Electricity: conductors and insulators – Conduits – cables or conductors – Preformed panel circuit arrangement
Reexamination Certificate
1999-07-19
2003-07-08
Talbott, David L. (Department: 2827)
Electricity: conductors and insulators
Conduits, cables or conductors
Preformed panel circuit arrangement
C174S260000, C174S262000, C257S698000, C361S803000
Reexamination Certificate
active
06590165
ABSTRACT:
TECHNICAL FIELD
This invention relates to a printed wiring board provided with via-holes formed by using a laser beam and a method of manufacturing the same.
BACKGROUND ART
The printed wiring board is formed by laminating plural insulating layers
91
~
93
one upon the other and electrically connecting innerlayer conductor circuits
95
,
97
arranged between the layers to an outer conductor circuit
94
existing on an outermost surface through metal plated films
96
formed on via-holes
99
a
,
99
b
as shown, for example, in FIG.
61
. As the insulating layers
91
~
93
is used a resin substrate such as glass-epoxy substrate or the like. The via-holes
99
a
,
99
b
are blind via-holes each covered at its one end and opened at the other end.
As a method of forming the via-hole, there are a method using a drill, a method using a laser beam and the like.
However, the above drilling method causes unevenness in the depth accuracy. And also, it is recently demanded to make more fine a diameter of the via-hole with the advance of high densification in a wiring pattern.
For this end, there is proposed the formation of holes through the laser beam (JP-A-62-216297, JP-A-3-165594).
According to the latter method, as shown in
FIG. 62
, the via-holes
99
a
,
99
b
can be formed in a region ranging from an outermost surface of a multilayer laminated plate up to innerlayer conductor circuits existing therein by utilizing a property that laser beams
81
reflect on the innerlayer conductor circuits
95
,
97
each made of a metal such as copper foil, metal plated film or the like.
In the printed wiring board, however, a relatively shallow via-hole
99
a
arrived at the innerlayer conductor circuit
95
near to the outermost surface of the printed wiring board and a relatively deep via-hole
99
b
arrived at the innerlayer conductor circuit
97
far away from the outermost surface are existent together as the via-hole as shown in FIG.
62
.
As a result, when the holes are formed through the laser beam
81
, as shown in
FIG. 63
, there may be caused damages
98
such as breakage, swell and the like in a central portion of the innerlayer conductor circuit
95
arranged in the bottom of the shallow via-hole
99
b
though the innerlayer conductor circuit
97
arranged in the bottom of the deep via-hole
99
b
is not damaged.
Once such damages are caused, when a metal plated film is formed on each surface of the innerlayer conductor circuit
95
and via-hole
99
a
and between such a surface and an outer conductor circuit, pieces
98
a
of the innerlayer conductor circuit broken due to the damage
98
remain in the via-hole
99
a
, so that the metal plated film may not be formed sufficiently. Such an insufficient metal plated film badly affects electric conduction between the innerlayer conductor circuit
95
and the outer conductor circuit
94
and sometimes rejects the printed wiring board itself.
The reason why the damage is caused in the innerlayer conductor circuit
95
as mentioned above is due to the fact that laser beams
81
having an intensity required for the formation of the deep via-hole
99
b
are irradiated to not only the shallow via-hole
99
a
but also the deep via-hole
99
b
as shown in FIG.
62
.
Therefore, it is also considered to irradiate a laser beam having an intensity in accordance with the depth of the via-hole to be formed. However, the number of via-holes formed in one printed wiring board is as many as, for example, 500~10000, so that it is complicated to adjust the intensity of the laser beam every via-hole and also it is required to use an expensive control device for such an adjustment.
Furthermore, a black oxide film is formed on the surfaces of the innerlayer conductor circuits
95
,
97
for ensuring an adhesion property to the insulating layers
91
,
92
. Since the black oxide film is high in the energy absorption of laser beam, there is a fear of causing damages such as breakage and the like due to fusion and swelling of the innerlayer conductor circuit provided on its surface with the black oxide film.
And also, the insulating layer made of the resin or the like is exposed in the via-hole, so that it is difficult to form the metal plated film. For this end, the joining property between he inner wall of the via-hole and the metal plated film is low and the peeling, dropping-out and the like of the metal plated film are caused, which have a fear of badly affecting the electric conduction of the via-hole.
The formation of the metal plated film on the via-hole is carried out by flowing an electric plating solution into the via-hole, but as the inner diameter of the hole becomes small, the flowing of the electric plating solution is difficult to make the formation of the plated film ununiform, so that there is caused a fear that the electric conduction of the via-hole is insufficient.
Further, it is attempted to provide the electric conduction by filling a solder in the via-hole instead of the metal plated film. In this case, the joining strength between the inner wall of the via-hole and the solder is low and there is a case that the solder is get out from the via-hole through an external pressure.
Moreover, it is required to utilize the irradiation of the laser beam to the formation of holes other than the via-hole.
In the light of the above problems, the invention is to provide a printed wiring board and a method of manufacturing the same which can form via-holes having a reliable electric conduction without causing damages of innerlayer conductor circuits through a laser beam and realize novel circuit formation through the laser beam.
DISCLOSURE OF INVENTION
A first aspect of the invention lies in a method of manufacturing a printed wiring board comprising at least two insulating layers made of a synthetic resin, an innerlayer conductor circuit arranged between the insulating layers, and a blind via-hole formed from an outermost surface of the insulating layer toward the innerlayer conductor circuit, characterized in that an opening hole is previously formed in a central portion of the innerlayer conductor circuit located in a bottom portion of the blind via-hole, and a laser beam is irradiated from the outermost surface of the insulating layer to form the blind via-hole, and then a metal plated film is formed on the innerlayer conductor circuit and the surface of the blind via-hole.
In the first aspect of the invention, it is most noticed that the opening hole is previously formed in the central portion of the innerlayer conductor circuit.
In the first aspect of the invention, the blind via-hole ranging from the outermost surface of the printed wiring board to the innerlayer conductor circuit is formed by irradiating the laser beam toward a portion forming the blind via-hole.
In this case, the insulating layer in the printed wiring board is vaporized and removed by a higher energy of the laser beam, whereby hole is gradually formed toward the inside of the printed wiring board. When the top of the laser beam arrives at the innerlayer conductor circuit, the laser beam is reflected by the innerlayer conductor circuit made of the metal. At this time, the irradiation of the laser beam is stopped. Thus, the formation of the blind via-hole is terminated.
It is important that the formation of many blind via-holes is carried out, for example, by successively and spottedly irradiating the laser beam every hole. On the other hand, the irradiation time and energy required for the formation of the hole differ between the shallow blind via-hole and the deep blind via-hole.
However, the irradiation is conducted successively and continuously as mentioned above, so that all holes are formed under the same condition every the hole by setting the time and energy so as to surely form the deep blind via-hole.
In the first aspect of the invention, the opening hole is formed in the innerlayer conductor circuit corresponding to the shallow blind via-hole.
In the formation of the shallow blind via-hole, therefore, even the laser beam already arrives at the innerlayer conduc
Kobayashi Hiroyuki
Kondo Mitsuhiro
Minoura Hisashi
Takada Masaru
Tsukada Kiyotaka
Alcala José H.
Ibiden Co. Ltd.
Talbott David L.
LandOfFree
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