1. Field of the Invention
The present invention relates to a press-fit pin connection checking method and system.
2. Description of the Related Art
In recent communications equipment, high-density packaging has proceeded in response to the demands for high performance and multi-functionality to devices to be packaged, so that an increase in number of printed wiring boards layered and a decrease in bonding area and conductor spacing are remarkably proceeding. A component mounting method is also changing from an insert mount technology (IMT) such that a lead is inserted into a through hole and is bonded by flow soldering to a surface mount technology (SMT) such that a component is mounted on a surface pattern and is bonded by reflow soldering, and the SMT is becoming mainstream. At present, the component mounting method is in the shift from the IMT to the SMT, and a printed circuit board (plug-in unit) using both the technologies as mixed is most dominating.
In such a recent trend, a connector component for connecting the printed circuit board to a back wiring board has also changed, and the shift from an insert mount device (IMD) to a surface mount device (SMD) as the connector component has been examined. However, a bonding force for each pin is reduced by adopting the SMT, and the connector component cannot endure a total pressure applied in connecting the printed circuit board and the back wiring board. To cope with this problem, a press-fit connector bonding technique (gastight bonding technique) of press-fitting a press-fit pin into a through hole has risen.
The press-fit connector bonding technique has such merits that the bonding force for each pin is high to ensure a strong holding force of the connector as a whole, that the flow soldering step as a main bonding method in the IMT can be omitted, that the shift to the SMT can be made smoothly, and that the connector is repairable. As seen from the connection between a plug-in unit and a back wiring board, it is considered that the press-fit connector bonding technique will become a dominating technique in the future connector bonding for communications equipment. However, although the IMT is being currently shifted to the SMT, there exist many IMDs that cannot support the SMT, and it is therefore difficult to completely shift the IMT to the SMT in the near future.
In recent communications equipment, not only the high-density packaging has proceeded, but also a signal transmission speed has been increased year by year. Accordingly, increasing a signal transmission speed between a plug-in unit (PIU) and a back wiring board (BWB) is also proceeding. The technique required for high-speed signal transmission includes the suppression of transmission loss, the suppression of reflected waves, and the unification of propagation delay. Accordingly, a connector structure supporting high-speed signal transmission includes a shielding structure, shortening the length of a press-fit pin, and equalizing the lengths of differential signal pair lines. A characteristic impedance is controlled by the shielding structure to suppress the transmission loss. The length of a press-fit pin is shortened to suppress the reflected waves. The lengths of differential signal pair lines are equalized to unify the propagation delay.
While a plug-in unit and a back wiring board are connected by a press-fit connector in general as described above, a plurality of press-fit pins are press-fitted into a plurality of through holes to thereby mount the press-fit connector on the back wiring board or the plug-in unit. Accordingly, it is necessary to check that the press-fit pins are completely press-fitted in the through holes. At present, whether or not the connection of the press-fit pins and the through holes after press-fitting the press-fit pins is acceptable is checked by only visual check for the plug-in unit and by visual check and electrical check in combination for the back wiring board.
FIG. 1 is a schematic sectional view for illustrating a plug-in unit checking method in the prior art. Reference numeral 2 denotes a plug-in unit having a plurality of through holes 4, and reference numeral 6 denotes a press-fit connector having a plurality of press-fit pins 8. The press-fit pins 8 of the press-fit connector 6 are press-fitted into the through holes 4 of the plug-in unit 2 to thereby mount the press-fit connector 6 on the plug-in unit 2. In the conventional visual checking method, whether or not the connection of the press-fit pins 8 and the through holes 4 is acceptable is checked by seeing the through holes 4 from one side (back side) of the plug-in unit 2 opposite to the press-fit connector 6 after press-fitting the press-fit pins 8 into the through holes 4 and by determining whether or not the front ends of the press-fit pins 8 project from the back side of the plug-in unit 2.
Referring to FIG. 2, there is shown a schematic sectional view for illustrating a back wiring board checking method in the prior art. Reference numeral 10 denotes a back wiring board having a plurality of through holes 12, and reference numeral 14 denotes a press-fit connector having a plurality of press-fit pins 16. The press-fit pins 16 of the press-fit connector 14 are press-fitted into the through holes 12 of the back wiring board 10 to thereby mount the press-fit connector 14 on the back wiring board 10. The press-fit connector 6 on the PIU side is preliminarily mounted on a checking printed circuit board 18. The press-fit connector 6 on the PIU side is engaged into the press-fit connector 14 on the BWB side to thereby electrically connect the checking printed circuit board 18 to the back wiring board 10. The checking printed circuit board 18 has a plurality of conductor patterns respectively corresponding to the press-fit pins of the press-fit connector 6 and a plurality of output lands respectively formed at the front ends of the conductor patterns.
In the conventional electrical checking method for the press-fit pins 16 on the BWB side as shown in FIG. 2, two checking printed circuit boards 18 are electrically connected to the back wiring board 10, and the output lands of the two checking printed circuit boards 18 are selectively connected to check the electrical continuity, thereby determining whether or not the press-fitted condition of the press-fit pins 16 is acceptable. The wiring in the back wiring board 10 is complicatedly connected to a plurality of plug-in units 2. Accordingly, to check the connection of all the press-fit pins 16 without omission, a continuity check program is prepared for each design of the back wiring board 10 and the plug-in units 2 in combination, and the continuity check is performed in accordance with this program. The visual check for the back wiring board 10 is similar to that for the plug-in unit 2 as mentioned above with reference to FIG. 1. That is, whether or not the connection of the press-fit pins 16 and the through holes 12 is acceptable is checked by determining whether or not the front ends of the press-fit pins 16 project from the back side of the back wiring board 10.
FIGS. 3A to 3C are sectional views showing an acceptable mode and a defective mode. More specifically, FIG. 3A shows an acceptable mode, and FIGS. 3B and 3C show defective modes. The defective modes shown in FIGS. 3B and 3C can be detected by the visual check. However, the defective mode shown in FIG. 3C cannot be detected by the electrical check, because the press-fit pin 16 is in electrical continuity to the through hole 12.
Although the visual check is low in efficiency and detection power to defective connection, all kinds of buckling of the press-fit pin 16 as shown in FIGS. 3B and 3C can be detected as detectable defective modes by the visual check. on the other hand, although the electrical check is high in efficiency, only the complete buckling of the press-fit pin 16 as shown in FIG. 3B such that:the press-fit pin 16 is not in contact with the through hole 12 can be detected as a detectable defective mode by the electrical check, and another kind of buckling of the press-fit pin 16 as shown in FIG. 3C such that the press-fit pin 16 is in contact with the through hole 12 cannot be detected as a defective mode by the electrical check.
In the conventional press-fit pin connection checking method, only the visual check is performed for the plug-in unit, so that the omission of detection of defectives is prone to occur. Also in the connection check for the press-fit pins on the BWB side, the defective mode shown in FIG. 3C can be detected only by the visual check, so that there is a possibility of omission of detection of defectives. In the case that the omission of detection of defectives occurs, the defectives omitted may be detected in subsequent function check or the like. However, a large number of man-hours are needed to seek real defectives.
Further, the conventional connection checking method requires a dedicated jig (including a checking printed circuit board on the PIU side, testing device, and program) for the electrical check for the back wiring board in each product, so that a cost and time for preparation of the connection check are required. Moreover, the visual check for detection of defectives is important in the conventional connection checking method, so that the length of each press-fit pin must be larger than the thickness of a substrate, so as to ensure the detection power. However, a reduction in length of each press-fit pin of a press-fit connector supporting high-speed signal transmission is now being pursued, and it is becoming general that the length of each press-fit pin is smaller than the thickness of the substrate. In this case, the front end of each press-fit pin does not project from the back surface of the substrate, and the visual check cannot therefore be performed.
It is therefore an object of the present invention to provide a press-fit pin connection checking method and system which can detect defective press-fit of all the press-fit pins by only electrical check.
It is another object of the present invention to provide a press-fit pin connection checking method and system which can detect defective press-fit of each press-fit pin even in the case that the length of each press-fit pin is smaller than the thickness of the substrate.
It is a further object of the present invention to provide a printed circuit board structure required for realization of such a press-fit pin connection checking method.
In accordance with an aspect of the present invention, there is provided a printed circuit board suitable for mounting of a press-fit connector having a plurality of press-fit pins, comprising a substrate; a plurality of through holes formed through said substrate in which said press-fit pins are adapted to be respectively press-fitted; and a checking conductor pattern formed on an upper surface of said substrate so as to be electrically insulated from all of said through holes and to surround all of said through holes for engagement with said press-fit connector; said checking conductor pattern being exposed without being covered with a resist.
Preferably, the upper surface of said substrate is exposed at a portion having a predetermined width between each of said through holes and said checking conductor pattern. Alternatively, the upper surface of said substrate may be covered with a resist at a portion having a predetermined width between each of said through holes and said checking conductor pattern. Preferably, the printed circuit board further comprises a checking output land electrically connected to said checking conductor pattern.
In accordance with another aspect of the present invention, there is provided a press-fit pin connection checking system comprising a first press-fit connector having a plurality of first press-fit pins; a first printed circuit board having a first substrate, a plurality of first through holes formed through said first substrate in which said first press-fit pins are adapted to be respectively press-fitted, and a first conductor pattern formed on an upper surface of said first substrate so as to be electrically insulated from all of said first through holes and to surround all of said first through holes for engagement with said first press-fit connector; a second press-fit connector having a plurality of second press-fit pins and adapted to engage with said first press-fit connector; a second printed circuit board having a second substrate, a plurality of second through holes formed through said second substrate in which said second press-fit pins are adapted to be respectively press-fitted, a plurality of second conductor patterns formed on said second substrate so as to be respectively connected to said second through holes, and a plurality of output lands respectively connected to said second conductor patterns; and means for selectively connecting said first conductor pattern to said output lands.
In accordance with a further aspect of the present invention, there is provided a press-fit pin connection checking method comprising the steps of providing a first printed circuit board having a plurality of first through holes in which a plurality of first press-fit pins of a first press-fit connector are adapted to be respectively press-fitted, and a first conductor pattern formed so as to be electrically insulated from all of said first through holes and to surround all of said first through holes for engagement with said first press-fit connector; press-fitting said plurality of first press-fit pins of said first press-fit connector into said plurality of first through holes of said first printed circuit board to thereby mount said first press-fit connector on said first printed circuit board; providing a checking jig including a second printed circuit board and a second press-fit connector mounted on said second printed circuit board, said second printed circuit board having a plurality of second through holes, a plurality of second conductor patterns respectively connected to said second through holes, and a plurality of output lands respectively connected to said second conductor patterns, said second press-fit connector having a plurality of second press-fit pins press-fitted in said plurality of second through holes of said second printed circuit board; engaging said second press-fit connector of said checking jig with said first press-fit connector mounted on said first printed circuit board; and selectively connecting said first conductor pattern of said first printed circuit board to said output lands of said second printed circuit board; wherein when there is no electrical continuity between said first conductor pattern and each of said output lands, it is determined that the connection of said first press-fit pins and said first through holes is acceptable, whereas when there is electrical continuity between said first conductor pattern and each of said output lands, it is determined that the connection of said first press-fit pins and said first through holes is defective.
Preferably, said first printed circuit board further has a checking output land electrically connected to said first conductor pattern; and the selective connection of said first conductor pattern and said output lands is provided by connecting a probe pin to said checking output land and selectively bringing said probe pin into contact with said output lands. The detection of no electrical continuity indicates an acceptable mode, and the detection of electrical continuity indicates a defective mode.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.