KR820001894B1 - Method for inspecting printed wiring boards - Google Patents

Abstract

In order that a slight positional deviation of a plated through hole such as having no substantial effect on the function of wiring should not be optically detected as a defect in a printed wiring board, the plated through hole is recognized as a part of the wiring pattern. This is achieved by making light representative of the plated through hole nearly equal in intensity to reflected light(36) from the wiring pattern. This is achieved by illuminating the printed wiring board with light from the black side or by placing a reflector(40) on the back side of the printed wirting board.

Description

Pattern inspection method of printed wiring board

1 is an enlarged plan view of a part of a general printed wiring board.

2 is a cross-sectional view along the line A-A '.

3 to 6 are views for explaining a conventional inspection method.

7 to 10 are views for explaining the inspection method according to an embodiment of the present invention.

11 and 12 are diagrams for explaining a test method according to another embodiment.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting a defect in a wiring pattern formed on a printed wiring board, and more particularly, to a method for detecting a defect generated in the process of forming a wiring pattern in comparison with wiring patterns of other printed wiring boards.

The structure of a general printed wiring board is shown in FIG. 1 and FIG.

FIG. 1 is a plan view seen from the wiring surface 2, and FIG. 2 is a cross-sectional view along the line A-A '.

In these figures, 4 and 5 are wiring patterns made of conductor foil such as copper, 6 are through holes for electrical connection with the rear wiring surface 3, and 7 are insulated. The base materials 13 and 14 are inner layer patterns used as the ground layer and the power supply layer, and are made of conductor foil such as copper as the wiring patterns 4 and 5.

In the wiring pattern shown in FIG. 1, the solid line (except the thick line) and the dotted line of FIG. 1 are generally copied onto the copper foil as an etching resist pattern by a photo disc (mask). It is formed by etching. If dust adheres to the photo disc or scratches on the photo disc during this forming process, micro adhesion (8), micro scratches (9), micro projections (10), etc. are generated. ) And excessive etching results in a narrow width 12 of the pattern. When such a defect occurs, in the small scratch (9), the narrow width (12) of the pattern, the circuit resistance increases, the current capacity decreases, disconnection due to abrasion when handling the printed circuit board, or the micro adhesion (8), micro projection (10) In the wide width 11 of the pattern, a solder bridge or the like occurs during short-circuit soldering of the circuit, and the original wiring line of the printed wiring board cannot be configured.

Such defects are particularly thoroughly carried out in high density as in recent years. For example, when the pattern width is about 0.1 mm, even if there are some defects, the defects must be accurately inspected and cannot be visually examined at this time. Therefore, a method of capturing and comparing each wiring surface of the comparative printed wiring board 1 'provided separately from the printed wiring board 1 to be inspected as an optical image in order to perform such inspection by a machine as shown in FIG. There is this.

This conventional method will be described below.

3 shows the configuration of the inspection apparatus for such a printed wiring board.

In Fig. 3, those having the same configuration except for the electric signal comparison device 27 are arranged left and right, and the right parts corresponding to the respective parts of the left side (under test printed wiring board side) are denoted by the same reference numerals with prime marks. .

Therefore, the functions and operations of the parts on the right side are represented by the description on the left side by explaining the functional operations of the parts on the left side, and replacing the description on the right side by adding a prime code to the code in the description.

Above the wiring surface 2 of the printed wiring board 1, the light of the light source 21 provided from the side is reflected and irradiated to the wiring surface 2, and the reflected light from this wiring surface is passed upward. The half reflecting mirror 23 and the lens 24 for collecting the light passing upward from the mirror 23 and connecting the optical images, and the contrast of the image at the position where the optical images are connected A photodiode array 25 for converting the electrical signal 26 into the electrical signal 26, and the electrical signal 26 obtained from the photodiode array 25 on the left side and the photodiode array 25 'on the right side. A comparator 27 that recognizes and compares 26 'as a wiring pattern is provided, and the comparator 27 makes it possible to point out the presence or absence of a defective portion or a defect location. Positioning of the printed wiring boards 1 and 1 'is performed by the positioning means which is not shown in figure.

For example, in the case of inspecting the printed wiring board as shown in FIG. 4 (a), the light from the light source 21 in FIG. 3 becomes parallel light in the lens 22 and changes downward in the mirror 23. As the light rays 31, 32, and 33 in FIG. 4, the respective portions of the wiring surface 2 of the printed wiring board 1 are irradiated.

The light beam 31 generates the low level reflected light 34 by the low reflectance of the insulating base 7, and the light beam 32 reflects the high level reflected light by the high reflectance of the wiring pattern 5 made of the same metal. 35 is generated, and since the light ray 33 passes through the through hole 6, that is, through the through hole to the wiring surface 3 on the back side, no reflected light is generated.

Light rays 34 and 35 reflected in this way are connected to the optical image on the photodiode array 25 via the half mirror 23 and the lens 24 in FIG. The photodiode array 25 is formed by arranging a plurality of micro light-receiving elements in a straight line. For example, 256 elements are arranged in a length of 5 mm. FIG. 4 (b) shows an electrical signal that appears when the reflected light 34, 35 in FIG. 4 (a) is formed on the surface of the photodiode array 25 with respect to all the light-receiving elements. It shows the electric signal level on the vertical axis and the device position of the photodiode array on the horizontal axis.

In the figure, I ₁ represents the electric signal level at the through hole position, and is low level because there is little reflected light from the wiring surface. I ₂ is the reflected light 34 from the insulating base 7 converted into an electrical signal, which is a low level higher than I ₁ . I ₃ is a level at which the reflected light 35 from the wiring pattern 5 has been converted into an electrical signal.

In order to make it easy to compare these various levels, it is necessary to convert into two types, that is, light levels and dark levels, that is, binary values. For this reason, as shown in Fig. 4 (b), the binarization circuit 28 made of, for example, a voltage comparator so as to make the light level when the electric signal level is higher than I _s and the dark level beneath it. By the conversion, the wiring pattern 5 is converted into a binary signal having a light level (binary " 1 "), an insulating base material 7, and a through hole 6 with a dark level (binary " 0 ").

The binary signal obtained in this manner is linear in the light receiving surface of the photodiode array 25, so that the linear information (line pattern as shown in the pattern of FIG. Information). Therefore, as the binary signal is stored in the memory 29 while the printed wiring board is moved in parallel with the printed wiring surface, surface information is obtained in the memory 29. After that, the surface information stored in this memory 29 is compared with the pattern comparator 30, and the portions which do not match are displayed as a combination.

According to the inspection method described above, it is surely performed, but there is a defect even if it does not affect the performance (wiring resistance, current capacity, presence or absence of a bridge at the time of soldering) as a slight deviation between the through hole and the wiring pattern. Since it is processed, a ratio becomes low and especially the fall of the ratio is remarkable in high density mounting. The operation in the case where a slight deviation of the through hole and the pattern occurs will be described with reference to FIGS. 5 and 6.

FIG. 5A shows the binary data stored in the memory 29, and the left side shows a case where the through hole is slightly to the right and the right side is slightly to the left. Figure (b) shows the electric signal level when the photodiode arrays 25 and 25 'are positioned on the line A-A' of (a), and the vertical axis represents the meaning of the horizontal axis as in Figure 4 (b).

FIG. 6 shows a comparison of the binary patterns of FIG. 5 (a) by overlapping each other. As shown in Fig. 6, the insulating substrates 7 and 7 'coincide with the dark level, and the wiring patterns 5 and 5' also coincide, but the through holes 6 and 6 '. Because of the inconsistency of the diagonal line (one is light level and the other is dark level), there is a drawback that this diagonal part is marked as a defective part.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above drawbacks, and to provide a method capable of detecting the deviation of the wiring pattern without detecting the relative deviation between the through hole and the wiring pattern as a defect.

In order to achieve the above object, the main feature of the present invention is that it does not detect the deviation of the through hole by recognizing the through hole as a light level such as a wiring pattern. Specifically, a light reflector is installed on the back surface of the printed wiring board. The reflection of the through-holes may not be detected by a method of reflecting the surface through the through-holes irradiated from the surface, and irradiating light on both the surfaces of the printed wiring board and the back surface.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 7 illustrates an embodiment of the present invention, and FIGS. 8 to 10 are views for explaining the operation of FIG.

In FIG. 7, 40 and 40 'are reflectors which irradiate from the upper side of the printed wiring boards 1 and 1' and pass through the through-hole again to return upward through the through-hole. The reflectors 40 and 40 'may be used to reflect all of the light like a mirror, to have a white coating with a relatively high reflectance, or to use a blank paper.

The other portions 21 to 27 and 21 'to 26' are the same as the same reference numerals in FIG. For example, when the printed wiring board 1 is inspected as shown in FIG. 8A, the light from the light source 21 in FIG. 7 becomes parallel light in the lens 22, and is turned downward in the mirror 23. Irradiated to each part of the wiring surface 2 as the light rays 31, 32, and 33 of FIG. The light rays 31 generate the low-level reflected light 34 by the low reflectance of the insulating base 7, and the high-level reflected light 35 by the high reflectance of the wiring pattern 5 in which the light ray 32 is made of the same metal. ), And the light ray 33 exits the through hole 6, ie, the through hole, and generates the reflected light 36 by the high reflectance of the reflector 40.

The reflected light rays 34 to 36 are connected as optical images on the photodiode array 25 through the half mirror 23 and the lens 240 of FIG. 7. When connected to the optical images, the photodiode array 25 The electric signal level in Fig. 8 (b) is such that the reflected light 34 in the insulating substrate 7 is at the low level I ₂ , and the reflected light 35 in the wiring pattern 5 is at the high level I _3. ), And the reflected light 36 in the through hole 6 becomes a high level I ₄ .

The meaning of the vertical axis and the horizontal axis of FIG. 8 (b) is the same as that of FIG. 4 (b).

When the electric signal level is higher than IS by the comparator 27, the binary level is converted into the light level and the lower level to the dark level, and surface information is again performed to compare the binary pattern.

FIG. 9 (b) shows the electrical signal level of the patterns of the printed boards 1 and 1 'generated in the photodiode arrays 25 and 25'. Signals higher than the level IS are bright and lower. The signal is a binary pattern shown in FIG.

As shown in Figs. 9A and 9B, the through-holes 6 and 6 'and the wiring pattern portions 5 and 5' are output signals of the photodiode arrays 25 and 25 '. Examples of when the binary level at I _s because of the different level higher than I _s level is the same level, people it is impossible to identify.

The meaning of the vertical axis and the horizontal axis of FIG. 9 (b) is the same as that of FIG. 4 (a). When the binary patterns of FIG. 9 (a) obtained in this way are overlapped with each other, the through holes 6 and 6 '(indicated by dashed lines) are not identified as shown in FIG. 10, and the deviation is not detected even when compared. .

Since other than the through-holes are identified in the same manner as in the conventional art, defects such as pattern deviation, micro pattern attachment, pattern groove, pattern width, and narrow width can be detected.

In this embodiment, since the light passing through the through-hole is reflected from above, one- or two-layer printed wiring boards using a light-transmissive substrate can also be inspected.

FIG. 11 is a view showing another embodiment, and FIG. 12 is a diagram for explaining an operation thereof.

In FIG. 11, 41 and 41 'are light sources for irradiating light on the back surface of the printed wiring board to generate light rays instead of the reflected light 36 of FIG.

The light sources 41 and 42 'need to have a brightness that is output as a light level when light emitted from the through hole is binarized at least, and preferably a light beam parallel to the through hole.

Since the other parts 21 to 27 and 21 'to 26' are the same as the same reference numerals in Fig. 3, the description is omitted. As shown in FIG. 12A, when the printed wiring board 1 is inspected, the reflected light 34 reflected from the insulating base 7 among the light beams applied from above is at level I ₂ , and the wiring pattern 5 is applied. Reflected light 35 reflected at is level I ₃ , and light beam 37 irradiated from the lower light source 41 is converted into an electrical signal of level I ₅ to be converted into photodiode arrays 25 and 25 '. Is output. This is binarized at level I _s to obtain surface information, and the binary patterns are compared.

This binary pattern is the same pattern as in FIG. 9 and overlaps with each other as in FIG. Therefore, also in this case, the through holes 6 and 6 '(indicated by dashed lines) are not identified, and even when compared, the deviation is not detected. Again, other than through-holes are identified, defects such as pattern deviation, micro pattern attachment, pattern grooves, pattern width, and narrow width can be detected by comparison.

In this embodiment, since the deflection of the through hole can be allowed only by irradiating a light beam from below, the configuration is simple.

As described above, according to the present invention, the through-hole portion is regarded as a part of the wiring pattern, and the comparison is made, and thus the deviation of the through-hole can be allowed. It has the effect of detecting defects such as width and narrow width, and greatly contributes to the ratio improvement.

Claims (1)

The wiring surface of the printed wiring board 1 in which the printed wiring board 1 in which the wiring pattern 5 was formed in the wiring surface 2 of the insulated base material 7 was formed, and the through-hole 6 penetrating this printed wiring board 1 was formed ( 2) printing to irradiate light to recognize the reflected light from the wiring surface 2 as an optical image, and to compare the optical image with an optical image obtained from the wiring surface 2 'of another printed wiring board 1'. In the pattern inspection method of the wiring board 1 ', recognition of the optical image is performed by placing the optical image of the wiring patterns 5 and 5' and the optical image of the through holes 6 and 6 'at the same first level. The optical images of the insulating substrates 7 and 7 'at a second level different from the optical images of the wiring patterns 5 and 5' and the through holes 6 and 6 '. Pattern inspection method of a printed wiring board, characterized in that.

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