addition, since the minimum diameter of a
penetrating hole is enlarged, warping in a printed wiring board is
suppressed. Furthermore, the reliability of the through-hole
conductor filled in a penetrating hole is enhanced.
[0042] FIG. 9 are cross-sectional views obtained by slicing a core
substrate with a plane that includes the first gravity line. The
arrow indicated to the left of the core substrate is axis Z, which
is perpendicular to the first surface of the core substrate. The
plus direction goes upward and the minus direction goes downward.
In FIG. 9(A), the core substrate is made of one material. As shown
in FIG. 9(A), in the first embodiment, first opening portion (33A)
is made up of (first-1) opening portion (33A-1) and (first-2)
opening portion (33A-2); and second opening portion (33B) is made
up of (second-1) opening portion (33B-1) and (second-2) opening
portion (33B-2). A penetrating hole is formed by the first opening
portion and the second opening portion which are joined inside the
core substrate. The (first-1) opening portion is an opening portion
that includes the first opening, and the (first-2) opening portion
is an opening portion that is contiguous to the (first-1) opening
portion in the core substrate. The (second-1) opening portion is an
opening portion that includes the second opening, and the
(second-2) opening portion is an opening portion that is contiguous
to the (second-1) opening portion in the core substrate. The inner
walls of the first opening portion bend in the direction of the
first gravity line at the boundary between the (first-1) opening
portion and the (first-2) opening portion. The inner walls of the
second opening portion bend in the direction of the first gravity
line at the boundary between the (second-1) opening portion and the
(second-2) opening portion. The first opening portion, the
(first-1) opening portion and the (first-2) opening portion become
gradually thinner from the first surface of the core substrate
toward the second surface. When the degree at which the (first-1)
opening portion becomes thinner is (.DELTA.W1), and the degree at
which the (first-2) opening portion becomes thinner is (.DELTA.W2),
(.DELTA.W2) is set greater than (.DELTA.W1). (.DELTA.W1) and
(.DELTA.W2) are the degrees at which the (first-1) opening portion
and the (first-2) opening portion become thinner in the minus
direction along axis Z.
[0043] (H1) in FIG. 9(A) is the inner diameter of (first-1) opening
portion (33A-1), and is the distance between the inner walls facing
each other at predetermined spots in the (first-1) opening portion.
The value of (H1) decreases from the first surface of the core
substrate toward the second surface (the value of (H1) decreases in
the minus direction along axis Z). The amount of change is
(.DELTA.H1). (H2) in FIG. 9(A) is the inner diameter of (first-2)
opening portion (33A-2), and is the distance between the inner
walls facing each other at predetermined spots in the (first-2)
opening portion. The value of (H2) decreases from the first surface
of the core substrate toward the second surface (the value of (H2)
decreases in the minus direction along axis Z). The amount of
change is (.DELTA.H2). (.DELTA.H2) is set greater than
(.DELTA.H1).
[0044] Second opening portion (33B), (second-1) opening portion
(33B-1) and (second-2) opening portion (33B-2) become gradually
thinner from the second surface of the core substrate toward the
first surface. When the degree at which the (second-1) opening
portion becomes thinner is (.DELTA.W3), and the degree at which the
(second-2) opening portion becomes thinner is (.DELTA.W4),
(.DELTA.W4) is set greater than (.DELTA.W3). (.DELTA.W3) and
(.DELTA.W4) are the degrees at which the (second-1) opening portion
and the (second-2) opening portion become thinner in the plus
direction along axis Z.
[0045] (H3) in FIG. 9(A) is the inner diameter of (second-1)
opening portion (33B-1), and is the distance between the inner
walls facing each other at predetermined spots in the (second-1)
opening portion. The value of (H3) decreases from the second
surface of the core substrate toward the first surface (the value
of (H3) decreases in the plus direction along axis Z). The amount
of change is (.DELTA.H3). (H4) in FIG. 9(A) is the inner diameter
of (second-2) opening portion (33B-2), and is the distance between
the inner walls facing each other at predetermined spots in the
(second-2) opening portion. The value of (H4) decreases from the
second surface of the core substrate toward the first surface (the
value of (H4) decreases in the plus direction along axis Z). The
amount of change is (.DELTA.H4). (.DELTA.H4) is set greater than
(.DELTA.H3).
[0046] FIG. 9(B) shows an example in which a core substrate is made
up of an insulative substrate and of resin insulation layers
sandwiching the insulative substrate. A (first-1) opening portion
is an opening that penetrates through a first resin insulation
layer, and a (first-2) opening portion is an opening formed in the
main-surface side of the insulative substrate. The (first-1)
opening portion becomes gradually thinner from the front surface of
the first resin insulation layer toward the back surface with a
degree of (.DELTA.W1). The (first-2) opening portion becomes
gradually thinner from the main surface of the insulative substrate
toward the secondary surface with a degree of (.DELTA.W2).
(.DELTA.W2) is set greater than (.DELTA.W1). (.DELTA.W1) and
(.DELTA.W2) are the degrees at which the (first-1) opening portion
and the (first-2) opening portion become thinner in the minus
direction along axis Z. (H1) in FIG. 9(B) is the inner diameter of
the (first-1) opening portion, and is the distance between the
inner walls facing each other at predetermined spots in the
(first-1) opening portion. The value of (H1) decreases from the
front surface of the first resin insulation layer toward the back
surface (the value of (H1) decreases in the minus direction along
axis Z). (H2) in FIG. 9(B) is the inner diameter of the (first-2)
opening portion, and is the distance between the inner walls facing
each other at predetermined spots in the (first-2) opening portion.
The value of (H2) decreases from the main surface of the insulative
substrate toward the secondary surface (the value of (H2) decreases
in the minus direction along axis Z). A (second-1) opening portion
is an opening that penetrates through a second resin insulation
layer, and a (second-2) opening portion is an opening formed in the
secondary-surface side of the insulative substrate. The (second-1)
opening portion becomes gradually thinner from the lower surface of
the second resin insulation layer toward the upper surface with a
degree of (.DELTA.W3). The (second-2) opening portion becomes
gradually thinner from the secondary surface of the insulative
substrate toward the main surface with a degree of (.DELTA.W4).
(.DELTA.W4) is set greater than (.DELTA.W3). (.DELTA.W3) and
(.DELTA.W4) are the degrees at which the (second-1) opening portion
and the (second-2) opening portion become thinner in the plus
direction along axis Z. (H3) in FIG. 9(B) is the inner diameter of
the (second-1) opening portion, and is the distance between the
inner walls facing each other at predetermined spots in the
(second-1) opening portion. The value of (H3) decreases from the
lower surface of the second resin insulation layer toward the upper
surface (the value of (H3) decreases in the plus direction along
axis Z). The amount of change is (.DELTA.H3). (H4) in FIG. 9(B) is
the inner diameter of the (second-2) opening portion, and is the
distance between the inner walls facing each other at predetermined
spots in the (second-2) opening portion. The value of (H4)
decreases from the secondary surface of the insulative substrate
toward the main surface (the value of (H4) decreases in the plus
direction along axis Z). The amount of change is (.DELTA.H4).
(.DELTA.H4) is set greater than (.DELTA.H3).
[0047] Since the value of (.DELTA.W1) is different from that of
(.DELTA.W2) in the first opening portion, the first opening portion
bends at the boundary between the (first-1) opening portion and the
(first-2) opening portion. In the same manner, since the value of
(.DELTA.W3) is different from that of (.DELTA.W4) in the second
opening portion, the second opening portion bends at the boundary
between the (second-1) opening portion and the (second-2) opening
portion.
[0048] Since the value of (.DELTA.H1) is different from that of
(.DELTA.H2) in the first opening portion, the first opening portion
bends at the boundary between the (first-1) opening portion and the
(first-2) opening portion. In the same manner, since the value of
(.DELTA.H3) is different from that of (.DELTA.H4) in the second
opening portion, the second opening portion bends at the boundary
between the (second-1) opening portion and the (second-2) opening
portion.
[0049] When forming opening portions under the same conditions
using a laser in an insulative substrate and resin insulation
layers that form a core substrate, forming opening portions in
resin insulation layers is preferred to be carried out more easily
than forming opening portions in the insulative substrate. A first
opening portion and a second opening portion with bent portions may
be formed more easily than a core substrate that is formed with one
material (FIG. 9(A)).
[0050] FIG. 10 show through-hole conductors obtained by filling
conductor in penetrating holes in the first embodiment and the
reference example (FIGS. 8, 9). FIG. 10(A) shows through-hole
conductor 360 of the reference example, and FIGS. 10(B) and 10(E)
show through-hole conductors of the first embodiment. In FIGS.
10(B) and 10(E), a first gravity line and a second gravity line are
offset. A core substrate in FIG. 10(B) is made up of an insulative
substrate and of a first resin insulation layer and a second resin
insulation layer sandwiching the insulative substrate. A core
substrate in FIG. 10(E) is made of one material. As a conductor for
filling a penetrating hole, plated-metal film and conductive paste
may be used. As for such plated metal film, electrolytic plated
film and electroless plated film may be listed. As for such a
through-hole conductor, a metal made of a seed layer formed on the
inner walls of a penetrating hole and of an electrolytic plated
film on the seed layer is preferred. Such electrolytic plated film
fills the penetrating hole. As for a seed layer, sputtered film and
electroless plated film may be listed. Through-hole conductor 36 of
the first embodiment is made of conductors filled in a (first-1)
opening portion, a (first-2) opening portion, a (second-1) opening
portion and a (second-2) opening portion. The conductor filled in
the (first-1) opening portion becomes thinner from the first
surface of the core substrate toward the second surface with a
degree of (M). The conductor filled in the (first-2) opening
portion becomes thinner from the first surface of the core
substrate toward the second surface with a degree of (.delta.2).
Since the value of (.delta.1) is different from that of (.delta.2),
the through-hole conductor bends in the core substrate.
Accordingly, the through-hole conductor in the first opening
portion contains bent portion (36d). The conductor filled in the
(second-1) opening portion becomes thinner from the second surface
of the core substrate toward the first surface with a degree of
(.delta.4). The conductor filled in the (second-2) opening portion
becomes thinner from the second surface of the core substrate
toward the first surface with a degree of (.delta.3). Since the
value of (.delta.3) is different from that of (.delta.4), the
through-hole conductor bends in the core substrate. Accordingly,
the through-hole conductor in the second opening portion contains
bent portion (36e). If a core substrate is made of an insulative
substrate and of a first resin insulation layer and a second resin
insulation layer sandwiching the insulative substrate, bent portion
(36d) is positioned at the interface of the first resin insulation
layer and the insulative substrate, and bent portion (36e) is
positioned at the interface of the second resin insulation layer
and the insulative substrate. Furthermore, the through-hole
conductor of the first embodiment contains bent portion (36f) at
the junction of the first opening portion and the second opening
portion. By contrast, the reference example has neither a (first-2)
opening portion nor a (second-2) opening portion. Thus, a
through-hole conductor of the reference example contains a bent
portion at the junction of a first opening portion and a second
opening portion, but does not contain a bent portion at the
boundary between a (first-1) opening portion and a (first-2)
opening portion or at the boundary between a (second-1) opening
portion and a (second-2) opening portion. FIGS. 10(C), (D) and (F)
show portions where through-hole conductors bend. Circled portions
are bent portions. FIG. 10(C) shows through-hole conductor 360 of
the reference example, and FIGS. 10(D) and (F) are through-hole
conductors 36 of the first embodiment. When a core substrate is
warped, it is thought that stresses tend to concentrate in bent
portions. If the reference example and the first embodiment are
compared in cross-sectional views, the number of bent portions of a
through-hole conductor in the reference example is two, whereas the
number of bent portions of a through-hole conductor of the first
embodiment is six. A through-hole conductor of the first embodiment
contains more bent portions than a through-hole conductor of the
reference example. Therefore, when the first embodiment and the
reference example are compared, it is thought that stresses on a
through-hole conductor are dispersed to more portions in the first
embodiment than in the reference example. Accordingly, it is
thought that a through-hole conductor of the first embodiment has
higher reliability than a through-hole conductor of the reference
example. When FIGS. 10(D) and 10(F) are compared, strengths in
resin insulation layers and an insulative substrate may be modified
in FIG. 10(D). When comparing the degree at which a through-hole
conductor bends at the boundary between a (first-1) opening portion
and a (first-2) opening portion, and the degree at which a
through-hole conductor bends at the junction of a first opening
portion and a second opening portion, the latter is greater. The
through-hole conductor tends to be damaged at the junction of the
first opening portion and the second opening portion. However,
since deformation of an insulative substrate is reduced by setting
the strength of the insulative substrate higher than the strength
of resin insulation layers, stresses that concentrate in the
junction of the first opening portion and the second opening
portion decrease. From such a point of view, it is preferred that a
core substrate be made of an insulative substrate and of a first
resin insulation layer and a second resin insulation layer
sandwiching the insulative substrate, and that the strength of the
insulative substrate be set greater than the strength of the first
and second resin insulation layers. Accordingly, a through-hole
conductor of the first embodiment is thought to have higher
tolerance against stresses generated in a warped core substrate or
the like than that of the reference example.
[0051] If a core substrate is made up of an insulative substrate
and of a first resin insulation layer and a second resin insulation
layer sandwiching the insulative substrate, an ingredient that
dissolves in a chemical may be contained in first resin insulation
layer (32A) and second resin insulation layer (32B). By dissolving
the soluble ingredient on the surfaces of resin insulation layers
using a chemical, the surfaces of resin insulation layers may be
roughened. By forming roughened surfaces (32.alpha.) on the
surfaces of core substrate 30, first and second circuits may be
formed on the first and second surfaces of core substrate 30 using
an additive method. Since circuits may be formed on the core
substrate using an additive method and not using a subtractive
method, the width of circuits or the distance between circuits may
be set smaller on the core substrate. Accordingly, the number of
built-up layers on the core substrate is reduced.
[0052] In the following, a method for manufacturing multilayer
printed wiring board 10 is described with reference to FIGS.
1-5.
[0053] (1) Insulative substrate 31 made of reinforcing material and
resin is prepared (FIG. 1(A)). The thickness of insulative
substrate 31 is set at 0.2-0.8 mm. Glass cloth, aramid fiber and
glass fiber may be listed as a reinforcing material. Glass cloth is
preferred as a reinforcing material from a viewpoint of strength.
Epoxy resin and BT (bismaleimide triazine) resin may be listed as a
resin. Hydroxide particles may be dispersed in a resin. As for
hydroxides, metal hydroxides such as Al(OH)3, Mg(OH)2, Ca(OH)2,
Ba(OH)2 and the like are preferred. The thermal expansion
coefficient may be set smaller in the insulative substrate. When
forming a (first-2) opening portion and a (second-2) opening
portion in the insulative substrate using a laser, values in
(.DELTA.W2) and (.DELTA.W4) may be set greater. Hydroxides are
disintegrated by heat, producing water. Thus, it is thought that
hydroxides may rob heat from the material that forms an insulative
substrate. Namely, if an insulative substrate contains a hydroxide,
it is thought that the insulative substrate is hard to process by a
laser. Forming a first opening portion made up of a (first-1)
opening portion and a (first-2) opening portion as well as forming
a second opening portion made up of a (second-1) opening portion
and a (second-2) opening portion become easier. When forming
opening portions using a CO.sub.2 laser, the insulative substrate
is preferred to contain a hydroxide.
[0054] On main surface (31A) and secondary surface (31B) of
insulative substrate 31, resin film for resin insulation layers 32
(brand name: ABF-45SH, made by Ajinomoto) is laminated. A core
substrate made of an insulative substrate and resin insulation
layers is obtained through thermal pressing (FIG. 1(B)). The core
substrate has first surface (30A) and second surface (30B) opposite
the first surface. A resin insulation layer formed on the main
surface of insulative substrate 31 is first resin insulation layer
(32A). The first resin insulation layer has a front surface and a
back surface opposite the front surface. The back surface faces the
main surface. A resin insulation layer formed under the secondary
surface of insulative substrate 31 is second resin insulation layer
(32B). The second resin insulation layer has an upper surface and a
lower surface opposite the upper surface. The secondary surface
faces the upper surface. Resin film for resin insulation layers
contains an ingredient which dissolves in a chemical agent and
inorganic particles for adjusting thermal expansion coefficients.
The material for the first resin insulation layer and the second
resin insulation layer may be the same as the material for the
insulative substrate. However, the first and second resin
insulation layers are preferred not to contain a reinforcing
material, and the insulative substrate is preferred to contain a
reinforcing material. The values of (.DELTA.W1) and (.DELTA.W2) may
be modified easily. The values of (.DELTA.W3) and (.DELTA.W4) may
be modified easily. The values of (.DELTA.H 1) and (.DELTA.H2) may
be modified easily. The values of (.DELTA.H3) and (.DELTA.H4) may
be modified easily.
[0055] (2) Using a CO.sub.2 gas laser, by irradiating a laser from
first surface (30A) of core substrate 30, first opening portion
(33A) is formed in the first-surface side of the core substrate
(FIG. 1(C)).
[0056] (3) Using a CO.sub.2 gas laser, by irradiating a laser from
second surface (30B) of core substrate 30, second opening portion
(33B) is formed in the second-surface side of the core substrate.
Penetrating hole 33 is formed by the first opening portion and the
second opening portion, which are joined in insulative substrate 31
(FIG. 1(D)).
[0057] FIGS. 11 and 14 show magnified views of penetrating hole 33
in FIG. 1(D). In FIG. 11, a core substrate is made of resin
insulation layers and an insulative substrate. The resin insulation
layers and insulative substrate may be formed with the same
material or different materials. Different materials are preferred.
In FIG. 14, a core substrate is made of either one insulative
substrate or one resin insulation layer. FIG. 11(A) and FIG. 14(A)
show examples where the first, second, third and fourth gravity
lines overlap each other. FIG. 11(B) and FIG. 14(B) show examples
where the first and third gravity lines overlap each other and the
second and fourth gravity lines overlap each other, but the first
gravity line and the second gravity line are offset from each
other. FIG. 11(C) and FIG. 14(C) show examples where the second and
fourth gravity lines overlap each other, but the first, second and
third gravity lines are offset from each other. FIG. 11(D) and FIG.
14(D) show examples where the first, second, third and fourth
gravity lines are offset from each other. The first opening portion
becomes thinner from the first surface of the core substrate toward
the second surface. In FIG. 11, the inner walls of the first
opening portion bend toward the inside of the first opening portion
at the interface of the insulative substrate and the first resin
insulation layer. The second opening portion becomes thinner from
the second surface of the core substrate toward the first surface.
The inner walls of the second opening portions bend toward the
inside of the opening portion at the interface of the insulative
substrate and the second resin insulation layer. The degree at
which the diameter of first opening portion (33A) decreases is set
greater in insulative substrate 31 than in the first resin
insulation layer. In the same manner, the degree at which the
diameter of second opening portion (33B) decreases is set greater
in insulative substrate 31 than in the second resin insulation
layer.
[0058] The first opening portion becomes thinner from the first
surface of the core substrate toward the second surface. In FIG.
14, the inner walls of the first opening portion bend toward the
inside of the first opening portion at the boundary between the
(first-1) opening portion and the (first-2) opening portion. The
second opening portion becomes thinner from the second surface of
the core substrate toward the first surface. The inner walls of the
second opening portion bend toward the inside of the second opening
portion at the boundary between the (second-1) opening portion and
the (second-2) opening portion. The degree at which the diameter of
first opening portion (33A) decreases is set greater in the
(first-2) opening portion than in the (first-1) opening portion. In
the same manner, the degree at which the diameter of second opening
portion (33B) decreases is set greater in the (second-2) opening
portion than in the (second-1) opening portion.
[0059] In the following, a method for forming penetrating holes
shown in FIGS. 11 and 14 is shown.
[0060] Penetrating holes shown in FIGS. 11 and 14 may be formed by
a processing method as follows. If a first opening portion and a
second opening portion are formed by laser irradiations having
multiple pulses, the laser intensity is set lower after a
predetermined number of pulses. For example, if a first opening
portion and a second opening portion are formed by two-pulse laser
irradiations, the laser intensity of the second pulse is set lower
than the laser intensity of the first pulse. Openings to be formed
by the first pulse are a (first-1) opening portion and a (second-1)
opening portion; openings to be formed by the second pulse are a
(first-2) opening portion and a (second-2) opening portion. In
doing so, openings to be formed by the first pulse may be formed
differently from openings to be formed by the second pulse. Since
the second pulse has weaker energy than the first pulse, the first
opening portion bends inward at the boundary between the (first-1)
opening portion and the (first-2) opening portion. In the same
manner, the second opening portion bends inward at the boundary
between the (second-1) opening portion and the (second-2) opening
portion. Positions of gravity lines are modified by adjusting
positions to be irradiated by a laser. More detailed descriptions
will be provided in the following.
[0061] Other examples are shown in the following. If a core
substrate is made of an insulative substrate which is hard to
process by a laser and of resin insulation layers sandwiching the
insulative substrate which are easy to process by a laser,
penetrating holes shown in FIG. 11 may be formed. In such examples,
when processing resin insulation layers and an insulative substrate
using the same laser intensity, the amount to be processed is
different in the resin insulation layers and the insulative
substrate. The amount to be processed is greater in resin
insulation layers than in the insulative substrate. In doing so,
openings formed in resin insulation layers may be formed
differently from openings formed in the insulative substrate.
Openings formed in resin insulation layers are a (first-1) opening
portion and a (second-1) opening portion, and openings formed in
the insulative substrate are a (first-2) opening portion and a
(second-2) opening portion. Since the insulative substrate is
harder to process by a laser than the resin insulation layers are,
the first opening portion bends inward at the boundary between the
(first-1) opening portion and the (first-2) opening portion. In the
same manner, the second opening portion bends inward at the
boundary between the (second-1) opening portion and the (second-2)
opening portion. In such situations, boundaries are positioned most
likely at interfaces of the resin insulation layers and the
insulative substrate. However, positions for the first opening
portion and the second opening portion to bend may be in the
insulative substrate, because the same effects as above are
achieved. Combination examples of an insulative substrate and resin
insulation layers will be listed in the following. An insulative
substrate is made of reinforcing material and resin, and resin
insulation layers are made of inorganic particles and resin. Since
the insulative substrate contains reinforcing material, the
insulative substrate is harder to process by a laser than resin
insulation layers are. Positions where the first opening portion
and the second opening portion bend are preferred to be between an
interface of a resin insulation layer and the insulative substrate
and a reinforcing material in the insulative substrate, including
an example where opening portions bend in the reinforcing material
(see FIG. 12(C)). Another example may be such that resin insulation
layers contain oxide particles and an insulative substrate contains
hydroxide particles. Since the insulative substrate contains
hydroxide particles, the insulative substrate is harder to process
by a laser than resin insulation layers are. As for oxide
particles, alumina, silica, barium oxide or the like may be
listed.
[0062] The insulative substrate is made of resin and reinforcing
material, and resin insulation layers are made of inorganic
particles and resin without reinforcing material. In such an
example, penetrating holes shown in FIG. 11 are obtained as well.
Moreover, it is preferred that the insulative substrate contain
hydroxide particles and that the resin insulation layers not
contain hydroxide particles.
[0063] Penetrating holes shown in FIG. 11(A) and FIG. 14(A) may be
formed by the following method (method example 1). A first-pulse
laser is irradiated in a predetermined spot on the first surface of
a core substrate. Such a position is set as spot (M). A
second-pulse laser is irradiated on the same spot. The first laser
pulse has greater energy than the second laser pulse. Accordingly,
a first opening portion is formed with a (first-1) opening portion
and a (first-2) opening portion. Next, a first-pulse laser is
irradiated on the second surface of the core substrate. The laser
position for a first pulse (spot (N)) is located opposite spot (M).
Namely, the laser position for a first pulse (spot (N)) is a point
where a straight line passing through spot (M) and perpendicular to
the first surface of the core substrate intersects the second
surface of the core substrate. A second-pulse laser is irradiated
at the same spot. The first laser pulse has greater energy than the
second laser pulse. The penetrating holes shown in FIG. 11(A) and
FIG. 14(A) are formed by joining the first opening portion and the
second opening portion. Core substrates which can employ the above
method are: core substrate 400 made of resin and inorganic
particles; core substrate 400 made of resin and reinforcing
material; core substrate 400 made of inorganic particles, resin and
reinforcing material; core substrate 400 made of hydroxide
particles, resin and reinforcing material; and core substrate 30
made of an insulative substrate and resin insulation layers
sandwiching the insulative substrate. If openings are formed under
the same conditions by a laser in an insulative substrate and resin
insulation layers, forming openings in resin insulation layers is
easier than forming openings in the insulative substrate.
[0064] A penetrating hole shown in FIG. 11(B) may be formed as
follows (method example 2). A core substrate shown in FIG. 11(B) is
formed with an insulative substrate which is made of reinforcing
material, metal hydroxide and resin, and with resin insulation
layers sandwiching the insulative substrate which are made of
inorganic particles and resin. A laser is irradiated at a
predetermined position (spot (O)) on the first surface of the core
substrate to form first opening portion (33A) made up of a
(first-1) opening portion and a (first-2) opening portion (FIG.
15(A)). Next, a laser is irradiated at a predetermined position
(spot (P)) on the second surface of the core substrate to form
second opening portion (33B) made up of a (second-1) opening
portion and a (second-2) opening portion (FIG. 15(B)). Spot (O) and
spot (P) do not face each other. Namely, spot (P) is located at a
predetermined distance from the point where a straight line passing
through spot (O) and perpendicular to the first surface of the core
substrate intersects the second surface of the core substrate.
Accordingly, a penetrating hole shown in FIG. 11(B) is formed by
the first opening portion and the second opening portion joined in
the insulative substrate.
[0065] Penetrating holes shown in FIG. 11(C) and FIG. 14(C) may be
formed by modifying method example 1 (method example 3). By
shifting the laser position for a first pulse and the laser
position for a second pulse (spot (Q)) to be irradiated on the
first surface of a core substrate in method example 1, penetrating
holes shown in FIG. 11(C) and FIG. 14(C) are formed. A penetrating
hole shown in FIG. 11(C) is obtained by joining a first opening
portion and a second opening portion. At that time, the diameter of
the second-pulse laser is preferred to be set smaller than the
diameter of the first-pulse laser.
[0066] A penetrating hole in FIG. 11(C) may be formed by modifying
method example 2 (method example 4). The number of laser pulses to
be irradiated on the first surface of a core substrate in method
example 2 is multiple, the same as in method example 1. By shifting
the laser position for a first pulse (spot (O)) and the laser
position for a second pulse (spot (S)) on the first surface of the
core substrate (FIG. 15(C)), the penetrating hole shown in FIG.
11(C) is obtained. The penetrating hole shown in FIG. 11(C) is
obtained by joining a first opening portion and a second opening
portion in the insulative substrate. At that time, the diameter of
the second-pulse laser is preferred to be set smaller than the
diameter of the first-pulse laser.
[0067] The penetrating holes in FIG. 11(D) and FIG. 14(D) may be
formed by modifying method example 3 (method example 5). In method
example 5, the laser position for a second pulse (spot (R)) to be
irradiated on the second surface of a core substrate is located at
a predetermined distance from the laser position for a first pulse.
The penetrating holes shown in FIG. 11(D) and FIG. 14(D) are
obtained by joining a first opening portion and a second opening
portion. At that time, the diameter of the second-pulse laser is
preferred to be set smaller than the diameter of the first-pulse
laser. The following does not overlap each other: a straight line
(straight line M) passing through spot (M) and perpendicular to the
first surface of the core substrate; a straight line (straight line
N) passing through spot (N) and perpendicular to the first surface
of the core substrate; a straight line (straight line Q) passing
through spot (Q) and perpendicular to the first surface of the core
substrate; and a straight line (straight line R) passing through
spot (R) and perpendicular to the first surface of the core
substrate (FIG. 15(D)).
[0068] A penetrating hole in FIG. 11(D) may be formed by modifying
method example 4 (method example 6). In method example 6, the
number of laser pulses to be irradiated on the second surface of a
core substrate is multiple. The laser position (spot (R)) for a
second pulse to be irradiated on the second surface of the core
substrate is located at a predetermined distance from the laser
position for a first pulse. At that time, the diameter of the
second pulse is preferred to be set smaller than the diameter of
the first pulse. The penetrating hole in FIG. 11(D) is obtained by
joining the first opening portion and the second opening portion.
The following does not overlap each other: a straight line
(straight line O) passing through spot (O) and perpendicular to the
first surface of the core substrate; a straight line (straight line
P) passing through spot (P) and perpendicular to the first surface
of the core substrate; a straight line (straight line S) passing
through spot (S) and perpendicular to the first surface of the core
substrate; and a straight line (straight line R) passing through
spot (R) and perpendicular to the first surface of the core
substrate.
[0069] In any of the method examples, it is preferable to irradiate
a laser having energy intensities shown in FIG. 12(A) and (B). The
lengths in the drawing schematically indicate laser intensity. The
intensity is greater in the center than on the periphery. Laser
intensity decreases from the center toward the periphery either
exponentially or in a straight line.
[0070] When the laser irradiation position to form a (first-1)
opening portion and the laser irradiation position to form a
(first-2) opening portion are located at a predetermined distance
from each other for offsetting the first gravity line and the third
gravity line, the laser diameter for forming the (first-1) opening
portion is preferred to be set greater than the laser diameter for
forming the (first-2) opening portion.
[0071] When the laser irradiation position to form a (second-1)
opening portion and the laser irradiation position to form a
(second-2) opening portion are located at a predetermined distance
from each other for offsetting the second gravity line and the
fourth gravity line, the laser diameter for forming the (second-1)
opening portion is preferred to be set greater than the laser
diameter for forming the (second-2) opening portion.
[0072] (4) Core substrate 30 with penetrating hole 33 is immersed
for 10 minutes in an 80.degree. C. solution containing 60 g/L
permanganic acid. Roughened surfaces (32.alpha.) are formed on the
surfaces of resin insulation layers 32 (FIG. 1(E)). The first
surface and the second surface of the core substrate are
roughened.
[0073] (5) Palladium catalyst (made by Atotech) is attached to the
surfaces of core substrate 30. After that, the core substrate is
immersed in an electroless plating solution. Electroless plated
film 23 is formed on the first and second surfaces of the core
substrate and on the inner walls of the penetrating hole (see FIG.
2(A)). As for such electroless plated film, electroless
copper-plated film and electroless nickel-plated film may be
listed. The thickness is 0.2 .mu.m-0.6 .mu.m. Plating resist 25 is
formed on electroless plated film 23 (FIG. 2(B)). Using electroless
plated film as a seed layer, electrolytic plated film is formed on
the electroless plated film left exposed by the plating resist.
Penetrating hole 33 is filled with electrolytic plated film 24
(FIG. 2(C)). Instead of electroless plated film, sputtered film may
be formed on the inner walls of penetrating hole 33 and on the
surfaces of the core substrate.
[0074] (6) Plating resist is removed. The electroless plated film
exposed by removing the plating resists is etched away. First
circuit (34A) is formed on the first surface of the core substrate.
Second circuit (34B) is formed on the second surface of the core
substrate (see FIG. 3(A)). Printed wiring board 1000 is completed.
The first circuit has first conductive circuit (34AC) and first
through-hole land (first land) (34AL). The first conductive circuit
is a circuit that is formed on the first surface of the core
substrate, and first through-hole land (34AL) is formed with a
circuit covering a through-hole conductor and a circuit formed on
the first surface of the core substrate surrounding the
through-hole conductor. The second circuit has second conductive
circuit (34BC) and second through-hole land (second land) (34BL).
Second conductive circuit (34BC) is a circuit that is formed on the
second surface of the core substrate, and second through-hole land
(34BL) is formed with a circuit covering a through-hole conductor
and a circuit formed on the second surface of the core substrate
surrounding the through-hole conductor.
[0075] In the above example, a core substrate is formed with resin
insulation layers and an insulative substrate. However, the core
substrate may be formed only with an insulative substrate or a
resin insulation layer. The manufacturing method is simplified.
Instead of the above method (FIGS. 1 through 3(A)), another method
for manufacturing a printed wiring board is shown in FIG. 13. In
that example, one insulative substrate or one resin insulation
layer is a starting material (FIG. 13(A)). Copper foils 401 are
laminated on single insulative substrate (400A) or single resin
insulation layer (400A) (FIG. 13(B)). A laser is irradiated on
first surface (30A) of the single insulative substrate or the
single resin insulation layer. First opening portion (33A) is
formed in the first-surface side of the single insulative substrate
or the single resin insulation layer (FIG. 13(C)). A laser is
irradiated on second surface (30B) of the single insulative
substrate or the single resin insulation layer. Second opening
portion (33B) is formed in the second-surface side of the single
insulative substrate or the single resin insulation layer.
Penetrating hole 33 is formed by first opening portion (33A) and
second opening portion (33B), which are joined in the single
insulative substrate or the single resin insulation layer (FIG.
13(D)). A core substrate with a penetrating hole is completed. The
penetrating hole may be formed by any of the above methods. Seed
layer 323 is formed on the surfaces of the core substrate and on
the inner walls of the penetrating hole by electroless plating or
the like. Electrolytic plated film 324 is formed on seed layer 323.
Penetrating hole 33 is filled with electrolytic plated film 324
(FIG. 13(E)). By forming conductive circuits (34AC, 34BC) and lands
(34AL, 34BL) on the core substrate by etching, printed wiring board
1000 is completed (FIG. 13(F)).
[0076] (9) Next, roughened layers (34.beta.) are formed on the
surfaces of first and second circuits (34A, 34B) (FIG. 3(B)).
[0077] (10) On both surfaces of core substrate 30 having circuits,
resin film for interlayer resin insulation layers (brand name:
ABF-45SH, made by Ajinomoto) is laminated. By curing the film,
interlayer resin insulation layers (50A, 50B) are formed on both
surfaces of the core substrate (FIG. 3(C)).
[0078] (11) Via-conductor openings 51 reaching conductive circuits
or through-hole lands are formed in interlayer resin insulation
layers (50A, 50B) using a CO.sub.2 gas laser (FIG. 3(D)).
[0079] (12) The substrate with via-conductor openings 51 is
immersed for 10 minutes in an 80.degree. C. solution containing 60
g/L permanganic acid. Roughened surfaces (50.alpha.) are formed on
the surfaces of interlayer resin insulation layers (50A, 50B)
including the inner walls of via-conductor openings 51 (FIG. 4(A)).
By immersing the substrate in a catalyst solution, catalyst nuclei
are attached on the surfaces of interlayer resin insulation layers
and on the inner-wall surfaces of via-conductor openings.
[0080] (13) Next, by immersing the substrate in an electroless
copper plating solution (Thru-Cup PEA) made by C. Uyemura Co.,
Ltd., electroless copper-plated film 52 is formed on the surfaces
of interlayer resin insulation layers (50A, 50B) including the
inner walls of via-conductor openings 51 (FIG. 4(B)).
[0081] (14) Plating resist 54 is formed on electroless
copper-plated film 52. Electrolytic copper-plated film 56 is formed
on the electroless plated film left exposed by plating resist 54
(FIG. 4(C)).
[0082] (15) Plating resist 54 is removed. By removing the
electroless plated film between portions of electrolytic
copper-plated film through etching, independent conductive circuits
(58A, 58B) and via conductors (60A, 60B) are formed (FIG. 4(D)).
Multilayer wiring board 300 is obtained.
[0083] (16) Roughened layers (58.alpha.) are formed on the surfaces
of conductive circuits (58A, 58B) and via conductors (60A, 60B)
(FIG. 5(A)).
[0084] (18) Next, solder-resist layers (70A, 70B) with openings
(71A, 71B) are formed on both surfaces of multilayer wiring board
300 (FIG. 5(B)). Top surfaces of conductive circuits (58A, 58B) and
via conductors (60A, 60B) are exposed through openings (71A, 71B).
Top surfaces of conductive circuits (58A, 58B) and via conductors
(60A, 60B) exposed through openings (71A, 71B) function as solder
pads (72A, 72B).
[0085] (19) A nickel-plated layer is formed on solder pads, and a
gold-plated layer is formed on the nickel-plated layer (FIG. 5(C)).
Instead of nickel-gold layers, nickel-palladium-gold layers may
also be formed on solder pads.
[0086] (21) After that, solder balls are loaded on opening portions
(71A, 71B) in the solder-resist layers, and reflowed at 230.degree.
C. Accordingly, solder bumps (78A, 78B) are formed on solder pads
(FIG. 6).
First Example
[0087] (1) Insulative substrate 31 made of glass cloth, epoxy resin
and magnesium hydroxide is prepared (FIG. 1(A)). The thickness of
insulative substrate 31 is 0.2 mm. Insulative substrate 31 has main
surface (31A) and secondary surface (31B) opposite the main
surface. Resin film for resin insulation layers 32 (brand name:
ABF-45SH, made by Ajinomoto) is laminated on both surfaces of the
insulative substrate. By thermal pressing the film, a core
substrate formed with an insulative substrate and resin insulation
layers is obtained (FIG. 1(B)). Resin insulation layers contain
ingredients that dissolve in a KMnO4 solution and silica for
adjusting thermal expansion coefficients. The first resin
insulation layer and the second resin insulation layer do not
contain reinforcing material.
[0088] (2) A CO.sub.2 gas laser is irradiated at a predetermined
position (spot 1) on first surface (30A) of core substrate 30. The
number of laser pulses to be irradiated is four. First opening
portion (33A) made up of a (first-1) opening portion and a
(first-2) opening portion is formed in the first-surface side of
the core substrate (FIG. 1(C)). The (first-1) opening portion is an
opening portion formed in the first resin insulation layer, and the
(first-2) opening portion is an opening portion formed in the
insulative substrate. Since first resin insulation layer (32A)
tends to be processed by a laser more easily than insulative
substrate 31, the first opening portion bends inward at the
boundary between the (first-1) opening portion and the (first-2)
opening portion. The bent positions are located substantially at
the interface of first resin insulation layer (32A) and insulative
substrate 31.
[0089] (3) A CO.sub.2 gas laser is irradiated at a predetermined
position (spot 2) on second surface (30B) of core substrate 30.
Spot 2 is where a straight line passing through spot 1 and
perpendicular to the first surface of the core substrate intersects
the second surface of the core substrate. The first gravity line
overlaps the second gravity line. The number of laser pulses is
four. Second opening portion (33B) made up of a (second-1) opening
portion and a (second-2) opening portion is formed in the
second-surface side of the core substrate (FIG. 1(D)). A
penetrating hole is formed by joining the first opening portion and
the second opening portion. The (second-1) opening portion is an
opening portion formed in the second resin insulation layer and the
(second-2) opening portion is an opening portion formed in the
insulative substrate. Since second resin insulation layer (32B)
tends to be processed by a laser more easily than insulative
substrate 31, the second opening portion bends inward at the
boundary between the (second-1) opening portion and the (second-2)
opening portion. The bent positions are located substantially at
the interface of second resin insulation layer (32B) and insulative
substrate 31. A penetrating hole shown in FIG. 11(A) is formed.
[0090] (4) Core substrate 30 with penetrating hole 33 is immersed
for 10 minutes in an 80.degree. C. solution containing 60 g/L
permanganic acid. Roughened surfaces (32.alpha.) are formed on the
surfaces of resin insulation layers 32 (FIG. 1(E)). The first
surface and the second surface of the core substrate are
roughened.
[0091] (5) A palladium catalyst (made by Atotech) is attached to
the surfaces of core substrate 30. Then, the core substrate is
immersed in an electroless copper-plating solution (made by C.
Uyemura Co., Ltd.). Electroless copper-plated film 23 is formed on
the first and second surfaces of the core substrate and on the
inner walls of the penetrating hole (see FIG. 2(A)). The thickness
of the electroless copper-plated film is 0.4 .mu.m. Plating resist
25 is formed on electroless plated film 23 (FIG. 2(B)).
Electrolytic copper-plated film 24 is formed on the electroless
plated film left exposed by plating resist 25 using electroless
plated film 23 as a seed layer. Penetrating hole 33 is filled with
electrolytic copper-plated film 24 (FIG. 2(C)).
[0092] (6) The plating resist is removed. Electroless copper-plated
film exposed by removing the etching resist is etched away. First
conductive circuit (34AC) and first through-hole land (34AL) are
formed on the first surface of the core substrate, and second
conductive circuit (34BC) and second through-hole land (34BL) are
formed on the second surface of the core substrate. Simultaneously,
through-hole conductor 36 is formed, connecting the first and
second conductive circuits (see FIG. 3(A)). The thickness of
electrolytic copper-plated film is substantially 15 .mu.m. Printed
wiring board 1000 of the first example is completed.
Second Example
[0093] (1) Prepreg 400 made of glass cloth and epoxy resin is
prepared (FIG. 13(A)). On both surfaces of the prepreg, 12
.mu.m-thick copper foil 401 is laminated. By thermal pressing, the
prepreg is cured, and core substrate 30 having copper foil is
obtained (FIG. 13(B)).
[0094] (2) A CO.sub.2 gas laser is irradiated at a predetermined
position (spot 10) on first surface (30A) of core substrate 30. The
number of laser pulses to be irradiated is four. The laser
intensity for the first pulse is set equal to that for the second
pulse, and the laser intensity for the third pulse is set equal to
that for the fourth pulse. The laser intensity for the first pulse
is set higher than the laser intensity for the third pulse. The
irradiation position (spot 10) is the same for all pulses. First
opening portion (33A) made up of (first-1) opening portion (33A-1)
and (first-2) opening portion (33A-2) is formed in the
first-surface side of the core substrate (FIG. 13(C)). Since the
laser intensity is set lower on and after the third pulse, first
opening portion (33A) bends inward at the boundary between
(first-1) opening portion (33A-1) and (first-2) opening portion
(33A-2).
[0095] A CO.sub.2 gas laser is irradiated at a predetermined
position (spot 11) on second surface (30B) of core substrate 30.
The number of laser pulses to be irradiated is four. The laser
intensity for the first pulse is set equal to that for the second
pulse, and the laser intensity for the third pulse is set equal to
that for the fourth pulse. The laser intensity for the first pulse
is set greater than the laser intensity for the third pulse. The
irradiation position (spot 11) is the same for all pulses. Second
opening portion (33B) made up of (second-1) opening portion (33B-1)
and (second-2) opening portion (33B-2) is formed in the
second-surface side of the core substrate. Penetrating hole 33 made
up of the first opening portion and the second opening portion is
formed (FIG. 13(D)). The point where a straight line passing
through spot 10 and perpendicular to the first surface of the core
substrate intersects the second surface of the core substrate is
located at a predetermined distance from spot 11. Since the laser
intensity is set lower on and after the third pulse, the second
opening portion bends inward at the boundary between the (second-1)
opening portion and the (second-2) opening portion. Penetrating
hole 33 is formed as shown in FIG. 14(B).
[0096] Copper film 323 is formed by sputtering on the first and
second surfaces of the core substrate and on the inner walls of the
penetrating hole. Using copper film 323 as a seed layer,
electrolytic copper-plated film 324 is formed on the first and
second surfaces of the core substrate. Simultaneously, penetrating
hole 33 is filled with electrolytic copper-plated film 324 (FIG.
13(E)). Etching resist is formed on the electrolytic copper-plated
film. The electrolytic copper-plated film, copper film and copper
foil left exposed by the etching resist are etched away.
[0097] First conductive circuit (34AC) and first through-hole land
(34AL) are formed on the first surface of the core substrate, and
second conductive circuit (34BC) and second through-hole land
(34BL) are formed on the second surface of the core substrate.
Simultaneously, through-hole conductor 36 is formed, connecting the
first and second conductive circuits. The thickness of the
electrolytic copper-plated film is substantially 15 .mu.m. Printed
wiring board 1000 of the second example is completed (FIG.
13(F)).
Third Example
[0098] The method for manufacturing a printed wiring board
according to the third example is a modified example of the first
example.
[0099] The method for forming a core substrate of the third example
is the same as in the first example. First and second laser pulses
are irradiated at a predetermined position (spot 10) on the first
surface of the core substrate. Then, third and fourth laser pulses
are irradiated at a position (spot 100) which is located at a
predetermined distance from spot 10. The laser intensity for the
first pulse is set equal to that for the second pulse, and the
laser intensity for the third pulse is set equal to that for the
fourth pulse. The laser intensity for the first pulse is set
greater than the laser intensity for the third pulse. The diameter
of the first laser pulse is equal to that of the second laser
pulse, and the diameter of the third laser pulse is equal to that
of the fourth laser pulse. The diameter of the first laser pulse is
set greater than that of the third laser pulse.
[0100] First through fourth laser pulses are irradiated at a
predetermined position (spot 20) on the second surface of the core
substrate. A point (point of intersection 1) where a straight line
passing through spot 10 and perpendicular to the first surface of
the core substrate intersects the second surface of the core
substrate is located at a predetermined distance from spot 20. In
addition, point (point of intersection 2) where a straight line
passing through spot 100 and perpendicular to the first surface of
the core substrate intersects the second surface of the core
substrate is located at a predetermined distance from spot 20.
Point of intersection 1, point of intersection 2 and spot 20 do not
overlap. The laser intensity for the first pulse is set equal to
that for the second pulse, and the laser intensity for the third
pulse is set equal to that for the fourth pulse. The laser
intensity for the first pulse is set greater than that for the
third laser pulse. A penetrating hole shown in FIG. 11(C) is
formed.
Fourth Example
[0101] The method for manufacturing a printed wiring board
according to the fourth example is a modified example of the third
example.
[0102] The method for forming a core substrate of the fourth
example is the same as in the first example. First and second laser
pulses are irradiated at a predetermined position (spot 10) on the
first surface of the core substrate. Then, third and fourth laser
pulses are irradiated at a position (spot 100) which is located at
a predetermined distance from spot 10. The laser intensity for the
first pulse is set equal to that for the second pulse, and the
laser intensity for the third pulse is set equal to that for the
fourth pulse. The laser intensity for the first pulse is set
greater than the laser intensity for the third pulse. The diameter
of the first laser pulse is equal to that of the second laser
pulse, and the diameter of the third laser pulse is equal to that
of the fourth laser pulse. The diameter of the first laser pulse is
greater than that of the third laser pulse.
[0103] First and second laser pulses are irradiated at a
predetermined position (spot 20) on the second surface of the core
substrate. Then, third and fourth laser pulses are irradiated at a
position (spot 200) which is located at a predetermined distance
from spot 20. A point (point of intersection 1) where a straight
line passing through spot 10 and perpendicular to the first surface
of the core substrate intersects the second surface of the core
substrate is located at predetermined distances from spot 20 and
spot 200. In addition, point (point of intersection 2) where a
straight line passing through spot 100 and perpendicular to the
first surface of the core substrate intersects the second surface
of the core substrate is located at predetermined distances from
spot 20 and spot 200. Point of intersection 1, point of
intersection 2, spot 20 and spot 200 do not overlap. The laser
intensity for the first pulse is set equal to that for the second
pulse, and the laser intensity for the third pulse is set equal to
that for the fourth pulse. The laser intensity for the first pulse
is set greater than that for the third pulse. The diameter of the
first laser pulse is set greater than that of the third laser
pulse. A penetrating hole shown in FIG. 11(D) is formed.
Example of Built-Up Wiring Board
[0104] Printed wiring board 1000 according to any one of the first
through the fourth examples may be used as a core substrate in a
built-up wiring board.
[0105] On both surfaces of a printed wiring board according to any
one of the first through fourth examples, resin film for interlayer
resin insulation layers (brand name: ABF-45SH, made by Ajinomoto)
is laminated. By curing the film, interlayer resin insulation
layers (50A, 50B) are formed on both surfaces of a core substrate
(FIG. 3(C)).
[0106] (11) Using a CO.sub.2 gas laser, via-conductor openings 51
are formed in interlayer resin insulation layers (50A, 50B),
reaching conductive circuits or through-hole lands (FIG. 3(D)).
[0107] (12) The substrate with via-conductor openings 51 is
immersed for 10 minutes in an 80.degree. C. solution containing 60
g/L permanganic acid. Roughened surfaces (50.alpha.) are formed on
the surfaces of interlayer resin insulation layers (50A, 50B)
including inner walls of via-conductor openings 51 (FIG. 4(A)). By
immersing the substrate in a catalyst solution, catalyst nuclei are
attached to the surfaces of the interlayer resin insulation layers
and to inner-wall surfaces of the via-conductor openings.
[0108] (13) Next, by immersing the substrate in an electroless
copper plating solution (Thru-Cup PEA) made by C. Uyemura Co.,
Ltd., electroless copper-plated film 52 is formed on the surfaces
of interlayer resin insulation layers (50A, 50B) including the
inner walls of via-conductor openings 51 (FIG. 4(B)).
[0109] (14) Plating resist 54 is formed on electroless
copper-plated film 52. Electrolytic copper-plated film 56 is formed
on the electroless plated film left exposed by plating resist 54
(FIG. 4(C)).
[0110] (15) Plating resist 54 is removed. By etching away the
electroless plated film between portions of electrolytic
copper-plated film, independent conductive circuits (58A, 58B) and
via conductors (60A, 60B) are formed (FIG. 4(D)). Multilayer wiring
board 300 is obtained.
[0111] (16) Next, roughened surfaces (58.alpha.) are formed on the
surfaces of conductive circuits (58A, 58B) and via conductors (60A,
60B) (FIG. 5(A)).
[0112] (18) Next, solder-resist layers (70A, 70B) with openings
(71A, 71B) are formed on both surfaces of the multilayer wiring
board (FIG. 5(B)). Top surfaces of conductive circuits (58A, 58B)
and via conductors (60A, 60B) are exposed through openings (71A,
71B). Top surfaces of conductive circuits (58A, 58B) and via
conductors (60A, 60B) exposed through openings (71A) work as solder
pads.
[0113] (19) A nickel-plated layer is formed on solder pads, and a
gold-plated layer is formed on the nickel-plated layer (FIG.
5(C)).
[0114] (21) After that, solder balls are loaded on opening portions
(71A, 71B) in the solder-resist layers, and reflowed at 230.degree.
C. Accordingly, solder bumps (78A, 78B) are formed on solder pads
(FIG. 6). A built-up wiring board is completed.
Second Embodiment
[0115] A multilayer printed wiring board according to the second
embodiment of the present invention is described with reference to
FIG. 16. In a multilayer printed wiring board according to the
first embodiment, plating is filled in penetrating hole 33 of a
core substrate. By contrast, in the second embodiment, through-hole
conductor 36 is formed on the side wall of penetrating hole 33, and
the inside of through-hole conductor 36 is filled with filling
resin 37. The reliability of a through-hole conductor is also
enhanced in a printed wiring board where resin is filled in the
through-hole conductor as shown in the second embodiment.
[0116] A printed wiring board of the present invention has the
following: a core substrate with a first surface and a second
surface opposite the first surface and having a penetrating hole
made up of a first opening portion which is formed in the
first-surface side and becomes thinner from the first surface
toward the second surface and of a second opening portion which is
formed in the second-surface side and becomes thinner from the
second surface toward the first surface; a first circuit formed on
the first surface of the core substrate; a second circuit formed on
the second surface of the core substrate; and a through-hole
conductor formed in the penetrating hole and connecting the first
circuit and the second circuit. In such a printed wiring board, the
first opening portion has a first opening on the first surface of
the core substrate, the first opening portion is made up of a
(first-1) opening portion which includes the first opening and of a
(first-2) opening portion contiguous to the (first-1) opening
portion, the second opening portion has a second opening on the
second surface of the core substrate, the second opening portion is
made up of a (second-1) opening portion which includes the second
opening and of a (second-2) opening portion contiguous to the
(second-1) opening portion, inner walls of the first opening
portion bend toward the inside of the penetrating hole at the
boundary between the (first-1) opening portion and the (first-2)
opening portion, and inner walls of the second opening portion bend
toward the inside of the penetrating hole at the boundary between
the (second-1) opening portion and the (second-2) opening
portion.
[0117] Obviously, numerous modifications and variations of the
present invention are possible in light of the above teachings. It
is therefore to be understood that within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
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