JPS62182688A - Detection of reference mark position on multilayer printed circuit board - Google Patents

Abstract

PURPOSE:To accurately detect the center position of a copper mark by machining a spot facing that requires no accuracy by displacing an eddy current type position sensor after only a copper foil layer over around a reference mark is removed by a machining. CONSTITUTION:A portion approximately above a copper mark 32 is machined with a spot facing. An eddy current type position sensor is positioned approximately above the copper mark 32 of a multilayer printed circuit board 30. A servomotor is operated to reciprocate the eddy current type position sensor 10. A drill is displaced to the position wherein the eddy current type position sensor detects the copper mark 32 and the drill 12 is lowered to conduct the machining of a reference hole.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Industrial Application Field The present invention is directed to a multilayer printed circuit board JJ:4! The present invention relates to a method for detecting the position of a mask.

(b) Conventional technology When creating a multilayer printed circuit board, it is necessary to align the patterns on the inner layer and the pattern on the outer layer.
Usually, a pattern on the outer layer is printed to match the fiducial marks on the inner layer. However, the reference marks on the inner layer are covered with a copper foil layer and cannot be visually confirmed from the outside.

For this reason, conventionally, in order to make the reference mark visible, the area where the reference mark is thought to be located has been counterbored using a counterboring device to expose the reference mark.

(c) Problems to be Solved by the Invention However, in order to expose the reference mark by counterbore processing, the outer layer of copper must be removed by removing only the layer and the bridle below, and the reference mark is approximately 35 μm thick. It is necessary to leave only a small part of the hole, and the accuracy of the counterbore process in the depth direction needs to be extremely high. This work had to be done by skilled workers and was difficult to automate. The present invention aims to solve these problems.

(d) Means for Solving the Problems The present invention solves the above problems by removing only the outer copper foil layer and detecting the fiducial mark using an eddy current position sensor. That is, in the method for detecting the position of a reference mark on a multilayer printed circuit board according to the present invention, after removing only the upper copper foil layer around the reference mark by machining, a position a predetermined distance RAM from the surface of the multilayer printed circuit board is detected using an eddy current method. The gist of this method is to move a position sensor and detect the reference mark position from changes in its output voltage or current.

(e) Effect When the eddy current position sensor is moved parallel to and above the multilayer printed circuit board, the current changes when it passes over the reference mark, even if it is covered by the bleep-wave and cannot be seen with the naked eye. do. Therefore, by reciprocating the eddy current type position sensor once in each of the X and Y directions, the center positions in the X and Y directions can be detected. Since the center position of the reference mark is thereby detected, the drill can be moved to this center position to drill the reference hole.

(F) Embodiments Hereinafter, embodiments of the present invention will be described based on FIGS. 1 to 7 of the accompanying drawings.

FIGS. 1 and 2 show a reference hole machining apparatus for a multilayer printed circuit board for carrying out the method of the present invention. A drill head 14 provided with an eddy current position sensor 10 and a drill 12 includes:
It is attached to a table 18 movable in the X direction by a servo motor 16, and this table 18 is further provided on a table 22 movable in the Y direction perpendicular to the X direction by a servo motor 20. The operation of servo motor 16 and servo motor 20 is controlled by controller 24, and the operation of servo motor 16 and servo motor 20 is controlled by controller 24.
, i.e., the X direction and Y direction of the drill head 14
A signal corresponding to the directional coordinates is detected by, for example, a pulse detector provided therein, and is input to the controller 24. A detection signal from the eddy current position sensor 10 is also input manually to the controller 24 .

Next, the method of the present invention using this apparatus will be explained. For example, the multilayer printed circuit board 30 has a four-layer structure, as shown in an enlarged view in FIG.
It is a copper foil layer 30a with a thickness of approximately μ, and a circular copper mark 32 (reference mark) is provided in the second layer from the top. Each layer is separated by a rib 30b. Therefore, although the copper mark 32 on the second layer from the top is not visible from the outside, its approximate position can be known in advance. First, the approximate upper part of the copper mark 32 is counterbored. The depth of the counterboring should be such that at least the outermost copper layer 30a can be removed, and the prebrave 30b is left as shown in FIG. Therefore, there is no problem even if the accuracy of the counterbore process in the depth direction is not high. Next, as shown in FIG. 3, the eddy current position sensor 10 is positioned approximately above the copper mark 32 on the multilayer printed circuit board 30 (point A in FIG. 3). Note that point A does not necessarily have to be located on the copper mark 32. However, the farther the point A is from the copper mark 32, the longer the time required for detection becomes. Next, the servo motor 16 is activated to reciprocate the eddy current position sensor 10 in the X direction as shown by the broken line in FIG. When moving rightward in FIG. 3 through point B, the output current detected by the eddy current position sensor 10 changes as shown in FIG. 4. The coordinate value indicated by the pulse signal from the servo motor 16 at the point where the current rises to a predetermined value (that is, this corresponds to point B) is stored in the controller 24.

Further, the output current of the eddy current position sensor 10 when moving to the left in FIG. 3 through point C also changes as shown in FIG. 5, and the coordinate value C at point C is stored. The controller 24 performs the calculation x=(b+c)/2, and this X indicates the coordinate value of the center position of the copper mark 32 in the X direction. Next, the servo motor 20 is operated to reciprocate the eddy current position sensor 10 in the Y direction, and the center position of the copper mark 32 in the Y direction is calculated by the same operation as described above. This means that the center position of the copper mark 32 has been detected. Next, the servo motor 16 and the servo motor 20 are operated to move the drill 12 to this center position. That is, from the state where the eddy current type position sensor 10 coincides with the center position of the detected copper mark 32, the servo motor 16 is operated by the distance a1 between the eddy current type position sensor 10 and the drill 12 to move the drill head 4. It will be in a moved state. Thereby, the drill 12 is aligned with the center position of the copper mark 32. Next, the drill 12 is lowered and the reference hole is machined. As a result, a reference hole is accurately formed in the center of the copper mark 32.

The eddy current type position sensor 10 is of a type that detects an eddy current that changes depending on the presence of a copper mark, etc., but even if the copper mark 32 is covered by the blibrave 30b, the presence of the copper mark 32- is detected. The method of the present invention was made possible by discovering that the current changes due to the change in current.

In this embodiment, the copper foil layer 30a is counter-bored from the beginning, but in the eddy current position sensor 10, the copper mark 32 is cut to some extent even from above the layer 30a. Since it can be detected by the grain size, the position should be detected from above the copper foil layer 30a before counterboring, and if a sufficient positional grain size cannot be obtained, perform counterboring and then detect the position again. It is also possible to detect the position in the same manner as above.

(g) As described in detail, according to the present invention, only the outermost copper foil layer is removed and an eddy current position sensor is used to detect the center position of the reference mark on the inner layer of a multilayer printed circuit board. This makes it possible to accurately detect the center position of the copper mark, which cannot be visually confirmed, by counterbore machining that does not require MR. This also makes it possible to automate the entire process.

[Brief explanation of drawings]

Figure 1 is a plan view showing the reference hole processing device, Figure 2 is a view seen in the direction of arrow II in Figure 1, Figure 3 is a diagram showing the locus of the copper mark and the eddy current position sensor, and Figure 4. 5 and 5 are diagrams showing changes in the output current of the eddy current type position sensor, FIG. 6 is an enlarged sectional view of the multilayer printed circuit board, and FIG. 7 is a diagram showing the state in which the copper foil layer has been removed. 10... Eddy current position sensor, 12... Drill,
30...Multilayer printed circuit board, 30a...Copper foil layer,
30b... Prebrave, 32... Copper mark (reference mark). Patent Applicant Japan Steel Works Co., Ltd. Agent Patent Attorney Toshiyuki Miyauchi Figure 2 Figure 3 A Electric Figure 4 Drop C Sensor Seal

Claims (1)

[Claims] A method for detecting the position of a fiducial mark on a multilayer printed circuit board, which detects the position of the fiducial mark on a multilayer printed circuit board in which another copper foil layer is provided on the layer on which the copper fiducial mark is provided. After removing only the upper copper foil layer around the reference mark by machining, the eddy current position sensor is moved a predetermined distance from the surface of the multilayer printed circuit board, and the reference is determined from the change in output voltage or current. A method for detecting the position of a reference mark on a multilayer printed circuit board, the method comprising detecting the position of the mark.