JP2002090315A - Method and device for surface inspection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a device for surface inspection, for accurately inspecting an object to be inspected by improving the measuring accuracy regardless of the large or small size of the object to be inspected. SOLUTION: The surface state and the like of the object to be inspected are inspected by measurement based on the operation of an electric signal obtained by the photoelectric conversion of a scattered reflected light L4 of scanning light L3 reflected by a surface 12a of the object to be inspected 12 while alternately performing unidirectional light scanning of the scanning light to the surface 12a of the object 12, and the intermittent relative movement of the object 12 in an orthogonal direction to the light scanning direction I. At this time, at least one of the light scanning speed of the scanning light L3, the relative moving speed of the object 12 or scanning light L3, and the sampling interval of the scattered reflected light L4 is arbitrarily made variable.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for optically scanning a surface of an object such as a circuit board, a liquid crystal panel element, a semiconductor wafer or a single electronic component on which components have been mounted, from the surface of the object. Inspecting the surface condition of the inspection object based on the reflected scattered reflected light, in particular, displacement, omission, defective soldering, floating of the component before soldering or defective shape of the component, etc., of the electronic component mounted on the circuit board. And a surface inspection apparatus for the same.

[0002]

2. Description of the Related Art In recent years, when inspecting the surface condition of a circuit board on which electronic components are mounted, a laser scanning type surface inspection apparatus has been widely used. This surface inspection apparatus is generally configured as shown in FIGS. That is, FIG. 6 is a schematic configuration diagram as viewed from the front, and FIG. 7 is a schematic configuration diagram as viewed from the right side. In these drawings, the laser beam L1 emitted from the semiconductor laser element 1 passes through the collimator lens 2. After being converted into the light beam L2, any one of eight mirror surfaces 4a provided around the polygon mirror 4 having a polygonal shape is provided.
And is reflected from the mirror surface 4a.

The polygon mirror 4 is rotated at a constant speed in the direction indicated by an arrow in the figure around the rotation axis 3 by a flat opposed flat motor 7 shown in FIG. As a result, the eight rectangular mirror surfaces 4a of the polygon mirror 4, which are arranged in parallel to the axial direction of the rotating shaft 3, are rotated around the rotating shaft 3, and are projected onto the rotating mirror surface 4a. Light beam L2
Is incident from a direction orthogonal to the rotation axis 3. Therefore, the light reflected by the mirror surface 4a is deflected in one direction indicated by an arrow I with the rotation of the mirror surface 4a as shown by a broken line in FIG. 5B.

As shown in FIGS. 6 and 7, the light deflected as described above is scanned by a plurality of (three in FIG. 3) lenses 9, 10, and 11 arranged coaxially. After being deflected and condensed by the fθ lens system 8, the surface 1 of the mounting circuit board 12 exemplified as the object to be inspected is
2a is imaged. The scanning light L3 imaged on the surface 12a of the mounting circuit board 12 in this manner is optically scanned on the surface 12a of the mounting circuit board 12 as the polygon mirror 4 rotates. As shown in FIG. 7, the scattered reflected light L4 reflected on the surface 12a of the mounting circuit board 12 by this light scanning is collected by the condensing lenses 13 arranged at symmetrical positions on both sides with respect to the optical axis of the scanning light L3. After the light is condensed by the light, the light is incident on the light receiving surface 14a of the opposing photodetector 14.

In this surface inspection apparatus, the scanning light L3
Focusing lenses 13 at symmetrical positions on both sides with respect to the optical axis of
Further, since the photodetector 14 is disposed, the scattered reflected light L4 is blocked by the step of the electronic component 18 to be inspected, and the scattered reflected light L4 does not enter one of the photodetectors 14. In such a case, the other photodetector 14 can detect the light.

The photodetector 14 photoelectrically converts the incident scattered reflected light L4, and outputs an electric signal corresponding to the light irradiation position of the scattered reflected light L4 on the light receiving surface 14a to the arithmetic unit 17. In the arithmetic unit 17, the photodetector 1
On the basis of the electric signal input from step 4, the height position of the surface of the electronic component 18 which is the inspection object mounted on the surface 12a of the mounting circuit board 12 is calculated by a known triangulation method.

On the other hand, the circuit board 12 to be inspected is placed on an automatic stage 19,
6 moves at a constant speed in a direction perpendicular to the light scanning direction by the scanning light L3 (the front-back direction in FIG. 6 and the left-right direction in FIG. 7). As the linear movement mechanism 20 of the automatic stage 19, a configuration in which a ball screw is rotationally driven by a motor, a linear motor, or the like is generally used.

The automatic stage 19 is provided with a movement origin detecting sensor 21 for detecting that the automatic stage 19 has reached the origin position at which movement is started and outputting a first synchronization signal.
Also, at a predetermined relative position with respect to the polygon mirror 4,
As shown in FIG. 5, an optical scanning origin detecting sensor 22 for detecting the origin light L5 reflected at the origin position at which each mirror surface 4a of the polygon mirror 4 starts optical scanning and outputting a second synchronization signal is provided. Has been established.

The measurement field of view, that is, the effective measurement area for effectively taking in the height measurement data of the electronic component 18 is set by the waiting time from the time when the first and second synchronization signals are respectively output. You. That is,
When the automatic stage 19 starts moving and reaches the origin position, the movement origin detection sensor 21 outputs a first synchronization signal shown in FIG. When a predetermined standby time T elapses from the time when the first synchronization signal is output, as shown in FIG. 4B, a period from this time until a predetermined time elapses is set as a movement direction effective area A. Is set. Subsequently, when a certain mirror surface 4a of the polygon mirror 4 reaches the origin position, the optical scanning origin detection sensor 22 detects the origin light L5, and the second synchronization signal shown in FIG. You. When a predetermined standby time t has elapsed from the time when the second synchronization signal was output, as shown in FIG. 4D, a period from this time until the predetermined time has elapsed is the optical scanning direction effective area B. Is set as

The arithmetic unit 17 fetches an electric signal from the photodetector 14 at predetermined regular intervals based on a predetermined sampling clock during the period of the effective area B in the optical scanning direction, calculates the electric signal, and calculates the electric signal. The height position of No. 18 is calculated. When the first effective area B in the light scanning direction is completed, the automatic stage 19 is driven to drive the mounting circuit board 12.
Is intermittently moved by a predetermined distance.

Next, in the second effective area B in the light scanning direction which is set when the standby time t has elapsed from the time when the second synchronizing signal is output, the arithmetic unit 17 operates in the same manner as described above. An electric signal is taken in from the photodetector 14 at predetermined regular intervals based on a predetermined sampling clock, and the height of the electronic component 18 is calculated by calculating the electric signal. By repeating the above-described measurement operation and the intermittent movement of the mounting circuit board 12 alternately within the period of the movement direction effective area A, each electronic component 18 existing in the entire effective measurement area set on the mounting circuit board 12 is Is measured based on the measurement points set in a matrix, and measurement data as a set of three-dimensional coordinates is obtained. Arithmetic unit 1
7 determines the state of each electronic component 18 based on the obtained measurement data, which is a set of three-dimensional coordinates.

[0012]

However, in the above-described surface inspection apparatus, the surface state of the inspection object can be effectively measured in a non-contact manner by photoelectrically converting the scattered reflected light L4 of the scanning light L3 reflected by the inspection object. On the other hand, since the optical scanning range and the sampling resolution are constant, effective measurement data can be obtained as the number of measurement points decreases, especially when the object to be inspected is small. Since the number of measurements is reduced, there is a problem that a measurement error increases and an accurate inspection result cannot be obtained.

In view of the above, the present invention has been made in view of the above-mentioned conventional problems, and a surface inspection capable of improving the measurement accuracy and accurately inspecting an object to be inspected regardless of the size of the object to be inspected. It is an object to provide a method and a surface inspection device.

[0014]

In order to achieve the above object, a surface inspection method according to the present invention comprises a method of optically scanning a surface of an object to be inspected in one direction with scanning light and a method of optically scanning the object to be inspected. The intermittent relative movement in the direction perpendicular to the direction is alternately performed, and the inspection light is measured based on a calculation based on an electric signal obtained by photoelectrically converting the scattered and reflected light reflected on the surface of the inspection object. When inspecting the surface condition of the object, at least one of the optical scanning speed of the scanning light, the relative movement speed of the object to be inspected or the scanning light, and the sampling interval of the scattered reflected light is arbitrarily variable. did.

In this surface inspection method, when the shape of the inspection object is small, at least one of the light scanning speed of the scanning light, the relative movement speed of the inspection object or the scanning light, or the interval at which the scattered reflected light is sampled is set as follows. By variably setting the value to a small value corresponding to the shape of the inspection object, the interval between the number of measurement points can be set small. Accordingly, since the number of measurement points does not decrease despite the shape of the inspection object being small, the measurement can be performed without lowering the sampling resolution, and the measurement error is reduced because the measurement data does not decrease. And the measurement accuracy is significantly improved as compared with the related art.

In the above-described surface inspection method, a first standby time from when the inspection object and the scanning light detect the origin position at which the relative movement starts, and at a time when the scanning light detects the origin position at which the optical scanning starts. It is preferable that the second standby time is set arbitrarily, and only the electric signal based on the scattered reflected light sampled from the time when the two standby times have elapsed is used for the calculation.

Accordingly, when the shape of the object to be inspected is small, an effective inspection area having a small area corresponding to the shape can be set. Similarly, only a part of data input set as an effective inspection area can be made effective. For this reason, when the shape of the inspection object is small, unnecessary measurement data due to extra sampling is excluded, and the inspection efficiency is significantly improved.

Further, the surface inspection apparatus of the present invention has a laser element that emits a laser beam, and a polygon having a peripheral surface formed by a plurality of mirror surfaces. A deflection scanning mirror for optically scanning the surface of the inspection object with scanning light that reflects the laser light incident on the mirror surface from a direction perpendicular to the center, and a rotation speed of the deflection scanning mirror is variably set. A rotation speed setting unit, a photodetector that receives scattered reflected light in which the scanning light is reflected on the surface of the inspection object, and an automatic detector that relatively moves the inspection object or the scanning light in a direction orthogonal to the optical scanning direction. A stage, a moving speed setting unit that arbitrarily sets the moving speed of the automatic stage, a moving origin detecting unit that outputs a first synchronization signal by detecting an origin position at which the automatic stage starts moving,
An optical scanning origin detecting unit that detects an origin position at which the deflection scanning mirror starts optical scanning and outputs a second synchronization signal;
After a predetermined standby time has elapsed from the time when the first and second synchronization signals have been output, an electric signal from the photodetector is taken in at a predetermined sampling interval, and the scattered reflection on the light receiving surface of the photodetector is obtained. And an arithmetic unit for calculating the surface state of the inspection object by calculating based on the incident position of the light.

This surface inspection apparatus is provided with a rotation speed setting unit for arbitrarily setting the rotation speed of the deflection scanning mirror and a movement speed setting unit for setting the movement speed of the automatic stage arbitrarily. The optical scanning speed of the scanning light and the relative moving speed of the inspection object or the scanning light can be set arbitrarily variably, and an arbitrary area can be obtained by including the moving origin detecting unit and the optical scanning origin detecting unit. Therefore, the surface inspection method of the present invention can be faithfully embodied, and the same effect as the surface inspection method can be reliably obtained.

It is preferable that the surface inspection apparatus has a variable sampling circuit for arbitrarily setting a sampling interval of the arithmetic unit. Thus, the sampling interval of the scattered reflected light can be arbitrarily changed and set, and the surface inspection method of the present invention can be more faithfully embodied.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram of a surface inspection device embodying a surface inspection method according to an embodiment of the present invention as viewed from the front, and FIG. 2 is a schematic configuration diagram of the surface inspection device as viewed from the right side. In these drawings, the same or equivalent components as those in FIGS. 6 and 7 are denoted by the same reference numerals, and description thereof will be omitted. The point that the surface inspection apparatus of this embodiment differs from the conventional surface inspection apparatus is that the flat facing motor 7 rotates the polygon mirror 4 based on the frequency of the control clock variably set in the clock control unit 23. , The arithmetic device 17 fetches electric signals from the photodetector 14 at equal intervals based on a sampling clock variably set in the variable sampling circuit 24, and performs the arithmetic operation. This is the only configuration in which the movement of the automatic stage 19 is controlled at the movement speed variably set in the setting unit 27. Therefore, the operation of measuring the height or the like of the inspection object by optical scanning is the same as that described in the conventional surface inspection scanning, and the description thereof will be omitted.

The flat opposed flat motor 7 controls the rotation of the polygon mirror 4 at a constant rotation speed within a range of 5000 rpm to 40,000 rpm based on the frequency of the control clock variably set in the clock control unit 23. Has become. The variable sampling circuit 24 sets the frequency of the reference sampling clock in the frequency dividing circuit to 1/2, 1 /
A variable frequency such as 4 is set, and a predetermined one of these variably set frequencies is selectively selected and output by a switch. The moving speed setting section 27 controls the frequency of the control clock variably set in the clock control section 23 or the variable sampling circuit 2.
The movement of the automatic stage 19 is controlled at a movement speed corresponding to the frequency of the sampling clock selected in step 4.

This surface inspection apparatus is provided with the above-described structure, and can cope with a reduction in the shape of the inspection object.
Switching so that the visual field of measurement, that is, the effective inspection area, can be set to 1/4, 1/16, 1/64 smaller than the inspection effective area of the conventional apparatus without reducing the number of measurement points compared to the conventional surface inspection device. It is characterized by being able to. FIGS. 4 and 5B referred to in the description of the related art are a timing chart when a reference inspection effective area is set and an optical explanatory view of the scanning light L3 serving as an effective measurement point. On the other hand, in the timing chart of FIG. 3, the effective inspection area is set to be smaller than the reference inspection effective area by one-fourth corresponding to a small inspection object. FIG. FIG. 7 is an optical explanatory diagram of a scanning light L3 serving as an effective measurement point when an area is set.

That is, when the automatic stage 19 starts moving and reaches the origin position, the movement origin detection sensor 21
By setting the standby time T from the point of time when the first synchronization signal shown in FIG. 3A is output to longer than that in FIG. 4, the movement direction effective area A shown in FIG. Is set to 短 く shorter than the reference. Further, when a certain mirror surface 4a of the polygon mirror 4 reaches the origin position, the standby time t from the time when the second synchronization signal shown in FIG. 4, the effective area B in the light scanning direction shown in FIG. 4D is set to be shorter than the reference in FIG. 4 by half. As a result, the entire measurement visual field itself actually scanned by light is the same as that of the conventional apparatus, but only a part of data input set as an effective inspection area is valid.

In the timing chart of FIG. 3, the rotation speed of the polygon mirror 4 is set to be the same as the rotation speed when the effective inspection area is set as a reference, and the frequency of the sampling clock of the variable sampling circuit 24 is changed in the light scanning direction. In response to the effective area B being shortened by half with respect to the reference, the switching is set to １ ／, and the moving speed of the automatic stage 19 is reduced by the fact that the moving direction effective area A is に 対 し with respect to the reference. The moving speed setting unit 27 has switched the setting to し て in response to the shortening.

FIG. 5A is an optical explanatory view showing the scanning light L3 serving as an effective measurement point when the effective area B in the light scanning direction is set as described above. As is clear from the comparison, the effective area B in the light scanning direction is narrow, but the number of effective scanning lights L3, that is, the number of measurement points is not reduced. As a result, even if the object to be inspected has a small shape, the effective inspection area is set to an optimum range according to the shape of the object to be inspected, but the number of measurement points does not decrease, thereby lowering the sampling resolution. Since the measurement can be performed without causing the measurement data to decrease, the measurement error can be reduced because the measurement data does not decrease, and the measurement accuracy is remarkably improved as compared with the conventional apparatus.

In the above embodiment, the rotation speed of the polygon mirror 4 is fixed at the same level as the reference, and the frequency of the sampling clock of the variable sampling circuit 24 and the moving speed of the automatic stage 19 are variably set to 1/2. Although the case where the effective inspection area is set to be smaller than the reference effective inspection area by 1/4 has been described, when the inspection object has a smaller shape, the frequency of the sampling clock of the variable sampling circuit 24 is changed. And the moving speed of the automatic stage 19 is 1/4 or 1/8, respectively.
, The effective inspection area can be set to be 1/16 or 1/64 smaller than the reference effective inspection area. In each case, the number of measurement points is the same as that of the reference.

In the above embodiment, the clock control unit 23 is provided so that the rotation speed of the polygon mirror 4 can be variably set, so that the effective inspection area can be reduced to 1/4, 1/16 or 1
/ 64, the frequency of the sampling clock of the variable sampling circuit 24 is fixed to be the same as the reference, and the rotation speed of the polygon mirror 4 and the moving speed of the automatic stage 19 are each reduced by half with respect to the reference. , 1 /
By setting to either 4 or 1/8, the same effect as described above can be obtained.

Further, when the magnification a with respect to the reference of the rotation speed of the polygon mirror 4 and the magnification b with respect to the reference of the frequency of the sampling clock of the variable sampling circuit 24 are simultaneously switched, the moving speed c of the automatic stage 19 is changed to By setting c = a × b, a measurement field of view that is c × c times can be obtained. At this time, two types of standby time T,
By selecting t to an appropriate value, an optimal effective inspection area corresponding to the shape of the inspection object can be set.
In any of the above cases, it is possible to perform measurement with a fixed number of measurement points while setting an inspection effective area corresponding to the shape of the inspection object.

The procedure of the surface inspection by measuring the height position of the electronic component 18 to be inspected is the same as that described in the prior art. The intermittent movement of the inspection object by the automatic stage 19 and the light by the scanning light L3 are performed. By alternately performing the scanning, the surface inspection of the inspection object such as the surface 12a of the mounted circuit board 12 can be performed. However, the object to be inspected is stationary, and the optical inspection mechanism including the semiconductor laser element 1, the collimator lens 2, the polygon mirror 4, the fθ lens system 8, the condenser lens 13, the photodetector 14, and the like is moved. Is also good.

[0031]

As described above, according to the surface inspection method of the present invention, when the shape of the inspection object is small, the light scanning speed of the scanning light, the relative moving speed of the inspection object or the scanning light, or the scattered reflection light. Can be variably set to a small value corresponding to the shape of the inspection object, so that the interval of the number of measurement points can be set small. Accordingly, since the number of measurement points does not decrease despite the shape of the inspection object being small, the measurement can be performed without lowering the sampling resolution, and the measurement error is reduced because the measurement data does not decrease. And the measurement accuracy is significantly improved as compared with the related art.

Further, according to the surface inspection apparatus of the present invention, a rotation speed setting unit for arbitrarily setting the rotation speed of the deflection scanning mirror and a moving speed setting unit for arbitrarily setting the movement speed of the automatic stage are provided. Since the optical scanning speed of the scanning light and the relative moving speed of the inspection object or the scanning light can be arbitrarily changed and set, and the moving origin detecting unit and the optical scanning origin detecting unit are provided. Thus, an effective inspection area having an arbitrary area can be set. Accordingly, the surface inspection method of the present invention can be faithfully embodied, and the same effect as the surface inspection method can be reliably obtained.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a surface inspection apparatus embodying a surface inspection method according to an embodiment of the present invention as viewed from the front.

FIG. 2 is a schematic configuration diagram of the same surface inspection apparatus as viewed from the right side.

FIG. 3 is a timing chart in a case where a surface inspection of an object having a small shape is performed by the surface inspection apparatus.

FIG. 4 is a timing chart in a case where the surface inspection apparatus performs a surface inspection of an inspection object having a reference shape.

FIGS. 5 (a) and 5 (b) show scanning light at a measurement point when performing a surface inspection on an object having a small shape and a surface inspection on an object having a reference shape in the surface inspection apparatus. FIG.

FIG. 6 is a schematic configuration diagram of a conventional surface inspection apparatus viewed from the front.

FIG. 7 is a schematic configuration diagram of the surface inspection apparatus of the above, viewed from the right side.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser element (laser element) 3 Rotation axis 4 Polygon mirror (deflection scanning mirror) 4a Mirror surface 12 Mounted circuit board (inspected object) 12a Surface 14 Photodetector 14a Light receiving surface 17 Arithmetic unit 19 Automatic stage 21 Moving origin detection Sensor (moving origin detecting unit) 22 Optical scanning origin detecting sensor (optical scanning origin detecting unit) 23 Clock control unit (rotation speed setting unit) 24 Variable sampling circuit 27 Moving speed setting unit L1 Laser light L3 Scanning light L4 Scattering reflection Light I Light scanning direction

Claims (4)

[Claims] 1. The method according to claim 1, wherein the optical scanning in one direction of scanning light on the surface of the inspection object and the intermittent relative movement of the inspection object in a direction orthogonal to the optical scanning direction are alternately performed. In a method for inspecting the surface state of the inspection object by measurement based on an operation of an electric signal obtained by photoelectrically converting scattered reflected light reflected by the surface of the inspection object, the optical scanning speed of the scanning light, A surface inspection method, wherein at least one of a relative moving speed of an inspection object or the scanning light and an interval of sampling the scattered reflected light is arbitrarily changed. 2. A first waiting time from a point of time when an inspection object and a scanning light detect an origin position at which relative movement starts, and
The second standby time from the time when the scanning light detects the origin position at which the optical scanning starts to be started is arbitrarily set, and only the electric signal based on the scattered reflected light sampled from the time when the two standby times have elapsed is validated. The surface inspection method according to claim 1, wherein the calculation is performed. 3. A laser element for emitting laser light, wherein the peripheral surface has a polygon formed by a plurality of mirror surfaces, and the mirror surface rotates in a direction perpendicular to the axis of the rotation axis while rotating around a rotation axis. A scanning mirror that optically scans the surface of the inspection object with the scanning light that reflects the laser light incident on the mirror; a rotation speed setting unit that arbitrarily variably sets a rotation speed of the deflection scanning mirror; A photodetector that receives scattered reflected light whose light is reflected on the surface of the inspection object, an automatic stage that relatively moves the inspection object or the scanning light in a direction orthogonal to the optical scanning direction, and movement of the automatic stage A moving speed setting unit that arbitrarily sets a speed; a moving origin detecting unit that detects an origin position at which the automatic stage starts moving and outputs a first synchronization signal; and the deflection scanning mirror performs optical scanning. The starting point An optical scanning origin detecting unit for detecting a position and outputting a second synchronization signal; and an electric signal from the photodetector after a predetermined standby time has elapsed from the time when the first and second synchronization signals are output. An arithmetic unit that captures a signal at a predetermined sampling interval and calculates a surface state of the inspection object by calculating based on an incident position of the scattered reflected light on a light receiving surface of the photodetector. Surface inspection equipment characterized by the above-mentioned. 4. A variable sampling circuit for arbitrarily setting a sampling interval of an arithmetic unit.
Surface inspection apparatus according to 1.