JPH037258B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for inspecting clogging of through holes in the manufacturing process of printed circuit boards (hereinafter referred to as PWBs) and other boards having perforations.

For example, in the PWB manufacturing process, through-holes may become clogged during processes such as drilling through-holes in laminates or foils (hereinafter referred to as base material), electroless copper plating, soldering, and flux. There is. Inspection of through-hole clogging in such a PWB manufacturing process has conventionally been performed visually by an operator. In this visual inspection, transmitted light is applied to the PWB, and the transmitted light of the through-hole part and the transmitted light of the base material part are compared,
Through-hole clogging was inspected based on differences in light intensity.

In such visual inspections, a decrease in inspection accuracy due to operator fatigue is unavoidable, so automation of the inspection process has been desired. However, in order to meet this demand, when the PWB is photographed using a photoelectric conversion camera as a means of inputting the pattern of the through hole to be inspected, depending on the position of the through hole on the PWB (for example, the periphery of the PWB 4), the axis of the through hole 5 faces diagonally with respect to the photoelectric conversion camera 6, as shown by the broken line in FIG.
There may be a portion inside the through hole 5 that cannot be seen by the photoelectric conversion camera (this is called vignetting).

Therefore, in such a case, even if the through hole is not clogged, the light that has passed through the through hole will not enter the photoelectric conversion camera 6 with normal light intensity due to vignetting, and the light that has passed through the through hole will not enter the photoelectric conversion camera 6 with the normal light intensity, and the The fatal drawback is that it cannot be accurately inspected.

Furthermore, regarding the contrast (S/N ratio) of the signal input to the photoelectric conversion camera 6 in such a configuration, when the light transmittance of the base material is extremely low, the light transmitted through the unclogged through hole is It is effective because it is relatively strong, but when using base materials with extremely high light transmittance, such as glass/phenol resin or glass/epoxy resin, which are currently widely used, the transmitted light between the base material part and the through hole part is Since there is no overwhelming difference in the strength of
It becomes difficult to detect clogged through holes.

In other words, when inspecting a PWB, when a predetermined inspection area is taken for convenience, the area (hereinafter referred to as a unit inspection pixel) is S ₀ (from the standards such as the IC pin spacing, the coordinate position of the through hole is It is usually plotted on the top, so for example
It should be 2.54mm square. ), the opening area of the through hole is S ₁ (e.g. 0.8 mmφ), the light transmittance of the base material is T ₀ (e.g. 30% for glass or epoxy resin), and the light transmittance of the through hole is 1 (100%). ), the intensity of transmitted light per unit inspection pixel of the base material part (I ₀ )
I ₀ ∽S ₀ ×T ₀ (=2.54 ² ×0.3≒1.94) …(1) On the other hand, the intensity of transmitted light when there is one through hole in the unit inspection pixel (I ₁ )
is I ₁ ∽(S ₀ −S ₁ )×T ₀ +S ₁ (=1.94+0.4 ² π
(1-0.3)≒2.29)…(2).

In this case, the light transmittance (T ₀ ) of the base material is somewhat smaller than the light transmittance of the through-hole portion, but since the unit inspection pixel S ₀ is large relative to the opening area (S ₁ ) of the through-hole, The intensity ratio (I ₁ /I ₀ ) of transmitted light per unit inspection pixel in the material portion and through-hole portion is not so large, making identification difficult.

This comparison is for the case where no circuit pattern is formed on the base material, so if the circuit pattern is actually formed on the base material, the PWB
Light absorption and scattering occur depending on the presence or absence of circuit patterns on the front and back sides, the presence or absence of printing ink, etc., which causes variations in the intensity of the transmitted light of the PWB, making it even more difficult to detect clogged through-holes.

In view of the above-mentioned circumstances, the present invention aims to provide a through-hole clogging inspection device that can quickly and reliably detect clogging of through-holes in various manufacturing processes of boards having perforations such as PWBs. a light source that irradiates light including light that is perpendicularly incident on the object to be inspected; a condenser lens that converges the light that has perpendicularly transmitted through the object to be inspected; It is equipped with a photoelectric conversion camera that receives light converged by a condensing lens and captures an optical image of the object to be inspected. The feature is that the clogging is inspected based on the strength.

Next, an embodiment of the through-hole clogging inspection device according to the present invention will be described based on the accompanying drawings.

FIG. 1 is an explanatory diagram schematically showing the outline of a through-hole clogging inspection device according to the present invention, and FIG.
The figure is a plan sectional view showing a mode in which a PWB is inspected by the inspection apparatus shown in FIG. 1.

In the figure, a pair of condensing lenses 1 and 2 are arranged facing each other, and between these lenses 1 and 2,
While positioning the PWB 3 to be inspected for clogging, inspect by moving it in the direction of the arrow. The light from light source 4 is
Converted into parallel light by condenser lens 1, PWB
It is incident perpendicularly to 3.

The light passing through the through hole 5 arranged on the PWB 3 travels straight and enters the condenser lens 2, is converged by the condenser lens 2, and enters the lens 7 of a photoelectric conversion camera, for example, a CCD camera 6. .

On the other hand, the light incident on the base material part of PWB3 is caused by copper,
It is absorbed by solder, ink, etc., or scattered by the base material. Among this scattered light, some of the light that enters the lens 7 of the CCD camera 6 is collected by the condensing lens 2, but it is extremely small and the lens 7
The amount of light incident on the PWB 3 is thought to be about 1% of the total solid angle of the scattering location.

On the incident side of the condenser lens 1, there is a correction filter 8 that equalizes the illuminance distribution of light in the CCD camera 6.
(hereinafter referred to as a gradient filter) is disposed so that the light from the light source 4 always uniformly enters the light receiving element 9 disposed within the CCD camera 6.
A constant output is obtained both at the center of the optical axis and at the periphery.

Therefore, the gradient filter 8 is not limited to the illustrated position, but may be placed at any position in the optical system. Further, the illuminance distribution in the CCD camera 6 may not be corrected by using such a gradient filter, but the output from the light receiving element 9 may be corrected electrically.

Before inspecting PWB3 for clogging, check a normal PWB with the same pattern as the PWB to be inspected.
A reference pattern photographed in the manner shown in FIG. 2 is stored in the memory 10 in advance.

The memory unit of this reference pattern is the minimum pitch at which the through hole is plotted when converted to the actual dimensions of the PWB (2.54 mm pitch if the through hole is plotted on a 1/10 inch grid).
It has been matched to

When performing a PWB clogging inspection, the PWB 3 to be inspected is placed in the same positional relationship as the reference pattern described above was photographed, photographed in the manner shown in FIG. The output signal is compared with the value at the same position of the reference pattern previously stored in the memory 10, and if there is a difference, it is determined that the through hole is clogged, and the output device 12 outputs the signal. Output.

As described above, the inspection device according to the present invention stores a normal hole pattern in advance in the memory. For example, when the PWB size is 20 inches square and the inspection unit pixel is 1/10 inch, In this case, the total number of pixels to be inspected is 200 x 200, and even if this is to be stored in 256 gradations, 40K bytes is sufficient, and if a 64K bit IC memory is used, 5
One piece is enough.

Also, if the above-mentioned 20 inch square PWB is inspected in 5 seconds, the processing time for one pixel is:
5sec/40000 (=125μsec), which provides enough time for software processing.

The output device 12 may be a printer that prints out the XY coordinates of the clogged position, or a marker that directly marks the clogged position on the PWB using the XY coordinate values.

The intensity ratio (I ₁ ′/I ₀ ′) of transmitted light per unit pixel in the base material portion and the through hole portion obtained by the through hole inspection device according to the present invention is as follows.

In other words, all the light passing through the through hole 5
When it enters the CCD camera 6, its coefficient is 1 (100
%), but on the other hand, the light that enters the base material part of the PWB is scattered at that point, and of this scattered light,
The proportion of light incident on the CCD camera 6 (D ₀ ) (varies depending on the aperture value and distance to the lens, but is usually considered to be around 1% since it is part of the solid angle of the scattering point. ), the intensity of transmitted light per unit inspection pixel (I ₀ ′) in the base material part is I ₀ ′∽S ₀・T ₀・D ₀ (=2.54 ² ×0.3×0.01≒0.02)
...(3), and on the other hand, the intensity of transmitted light when there is one through hole in the unit inspection pixel (I ₁ ′)
I ₁ ′∽(S ₀ −S ₁ )・T ₀・D ₀ +S ₁ =S ₀・T ₀・
D ₀ +S ₁ (1-T ₀・D ₀ ) (=0.02+0.4 ² π(1-0.3×0.01)≒0.5
2)…(4), and the intensity ratio of the transmitted light (I ₁ ′/I ₀ ′) is the intensity ratio of the transmitted light (I 1 /I ₀ ′) in the case described at the beginning.
I ₀ ), it can be made extremely large.

Therefore, it is possible to very clearly distinguish and judge the light incident on the base material portion and the light incident on the through hole portion.

In the description of the above-mentioned embodiments, the case where no circuit pattern is formed on the base material is explained, but when the circuit pattern is formed on the base material, the light incident on the base material part is Furthermore, since it only promotes absorption, blocking, or scattering, the intensity (I ₀ ′) of the transmitted light in this part becomes even smaller, but
Since I ₀ ′ is originally small, its strength difference (I ₁ ′−I ₀ ′)
is virtually unchanged and can be identified very clearly as if there were no circuit pattern (or with slightly improved ease of identification).

According to what the inventor has confirmed through experiments, the circuit pattern is formed not only on a base material that has a light-shielding property, but also on a glass/epoxy resin base material that has an extremely high light transmittance. Even if the pixel contains a through hole, as long as it has light scattering properties, only the test pixel containing the through hole will be extremely bright, and the test pixel that does not contain the through hole will be extremely dark. I was able to get an image of it.

Moreover, when performing an inspection under indoor lighting, it is generally considered desirable to shield the PWB from light since the contrast decreases when the indoor lighting light hits the PWB. Under relatively weak indoor lighting, if you are careful not to cast shadows in the PWB's inspection field of view, the intensity of the light passing through the through-hole is extremely strong, so you can inspect it without any problems. .

In addition, in the above-mentioned embodiment, since the light from the point light source 4 is projected onto the PWB 3,
A condenser lens 1 is interposed to convert the emitted light from the point light source 4 into parallel light, but the PWB 3
However, as long as the light includes at least perpendicularly incident light, the condenser lens 1 is not necessarily necessary. For example, when the light source 4 is placed at a sufficient distance from the PWB 3, or when parallel light using a concave mirror or the like is used, close to ideal light can be obtained.

As is clear from the above description, the light-receiving element of the camera used in the inspection device according to the present invention may include one-dimensional (line) type light-receiving element group or two-dimensional (plane) type light-receiving element group. You can use any one you have.

When using the former one-dimensional camera, by making the condensing lenses 1 and 2 rectangular and moving the PWB 3 and the optical system relative to each other, the through-holes can be prevented from clogging over the entire PWB. Perform inspection. With such a configuration, the inspection device itself can be miniaturized, which is extremely advantageous in practice.

When using the latter two-dimensional (surface) type camera, the condenser lenses 1 and 2 may be large enough to cover the entire surface of the PWB 3 for photographic inspection. In this case, there is an advantage that both the PWB 3 and the optical system can be inspected in a stationary state.

Also, compared to the number of pixels of a two-dimensional camera,
If the PWB has a large number of pixels, the camera or PWB
may be moved intermittently so that the entire PWB area is processed several times.

Although ordinary thick lenses may be used as the condenser lenses 1 and 2, it is advantageous to use Fresnel lenses. When using this Fresnel lens, especially when using the above-mentioned one-dimensional camera and rectangular condensing lens, the Fresnel lens 13
It is better to match the pitch P of the stepped portion with the pitch of the through hole so that the through hole does not cover the stepped portion of the Fresnel lens (see FIG. 3).

The through-hole clogging inspection device according to the present invention has the above-described configuration, so even if the base material used for PWB does not have a light-shielding property, glass phenol with extremely high light transmittance can be used. Even when resin, glass, epoxy resin, etc. are used, extremely high inspection accuracy can be obtained as long as the base material has light scattering properties. Moreover, the light projected onto the PWB is
Since the incident is always perpendicular to
This is extremely advantageous because there is no scattering of light at the through-hole portion, and it is possible to inspect every corner of the through-hole regardless of whether it is in the center or the periphery of the optical axis.

In addition, by using a one-dimensional CCD camera and a rectangular condensing lens, the inspection device itself can be made more compact.If the condensing lens is a Fresnel lens, the pitch of the stepped portion can be changed to a through hole. By adapting it to the installation pitch, it is possible to avoid being affected by the stepped portion of the Fresnel.

Furthermore, in order to make the illuminance distribution of the projected light uniform, it is possible to extremely uniformize the illuminance distribution by placing a gradient filter at an arbitrary position in the optical system or by electrically correcting the output from the light receiving element of the CCD camera. Can be easily corrected.

The through-hole clogging inspection device according to the present invention has extremely advantageous effects in practice as described above.

In the above-described embodiment, a case was described in which clogging of a through hole of a PWB was inspected, but it goes without saying that the present invention is not limited to the case of a PWB.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram schematically showing the outline of a through-hole clogging inspection device according to the present invention, and FIG.
The figure is a plan view showing the case of clogging inspection using the embodiment device according to the present invention, and Fig. 3 shows the positional relationship between the step pitch and the through hole when a Fresnel lens is used in the present invention. The explanatory diagram shown in FIG. 4 is a schematic plan view showing a photographing mode in the conventional method. 1, 2...Condensing lens, 3...PWB (object to be inspected), 4...Light source, 5...Through hole, 6...
CCD camera, 7...lens, 8...gradient filter, 9...light receiving element, 13...Fresnel lens, P...cutting pitch.

Claims (1)

[Scope of Claims] 1. A light source that irradiates light including light that is perpendicularly incident on an object to be inspected, a condenser lens that converges the light that has perpendicularly passed through the object to be inspected, and a condenser of the condenser lens. a photoelectric conversion camera that is installed at a certain position and receives the light converged by the condensing lens to take an optical image of the object to be inspected; A through-hole clogging inspection device characterized by inspecting for clogging based on the intensity of light transmitted through the hole. 2. Clogging of the through hole according to claim 1, characterized in that a condensing lens that converts light from a light source into parallel light is disposed between the light source and the object to be inspected. Inspection equipment. 3. The through-hole clogging inspection device according to claim 1 or 2, wherein the condensing lens is a Fresnel lens. 4. The through hole according to claim 3, wherein the pitch of the stepped portion of the Fresnel lens is the same as the minimum pitch of the through hole, and the through hole is located between each cutting surface. clogging inspection device. 5. The photoelectric conversion camera is a camera equipped with a one-dimensional light-receiving element group, the condensing lens is shaped like a strip corresponding to the light-receiving element group, and the object to be inspected is moved relative to the optical axis. 5. The through-hole clogging inspection device according to claim 4, wherein the through-hole clogging inspection device sequentially inspects the entire object to be inspected. 6. The photoelectric conversion camera is a camera equipped with a two-dimensional light-receiving element group, the condensing lens is shaped enough to cover the entire object to be inspected, and the object to be inspected is inspected in a stationary state. A through-hole clogging inspection device according to any one of claims 1 to 4, characterized in that: 7. Claim 1, characterized in that a filter for correcting the illuminance distribution from the light source is arranged on the incident side of the condensing lens in the optical path from the light source to the camera.
A through-hole clogging inspection device according to items 6 to 6.