JPS6361155A - Apparatus for inspecting internal flaw - Google Patents

Abstract

PURPOSE:To effectively inspect the soldering part of a mounting part, by inclining a specimen stand having a circuit part to be inspected mounted thereon and making the characteristic distribution of X-rays allowed to irradiate variable to detect transmitted X-rays. CONSTITUTION:A specimen 3 to be inspected such as an electronic circuit module is mounted on a specimen stage 4 and an electron beam target 10 is controlled by a voltage control apparatus 9 to control the acceleration voltage of the beam from an X-ray source 1. Further, the positions and angles theta1, theta2 of inclination of the specimen stage 4 in X- and Y-direction are controlled by a stage control apparatus 5. The X-rays transmitted through the specimen 3 to be inspected are detected by an X-ray detector 2 and a fluoroscopic image is stored in image memories 7a-7n. At this time, the generation voltage of X-rays allowed to irradiate is changed and the density value between fluoroscopic images to each metal material of solder is changed to extract the image only of a solder connection part by a computer 8. Since the image of the solder connection part is extracted from the fluoroscopic images in which the images corresponding to a plurality of metal materials constituting the circuit module are present in a mixed state, the internal flaw of the solder connection part can be detected with high reliability.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention utilizes an internal fluoroscopy technique using radiation such as XWA.
It relates to technology for inspecting soldered parts of circuit components and organ materials.

[Conventional technology]

XI! As a conventional inspection device using
As described in s C1985) p, p, 5' to 60), examples include an X-ray CT scanner and an X-ray television device.

These are methods for non-destructively inspecting internal defects of a target object from a perspective image or a projection image obtained by irradiating the target object VCXi.

[Problem that the invention seeks to solve]

Although the conventional X-ray television apparatus has a high resolution (generally about 20 to 30 .mu.m), it has the following problems when transparently inspecting the circuit components and wiring materials that are the subject of the present invention.

That is, electronic circuit modules are normally mounted in these circuit components at high density.

In a fluoroscopic image obtained by an X-ray television device, an image in which projected images of not only soldered parts but also metal materials constituting electronic components, circuit wiring, etc. are superimposed is generated. Therefore, the identifiability of the solder connection portion to be inspected cannot be improved.

More specifically, when a multilayer wiring board or the like is selected as an object to be inspected, a dark shadow of metal wiring with buried through holes is detected, which becomes an obstacle to the object to be inspected which is detected more faintly.

On the other hand, the conventional XIWCT scanner has a resolution of 200 to 500 μm, which is lower than the resolution required for the fluoroscopic examination of the present invention. Furthermore, a CT scanner reconstructs the cross-sectional shape of an object from a plurality of one-dimensional projection images, and performs image processing by irradiating X-rays from around the object, resulting in an increase in the size of the device.

Inspection time will be longer.

As mentioned above, there are no devices that can inspect the solder parts of electronic circuit modules mounted on one circuit component, and the object of the present invention is to inspect the solder parts of electronic circuit modules mounted on one circuit component. An object of the present invention is to provide an inspection technique that can effectively inspect solder parts.

[Means for solving problems]

A device configured to irradiate the inspection object with X-rays with different wavelength distributions and process the obtained fluoroscopic image according to a correction value calculated from the X-ray absorption coefficient of the inspection object, opens a predetermined inspection area, Detect defects in the relevant part.

More specifically, a plurality of fluoroscopic images are taken by irradiating X-rays with different wavelength distributions onto a component-mounted circuit board to be inspected. And the metal material that makes up the circuit board
Using the correction value calculated from the WM absorption coefficient, the projection image of the metal material that was an obstacle to the inspection can be corrected by converting the density value of the image and calculating the difference image. Erase.

Perform defect inspection.

[Effect]

Changes in the accelerating voltage of X-rays appear as changes in radiation energy mainly on the shorter wavelength side in the X-ray spectrum. Since this changing region is a region that transmits through metal, the influence of the metal on the image can be removed by setting an appropriate threshold value and image processing for detecting transmitted X-rays.

Therefore, it is possible to perform image processing that cancels out a dark image in a transmitted X-ray image, which was difficult with the prior art, and it is effective as a pre-processing for image processing of an inspection object that is projected more faintly.

[Example] An example of the present invention will be described below. FIG. 2 shows an example of an electronic circuit module to be inspected, which has a structure in which an IC chip 12 is soldered and mounted on a ceramic substrate 20. Figure 5 is.

This cross-sectional structure is shown, and the ceramic substrate 20 has a multilayer structure in which wiring layers 14α to 14d are laminated.

There are through holes 16 filled with metal at predetermined lattice size positions between each layer, and each wiring layer is provided with circuit wiring made of thin metal. Connecting pins 15 are provided on the lower surface of this ceramic substrate 20, and an IC chip 12 is mounted on the upper surface and connected with solder 18. An object of the present invention is to inspect solder connections for defects such as solder bubbles 16 and defective solder 19.

A radiation source 1 is provided to perform X-ray irradiation, and an X-ray detector 2 can take a fluoroscopic image. In addition, in order to control the energy of this irradiated X-ray, a voltage controller 9 is provided,
By controlling the acceleration voltage of the electron beam supplied to the X-ray generation target 10 of the radiation source 1, the energy intensity of the irradiated X-rays can be varied according to the command value of the computer 8.

A stage controller 5 is used for the sample stage.

According to the command signal from the computer, the position in each of the X and Y directions and the inclination angle θ1. θ2 can be set automatically. The fluoroscopic image taken by the X-ray detector 2 is configured to be stored in 5 image memories 7α to 7n after AD conversion and read out from the computer 8, and through this arithmetic processing, an image of only the solder joint is extracted. , a defect inspection is carried out and displayed on a monitor television 11 together with 5 to enable visual confirmation.

When inspecting solder joints, the test sample is mounted on the sample stage, and the transparent position (X, Y) of the solder joint is
After moving to the tilt angle σ1. Set evening 2. Next, while sequentially switching the X@ generation voltage to a predetermined value, a fluoroscopic image for the irradiated X-ray under each condition is detected and stored in the one-image memories 7α to 7d.

FIG. 4 α shows an example of a perspective image of the test sample obtained at this time, and shows solder joints 30 and metal-filled through holes 31, which have a higher X-ray absorption coefficient than ceramic substrates and wiring circuits. Alternatively, a perspective image of the metal part of the connection pin is obtained as an image with high density values. Since the perspective images overlap each other, it is difficult to identify the solder joints.

On a fluoroscopic image detected by changing the generated voltage of irradiated X-rays,
The density value ratio between the perspective images for each metal material shows different values. In other words, a difference in shading occurs in the projected images of metal parts of the same color tone.

This is because the X-ray absorption coefficients of metal materials such as lead, tungsten, and molybdenum shown in Figure 5 differ depending on the wavelength distribution of the irradiated X-rays, and the wavelength distribution of the X-rays shown in Figure 6 This is due to the fact that the line-generated voltage significantly increases or decreases in short wavelength components. In other words, increase or decrease the X-ray generation voltage.

The X-ray wavelength around 0.1X in FIG. 6 increases or decreases, and since this X-ray transmits through metals such as tungsten and lead, the shading of the transmitted image becomes clear.

The present invention extracts and inspects images of solder parts from these images through processing by a computer 8.

Hereinafter, a method for extracting an image of a solder joint from a fluoroscopic image detected under each condition will be explained when the X-ray generation voltage is set to two conditions, V+ and V2.

Using the X-ray source of one apparatus, the X-ray absorption coefficient (average absorption coefficient in the distribution wavelength range of the irradiated X-rays) of each metal material at the X-ray generation voltage v1v2 is determined in advance.

The X-ray absorption coefficient μ is calculated by assuming that the irradiation X-ray dose is 1 inch, the transmitted X-ray dose is Iotbt, and the thickness of the target material is T.

IoJ = Iin −e−μ°T It is expressed as From this, the X-ray generation voltage is set to V+.

Under each condition set as v2, the detected values of X-rays directly incident on the detector J+, I2 and the detected values of X-rays passing through the metal sample (thickness T) of the target material oLLt1
゜If ICmt2 is determined, the X-ray absorption coefficient μm, I2
teeth.

μ+ = = 〒Ln (Imtl /■in1)I
2 = −y An (Iout2/bjL2')
It can be expressed as

This is how I found it. The X-ray absorption coefficient of the solder at the X-ray generation voltage V+, V2 is μs+, μ82. The X-ray absorption coefficient of the through-hole filling metal is μt1. If μth2, other materials on one circuit module with a small X-ray absorption coefficient can be ignored, so the fluoroscopic images PICx, y) and P2Cx, y) at the X-ray generation voltage V1°V2 are expressed as follows. .

However, 3:, ν represents the coordinate position on the two-dimensional image,
'p+(:c, 2), P2C3:, l) is the detected value of transmitted X-rays at each position, Ts (x, y),
Tth (x, y) is the distribution of the amount of solder and through-hole filling metal (X-ray passing distance); 11. I2 represents the irradiated X-ray dose at each generated voltage (V+, V2).

(1), (If we logarithmically transform equation 21, we get (31, (4
One formula is obtained.

(3+, (From equation 41, distribution of solder amount TsCx, y
) is determined.The principle of the present invention is based on (5), and the irradiation X-ray dose ■+ , I2 and μs+ , I82 , μ
th+, μth2, and inspection.

Detected value p+(z,y) of transmitted X-rays for the target sample
.

Using P2 (ZJ), solder amount distribution Ts by a total of 74 machines
(3:, y), and as a result, it is possible to extract an image of only a perspective solder image, as shown in the example of FIG.

From each solder extraction image obtained in this way, this device
Solder area - 'P diameter in the horizontal direction.

Alternatively, solder connection defects are detected by detecting the circumferential length and the presence or absence of bubbles and comparing them with reference values.

As a result, bubble defects q and b are formed as shown in FIG. 7 α.

It is possible to detect excessive or insufficient amount of solder, defective shape, etc. as shown in C.

When extracting an image of a solder part, if the inspection target is made of three or more types of materials, the same calculation process can be performed by switching the x-ray generation conditions the corresponding number of times and detecting each fluoroscopic image. , a perspective image of the solder joint can be extracted.

〔Effect of the invention〕

According to the present invention, it is possible to carry out X-ray fluoroscopic inspection of a mounted circuit board, which was previously impossible.

More specifically, it is now possible to extract images of solder connections from a perspective image containing a mixture of images corresponding to multiple metal materials that make up one circuit module, allowing for high-density wiring and
Highly reliable measurement of internal defects in solder joints can also be performed on mounted circuit modules.

[Brief explanation of the drawing]

FIG. 1 is an overall configuration diagram of an embodiment according to the present invention, FIG. 2 is an overview diagram of the object to be inspected, and FIG. 5 is a sectional view of the object to be inspected in FIG.
Figure 4 α is a diagram showing the detected fluoroscopic image, Figure 4 is a diagram showing the extracted result of the image of the solder joint, Figure 5 is a diagram showing the X-ray absorption coefficient of metal materials, and Figure 6 is a diagram showing the X-ray absorption coefficient of metal materials. The figure shows the wavelength distribution of output X-rays when the generated voltage is changed, and FIG. 7 is a diagram showing an example of a perspective image of a solder defect. 1... X-ray source, 2... X-ray detector, 3... Inspection materials. 4.5. Material stage, 5... Stage control device, 6
...AD converter, 7α~Full...Image memory, 8.
··calculator. 9... X-ray generation voltage controller, 10... Electron beam target. Departure l concave 2nd fall] mouth 4th Kotobuki 5ro θ σ, l σ, 2 θzu σ, 4 15
θOtoecho [su] Yu≦Country0 0.1 θ, 2 θ, 56. Δρ,
6. Chief [A] 7. Procedural amendment for the purpose of 7. Showa 1961 patent application No. 114504 Name of the invention Person who corrects the internal defect calibration device 1 Relationship with the patent applicant Name 51) Stocks ] Kano I] Standing
Manufacturer's Billing Fee Management Person's Amendment (7) Contents of the amendment in the brief explanation of drawings in the specification

Claims (1)

[Scope of Claims] 1. A sample stage on which an object to be inspected is placed tiltably; an X-ray source with variable characteristic distribution of irradiated X-rays; a detector for detecting transmitted X-rays from the object to be inspected; controlling the inclination of the table to vary the characteristic distribution of the irradiated X-rays;
An internal defect inspection device comprising an electronic device for processing signals from the detector. 2. The internal defect inspection apparatus according to claim 1, wherein the X-ray source has a characteristic distribution variable by a voltage controller that changes the electron beam acceleration voltage for generating X-rays.