JPH06118012A - Via-hole inspecting method - Google Patents

Abstract

PURPOSE:To make adequate 'good or not' judgment by judging whether a via-hole exists or not in place in accordance with a two-valued pattern and whether the sectionally horizontal shape of the opening is reasonable or not, and comparing the sum of multivalued shape signals containing a multivalued pattern with a reference value to judge whether residuals are in the via-hole or not. CONSTITUTION:When laser light 21 is irradiating the surface of a polyimide 32, the intensity of reflected light is almost constant but abruptly lower at the opening and the maximum on a metal layer 34 at a hole because of its completely reflected light. The intensity of the reflected light from polyimide residuals at the hole bottom is lower than that level on the layer 34 and higher than that level on the polyimide 32. These signals are converted into multivalued digital signals by setting a required level between a level 1 and a level 2. Data for picture elements corresponding to the opening area set up in a binarized area setting circuit is binarized by the binarizing circuit and judgment whether a via-hole exists or not and its shape is reasonable or not is given to the obtained binarized pattern by logical processing. The integrated value of the reflection intensity at the opening bottom is compared with a reference value to judge the residual quantity and whether a product is good or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a via hole formation state of a printed circuit board, and in particular, converting aperture information obtained by optical means into a digital quantity, and by the result of the logical operation, complete / impossible of the opening is detected. Involved in the method of determining perfection.

Vias are provided in a printed circuit board having wirings provided on the surface of a ceramic substrate and covered with a resin layer on the printed circuit board for connection with wirings on the resin layer and pins of an IC package. Since the diameter of this via hole is comparatively small, in order to make good electrical connection, the opening is not only penetrating through the resin layer, but also is shaped exactly according to the set shape. Must be

FIG. 5 is a perspective view showing the external appearance of a printed board provided with via holes. Reference numeral 31 in the figure is a ceramic substrate, and a plurality of via holes 33 are provided in a thin polyimide layer 32 laminated on the ceramic substrate. The thickness of the polyimide layer is about 30 μm, while the diameter of the via hole is about 60 μm.

FIG. 6 is a view showing cross-sectional shapes of good and bad via holes. FIG. 7A shows a perfectly good product, in which the opening diameter exactly matches the set value, and the opening position is centered in the metal layer 34 without displacement. Moreover, the polyimide is completely opened to the bottom of the hole, and there is no residue of polyimide.

On the other hand, FIGS. 2B to 2G are defective via holes having some defects. Figures (b) and (c) show the case where the opening position is wrong, and the part where the via hole should be provided is not opened (Figure (b)),
The part that should not be provided is opened (Figure (c))
Is. In addition, a hole having a correct opening position but having a too large opening diameter (Fig. (D)) and too small opening (Fig. (E)) are also defective as via holes.

Further, there are cases where the position and the opening diameter are correct, but there is a case where the holes do not come out cleanly to the bottom of the hole. This is the case when the polyimide remains.

[0007]

2. Description of the Related Art Conventionally, the following method has been used to optically detect various defective apertures.

As shown in FIG. 7 (a), when a printed board, which is an object to be inspected, is irradiated with laser light, the polyimide is irradiated from the irradiation point.
32 fluorescence is emitted. Since this fluorescent light has wavelength characteristics as shown in Fig. 2 (b), the laser light is cut by the filter with the characteristics shown in Fig. 1 (b), and the light is received by the sensor and photoelectrically converted into the printed board surface shape. Information related to.

FIG. 8 shows a situation in which the intensity of the fluorescence detection signal, which is the sensor output, changes when a via hole portion having a polyimide residue in the opening is scanned with laser light.
Although the laser light is constant during scanning the polyimide surface, it sharply decreases to almost 0 at the via hole portion and returns to the original value again when passing through the hole portion. When scanning on the bottom residue, a slight amount of fluorescence is generated, and the signal intensity is slightly increased as shown in the figure.

By setting the slice level 1 entered in the figure and binarizing the fluorescence detection signal, and confirming that it is 0 in a predetermined area and 1 in other areas, the opening position and shape are appropriate. It can be determined that there is. However, it is not possible to judge whether or not the polyimide remains at the bottom of the hole, so if slice level 2 is set and the completeness / incompleteness of the opening is judged based on the binarized signal, the bottom of the hole can be judged. Even if there is a residue in, it can be detected.

As described above, the two fluorescence levels can be binarized by setting the two slice levels according to the circuit of FIG. 9, and the shapes of the openings recognized by the respective binarized signals are the same. It becomes like pattern 1 and pattern 2 depicted in the figure.

FIG. 10 shows the configuration of a logic circuit for making a pass / fail judgment based on these two types of signals. First, pattern 1
In the determination process using the signal corresponding to, the via hole presence / absence determination circuit 43 examines the shape of the via hole center position designated by the design data. The part is pattern 1
If it is not “open”, it is determined that there is no via hole at the specified position.

Further, the shape inspection logic circuit similarly inspects whether or not the shape of the opening has a predetermined size or shape by using the signal corresponding to the pattern 1. If the deformation amount from the regular shape exceeds the allowable range, it is determined to be defective.

In the inspection of the bottom residue by the signal corresponding to the pattern 2, the area of the exposed bottom surface is calculated from the pattern 2 by the area measuring circuit, and it is checked whether or not it is within the preset area value range. If the bottom area is smaller than the set value, it is considered that there is a residue in the hole, and it is determined as defective.

[0015]

When a binary signal corresponding to pattern 2 in the figure is to be obtained by the circuit in FIG. 9, the slice level 2 must be set properly, but the allowable range is extremely high. narrow. Because the intensity of the fluorescence as the detection signal is also affected by the mass of the irradiated material, the fluorescence generated from the thin polyimide remaining on the bottom of the hole is weak, and the change range of the sensor output is also small. is there. If the voltage range in which the slice level is set is narrow in this way, the set value is likely to deviate from the proper range even slightly, and therefore, the quality judgment is often erroneous.

An object of the present invention is to improve the digitization process of the detection signal in the process of judging the quality of the via hole by the above-mentioned shape inspection logic, and use the improved detection signal to obtain a more accurate quality. It is to provide an inspection method for making a determination.

[0017]

In order to achieve the above object, in the via-hole inspection method of the present invention, the surface of a printed board as an object is virtually divided into pixel matrices, and the entire area of the matrix is irradiated with laser light. The printed board is provided with a multi-valued shape signal indicating the intensity of the reflected light from each pixel by irradiating in a scanning manner and receiving the reflected light on the sensor, and digitizing the output signal from the sensor by multi-value digitization. The via hole opening area is set based on the via hole center data in the design data, and the multi-valued shape signal corresponding to the pixel in the opening area is binarized to obtain a binarized pattern of the opening area. The presence / absence of a via hole at the predetermined position is determined based on a binary pattern, and the appropriateness of the horizontal cross-sectional shape of the opening is determined, and further, multi-valued conversion is performed by the multi-valued signal of the pixel corresponding to the opening region. The turn is extracted, the sum of the multi-valued shape signals included in the multi-valued pattern is compared with a reference value to determine the presence or absence of a residue inside the via hole, and the results of these determinations are combined. The quality of the via hole is determined.

According to another via hole inspection method of the present invention, the presence / absence of a via hole is determined based on the binary pattern obtained by the binarization process, and the appropriateness of the opening horizontal cross-sectional shape is determined, and the binary value is determined. The number of pixels of the truly opened portion of the opening area is obtained from the pattern, and the sum of the multi-valued shape signals obtained from the extracted multi-valued pattern,
The presence or absence of a residue in the via hole is determined by comparing the quotient divided by the number of pixels with a reference value.

[0019]

When the suitability as an optical signal for judging the shape of the via hole is evaluated, there is a drawback that the fluorescence generated from the polyimide layer has a small change width when a thin polyimide is present, that is, the contrast is weak. On the other hand, in the laser reflected light used in the present invention, the reflection from the metal surface exposed at the hole bottom is strong, and when the metal surface is covered with polyimide, the strength is clear even if it is thin. There is a feature that it decreases to. That is, since the contrast of the optical signal is strong, it is easy to set the slice level for determining the presence or absence of the polyimide residue, and the quality determination with few errors is performed.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the generation state and intensity distribution of an optical signal according to the present invention, and the optical system of an inspection apparatus used for implementing the present invention is schematically shown in FIG. Figure 1 (a)
Corresponds to FIG. 7 in the prior art, and for convenience of description, the via hole is drawn with an emphasis on the side slope.

Referring to FIG. 2, the printed board 1 as the subject is set on the moving stage 2 and is intermittently moved in the XY directions. On the other hand, the laser light emitted from the laser light source 3 enters the rotary polygon mirror 6 via the beam expander 4 and the mirror 5, and the emission direction thereof continuously changes with the rotation. The emitted light is condensed by the scanning lens 7, the optical path is changed by the mirror 8, and the printed board 1
Is irradiated in a scanning manner. The reflected light from the irradiation point travels in the opposite direction on the above optical path, changes its direction by the beam splitter 9, and enters the optical sensor 11 via the wavelength filter 10.

In FIG. 1A, the intensity change of the reflected light when the laser light scans the via hole portion is as shown in FIG. That is, the intensity of the reflected light when the laser beam irradiates the surface of the polyimide plate is almost constant at a certain level, and when the laser beam reaches the opening, the reflection direction deviates from the vertical direction, so the intensity sharply increases. descend. When the metal surface at the bottom of the hole is irradiated past the inclined surface of the opening, total reflection occurs here, and the reflected light intensity rises significantly above the level on the polyimide surface.

The intensity of the reflected light drops sharply even when the opposite slope is scanned, and when the light passes through the opening, the intensity of the reflected light returns to the initial level. If there is a residue of polyimide on the bottom of the hole, the intensity of the reflected light from that portion is lower than the level on the metal surface, but is higher than the intensity on the polyimide surface.

In the present invention, the signal thus obtained is multilevel by setting, for example, a level of 256 between the level 1 shown in FIG. 1 (b) and the level 2 which is the level of total reflection. Convert to digital signal. This multi-valued processing is the same as the normal AD conversion. In the first embodiment, the flow of the process for determining the quality of the via hole using this multi-valued signal is shown in FIG. 3, which will be described below with reference to FIG.

Also in the present invention, a binarized signal is used in the determination of the presence or absence of a via hole and the determination of the overall opening shape as in the prior art, but the processing for obtaining a binarized signal is conventionally performed. It is slightly different from the technology and adapted to the present invention. That is, level 1 in FIG. 1B is binarized as a slice level, and a pixel group of 1 surrounded by pixels of 0 is selected to be a binary signal (binarization pattern). The binarized pattern thus obtained represents an actual aperture shape.

When judging the presence / absence of a via hole and the judgment of suitability of an opening shape by using a binarization pattern in the logic processing flow of FIG. 3, the opening area set by the binarization area setting circuit 41 is detected. The data of each corresponding pixel is binarized by the binarization circuit 42, and the presence or absence of the via hole and the adequacy of the shape are determined for the obtained binarized pattern by the same logical processing as in the prior art.

In the determination of the presence / absence of a residue in the via hole, which is a feature of the present invention, first, the in-aperture data extraction circuit 45.
The multi-valued signal of the pixel which has become 1 in the binarization pattern is selected by the above, and this is set as the multi-valued pattern. Then
The sum measuring circuit 46 calculates the sum. This work is equivalent to obtaining the integrated value of the reflection intensity from the bottom of the opening, but the total sum in the presence of residue should be smaller than the total sum in the absence of residue.

In the total sum judgment circuit 47, this total sum value is compared with a reference value prepared in advance. If the difference between the two is within the specified range, it is judged that a small amount of residue is good, and if it exceeds the specified value, it is judged that there is residue. This determination result is combined with the presence / absence of the via hole and the determination result of the quality of the opening, and is output as defect information. In a normal purpose inspection, a product that passes all of these judgments is judged as a non-defective product.

Next, the processing for determining the quality of a via hole using a multilevel signal in the second embodiment of the present invention will be described.
The flow of the logical processing of this embodiment is shown in FIG. 4, which will be described below with reference to FIG.

Also in this embodiment, the presence / absence of the via hole and the suitability of the opening shape are determined by using the binarized pattern obtained by the same processing as in the first embodiment, and the applied logical processing is also performed. This is the same as the first embodiment. This becomes clear by comparing FIG. 4 and FIG. The characteristic point of this embodiment lies in the method for determining the presence or absence of residue, and although the basic processing is common to the first embodiment, the contents of the processing actually performed are different.

In the first embodiment, it is assumed that the sum of multi-valued signals of the pixels in the opening area corresponds to the metal exposed area at the bottom of the opening.
The variation of the actual opening area is regarded as an error and compared with a reference value set. However, in reality, the opening shape and the area are different for each via hole, and it is sufficient if it is within a predetermined range and completely penetrates the polyimide layer. The following processing is performed to compensate for the difference in opening area.

First, paying attention to the fact that the binarized pattern represents the horizontal sectional shape of the opening, and calculating the sum thereof, the actual opening area is obtained. Next, the total sum of the multi-valued signals obtained as described above is divided by this opening area, and the quotient is used to determine the presence or absence of residue. As shown in FIG. 4, the work for obtaining the sum of the binary signals is performed by the area measuring circuit 48.
Division using this is performed in the division circuit 49.

The work for obtaining this quotient corresponds to the work for finding the average value of the intensities of the reflected light from the pixels actually arranged in the opening, and the difference between the via hole with little residue and the via hole with many residues is large. As a result, a more appropriate pass / fail judgment is made.

[0034]

As described above, in the prior art, shape information is obtained by detecting fluorescence generated by irradiating a subject with laser light, whereas in the present invention, reflected light with high contrast is detected. Since the shape information is used as the shape information, the reliability of the signal itself is improved. Furthermore, in the presence / absence determination, since the quality judgment is performed by the logical operation of the multi-valued signal, it is more appropriate according to the actual situation. Judgment is made.

[Brief description of drawings]

FIG. 1 is a diagram showing generation and intensity distribution of an optical signal according to the present invention.

FIG. 2 is a schematic diagram showing the configuration of an apparatus used in the present invention.

FIG. 3 is a diagram showing a flow of logical processing of the first embodiment.

FIG. 4 is a diagram showing the flow of logical processing of the second embodiment.

FIG. 5 is a perspective view showing the appearance of a printed board.

FIG. 6 is a view showing a sectional shape of a via hole.

FIG. 7 is a diagram showing optical processing according to the related art.

FIG. 8 is a diagram showing a change in a detection signal when there is a residue.

FIG. 9 is a diagram showing binarization processing of a detection signal.

FIG. 10 is a diagram showing a flow of a logical process of a conventional technique.

[Explanation of symbols]

 1 Subject (printed board) 2 Moving stage 3 Laser light source 4 Beam expander 5 Mirror 6 Rotating polygon mirror 7 Scanning lens 8 Mirror 9 Beam splitter 10 Wavelength filter 11 Optical sensor 21 Laser light 22 Reflected light 23 Fluorescence 31 Ceramic 32 Polyimide 33 Via hole 34 Metal layer 35 Residue 40 Multi-valued circuit 41 Binarized area setting circuit 43 Via presence / absence judgment circuit 44 Shape inspection logic circuit 45 In-aperture data extraction circuit 46 Sum total measurement circuit 47 Sum total judgment circuit 47 'Area judgment circuit 48 Area Measuring circuit 48 'Area measuring circuit 49 Dividing circuit

Claims (4)

[Claims] 1. A surface of a printed board, which is an object, is virtually divided into a pixel matrix, the entire area of the matrix is scanned and irradiated with laser light, the reflected light is received by a sensor, and the output from the sensor is output. A signal is multi-value digitized to obtain a multi-valued shape signal indicating the intensity of reflected light from each pixel, and the via-hole opening area is set based on the via-hole center data in the printed board design data, The multi-valued shape signal corresponding to the pixels in the opening area is binarized to obtain a binarized pattern of the opening area, the presence / absence of a via hole at the predetermined position is determined based on the binary pattern, and the opening is determined. Whether or not the horizontal cross-sectional shape is appropriate is determined, and a multi-valued pattern composed of the multi-valued signal of the pixel corresponding to the opening area is extracted, and the multi-valued shape signal included in the multi-valued pattern is extracted. The standard value is the sum Via hole inspection method characterized by determining the presence or absence of residue inside the via hole by comparison. 2. The via hole inspection method according to claim 1, wherein the presence / absence of a via hole is determined based on the binary pattern obtained by the binarization process, and the appropriateness of the horizontal sectional shape of the opening is determined. The number of pixels in the truly opened portion of the opening area is obtained from the binary pattern, and the quotient obtained by dividing the sum of the multi-valued shape signals obtained from the extracted multi-valued pattern by the number of pixels is a reference value. A method for inspecting a via hole, characterized in that the presence or absence of a residue in the via hole is determined by comparing with. 3. An inspection apparatus for carrying out the inspection method according to claim 1, comprising: (a) irradiating a surface of a printed board, which is an object, with a laser beam, and sweeping the irradiated light. An optical system (3 to 10) that receives the reflected light from each pixel of the pixel matrix assumed in (1) to the optical sensor (11), and (b) a means (40) for converting the output of the sensor into a multilevel digital signal. ,
(c) means (41) for setting a via hole opening area based on the printed board design data, and (d) binarizing the multi-valued digital signal corresponding to the pixels included in the opening area into a binary value. Means (42) for obtaining a digitized pattern, and (e) means (43) for determining the presence or absence of the via hole based on the binarized pattern
And means (44) for judging the suitability of the horizontal cross-sectional shape of the via hole based on the binary pattern, and (f) means for obtaining the sum of the multi-valued digital signals corresponding to the pixels included in the opening region. (45, 46), and (g) a via-hole inspection device comprising means (47) for judging the presence or absence of residue in the via-hole by comparing the total value with a reference value. . 4. An inspection apparatus for carrying out the inspection method according to claim 2, comprising the constituent features (a) to (f) of the via hole inspection apparatus according to claim 3, wherein the opening area is truly opened. Means (48) for obtaining the number of pixels in the portion and (g ') the residue in the via hole by comparing the quotient obtained by dividing the sum obtained by the means (f) by the number of pixels with a reference value. A via-hole inspection device comprising means (49, 47) for determining the presence or absence of