Layered circuit-board designing method and layered circuit-board

A layered circuit-board designing method and layered circuit-board where circuit-boards to be overlaid are connected at the center or an arbitrary position of each circuit-board. The layered circuit-board includes an upper-layer first circuit-board, a lower-layer third circuit-board, and an intermediate-layer second circuit-board between the first and third circuit-boards. A first connector is mounted on the first circuit-board, a second connector is mounted on the third circuit-board, a third connector is mounted on the top surface of the second circuit-board, while maintaining the positional relation between the third connector and the first connector, and a fourth connector is mounted on the bottom surface of the second circuit-board, while maintaining the positional relation between the fourth connector and the second connector. In addition, through holes are provided at pins of the third and fourth connectors for passing through the front and bottom surfaces of the second circuit-board.

BACKGROUND OF THE INVENTION 
This invention relates to a layered circuit-board (circuit-board) designing 
method and layered circuit-board in which, three circuit-boards, for 
example, are overlaid as an upper circuit-board, an intermediate 
circuit-board and a lower circuit-board, and these circuit-boards are 
electrically connected by using a plurality of connectors. 
Conventional multiple circuit-boards are laid in layers, and connecting the 
upper-layer circuit-board and the lower-layer circuit-board. If there is 
an intermediate-layer circuit-board between the upper-layer circuit-board 
and the lower-layer circuit-boards, these layer circuit-boards must be 
connected as shown in FIG. 5. 
FIG. 5 is a perspective view illustrating the structure of the conventional 
layered circuit-board. To provide a circuit-board where three 
circuit-boards of approximately the same shape are overlaid, as the upper, 
intermediate and lower circuit-boards, as shown in FIG. 5, the 
constituents must be prepared as follows. First, an upper-layer 
circuit-board 101, a lower-layer circuit-board 103 and an 
intermediate-layer circuit-board 102 are provided, then connectors 111, 
112 and 113 are mounted on the respective circuit-boards. The upper-layer 
circuit-board 101, the intermediate-layer circuit-board 102, and the 
lower-layer circuit-board 103 are electrically connected by using cables, 
wire harnesses, and flexible ribbon cables 120. 
However, in the conventional art using cables and wire harnesses for 
connecting the circuit-boards, if there is insufficient space between the 
respective circuit-boards, it is impossible to connect the circuit-boards 
at the central position of each circuit-board, thus causing serious 
constraint on circuit-board designing. 
Further, the cables, wire harnesses or flexible substrates, provided so as 
to pass around the end portions of the circuit-boards, emit radiation 
noise and function as antennas to receive radiation noise from the 
outside. This may cause bad influence on signals to be transferred. For 
this reason, some circuit-boards employ noise-proof special wire material. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention has been made in consideration of the 
above situation, and has its object to enable connection of layer 
circuit-boards, at the central portion or an arbitrary position of each 
circuit-board, to ensure freedom in circuit-board designing, and to 
eliminate cables, wire harnesses or flexible substrates, so as to provide 
a layered circuit-board designing method and layered circuit-board with no 
bad influence on signals to be transferred. 
According to the present invention, the foregoing object is attained by 
providing a layered circuit-board designing method for overlaying an 
upper-layer first circuit-board, a lower-layer third circuit-board, and an 
intermediate-layer second circuit-board existing between the first and 
third circuit-boards, comprising mounting a first connector on the first 
circuit-board, mounting a second connector on the third circuit-board, 
mounting a third connector on the top surface of the second circuit-board, 
while maintaining the positional relation between the third connector and 
the first connector, and mounting a fourth connector on the bottom surface 
of the second circuit-board, while maintaining the positional relation 
between the fourth connector and the second connector, wherein 
through-connection means for connecting pins of the third and fourth 
connectors on the front and bottom surfaces of the second circuit-board is 
provided. 
In accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and is provided at a position where at least pins 
for signals, to be connected between the third and fourth connectors, are 
overlapped, and wherein pin arrangement on the third connector and that on 
the fourth connector correspond with each other. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and is formed as a through hole at a position where 
at least pins for signals, to be connected between the third and fourth 
connectors, are overlapped. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and is formed as a through hole at a position where 
at least pins for signals, to be connected between the third and fourth 
connectors, are overlapped, and wherein a ground pattern is provided 
around the through hole. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and the through-connection means guides aligning 
members formed on the third and fourth connectors to aligning holes formed 
on the second circuit-board. 
Further, in accordance with the present invention as described above, a 
layered circuit-board formed by overlaying an upper-layer first 
circuit-board, a lower-layer third circuit-board, and an 
intermediate-layer second circuit-board existing between the first and 
third circuit-boards, comprising a first connector mounted on the first 
circuit-board, a second connector mounted on the third circuit-board, a 
third connector mounted on the top surface of the second circuit-board, 
while maintaining the positional relation between the third connector and 
the first connector, and a fourth connector mounted on the bottom surface 
of the second circuit-board, while maintaining the positional relation 
between the fourth. Also provided is the second connector, and 
through-connection means for connecting pins of the third and fourth 
connectors on the front and bottom surfaces of the second circuit-board. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and is provided at a position where at least pins 
for signals, to be connected between the third and fourth connectors, are 
overlapped, and wherein pin arrangement on the third connector and that on 
the fourth connector correspond with each other. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at a pin-pitch common to the third 
and fourth connectors, and is formed as a through hole at a position where 
at least pins for signals, to be connected between the third and fourth 
connectors, are overlapped. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at pin-pitch common to the third and 
fourth connectors, and is formed as a through hole at a position where at 
least pins for signals, to be connected between the third and fourth 
connectors, are overlapped, and wherein a ground pattern is provided 
around the through hole. 
Further, in accordance with the present invention as described above, the 
through-connection means is provided at pin-pitch common to the third and 
fourth connectors, and the through-connection means guides aligning 
members formed on the third and fourth connectors to aligning holes formed 
on the second circuit-board. 
According to the present invention, the above structure can directly 
connect signals by connecting the first circuit-board and the third 
circuit-board by using the connectors. That is, the respective connectors 
are provided at pin-arrangement positions in accordance with the designing 
method, which realizes the connection of identical signal pins of the 
respective connectors, via through holes on lands (circuit pads) for the 
pins, or through holes at the minimum distance from the pin lands. 
Further, the structure can avoid superfluity of parts such as boss holes 
used for connector alignment, by virtue of arrangement of pins where the 
only signal pins connected via the circuit-board are overlapped. 
Other objects and advantages besides those discussed above shall be 
apparent to those skilled in the art from the description of a preferred 
embodiment of the invention which follows. In the description, reference 
is made to accompanying drawings, which form a part thereof, and which 
illustrate an example of the invention. Such example, however, is not 
exhaustive of the various embodiments of the invention, and therefore 
reference is made to the claims which follow the description for 
determining the scope of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Preferred embodiments of the present invention will now be described in 
detail in accordance with the accompanying drawings. 
As a preferred embodiment of the present invention, an example for 
connecting two of three circuit-boards via an intermediate circuit-board 
will be described. In this embodiment, connection is made between two 
connectors, however, the connection method can also be applied to 
connection of circuit-board to one connector and to a plurality of 
connectors. 
FIG. 1 is a perspective view showing a first embodiment of the present 
invention. This figure shows connection of three circuit-boards, where the 
upper and lower circuit-boards are connected via the intermediate 
circuit-board. Specifically, in FIG. 1, an upper-layer circuit-board 1, an 
intermediate-layer circuit-board 2, and a lower-layer circuit-board 3, 
having approximately the same size, are overlaid in layers. 
To realize this layered structure, a connector 11 represented with a broken 
line, for signal transfer to the circuit-board 2, is mounted on a bottom 
surface 1b of the circuit-board 1, and is precisely positioned in both X 
and Y directions. A connector 12 for signal connection with the 
circuit-board 1 is mounted on a top surface 2a of the circuit-board 2; a 
connector 13, represented with a broken line, for signal connection with 
the circuit-board 3 is mounted on a bottom surface 2b of the circuit-board 
2; and a connector 14 for signal connection with the circuit-board 2 is 
provided on a top surface 3a on the circuit-board 3. 
As shown in FIG. 2 illustrating connection status, the circuit-boards 1 and 
2 connect signals by connection of the connectors 11 and 12. Similarly, 
the circuit-boards 2 and 3 connect signals by connection of the connectors 
13 and 14. 
Next, signal transfer in the above structure will be described in a case 
where four signals A to D of the circuit-board 1 are transferred to the 
circuit-board 3, by using the connectors 11 to 14 for signal transfer from 
the circuit-board 1 to the circuit-board 3. 
FIG. 3A is an expanded top plan view showing a significant part of the 
circuit-board 2, mainly the connectors 12 and 13. FIG. 3B is a table 
showing pin numbers of the connectors. As shown in FIG. 3A, the 
arrangement of the connectors 12 and 13 on the circuit-board 2 is made 
such that the positions of four pins of the respective circuit-boards are 
overlapped, when viewed from above the circuit-board 2. 
In this pin arrangement where some pin positions are overlapped, the signal 
arrangement of the connector 12 and that of the connector 13 correspond 
with each other, when viewed from above the circuit-board 2. 
That is, in FIG. 3B, in the arrangement of connector pins in the connectors 
12 and 13, a 1 pin of the connector 12 and a 2 pin of the connector 13 
correspond (overlapped). Also, a 2 pin of the connector 12 and a 1 pin of 
the connector 13 correspond (overlapped). Then, by providing a through 
hole 24 at a land 23 for the 2 pin of the connector 12, the signal B 
connects the connectors 12 and 13 with the shortest wiring length, through 
the through hole 24 which reaches the land for the 1 pin of the connector 
13 on the bottom surface 2b of the circuit-board 2. 
As to the signal A, by providing the through hole 24 at the land 23 for the 
1 pin of the connector 12, the signal A connects the connectors 12 and 13 
with the shortest wiring length through the through hole 24 which reaches 
the land for the 2 pin of the connector 13 on the bottom surface 2b of the 
circuit-board 2. 
Similarly, the signals C and D can connect the connectors 12 and 13 with 
the shortest wiring length, by using 7 pins and 8 pins of the connectors. 
On the other hand, if a through hole cannot be provided at a land, it may 
be arranged, as connection of the 7 pin of the connector 12 and the 8 pin 
of the connector 13, such that a short straight-line wiring pattern 26 is 
extended from the land 23, and a through hole 25 is provided at the end of 
the wiring pattern 26, so that the signals C and D can be connected with 
the short wiring length. 
According to the connection as shown in FIG. 3A, the positions of pins for 
four signals to be transferred to the circuit-boards 1 and 3 are 
overlapped, this avoids overlapped arrangement of boss holes 21 of the 
connectors 12 and 13. That is, a pair of boss holes 12a for the alignment 
of the connector 12 and a pair of boss holes 13a for the alignment of the 
connector 13 can be shifted in the Y direction, accordingly, the 
connectors 12 and 13 can be attached while maintaining the overlapped 
status of the four pins of the connectors. 
As described above, the structure of the present embodiment attains direct 
connection between the connectors at the central portion or an arbitrary 
position of the connectors. Further, this structure eliminates 
conventional cables, wire harnesses and the like, which may function as 
antennas, thus realizes an excellent noise-proof circuit-board with 
layered structure that has no bad influence on signals to be transferred. 
FIG. 4 is an expanded plan view showing an another embodiment of the 
present invention, on the assumption that the structure has the same 
wiring as that in the first embodiment. FIG. 4 shows that the 1, 2, 7, and 
8 pins of the connector 12, and the 2, 1, 7, and 8 pins of the connector 
13, are wired through the through holes. As shown in FIG. 4, the wiring is 
made within the minimum circuit-board area and the holes are enclosed by a 
grounded land around the connector pins, i.e., a ground plane 31 as a 
signal guard pattern. This can maintain signal quality and constraint of 
radiation noise more effectively. 
As described above, in this structure, signals can be directly transferred 
via connectors without wire harness, and also, circuit-boards can be 
connected at the central portion of each circuit-board. Thus, the 
structure simplifies operation in assembling the circuit-board. Since this 
eliminates cables or harness, the layered circuit-board can be 
manufactured with lower costs. Further, this structure can avoid reception 
of radiation noise from such cables and harness functioning as antennas. 
Furthermore, this avoids superfluity of boss holes, more than a necessary 
number for mounting connectors. 
Furthermore, the length of wiring from a connector, mounted on the top 
surface of an circuit-board to a connector mounted on the bottom surface 
of the circuit-board can be minimized. Therefore, a ground plane can be 
provided in an empty area around the connectors. This attains more 
effective signal quality and constraint on radiation noise. 
As described above, according to the present invention, in layered 
circuit-board structure, the connection of the respective circuit-boards 
can be made at the central portion or an arbitrary position of each 
circuit-board, and freedom of circuit-board designing can be ensured, 
without using cables, wire harnesses, flexible substrates and the like 
that pass around the end portions of the respective circuit-boards. Thus, 
the present invention can provide a layered circuit-board designing method 
and layered circuit-board that has no bad influence on signals to be 
transferred. 
The present invention is not limited to the above embodiments and various 
changes and modifications can be made within the spirit and scope of the 
present invention. Therefore, to apprise the public of the scope of the 
present invention, the following claims are made.