Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2002-07-10
2004-10-12
Tugbang, A. Dexter (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S831000, C029S846000, C029S847000, C029SDIG001, C216S013000, C216S017000, C427S096400, C427S097100, C174S255000, C174S261000, C361S736000
Reexamination Certificate
active
06802120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a printed wiring board enabling insertion components having leads to be mounted on both front and back surfaces, and its manufacturing method. More particularly, the invention relates to a printed wiring board having a non-through lead mounting hole on both surfaces, and its manufacturing method.
BACKGROUND OF THE INVENTION
In the course of the development of the technology, reductions in size, weight and thickness of electronic equipment have associatively brought about progresses in high density mounting technology. For example, in mounting of components on a printed wiring board, in place of a component mounting method of obtaining electrical and mechanical coupling by inserting a lead into a through-hole, a surface mounting method of soldering a component electrode on a pad formed on a plane of the printed wiring board has mostly been used.
The surface mounting method is effective high density mounting means because of its capability of mounting surface mounted components not only on one surface but also both front and back surfaces of the printed wiring board. On the other hand, regarding a component mounted by inserting a component lead into the through-hole of the printed wiring board (referred to as inserting component having a lead, hereinafter), not only its component main body occupies a mounting surface area, but also it is impossible to mount the component on the back surface of the same position where the component lead penetrates from the front surface to the back surface. Further, a land formed in an outer edge of the through-hole limits disposition of an outer layer circuit pattern of the back surface for lead mounting.
Therefore, components still keeping insertion component shapes have mostly been limited to those, in which a great force is possibly applied to a joined portion with the printed wiring board. A component having a very large mass of a component main body, a connector or the like is an example of such components. It is because the surface mounted component pad formed on the plane of the printed wiring board is considerably lower in peel strength compared with the through-hole.
Regarding the method of mounting the inserting component having a lead on the printed wiring board, there are two methods. In one method, the component lead is inserted into the through-hole and then soldered. The other method is so-called press fitting method, in which a component with leads having elasticity in an axial radial direction is used, and electrical and mechanical connection is obtained by pressing the leads into a through-hole. As soldering is not necessary, this method has generally been used widely as a press-fitting connector on a large printed wiring board, especially in the case of a mother board or the like including a number of connectors disposed on a full surface of the printed wiring board.
Still, however, many of the connectors have large sizes while other mounted components are miniaturized. Further, the number of leads is large because of functionality, and lead pitches are narrow in most cases. Thus, constraints inevitable on pattern disposition and component mounting on the back surface of the printed wiring board are also very large.
However, the above constraints on the pattern disposition and the component mounting on the back surface can be partially reduced by using a recently disclosed technology, for example a plated non-through hole disclosed in Unexamined Japanese Patent Publication (KOKAI) No. 10-51093. A method of manufacturing a plated non-through hole by this prior art will be described by referring to schematic sectional views of
FIGS. 10A
to
10
F.
In
FIG. 10A
, a reference numeral
101
denotes a double-sided or multilayer copper-clad laminate. First, a through-hole
102
is bored in the copper-clad laminate
101
by a drill. Then, first copper plating is carried out to form a through-hole plated layer
103
(FIG.
10
B). Further, the through-hole
102
is filled with a resin
104
inside, and a surface of the resin is finished to be smooth after drying and curing (FIG.
10
C).
Then, second copper plating is carried out to form a second plated layer
105
(FIG.
10
D). Further, etching is carried out so as to achieve a predetermined surface outer layer conductor, forming a circuit pattern
106
and a land
107
(FIG.
10
E). At this time, a surface component mounting pad
108
or a circuit pattern can be disposed on a behind side of a plated non-through hole.
Lastly, the resin
104
is removed by chemical solution or laser processing to form a non-through hole
109
(FIG.
10
F). By using the non-through hole thus formed, as shown in
FIG. 11
, an insertion component
110
having a lead can be disposed on an opening side of the non-through hole, and the connection pad
108
of a surface mounted component
111
or a pattern can be disposed on an opposite side on the same position of a grid pattern.
However, in the foregoing conventional technology, it is only a surface mounted component or a pattern that can be disposed on the back surface of the insertion component having a lead, which is mounted on the printed wiring board. Thus, this technology cannot be a sufficient method for increasing a density in component mounting. In other words, if a similar insertion component having a lead can be oppositely mounted on the back surface of the insertion component having a lead, an enormous advantage can be expected.
For example, if connectors having insertion leads can be mounted on both front and back surfaces in the same position on the printed wiring board, an area necessary for the mounting can reduced to one half.
Further, in a large information processor for processing a great amount of information at a high speed, to increase a mounting density of the processor, as shown in
FIG. 12
, mother boards
201
A and
201
B have conventionally been disposed in the processor
210
, and daughter boards
202
have been mounted from both front and back sides of the processor
210
. However, electrical connection between the mother boards
201
A and
201
B has been made by a plurality of cables
203
.
In recent high-speed digital transmission, however, an excessive length of a transmission path from end to end of two mother boards has caused delay of an electric signal or crosstalk between transmission lines, which has been a great obstacle to sufficient performance and reliability.
Thus, as shown in
FIG. 13
, if one mother board
204
is disposed on the center, and connectors are mounted to connect the daughter boards
202
to both sides thereof, a mounting density can be increased, and a transmission path can also be shortened greatly.
In this case, the front and back connectors may be shifted in position on the mother board, and connectors of through-leads may be alternately disposed. By this method, however, a number of through-holes make it difficult to draw around a pattern on all the layers and thus high-density mounting cannot be achieved.
Regarding processing of the printed wiring board, in the foregoing conventional processing method, a complex manufacturing process must be carried out, which includes drying and curing of the resin having filled the through-hole, polishing the surface to be smooth, further plating and etching, and then entirely removing of the resin supplied and cured in the previous step.
In addition, it is technically difficult to remove the resin having filled the non-through hole without any residuals. This difficulty combines with the complex manufacturing process to cause a reduction in printed wiring board yield, i.e., an increase in costs.
SUMMARY OF THE INVENTION
The present invention was made to solve the foregoing problems, and it is a first object of the invention to provide a printed wiring board having no-through lead mounting holes, which enables insertion component having leads to be mounted on both front and back surfaces of the printed wiring board, a mounting density to be increased, freedom of circuit design to be increased, and a trans
Nippon Avionics Co. Ltd.
Tugbang A. Dexter
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