Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1999-07-07
2001-09-04
Lam, Cathy (Department: 1775)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S901000, C174S255000, C174S261000, C257S779000, C257S780000
Reexamination Certificate
active
06284353
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a printed wiring board and its manufacturing method, and particularly relates to a printed wiring board capable of forming a very small opening portion and a hole for conductivity and be mounted at high density, an electric conducting method between upper and lower faces of an insulating substrate, electric connection of a pad for external connection and the hole for conductivity, and a plating lead used in electric plating.
BACKGROUND ART
As shown in
FIGS. 28 and 29
, conventionally there is a printed wiring board having a mounting portion
970
for mounting electronic parts to an insulating substrate
97
and a conductor circuit
96
arranged around this mounting portion
970
. A bonding pad portion
969
forming an end tip of the conductor circuit
96
is formed near the mounting portion
970
. A pad portion
961
for joining a soldering ball, etc. is formed in the conductor circuit
96
.
The mounting portion
970
is constructed by a concave portion surrounded by a mounting hole
971
formed in the insulating substrate
97
and a heat radiating plate
98
covering one end of the mounting hole
971
.
As shown in
FIG. 29
, a surface of the insulating substrate
97
is covered with an insulating film
91
except for the pad portion
961
and the bonding pad portion
969
. In other words, this insulating film
91
exposes the pad portion
961
and the bonding pad portion
969
by arranging an opening portion
910
above the pad portion
961
and the bonding pad portion
969
.
A manufacturing method of the above printed wiring board will be explained next.
First, as shown in
FIG. 30
, a mounting hole
971
is bored in an insulating substrate
97
which is sticking a copper foil thereto. Next, the copper foil is etched so that a conductor circuit
96
having a pad portion
961
and a bonding pad portion
969
is formed.
Next, as shown in
FIG. 28
, solder resist constructed by thermosetting resin is printed on a surface of the insulating substrate
97
. At this time, surfaces of the above pad portion
961
and the bonding pad portion
962
are exposed as they are without the solder resist printing.
Next, the solder resist is thermally cured and is set to an insulating film
91
.
Thereafter, a heat radiating plate
98
is adhered to the surface of the insulating substrate
97
by using an adhesive
981
so as to cover one end of the mounting hole
971
.
Thus, a printed wiring board
9
is obtained.
However, the above conventional manufacturing method of the printed wiring board
9
has the following problems.
Specifically, as shown in
FIG. 31
, except for a portion of the pad portion
961
no very small opening portion
910
can be formed in the insulating film
91
in a method for partially printing the above solder resist. Therefore, it is impossible only to expose a very small portion in the conductor circuit
96
. As a result, no high density mounting can be improved.
In contrast to this, a manufacturing method as shown in
FIG. 32
is proposed. In this method, an entire surface of the insulating substrate
97
forming the conductor circuit
96
therein is covered with a solder resist
912
constructed by an optical curing type resin. The solder resist
912
is exposed in a state in which a light interrupting mask
94
is arranged above an opening portion forming portion.
In this method, the solder resist
912
in a portion of light
940
interrupted by the mask
94
is not cured and is left as it is. In this state, the solder resist in an exposed portion is cured and forms an insulating film. Next, the insulating substrate
97
is dipped into a developing liquid and the solder resist in an uncured portion is removed from the insulating substrate
97
. Thus, an opening portion
910
is formed in the cured insulating film
91
and one portion of the conductor circuit
96
is exposed.
However, in this method, since the optical curing type resin used as the solder resist has a property of absorbing humidity, no solder resist is suitable as the insulating film.
Further, since the above light has scattering light, the above light cannot be sufficiently interrupted so that no opening portion
910
can be formed in a sharp state. Therefore, for example, it is almost impossible to form a very small opening portion having a size equal to or smaller than
0
.
60
mm. Therefore, no high density mounting can be improved.
By using a drill there is also the method for boring a hole for conductivity. However, in this case, it is also difficult to form a very small hole for conductivity.
Further, there is a case in which various kinds of conductive members are formed around the hole for conductivity. Tangibly, such conductive members are constructed by a land surrounding a peripheral portion of the hole for conductivity, a pad for externally joining a soldering ball, a plating lead for forming electric plating, etc. High density is also desirable when these conductive members are formed.
With consideration to such conventional problems, the present invention provides a printed wiring board able to form an insulating film having a very small opening portion and be mounted at high density, and a manufacturing method of the printed wiring board.
DISCLOSURE OF THE INVENTION
A first invention is a manufacturing method of a printed wiring board characterized in that a conductor circuit is formed on the surface of an insulating substrate;
a solder resist made of thermosetting resin is next printed on the surface of said insulating substrate;
an insulating film having a coefficient thermal expansion equal to or smaller than 100 ppm/° C. is next formed by thermally curing the solder resist; and
the conductor circuit is next exposed by irradiating a laser beam to an opening portion forming portion in the insulating film and burning-out the insulating film of said opening portion forming portion and forming an opening portion.
An operation and effects of the first invention will be explained.
In the first invention, the entire surface of the insulating substrate is covered with the insulating film and the laser beam is irradiated to a portion for forming the opening portion. High energy is given by a laser to the irradiating portion of the laser beam so that this irradiating portion has a very high temperature and is burnt out. Therefore, a very small opening portion can be formed in the insulating film.
Further, no light is scattered since the laser beam is parallel light. Therefore, a very small opening portion having an approximately size from 0.05 to 0.60 mm can be formed in desirable position and size. Accordingly, many opening portions can be formed in a small space so that high density mounting can be realized.
Thermosetting resin used in the solder resist has a low coefficient thermal expansion equal to or smaller than 100 ppm/° C. Therefore, the thermosetting resin has a property in which generation of stress of the solder resist is reduced by a temperature cycle test, etc. Accordingly, a close attaching property of the solder resist and the conductor circuit is improved.
In contrast to this, when the coefficient thermal expansion exceeds 100 ppm/° C., a problem exists in that the stress of the solder resist is increased by the temperature cycle test, etc.
A lower limit of the coefficient thermal expansion of the thermosetting resin includes 0 ppm/° C., but is preferably set to 1 ppm/° C. to more effectively show the above effects of the present invention.
The coefficient thermal expansion of the thermosetting resin used in the solder resist is preferably further set to range from 30 to 50 ppm/° C.
The above solder resist is preferably constructed by epoxy resin, triazine resin, polyimide resin, or a modified material thereof. In this case, a heat resisting close attaching property is improved between the solder resist and the conductor circuit. Further, an insulating substrate having a low water absorbing ratio is obtained through thermal curing of the solder resist.
A metallic plating film is preferably formed on a surface of the exposed
Chihara Kenji
Kobayashi Hiroyuki
Kondo Mitsuhiro
Minoura Hisashi
Takada Masaru
Ibiden Co. Ltd.
Lam Cathy
Tolpin Thomas W.
Welsh & Katz Ltd.
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