JP4653345B2 - Pattern inspection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pattern inspection method for inspecting a surface pattern of an object. More specifically, the present invention relates to a pattern inspection method capable of obtaining a significant contrast between a pattern portion and other portions regardless of the polishing state of an object.
[0002]
[Prior art]
Conventionally, for a circuit board or the like having a pattern on the surface, the quality of the pattern has been inspected. In general, this pattern inspection is performed by irradiating an object with light and discriminating between a pattern portion and other portions according to the reflection state of the light. In the wiring board which is a main object of pattern inspection, the pattern portion is copper, and the other base portion is resin. For this reason, since the reflectance of light differs in the location of a pattern, and other locations, both can be identified.
[0003]
[Problems to be solved by the invention]
However, the conventional pattern inspection method described above has the following problems. In other words, the wiring board that has been widely used heretofore has been obtained by finishing the pattern after pattern formation by jet scrubbing. For this reason, the light reflectance of the pattern portion was high (it looks like the surface of a new coin with the naked eye), and the difference from the light reflectance of the ground was large. In recent years, however, chemical polishing has been used instead of jet scrub polishing. In the case of a chemically polished product, the light reflectance at the pattern portion is not so high (it looks like the surface of a used coin with the naked eye), so the difference from the light reflectance of the base is small. For this reason, apart from observation with the naked eye, there was insufficient discrimination between the pattern and other parts.
[0004]
The present invention has been made to solve the problems of the conventional pattern inspection method described above. That is, the problem is to provide a pattern inspection method capable of good inspection even when the object is a chemically polished product.
[0005]
[Means for Solving the Problems]
In the pattern inspection method of the present invention made for the purpose of solving this problem, first, an object to be inspected having a chemically polished copper pattern is soft-etched. Next, the surface of the object after soft etching is irradiated with light. Then, the quality of the pattern is inspected based on the difference in the light reflection state between the pattern portion and the other portions.
[0006]
In this inspection method, the object is soft-etched before irradiating the object with light. This soft etching has the effect of removing and smoothing fine irregularities on the surface of the pattern portion of the object. For this reason, soft etching reduces diffuse reflection when light is applied to the pattern portion, and the luminance at the pattern portion is increased. As a result, the difference between the light reflectance of the pattern portion and the light reflectance of the other portions not affected by the soft etching is increased, and a remarkable contrast can be obtained. For this reason, the pattern portion can be distinguished from other portions by the difference in the light reflection state, and the pattern can be inspected.
[0007]
The present invention performs soft etching with an acidic etching solution containing hydrogen peroxide, the etching amount may be within the range of 0.2 to 1.0 [mu] m. Within this range, a sufficient contrast can be obtained between the pattern portion and other portions, and a good pattern inspection can be performed.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, the present invention is embodied as a pattern inspection method in the case where the inspection target is a chemically polished printed wiring board.
[0009]
The object to be inspected in this embodiment is a printed wiring board as shown in FIG. The surface of the printed wiring board 1 includes a pattern portion 2 that is a conductor pattern and a base portion 3 that is a portion where the insulating resin is exposed. Moreover, the pattern part 2 is copper and the finishing process by chemical polishing is given.
[0010]
Next, a pattern inspection procedure for the printed wiring board 1 will be described. First, the printed wiring board 1 is soft etched. Soft etching here is a process of slightly dissolving copper in order to make the pattern surface a metal surface with high light reflectance. The etching solution is an acidic aqueous solution containing hydrogen peroxide. For example, one having a hydrogen peroxide concentration of about 10 g / L and a sulfuric acid concentration of about 45 g / L is used. In the present embodiment, the surface of the pattern portion 2 is thereby smoothed, and a metal surface having a high light reflectance is obtained.
[0011]
FIG. 2 is an SEM photograph (magnification at the time of photographing: 20000 times) obtained by photographing the surface of the pattern part 2 before the soft etching process. On the surface before the treatment, the unevenness due to the chemical polishing performed in advance as a finish is conspicuous. For this reason, when the surface of the pattern part 2 is irradiated with light, the diffuse reflection component of light is large and high luminance cannot be obtained. On the other hand, FIG. 3 is a SEM photograph (magnified 20000 times) of the surface of the pattern portion 2 after the soft etching process. On the treated surface, the unevenness in the chemical polishing process is not noticeable. For this reason, when the surface of the pattern part 2 is irradiated with light, high luminance can be obtained with less irregular reflection of light.
[0012]
Next, an optical appearance inspection is performed as a pattern inspection. In this optical appearance inspection, the printed wiring board 1 is irradiated with light, and the quality of the pattern portion 2 is inspected based on the difference in the reflection state of the light. In this embodiment, a halogen lamp is used as the main light source.
[0013]
Here, an example in the case of performing a pattern inspection on a part of the printed wiring board 1 as shown in FIG. 4 will be described. First, FIG. 4A shows the luminance distribution on the line indicated by A in FIG. 4 for the inspected object after the soft etching process. High luminance is shown on the pattern portion 2 in FIG. On the other hand, in the base portion 3, low luminance is shown. Thus, there is a sufficient difference between the high luminance portion and the low luminance portion, and pattern inspection can be performed by setting an appropriate threshold value. On the other hand, FIG. 4B shows the luminance distribution of the test object before the soft etching process. In FIG. 4B, there is only a slight difference in luminance. Furthermore, since the brightness increases or decreases for each inspection object due to various conditions such as finishing, an appropriate threshold cannot be set. For this reason, pattern inspection cannot be performed.
[0014]
Next, with regard to the soft etching in the present embodiment, whether or not the inspection is possible for each etching amount and the test results obtained by measuring the voltage necessary for the halogen lamp will be briefly described. The voltage measured here is a voltage necessary for good visual inspection. The etching amount is managed by time. FIG. 5 is a table showing the experimental results of the soft etching amount. In the table, the first column indicates the etching amount, the second column indicates the voltage of the halogen lamp, and the third column indicates whether optical appearance inspection is possible. First, when soft etching was not performed (soft etching amount 0.00 μm), it was not possible to obtain a contrast capable of inspecting the pattern portion even when the halogen lamp voltage was increased to 15.0V. For this reason, the third column is “No”. Next, when the soft etching amount was 0.28 μm, it was possible to obtain a contrast capable of inspecting the pattern portion when the halogen lamp voltage was 13.1V. Similarly, when the etching amount is 0.42, 0.61, 0.71, and 1.03 μm, the halogen lamp voltage is 12.2, 12.2, 11.3, and 10.7 V, respectively. Contrast with which the pattern portion can be inspected was obtained. For this reason, the third column is “OK”.
[0015]
Based on the result of FIG. 5, FIG. 6 shows a graph of the relationship between the soft etching amount and the light source voltage. From the measurement data, it can be seen that the smaller the soft etching amount, the higher the required voltage. For example, it can be seen that an etching amount of 0.2 μm or more is necessary in order to inspect at a voltage of 13.5V.
[0016]
As described in detail above, in the inspection method of this embodiment, the printed wiring board 1 to be inspected is soft-etched. The pattern part 2 of the printed wiring board 1 is a copper pattern, and the surface is smoothed by soft etching. Next, light is irradiated to the soft-etched printed circuit board 1. Since the pattern part 2 is a smoothed metal surface, it can reflect light. That is, the contrast between the pattern portion 2 and the base portion 3 necessary for inspection is ensured by soft etching. For this reason, the pattern part 2 and the base | substrate part 3 can be identified by the difference in the reflective condition of light, and the quality of the pattern part 2 can be test | inspected.
[0017]
The etching solution for soft etching uses an acidic aqueous solution containing hydrogen peroxide. Moreover, it turns out that the etching amount exists in the range of 0.2-1.0 micrometer by a test. As a result, a pattern inspection method capable of performing a good inspection even when the inspection object is the printed wiring board 1 which is a chemically polished product is realized.
[0018]
Note that this embodiment is merely an example, and does not limit the present invention. Therefore, the present invention can naturally be improved and modified in various ways without departing from the gist thereof.
[0019]
【The invention's effect】
As is apparent from the above description, according to the present invention, there is provided a pattern inspection method capable of performing a good inspection even when the object is a chemically polished product.
[Brief description of the drawings]
FIG. 1 is a printed wiring board used in an embodiment.
FIG. 2 is an SEM photograph of a copper pattern surface before soft etching treatment.
FIG. 3 is an SEM photograph of the copper pattern surface after soft etching treatment.
FIG. 4 is a luminance distribution of a printed wiring board before and after a soft etching process.
FIG. 5 is a table showing experimental results of the soft etching amount.
FIG. 6 is a graph showing the relationship between the soft etching amount and the light source voltage.
[Explanation of symbols]
1 Printed wiring board 2 Pattern part 3 Base part

Claims (2)

In a method for inspecting a surface pattern of an object,
The surface pattern of the object is a chemically polished copper pattern,
Soft-etch the object,
Irradiate the surface of the object after soft etching,
A pattern inspection method for inspecting the quality of a pattern based on a difference in reflection state of light between a pattern portion and other portions. The pattern inspection method according to claim 1 ,
The soft etching is performed in an acidic etching solution containing hydrogen peroxide,
A pattern inspection method, wherein an etching amount is in a range of 0.2 to 1.0 μm.

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