JPH0829489A - Method for correcting error between probes of x-y system in-circuit tester - Google Patents

Abstract

PURPOSE:To correct errors between the same or different kinds of probes in a short time and with high accuracy without being affected by dust sticking to the probes. CONSTITUTION:Camera mounting error is corrected, and after dints are formed on dint sheets 48a, 48b, 48c, the image of each dint in good shape photographed in advance by an image camera 42 is subjected to multiple-valuing by an image processing device 40 to originate a reference model for each dint, and the center of gravity of each reference model is stored so that it coincides with the corresponding specific coordinates at which the dint was intended to be made. The image of each dint photographed by the image camera 42 for the purpose of error correction is similarly subjected to multiple-valuing by the image processing device 40, and then the dint position which has the maximum similarity to the dint of each reference model is searched through normalization correlation, and the barycentric coordinates of each dint are determined, and the error of each probe 44a, 44b, 44c is corrected in accordance with the coordinates of a special board 50 by means of a difference between the barycentric coordinates and the corresponding specific coordinates at which the dint was intended to be made.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting an error between probes of an XY type in-circuit tester used for judging the quality of a mounting board.

[0002]

2. Description of the Related Art Conventionally, a mounting board, that is, a printed circuit board to which a large number of electronic components are soldered, uses an in-circuit tester, and a probe is appropriately contacted with a necessary measurement point on the board to determine the presence or absence of each component. Is electrically detected, or the characteristic value of each part is electrically measured to determine the quality of the substrate. In particular, the one in which the XY unit is installed on the measuring table on which the substrate to be inspected is mounted and fixed is provided with the Z-axis unit movable in the Y-axis direction on the arm movable in the X-axis direction, and the Z-axis unit The unit supports the probe so that it can move in the Z-axis direction, so it is easy to use. When the X-Y unit is controlled, the probe is moved from above the substrate to the X-axis, Y-axis, and Z-axis.
By appropriately moving in the axial direction, it is possible to sequentially contact each preset measurement point. In addition, when inspecting the board, it is necessary to simultaneously measure a plurality of measurement points for each part, so that an XY type in-circuit tester is usually equipped with a plurality of sets of XY units.

The XY units of such an XY type in-circuit tester have different assembling accuracy, reproducibility of screw-in angle when exchanging the probe, inherent difference of the probe itself, etc., so that there is an error between the probes. It is easy to occur. Therefore, even if each probe tries to come into contact with the same coordinates on the substrate, it becomes difficult to come into contact with the same coordinates unless the inter-probe error is corrected.

Therefore, the present applicant previously filed Japanese Patent Application No. 5-145.
As No. 780, in order to correct the error between the probes, a camera mounting error correction mark 10 as shown in FIG.
An error correction board 14 having a probe dent sheet 12 appropriately attached at an arbitrary position is placed and fixed, and a set of XY is formed.
Mark with the image camera equipped on the Z-axis unit of the unit
0 is copied, the center of gravity of the mark 10 is measured by the image processing device connected to the camera, and the camera is mounted according to the coordinates of the special board by the difference between the measured center of gravity coordinates and the coordinates of the center of gravity of the mark 10 according to the coordinates of the special board. After correcting the error, the XY unit or other XY units
The probe provided in the Z-axis unit of the unit is brought into contact with each corresponding dent mark sheet to leave a dent mark, and each dent mark is moved and moved by the image camera. The method of measuring the center of gravity of each probe and correcting the error of each probe according to the coordinates of the dedicated board by the difference between the measured respective coordinates of the center of gravity and the corresponding specific coordinates that were to be hit was presented.

[0005]

However, in such an inter-probe error correction method as described above, when measuring the center of gravity of a dent, as shown in FIG. , The dark part 20 where the light reflection is small is binarized with a slice level such that it becomes black 22, and the area (N) of the black part corresponding to the closed figure having the predetermined area is calculated as shown in FIG. Calculated from the number of pixels, the added value X of the X coordinate (X1 to Xn) is calculated by the expression of Formula 1, and the added value Y of the Y coordinate (Y1 to Yn) is calculated from Formula 2
After calculating from the formula, the center of gravity (centroid) coordinates (Xg, Yg
) Is calculated from the equations Xg = X / N and Yg = Y / N. Therefore, even if the scratches of the probe are initially circular as shown in FIG. 8, flux (dirt), dust, etc. adhere to the tip during use, and the scratches as shown in FIG. 9 are not formed. Portions 24 may result in different shapes. Then, as shown in FIG. 10, the actually measured barycentric coordinates 26
Is deviated from the barycentric coordinate 28 that should be originally measured, so that the accuracy of correcting the error between the probes becomes inferior unless flux and dust are removed. Therefore, it is necessary to constantly pay attention to the tip of each probe to remove dust and the like, so that the error between the probes cannot be corrected in a short time.

[Equation 1]

[Equation 2]

The present invention has been made by paying attention to such a conventional problem, and it is highly accurate in a short time without being affected by the flux, dust, etc. adhering to the contact probe, and the same kind and different kinds of probes. X that can correct the error between
An object of the present invention is to provide a method for correcting an error between probes of a Y-type in-circuit tester.

[0007]

In order to achieve the above object, in the present invention, as an inter-probe error correction method for an XY type in-circuit tester, each dent having a good shape previously captured by the image camera 42 is used. Image is subjected to multi-value processing by the image processing device 40, a reference model 54 of each dent is created in advance, and the barycentric position of the reference model 54 comes to each corresponding specific coordinate to be hit. Then, the image of each dent taken by the image camera 42 for error correction is similarly multivalued by the image processing device 40, and the dent having the maximum similarity to the nick of each reference model 54 is hit. The trace positions are searched for by the normalized correlation, the barycentric coordinates 60 of the positions 56 of the respective dents are determined, and the measured barycentric coordinates 60 and the corresponding specific coordinates to be hit are determined. Calculate the difference between Each probe in accordance with the 50 coordinate 4
The feature is that each of the four error corrections is performed.

[0008]

When the image of each dent taken by the image camera 42 is multi-valued with the above-described structure, the brightness from white to black can be represented by some grays, so that compared with the binarization processing. The features of dents can be captured more accurately. Therefore, when the barycentric coordinates (barycentric position) 60 of the position 56 of the found dent is determined, flux, dust or the like adheres to the tip of the probe 44 during use, and a part of the nick is missing or partly bright. Even if the dent shape changes due to changes in the dent shape, etc., the dent position having the maximum similarity to the dent of the reference model 54 is obtained by the normalized correlation.
No deviation occurs. Therefore, even if the tip shape of the probe 44 provided in the Z-axis unit of each XY unit is different, the error correction between the probes 44 can be similarly performed.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing a correspondence relationship between an XY type in-circuit tester with an image processing apparatus to which the present invention is applied and an error correction dedicated board. In the figure, 30 is an XY in-circuit tester with an image processing device, 32
Is an operation unit thereof, 34 is an XYZ control unit, 36 is a measuring unit, 38 is a controller, and 40 is an image processing apparatus.
The operation unit 32 includes a keyboard, a display device, a printer,
Equipped with input / output devices such as floppy disk drivers.
Then, for example, three sets of X- are controlled by the XYZ control unit 34.
An image camera 42 such as a CCD camera provided in the Z-axis unit of one set of XY units by driving servo motors and the like respectively provided in Y units (not shown) and controlling those XY units. A contact probe 44a, and contact probes 44b and 44c provided on the Z-axis unit of each of the other sets of XY units on the measurement table.
Move appropriately in the axial direction. Further, the measuring unit 36 has a resistance measuring circuit and the like, and applies an appropriate DC constant voltage or the like to a probe 44 provided in the Z-axis unit of each XY unit, and leads of electronic parts with which these probes 44 come into contact. The electric current etc. flowing in the pattern, etc. is detected and the resistance value etc. are measured.

The controller 38 is, for example, a microcomputer provided on the main body side, and has an operating section 32 and XYZ.
The image processing device 40 is controlled together with the control unit 34, the measurement unit 36, and the like. This microcomputer is CP
U (Central Processing Unit), ROM (Read Only Memory),
It is composed of a RAM (readable / writable memory), an input / output port, a bus line, and the like. The image processing device 40 is also equipped with a microcomputer and the like.

When performing the probe-to-probe error correction of the XY type in-circuit tester equipped with such an image processing apparatus, first, the camera mounting error correction mark 46 is predetermined on the measuring table before the substrate to be inspected is fixed. The error correction dedicated board 5 in which the sheet for scratching the probe 48 (48a, 48b, 48c) is attached to any position by the number of probes provided in the Z-axis unit of each XY unit.
Place 0 and fix. Next, Z of one set of XY unit
The image camera 42 provided in the shaft unit captures the mark 46, and the image processing device 40 multi-values the image to calculate the barycenter of the mark. At that time, the image camera 42 is moved and photographed so that the mark is located at the center of the light receiving surface of the image camera 42. The position of the mark can be monitored on the screen of the display device.

Next, the controller 38 calculates the difference between the measured barycentric coordinates and the barycentric coordinates of the mark based on the coordinates (reference coordinates) of the special board 50, and corrects the error in mounting the camera in accordance with the coordinates of the special board 50. To do. After that, first, an XY unit with an image camera 42 or other X-Y units
-The probe 44 provided in the Z-axis unit of the Y unit is brought into contact with the corresponding dent sheet 48 to leave dents, and then the nicks are moved by moving the image camera 42. . Note that FIG. 2 is a diagram showing an example of patterns of various dents based on the difference in the tip shape of various contact probes.

Then, in order to create a reference model of each dent, the image of each dent having a good shape previously photographed by the image camera is multivalued by the image processing device 40, and the reference of each dent is obtained. A model is created and stored so that the center of gravity of the reference model is located at each corresponding specific coordinate (center position of each monitor screen) to be hit. Next, the image of each dent taken by the image camera 42 for error correction is similarly multivalued by the image processing device 40, and the dent position with the maximum similarity to the nick of each reference model is determined. Search by normalized correlation respectively. At that time, since the monitor screen 52 corresponding to the light receiving surface of the image camera 42 as shown in FIG. 3 is the inspection target area, for example, a circular pattern 54 of the reference model is arranged on the screen 52 from the left for each reference model. After moving to the right, when it reaches the right end, it is lowered and returned to the left end, and raster scan is performed from left to right on the screen 52 to search for dents. Then, when f is a brightness value at an arbitrary position of the search image, g is a brightness value at an arbitrary position of the pattern image, F is an average brightness value of the search image, and G is an average brightness value of the pattern image, the normalized correlation value ρ is It can be calculated from the formula of Formula 3. Therefore, the output correlation value S is obtained from the equations 4 when ρ> 0 and S = 0 when ρ <0, and the output correlation value S is set to a value from 0 to 1000. When S = 0, there is no correlation, and S =
There is a maximum correlation at 1000.

(Equation 3)

[Equation 4]

As described above, when the image of each dent taken on the image camera 42 is multi-valued, the brightness from white to black can be represented by some grays. It becomes possible to handle objects that have changed gently to black and complicated objects, and the features of dents can be more accurately captured. Therefore, it becomes easy to find the position with the maximum degree of similarity using the reference model created in advance. Therefore, the barycentric coordinates of the struck position 56 found are determined. Then, as shown in FIG. 4, during use, flux, dust or the like is attached to the tip of the probe 44, and a part of the dent is missing or the brightness of a part of the dent changes, so that the shape of the dent changes. Even if the portion 58 and the like having no dent mark are taken into consideration, however, the center of gravity position 60 is not displaced. In addition,
It is well known that such a multi-valued pattern matching measurement method is implemented by a program stored in the memory of the image processing device 40.

When the barycentric coordinates are measured from the position 56 of the dent in this way, the barycentric coordinates are as close as possible to the ideal barycentric coordinates to be obtained. Therefore, the difference between each barycentric coordinate obtained by the multivalued pattern matching measurement method and each corresponding specific coordinate (center position on the monitor screen) to be hit is calculated, and the difference is adjusted to the coordinate of the dedicated board 50. Error correction of each probe 44 is performed. At this time, even if the tip shapes of the probes 44 provided in the Z-axis units of the respective XY units are different, the barycentric coordinates are obtained, and therefore the error correction between the probes 44 can be naturally performed. Note that the controller 38 performs the process after obtaining each barycentric coordinate by the multi-valued pattern matching measurement method.
It is implemented by the program stored in the memory.

[0016]

According to the present invention described above, since the reference model is created by the multi-valued pattern matching measurement method and the position of the dent is searched for, even if the shape of the dent changes, the dent is changed by the reference model. If the position of can be searched for, the deviation of the barycentric coordinates will not occur, and the barycentric coordinates close to the ideal can be measured. Therefore, even if flux, dust, or the like adheres to the tip of the contact probe during use, it is unlikely to be affected by this, and error correction between the same type and different types of probes can be performed in a short time with high accuracy.

[Brief description of drawings]

FIG. 1 is a block diagram showing a correspondence relationship between an XY type in-circuit tester with an image processing apparatus to which the present invention is applied and an error correction dedicated board.

FIG. 2 is a diagram showing an example of a dent pattern of various contact probes provided in the XY in-circuit tester.

FIG. 3 is a diagram showing a process of investigating a dent position using a reference model on a monitor screen of the same XY in-circuit tester.

FIG. 4 is a diagram showing a relationship between a dent position discovered through the same investigation process and barycentric coordinates of a reference model.

FIG. 5 is a plan view showing a state in which one probe dent sheet is attached to an error correction board.

FIG. 6 is a diagram showing a correspondence relationship before and after binarization processing.

FIG. 7 is a diagram showing a coordinate system of an image after binarization processing.

FIG. 8 is a diagram showing a good dent shape of a contact probe.

FIG. 9 is a diagram showing a deformation of a dent shape that occurs while using the contact probe.

FIG. 10 is a diagram showing a shift of a center of gravity position before and after deformation of the same dent.

[Explanation of symbols]

30 ... XY system in-circuit tester with image processing device 32 ... Operation part 34 ... XYZ control part 36 ... Measuring part 38 ... Controller 40 ... Image processing device 42
Image camera 44 Contact probe 46 Camera installation error correction mark 48 Probe dent sheet 50 Error correction board 52 Monitor screen
54 ... Reference model 56 ... Bite position 58 ... Bent chipped portion 60 ... Center of gravity position

Claims (1)

[Claims] 1. A Z-axis unit movable in X-axis direction and Y-axis direction is provided on a measuring table on which a substrate to be inspected is mounted and fixed, and at least one of an image camera and a contact probe is Z-axis unit by the Z-axis unit. X that supports movably in the direction
-By using an XY type in-circuit tester with an image processing device having a plurality of Y units installed, a camera mounting error correction mark is marked at a predetermined position on the measuring table,
Mount the error correction board with the probe dent sheet attached at an arbitrary position and fix it, and set the Z of one XY unit.
An image camera provided on the axis unit copies the camera mounting error correction mark, the image is processed by the image processing device to calculate the center of gravity of the mark, and the measured barycentric coordinates and the barycentric coordinates of the mark based on the coordinates of the dedicated board are calculated. After calculating the difference and correcting the camera mounting error according to the coordinates of the special board, put the probe provided on the Z-axis unit of the XY unit or each other XY unit on the dent sheet. Error between probes of XY method in-circuit tester that touches each other and leaves dents, and moves each image by moving the image camera and correcting the error of each probe according to the coordinates of the special board. In the correction method, the image of each dent having a good shape previously photographed by the image camera is multivalued by an image processing device, and a reference model of each dent is created in advance, After storing so that the center of gravity of the reference model would come to each corresponding specific coordinate that was tried to be applied, the image of each dent taken by the image camera for error correction was similarly multivalued by the image processing device. , The dent position with the maximum similarity to the dents of each reference model is searched for by the normalized correlation, and the barycentric coordinates of each of the dents are determined,
An XY type in-circuit tester characterized by calculating a difference between each barycentric coordinate and each corresponding specific coordinate to be hit and correcting the error of each probe in accordance with the coordinate of the dedicated board. Error correction method between probes.