JP2002122554A - Device for inspecting via hole in printed wiring board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a via hole inspecting device capable of speedily, easily, and accurately detecting resin residues in via holes in a printed wiring board. SOLUTION: In the via hole inspecting device 1, via holes in a build-up substrate S in which insulating resin layers and conductor layers are laminated. The via hole inspection device 1 is provided with a light source part 2 provided with a plurality of semiconductor light emitting elements 21 for sequentially switching a plurality of rays of light with different center wavelengths with one another and irradiating the via holes with them, a light receiving part 3 provided with a plurality of two-dimensionally arranged light receiving elements for detecting reflected light from the via holes, and a signal processing part 4 for sequentially acquiring output signals from the light receiving part 3 according to the switching of the plurality of rays of light and determining the degree of resin residues in the via holes on the basis of the acquired output signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a via hole inspection apparatus for a printed wiring board such as a build-up substrate, a flexible substrate, a ceramic substrate, and an MCM substrate. The present invention relates to a via hole inspection device configured to be able to determine the degree of resin residue.

[0002]

2. Description of the Related Art In recent years, build-up boards are advantageous in that they can be made lighter and thinner by high-density mounting and can be manufactured at a reduced cost. At the beginning, it is widely used as a mobile mounting board, BGA (ball grid array), CSP (chip size package), MCM
(Multi-chip modules) are rapidly spreading as interposers.

The build-up board is formed by alternately laminating a conductor layer made of copper foil or the like and an insulating resin layer made of epoxy or the like. Further, in order to electrically connect the conductor layers, via holes are formed at predetermined positions of the build-up board so as to penetrate the insulating resin layer. For forming such via holes, 50 μm to 70 μm
A predetermined portion of the insulating resin layer having a thickness of about m
A method called a photo method or a laser method is used in order to penetrate with a diameter of about 200 μm.
In some cases, an insulating resin having a thickness of about μm remains (the remaining resin is referred to as “resin residue”). Such a resin residue has a problem in that it adversely affects the conduction of the substrate in a later process and lowers the yield of products.

Conventionally, as a method of inspecting the resin residue in the via hole, a method of visually inspecting using a microscope, a method of using a laser itself when forming a via hole by a laser method, and the like are known. .

[0005]

However, in the case of the visual inspection using a microscope, there are drawbacks in that the inspection requires time and labor, and there is a lack of objectivity due to individual differences among examiners. The method of inspecting using a laser by the laser method is a method of measuring the thickness of the resin residue by detecting the phase difference of the reflected light from the via bottom,
In general, the laser method uses a carbon dioxide gas laser having a wavelength of about 10 μm, so that there is a problem that only a residue having a thickness of about 2 μm or more can be detected due to a limitation of resolution.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is a via hole inspection capable of quickly, easily and accurately detecting a resin residue in a via hole of a printed wiring board such as a build-up board. It is intended to provide a device.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the resin residue was reduced to 1 μm.
In many cases, the resin residue has a thickness of about m or less, and since it has light transmittance, if such a resin residue is considered to be a kind of thin film formed on a conductor layer, an optical thin film measuring technique is applied. They have found what they can do and completed the present invention.

That is, the present invention is an apparatus for inspecting a via hole in a printed wiring board on which an insulating resin layer and a conductor layer are laminated, wherein a plurality of lights having different center wavelengths are sequentially switched to the via hole. A light source unit for irradiating, a plurality of light receiving elements arranged two-dimensionally, a light receiving unit for detecting reflected light from the via hole, and an output signal from the light receiving unit in response to switching of the plurality of lights And a signal processing unit for sequentially determining the degree of resin residue in the via hole based on the obtained output signal.

According to the invention, the light emitted from the light source unit to the via hole is reflected on the front and back surfaces (the surface in contact with the conductor layer) of the resin residue, and each of these reflected lights is dependent on the thickness of the resin residue. A phase shift occurs and interferes with each other, and is detected by the light receiving unit. The light amount (brightness and darkness) of the interference light according to the degree of the phase shift differs depending not only on the thickness of the resin residue but also on the wavelength of the light to be irradiated. Therefore, by irradiating light of a plurality of wavelengths and detecting the amount of interference light for each wavelength as in a known film thickness measurement method,
It is possible to calculate the thickness of the resin residue. In this regard,
Since the light source unit of the present invention is configured to sequentially switch and emit a plurality of lights each having a different center wavelength,
The light receiving unit sequentially detects interference light corresponding to a plurality of wavelengths. The signal processing unit obtains an output signal of the light receiving unit, that is, a signal corresponding to the amount of interference light for each wavelength, and thus can determine the degree of the thickness of the resin residue based on the signal. Further, since the light receiving section includes a plurality of light receiving elements arranged two-dimensionally, the entire via hole can be inspected at a time.

[0010] Preferably, the light source unit includes a plurality of light emitting diodes, and a diffusion plate is provided in front of a light emitting surface of the light emitting diodes.

When a plurality of light emitting diodes (hereinafter, sometimes referred to as LEDs) are used in the light source unit, even if mechanically precise optical axis adjustment is performed, the bonding of the LEDs, the shape of the light emitting unit, and the shape of the light emitting chip. Due to the location and other factors,
There is a problem in that the light axes of all the LEDs cannot be handled as the same light source. Although such mismatch of the optical axis is a small angle, when the unevenness of the surface is severe compared to a thin film formed on a semiconductor substrate, such as an insulating resin layer or a conductor layer of a build-up substrate, each LED Comparing the reflected lights corresponding to (1) and (2), the position of focusing on the light receiving element may be shifted by several elements even if the reflected light is from the same place. Such displacement is not preferable in determining the thickness of the resin residue described above.

According to the present invention, since the diffusion plate is provided in front of the light emitting surface of the LED, it is possible to correct the variation of the optical axis of each LED and treat the light passing through the diffusion plate as a light source close to parallel light. Therefore, it becomes possible to inspect the resin residue with higher accuracy.

[0013] Preferably, the plurality of light emitting diodes include one white light emitting diode and a plurality of monochromatic light emitting diodes, and the signal processing unit is configured to obtain the light emitting diode for each irradiation by each of the light emitting diodes. The output signal from the light receiving unit is stored as a plurality of images, and from the image when illuminated by the white light-emitting diode, an area having a gray level value equal to or higher than a predetermined value is extracted, and when illuminated by the plurality of monochromatic light-emitting diodes From the image, a gray value of a pixel corresponding to the region is detected, a relative spectral reflectance curve is calculated for each pixel constituting the region based on the detected gray value, and the relative spectral reflectance is further calculated. The degree of the resin residue in the via hole is determined based on the number of extreme values of the curve.

As described above, since the surface of the insulating resin layer and the conductor layer of the build-up substrate have severe irregularities, the reflected light is irregularly reflected, and the amount of light detected by the light receiving portion is reduced.
It may be difficult to use as data for determining the degree of resin residue (see FIG. 6). That is, at the top or bottom of the surface profile of the conductor layer and the insulating resin layer, the vertically incident light is directly reflected as it is, but the light incident on the inclined portion is reflected according to the inclination. When the light-receiving part is installed, the amount of light received at the top or bottom becomes large, whereas the amount of light received at the inclined part becomes small.If the amount of light received from such an inclined part is used as resin residue determination data, In some cases, this may cause noise and lower the accuracy of resin residue determination.

According to the present invention, an area having a gray value equal to or more than a predetermined value is extracted from an image illuminated by a white light emitting diode, and the degree of resin residue is determined only for pixels in the extracted area. , It is possible to eliminate the above-mentioned decrease in accuracy. That is, from the image when illuminated by a plurality of monochromatic light emitting diodes, to detect the gray value of the pixel corresponding to the region, based on the detected gray value, to determine the degree of resin residue, as described above, The amount of received light (shading value) is reduced, and data of the inclined portion that is likely to be a noise factor is omitted, and it is possible to determine the resin residue with higher accuracy. In addition, in determining the resin residue, since the determination based on the number of extreme values of the calculated relative spectral reflectance curve is performed, it is necessary to take into account the complicated procedures necessary for measuring the exact thickness of the resin residue. And easy and quick determination is possible.

[0016]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a conceptual diagram showing one embodiment of a via hole inspection device for a build-up substrate according to the present invention, and FIG. 2 is a cross-sectional view of a build-up substrate to be inspected. As shown in FIGS. 1 and 2, a via hole inspection apparatus 1 according to the present embodiment includes a conductor layer S1 made of copper foil or the like, and an insulating resin layer laminated on the conductor layer S1 and made of epoxy, resin, polyimide, or the like. S2
And a build-up substrate S having
The purpose is to inspect the extent of the resin residue S21 remaining at the bottom of the via hole H formed at a predetermined location in the insulating resin layer S2.

As shown in FIG. 1, a via hole inspection apparatus 1
The light source unit 2 includes a plurality of LEDs 21 arranged in a ring shape so as to sequentially switch and irradiate a plurality of lights having different center wavelengths to the build-up substrate S, and includes a plurality of CCD elements arranged two-dimensionally. And build-up board S
A CCD image sensor 3 for detecting reflected light from a predetermined area including the via hole H collectively, and an output signal from the CCD image sensor 3 in response to the switching of the plurality of lights, and the acquired output signal And an image processing device 4 for determining the degree of resin residue in the via hole of the build-up substrate S based on the result of the determination and displaying the result.

The via hole inspection apparatus 1 includes a light source unit 2
Lenses L1, L2 and L3 and a half mirror M1 for converging the light emitted from the lens and irradiating the light on the build-up substrate S from a substantially vertical direction. Further, a pinhole P is provided at a position corresponding to the focal length of the lens L1 in order to remove noise of emitted light. Further, a reflection mirror M2 and a lens L4 are provided to focus the reflected light from the build-up substrate S onto the CCD element of the CCD image sensor 3 via the half mirror M1.

The light source unit 2 has a plurality of LEDs 21 arranged in a ring as described above. In this embodiment, 1
White LEDs, each having a center wavelength of 470 nm, 5
02 nm, 525 nm, 590 nm, 612 nm, 62
9 which is 3 nm, 644 nm, 700 nm, and 735 nm
The single-color LEDs are arranged in a ring. Also, in front of the light emitting surface of each LED 21, each LED 2
A diffusing plate 22 is provided so as to correct the variation of the optical axis 1 and make the emitted light substantially parallel. As such a diffusion plate 22, for example, a diffuser having a transmission wavelength range of 365 nm to 1600 nm and a uniformity of transmitted light of 85% or more can be used.

Further, the light source unit 2 includes a reflection mirror M3 connected to a rotary motor 23 to guide the light transmitted through each diffusion plate 22 to the lens L1. By driving the rotation motor 23 to rotate the reflection mirror M3, the light emitted from each LED 21 is transmitted to the build-up substrate S
It is possible to sequentially switch and irradiate.

The CCD image sensor 3 has a size of 50 μm to 2 μm.
In order to accurately inspect the via hole H having a diameter of about 00 μm, a CCD element of about 640 × 480 pixels is required.
Approximately 3 μm on via hole H
It is arranged so that the reflected light from the square area is focused on one CCD element.

The image processing device 4 obtains an output signal (video signal) from the CCD image sensor 3 in accordance with the switching of the LED 21 and stores the output signal (video signal) from the CCD image sensor 3 as a plurality of digital images corresponding to each LED 21. A / D converter and a memory (not shown) are provided. Further, based on the stored image, software for determining the degree of resin residue in the via hole of the build-up substrate S is installed, and a monitor (not shown) for graphically displaying the determination result is provided. Have.

Although not shown, the via-hole inspection apparatus 1 is mounted on a biaxial stage, and sequentially moves to a via-hole H forming position of the build-up substrate S sucked by a blower on a predetermined base. It is configured so that inspection can be performed continuously.

Hereinafter, the operation of the via hole inspection apparatus 1 having such a configuration will be described. First, after the build-up board S to be inspected is mounted on the gantry, the via-hole inspection apparatus 1 places the lens L directly above the via-hole H specified based on data such as CAD and NC.
3 is moved to the position, and is automatically aligned by image processing by the image processing device 4, and further, is auto-focused.

Next, the reflection mirror M3 is rotated to a predetermined position so that the light emitted from the white LED 21 of the light source unit 2 irradiates the via hole H to be measured, and the reflected light is detected by the CCD image sensor 3. The output signal from the CCD image sensor 3 is taken into the image processing device 4 and stored as an image. As shown in FIG. 3, the image processing device 4 extracts a predetermined number of pixels (for example, 100 pixels) from a plurality of pixels corresponding to the via holes H in the stored image in descending order of shading values. (Hereinafter, the extracted pixels are referred to as “bright spots”). The present invention is not limited to such an extraction method, and it is also possible to specify a predetermined grayscale value in advance, and to extract a pixel having a grayscale value equal to or higher than the specified grayscale value.

Next, the reflection mirror M3 is rotated by a predetermined amount, and the light emitted from the monochromatic LED 21 different from the white LED 21 is applied to the via hole H to be measured. The light reflected from the via hole H is detected by the CCD image sensor 3 and stored in the image processing device 4 as an image, as in the case of the white LED 21. The above operation is
The rotation of the reflection mirror M3 is sequentially performed for all the single-color LEDs 21.
Nine images corresponding to each of the single-color LEDs 21 are stored. These nine images are the white L
Although the image obtained by the ED21 irradiation has a different wavelength of the irradiation light, the field of view is the same.

The image processing device 4 converts the nine images into
The gray value of the pixel corresponding to the position of the bright spot is sequentially detected (see FIG. 3). That is, for each pixel constituting the bright spot, a gray value corresponding to nine wavelengths is detected. When the gray values corresponding to these nine wavelengths are all equal to or less than a predetermined value (for example, when the reflectance is 30% or less based on bare silicon or a copper plate), the data is used as data for determining the degree of resin residue. Has been deprecated.

Next, the image processing device 4 calculates a relative spectral reflectance curve based on the nine discrete gray levels detected for each pixel constituting the bright spot. Here, the relative spectral reflectance curve can be calculated by fitting a spline function or a polynomial function to the discrete gray value using a known approximation method, for example, a least square method. FIG.
Is an example of calculating such a spectral reflectance curve, and FIG.
Shows the case where there is no resin residue, and (b) shows the case where there is a resin residue. 4, the points plotted at locations indicated by lambda ₁ to [lambda] _9, a nine discrete gray values detected for each pixel constituting the bright spot. The illustrated curve is a relative spectral reflectance curve calculated based on the discrete grayscale values. In FIG. 4, the calculated grayscale value and the relative spectral reflectance curve are simultaneously displayed for all the pixels constituting the bright spot.

Next, the image processing device 4 counts the number of extreme values of the relative spectral reflectance curve calculated as described above, and determines the degree of resin residue. As shown in FIG. 4, the number of extreme values increases when there is a resin residue, as compared with the case where there is no resin residue. Further, although not shown, even when there is a resin residue, the number of extreme values increases as the thickness of the resin residue increases. Therefore, by counting the number of such extreme values, the degree of the thickness of the resin residue can be easily determined without strictly measuring the thickness of the resin residue. Note that, in the present embodiment, it is configured such that a determination is made in four stages according to the number of extreme values. However, if the optical constants (reflection coefficient and absorption coefficient) of the resin are determined, it is possible to perform strict thickness measurement (calculation of the absolute value of the film thickness) of the resin residue.

Further, the image processing device 4 displays the result of the determination on a predetermined monitor. FIG. 5 shows an example of such a graphical display. As shown in FIG. 5, the monitor displays ranks A to D for each pixel constituting a bright spot in the via hole H.
The determination results up to the D rank are displayed (actually displayed in different colors), and the user can easily recognize the degree of the resin residue.

The operation described above is sequentially repeated for all the via holes H to be inspected, and the inspection of the build-up substrate S is completed.

[0032]

As described above, according to the via hole inspection apparatus of the present invention, the light source unit switches the plurality of semiconductor light emitting elements so as to sequentially switch the plurality of lights having different center wavelengths to irradiate the via holes. For this purpose, the light receiving section sequentially detects interference light corresponding to a plurality of wavelengths. The signal processing unit obtains an output signal of the light receiving unit, that is, a signal corresponding to the amount of interference light for each wavelength.
The degree of the thickness of the resin residue can be easily and accurately determined based on the signal. In addition, since the light receiving section includes a plurality of light receiving elements arranged two-dimensionally, the entire via hole can be collectively and quickly inspected. As described above, the present invention has an unprecedented excellent effect that resin residues in via holes of a printed wiring board such as a build-up board can be detected quickly, easily, and accurately.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing one embodiment of a via hole inspection apparatus for a printed wiring board according to the present invention.

FIG. 2 is a cross-sectional view of a build-up board to be inspected by the via hole inspection apparatus according to the present invention.

FIG. 3 is a schematic diagram illustrating a relationship between respective LED irradiation images stored in the image processing apparatus illustrated in FIG. 1;

FIG. 4 shows an example of a relative spectral reflectance curve calculated by the image processing apparatus shown in FIG.

FIG. 5 shows an example of a determination result displayed by the image processing apparatus shown in FIG.

FIG. 6 is a schematic diagram showing a state of incident light and reflected light in an insulating resin layer of a build-up substrate.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 via hole inspection device 2 light source unit 3 CCD image sensor 4 image processing device 21 semiconductor light emitting device (LED) 22 diffusion plate S build-up substrate H via hole

Continued on the front page F-term (reference) 2F065 AA30 BB05 CC01 DD03 DD04 DD06 FF51 GG07 GG14 GG23 HH04 HH13 JJ03 JJ09 JJ26 LL00 LL12 LL30 LL49 MM02 NN06 PP12 QQ18 QQ51 RR08 SS04 SS13 UU01 AU12CB 02020 CC32 CC55 CD16 CD24 CD36 CD37 CD52 2G051 AA65 AB20 BA01 BA04 BA08 BB03 BB07 BC01 CA03 CB01 DA07 EA11 EA14 EA30 EB01 EC01 FA02 5E346 AA12 AA15 AA32 AA41 AA43 CC08 EE31 FF01 FF03 GG15 GG16GG33

Claims (3)

[Claims] An apparatus for inspecting a via hole of a printed wiring board on which an insulating resin layer and a conductive layer are laminated, wherein a light source unit for sequentially switching and irradiating a plurality of lights, each having a different center wavelength, to the via hole. A plurality of light receiving elements arranged two-dimensionally, a light receiving unit detecting reflected light from the via hole, and an output signal from the light receiving unit sequentially acquired in accordance with switching of the plurality of lights. A signal processing unit for determining a degree of resin residue in the via hole based on the obtained output signal. 2. The via hole inspection apparatus according to claim 1, wherein the light source unit includes a plurality of light emitting diodes, and a diffusion plate is provided in front of a light emitting surface of the light emitting diodes. 3. The light-emitting diode includes one white light-emitting diode and a plurality of single-color light-emitting diodes, and the signal processing unit is configured to receive the light received by each of the light-emitting diodes. The output signal from the unit is stored as a plurality of images, an area having a gray value equal to or greater than a predetermined value is extracted from the image illuminated by the white light emitting diode, and the image illuminated by the plurality of monochromatic light emitting diodes A gray level value of a pixel corresponding to the area is detected, and a relative spectral reflectance curve is calculated for each pixel constituting the area based on the detected gray level value. The via hole inspection apparatus according to claim 1, wherein the degree of the resin residue in the via hole is determined based on the number of extreme values of the via hole.