JPS63261145A - X-ray tomographic apparatus - Google Patents

Abstract

PURPOSE:To correct the geometrical distortion of an X-ray inspection image and the fluctuation in irradiation X-ray intensity by previously measuring the distortion of the image detected by a detector and monitoring and detecting the irradiation X-ray intensity simultaneously at the time of the X-ray image detection of an inspection sample. CONSTITUTION:The X-ray image obtd. by projecting X-rays from an X-ray source 1 is detected on a scale which is previously provided with slit-shaped graduations on a plate consisting of a material having an X-ray shielding characteristic and the detected image data is stored via a buffer memory 9 or 10a, 10b in a scale image memory 11, an image memory 12 and memories 13a, 13b for detecting the fluctuation in irradiation intensity. The detection data is read out and the correction of the geometrical distortion of the detected X-ray image generated by a X-ray fluorescent image multiplier 4 is executed at the time of detecting the X-ray image. The intensity of the direct incident X-rays without passing the sample 2 is also simultaneously detected by a linear image sensor 6 and the irradiation X-ray intensity distribution at the time of detecting the X-ray image is corrected in the case of successively detecting X-ray images in the plural directions with respect to the inspection sample 2.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides an xH tomography apparatus for detecting minute internal defects in industrial components, such as soldering defects in electronic components in electronic circuit board modules. In particular, high-precision
The present invention relates to an X-ray tomography apparatus suitable for obtaining a ray image.

[Conventional technology]

Conventional inspection equipment using X-rays includes Koki: 1-Recent non-destructive transverse strain technology ("Piping and Equipment", Vol. 25,
No. 5 (1985) pp. 54-60), there are X-ray CT scanners and Xi television devices.

These devices attempt to nondestructively inspect internal defects in objects by obtaining cross-sectional images of the objects from X-ray fluoroscopic images or X-ray projection images obtained by irradiating the objects with X-rays. be.

The above-mentioned
By using an XM source with a high
There are some that have obtained a thickness of about 0 to 60 μm). However, since this method deals with a simple fluoroscopic image of the object, if other substances overlap and exist on the X-ray passage path, it becomes difficult to clearly identify internal defects in the target area.

In addition, an X-ray CT scanner detects an X-ray projection image of the object from all directions and uses this projection image to reconstruct the cross-sectional shape, but the obtained yIN power is 200 to 5.
It is too large, about 0.00 μm, and is not suitable for detecting minute defects.

On the other hand, using an X-ray source with a minute spot size, an enlarged projected image of the object is detected with high resolution using a linear image sensor via an X-ray fluorescence image intensifier, and this detection data is used to detect the object. There is a device that reconstructs the cross-sectional shape of.

[Problem that the invention seeks to solve]

Conventionally, in devices using the above-mentioned linear image sensor,
Geometric distortion of the X-ray inspection image caused by the fluorescent image intensifier tube and fluctuations in the intensity of the irradiated X-rays cause calculation errors and become obstacles to reconstructing highly accurate cross-sectional shapes. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray tomography apparatus that corrects geometric distortion of an X-ray examination image caused by an X-ray fluorescence image intensifier and intensity fluctuations of the irradiation X-suit.

[Means for solving problems]

The above purpose is to measure the distortion of the image detected by the detector in advance for the first point, and use the measured data as correction data, and for the second point, to measure the distortion of the image detected by the detector. This is achieved by simultaneously monitoring and detecting the irradiation Xi intensity at the time of detection, and correcting the X-ray image data of the detected object using that data.

[Effect]

In the present invention, an X-gland image obtained by irradiating X-rays onto a scale having a large number of slit-like graduations on an X-ray shielding plate is detected in advance and stored in a detected image memory. When detecting an XG image of an object, image data is read out from the memory, the amount of geometric distortion of the image detected by the X-ray detector is measured, and the amount is used to correct the coordinate position of the detected image data.

In addition, when detecting an X-ray image of an object, the intensity of the X-rays that directly enter the object without passing through it is also detected by the detector, and the detected data is used as irradiation X-ray intensity fluctuation correction data when reconstructing the cross-sectional shape. use

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2(a) shows an example of an LSI chip carrier to be inspected in this embodiment, and has a structure in which an LSI chip 22 is mounted on a ceramic substrate 21 by a CCB solder connection portion 23. Fig. 2(b) C, cross section Wi of m
In this example, the ceramic substrate 21 has a wiring layer 2.
It has a multilayer structure in which layers 4a to 24d are stacked, and there are through holes 26 filled with metal between each layer, and circuit wiring 27 made of metal is provided in each wiring layer.

The device of this embodiment has an L
It is used to inspect defects such as solder bubbles 27 and shape defects 28 that occur in the CCB solder joints of SI chip carriers.

FIG. 1 shows the overall configuration of the device of this embodiment.
A microfocus X-ray source 1 is provided to irradiate the test sample 2 held by a sample holder 10 with X-rays, and the transmitted X-ray image is transmitted to an X-ray fluorescence image intensifier 4.
After converting the image into a visible image, it can be detected by a linear image sensor 6 via a relay lens 5.

The X-ray detection image data output from the linear image sensor 6 in synchronization with the clock signal of the clock control circuit 7 is sequentially quantized by the A-D converter 8 and then sent to the buffer memory 9 or 10a, 10b. The data is stored in the scale image memory 11, the image memory 12, and the irradiation intensity variation detection memo'J13a and 13b, and is configured to be readable from the computer 15.

Further, according to instructions from the computer 15, the drive mechanism section 3 has a function of rotationally driving the sample holder 10 in the θ direction at a Δθ pitch.

Next, the operation of detecting the cross-sectional shape of a solder joint by the apparatus of this embodiment will be described.

First, a scale plate with slits 42 provided at equal intervals is set on an X-ray shielding plate 41 as shown in FIG. 4 at the sample detection position, and this detected image is stored in the scale image memory 11.

Generally, the light-receiving surface of an X-ray fluorescence image intensifier is spherical, as shown in FIG. 3(a). For this reason, a bottle cushion-like geometric distortion occurs in the detected image, as shown in FIG. 3(b). The detected image of the scale plate is used for the purpose of obtaining correction data for this geometric distortion. That is, the information stored in the scale image memory 11 is read out by the clearing machine 15, and as shown in FIG. 5(a), the detected coordinates r+' of each slit,
rI',...rn' are calculated, and as shown in the same figure (b), the calibration characteristics of the detection coordinate r' and the absolute position r are obtained, and the geometric distortion of the detected image of the sample is corrected. used for

Next, the test sample 2 set in the sample holder 10 is placed in the sixth
After setting the inspection position as shown in the figure, the drive mechanism 3 sequentially records the X-ray projection image I(r', θ) of the sample onto the image memory 12 while rotating intermittently in the θ direction at a Δθ pitch. Store in. Here, Bi indicates a detection position on the linear image sensor 6. At the same time, as shown in Figure 6(a),
A light receiving pixel 61a on the linear image sensor 6 receives irradiated X-rays that do not pass through the sample.

61b, Io (ra', θ) and I
c(rb', θ) and stored in the irradiation intensity variation detection memories 13a and 13b.

Furthermore, the irradiated X-ray intensity distribution I. In order to detect (r'), directly irradiated X-rays are detected by the linear image sensor 6 with the sample removed and stored on the image memory 12. At the same time, the detection value Ic (
ra') + Io (rb is also stored on the irradiation intensity variation detection memories 13a and 13b.

FIG. 7 shows image data I( An example of rθ) is shown below.

Hereinafter, a method of reorganizing the cross-sectional shape by calculation by the computer 15 using these detection data will be explained.

Image data I(r, θ) is expressed by the following relational expression, where μ(x, y) is the distribution of the X-ray absorption coefficient of the object.

I(r, θ)=I. ,/μ(x,y)d,1 ,,
,,, (1) Here, fμ(x,y)dl is the integral value of the Xi absorption coefficient μ(x,y) at the X-ray beam passing position.

In addition, o is the irradiated X-ray intensity.

If we reevaluate equation (1), we get the following equation.

/L(x, 3')dl=1n(Io/I(r, θ)
)−= (2) The problem of cross-sectional reconstruction is to give the actually measured image data I (r + θ) to equation (2) and find the distribution of the X-ray absorption coefficient μ(x, y). However, the distribution of the 8. irradiation X-ray intensity factor 0 introduced here differs depending on the detection position r, and also varies over time, which causes errors in calculation processing. Therefore, in this example, the coordinate correction data ○(r, θ) of the Xi irradiation intensity distribution ○(r/, θ) actually measured as described above is further corrected for temporal fluctuations. , the previously mentioned fluctuating detected value o(r a
' + θ) and Io (rb', θ), and the value calculated by the following formula is used.

・・・・・・(3) Therefore, by rewriting equation (2), we obtain the following equation.

=P(r, θ) (4) Here, P(r, θ) is called projection data.

Although various methods are known for calculating μ(x, y) from projection data P(r, θ), an overview will be given of an example in which the convolution method is applied.

This reconstruction principle is based on P o
(r a , θ.), a predetermined filter function is first applied to this to obtain a composition function for projection data in each direction.

Next, these convolution functions are combined to obtain a cross-sectional image. If these are expressed as an arithmetic expression, it will be as follows.

(5) Here, ro, ..., in and ro, max indicate the minimum and maximum values of the coordinate range from which projection data can be obtained.

Also, g(r,) represents a filter function, and Shesob(s
It has been demonstrated that highly accurate images can be obtained using the following method developed by L.H.P.H.P.H.P.H.P.H.P. and LOL.

However, r,=nil (n=0, ±1.±2...
), and a is the sampling interval at which projection data is obtained.

In the case of this example, since the projection data P(r, θ) is detected by a fan beam, P (
It is necessary to obtain projection data P (re + θ.) in the parallel beam coordinate system from r + θ.

This can be converted from the following relational expression, as shown by the geometrical relation in FIG.

θ. 20+t, an-' r/s -
・=(7) r o = D sin 96= D si
n (θ−θO) ・−・−・(a) Here, S
Let D represent the distance from the X-ray source to the detector, and D represent the distance from the X-ray source to the center of rotation of the test sample.

As shown above, using equations (7) and (8), projection data Pa(ro, θ
. ) Pa (ro, θ.) is calculated and the cross-sectional shape is reconstructed.

〔Effect of the invention〕

According to the present invention, in the Xi tomography apparatus, cross-sectional images can be obtained with high accuracy and high resolution without being affected by the geometric detector by the X-ray fluorescence image intensifier or by the intensity fluctuations of the irradiated X-rays. This makes it possible to detect minute internal defects in soldering parts of electronic circuits.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment of an X-ray tomography apparatus according to the present invention, FIG. 2 is an explanatory diagram of an object to be inspected in this embodiment, and FIG. 3 is a diagram showing geometric distortion of an X-ray detected image. 4 is an external view of the test plate for measuring geometric distortion, FIG. 5 is a diagram showing a detected image of the test plate and an example of detected distortion correction characteristics, and FIG. 6 is a diagram showing the test sample. FIGS. 7 to 9 are explanatory diagrams showing the geometrical positional relationship between the detector and the detector, and FIGS. 7 to 9 are diagrams for explaining a method of reorganizing the cross-sectional shape of the test cutting by calculation. 1... Microfocus X-ray source, 2... Inspection sample, 4...
X-fluorescent image intensifier, 6... linear image sensor, 7
... Rack control, 8... A-D '& converter, 9... Image buffer memory, 10a, 10b...
・Buffer memory, 11...Scale image memory, 1
2... Image memory, 13a, 13b... Irradiation intensity variation detection memory, -12. 15... Calculator.

Claims (1)

[Claims] 1. An X-ray source with a minute spot size and X-rays from the X-ray source
An X-ray fluorescence image intensifier that detects an X-ray transmitted image of an object enlarged and projected using a ray, converts it into a visible image, and multiplies the amount of light; and the X-ray fluorescence image intensifier In an X-ray tomography apparatus comprising a linear image sensor that receives an output image of and converts it into an electric signal, and a means for reconstructing the cross-sectional shape of the object based on the output signal of the linear image sensor, Detecting an X-ray image obtained by irradiating X-rays from the X-ray source onto a scale having slit-like graduations on a plate made of a material having X-ray shielding properties, and storing the detected data. The X-ray apparatus is characterized in that the X-ray apparatus comprises a means for reading out the detected data when detecting an X-ray image and correcting geometric distortion of the X-ray detected image generated by the X-ray fluorescence image intensifier. Linear tomography device. 2. In the X-ray tomography apparatus according to claim 1, when sequentially detecting X-ray images of a target object in multiple directions, the intensity of X-rays that directly enter the target object without passing through it is also An X-ray tomography apparatus characterized in that simultaneous detection is performed using a linear image sensor, and the irradiated X-ray intensity distribution at the time of X-ray image detection is corrected based on the detected data.