CN1448043A - Three-D inspection of leaded Ics - Google Patents

Abstract

The invention relates to an optical inspection system for inspecting an object in the form of an IC component with leads, wherein the object (10) is positioned in overlapping relation to the opening (2) of a reference (1) and is The horizontal diffuse light source (3) is irradiated, so as to project the reference contour of the reference edge (12) and the contour image of the object (10) in several projection directions through the opening (2). Optical side prisms (5) and central prisms (6) are provided to receive projection light from two different angles of incidence, thus defining two different projection paths (91, 92), so that by analyzing With the light of these two projection paths, a three-dimensional image can be obtained. The side prisms (5) and central prism (6) are designed and positioned so that the projection paths (91, 92) of the first and second projections are between the leaded contour of the object (10) and the imaging plane (110) of the system have the same optical path.

Description

For 3D inspection of integrated circuits with leads

technical field

The present invention relates to a device for three-dimensional inspection of integrated circuits (ICs) with leads.

Background technique

In the manufacture of electronic components having multiple pins or leads, such as integrated circuits, inspection systems using optical systems have been proposed which provide three-dimensional inspection of electronic components.

In order to obtain a three-dimensional inspection of IC components, it has also been proposed to provide at least two optical paths along which different images of the inspected integrated circuit are transmitted to the image sensor.

For example, US Pat. No. 5,909,285 discloses a method for inspection of integrated circuits that includes a camera that images a deposited precision pattern mask onto a transparent reticle to be inspected. The integrated circuit under inspection is illuminated with diffuse light. Using a mirror or prism above, the side view of the IC is reflected onto the camera. However, this method uses front lighting and also requires the integrated circuit to be perfectly precisely positioned on the transparent reticle.

From US Pat. No. 5,910,844 is known a vision inspection system in which eight optical images are recorded simultaneously in a singular number of image frames, which are output from two optical cameras. The detection system according to US Pat. No. 5,910,844 requires a complex optical reflection arrangement using multiple optical orientation components. However, according to US Pat. No. 5,910,844, the optical orientation components have to be selectively adjusted when inspecting objects of different sizes.

Furthermore, an optical detection system is known from US patent application 09/205,852 for determining positional information of an object relative to a reference object. A fiducial used as a system reference is placed near the object being inspected. Additionally, a diffuse light source for illuminating the subject is provided. The light source is arranged so that the points on the object and the points on the fiducial are in the same plane as their images along at least two light paths which form an angle with each other. Additionally, an imaging subsystem is provided to acquire images along the two optical paths. The acquired images are correlated and analyzed by the imaging subsystem in order to provide positional information of points on the object relative to points on the fiducials. According to US Patent Application 09/205,852, it is possible to form two optical paths by using a trapezoidal prism to form one optical path, and a flat mirror to form the other optical path, which are relayed to the imaging subsystem. Furthermore, it is also possible to use a single trapezoidal prism to provide two light paths. By this method, one optical path is formed along the inner surface of the trapezoidal prism, and the other optical path is formed along the outer surface of the trapezoidal prism.

However, according to US Patent Application 09/205,852, the optical paths of these two optical paths are different, so that the image quality, and therefore the accuracy of the detection system, is compromised. Furthermore, both sides of an object such as a double-sided integrated circuit are inspected by using two optical structures each providing two optical paths as disclosed in US Patent No. 09/205,852, in which case due to the There is a large blank area in the middle of the image, and the optical subsystem requires a large sensor area to acquire images from both light paths.

Contents of the invention

The present invention provides a detection system for a leaded integrated circuit (IC). The system according to the present invention is capable of testing the leads of wide body IC packages in a confined space. In other words, the object of the present invention is to allow three-dimensional measurement of IC leads in a very compact manner.

The system according to the invention comprises a datum in which there is an opening defined by a reference edge, said datum providing a reference plane at least substantially perpendicular to the optical axis of the system, wherein the object to be inspected is positioned relative to the datum The openings of are in an overlapping relationship. The system also includes: a lateral diffuse light source for laterally illuminating diffused light onto the object through the aperture, thereby performing an image of the contour of the positioned object including the outline of the lead and the contour image of the reference edge through the aperture in several projection directions. Projection; an optical side prism for receiving the first projection light of the profile image from the first projection direction. The side prism has: an incident surface, an exit surface and an internal reflection surface, and the internal reflection surface cooperates with the incident surface and the exit surface to internally reflect the first projected light so that it passes through the exit surface of the side prism and points to the imaging in the exit direction surface, the system includes an optical central prism positioned to receive the second projected light of the profile image from the second projection direction, said central prism having at predetermined positions: an incoming refractive surface and an outgoing refractive surface cooperating with the incoming refractive surface, The second projection light is refracted to the imaging surface by the incident refraction surface and the exit refraction surface. The side prisms and central prisms are designed and placed so that the projection paths of the first and second projections have the same optical path between the outline of the subject with the lead and the imaging plane.

In order to provide the same optical path for the two projection paths between the outline of the object including the leads and the imaging plane determined by the side prisms and the central prism, respectively, the profile of the side prisms must be changed to correspond to the profile of the central prism and the light source from The optical path from the object silhouette to the imaging plane through the central prism and vice versa. In other words, the size and placement of the side prisms and the central prism must be coordinated with each other, ie paired. Based on the principle that the optical path of light is different when passing through different optical media, the optical path is a function of geometric length and optical media. Therefore, by providing two different optical media for the side prisms and the central prism respectively, and the third medium air, by considering the specific structure in the third medium air to change the size of each prism, the optical path conforming to the same optical path can be obtained. match.

According to a preferred embodiment of the present invention, two or more identical optical side prisms can be configured for measuring or inspecting two or more sides of an IC component such as double or more sides. This means that a system with a single side prism and a central prism is mirrored about the central axis, so that multiple side prisms are placed symmetrically around the optical axis of the system, they are also symmetrically placed about a common central prism, which in turn is also placed around the optical axis of the system. The central axis of the system is placed symmetrically. As a result, the projections of the contours of the various faces of the IC pass through the respective side prisms and the central prism, determining two projections for each face of the object. Therefore, each side of an IC component having a plurality of sides can be inspected simultaneously.

Furthermore, in the preferred embodiment, in order to reduce the image area required to acquire the projected image provided by one or two optical side prisms and the central prism, a partial rectangular prism is provided which will affect the first and the second projection is moved parallel to and close to the optical axis of the system. The image area used for detection is thus reduced, which leads to an increase in the effective pattern resolution and thus to improved measurement accuracy.

Preferably, the images produced by the inspection system are captured by a video camera through a lens, and then digitized and processed by the computer's processor to determine the three-dimensional coordinates of the object relative to the reference.

Description of drawings

In order to illustrate the present invention, preferred embodiments will be described herein with reference to the following figures, in which:

Fig. 1 shows a schematic diagram of a detection system according to a preferred embodiment of the present invention;

Figure 2 shows the paths of the two illumination beams of the side prism and the central prism, respectively;

Detailed ways

According to a preferred embodiment of the present invention, an inspection system for inspecting an object in the form of an IC component with leads is shown in FIG. , the datum 1 provides a reference plane perpendicular to the optical axis A of the system; the object bracket 30 is used to position the object 10 so that it overlaps with the opening 2 of the datum 1, and thus lies on the plane focused by the system; the diffuser The light source 3 is used to emit diffused light through the opening 2, so that the outline of the object 10 including the lead line and the outline of the reference edge 12 is projected through the opening 2 in several projection directions. The system also includes two optical side prisms 5 for receiving projections of contours and leads; a central prism 6 and an image detection system 9 comprising lenses and a camera with an image sensor.

As shown in Figure 1, the light 3 is preferably placed laterally on top of the datum 1, but can also be placed above the datum. Preferably, the light 3 emits light of a single wavelength or a narrow bandwidth of wavelengths to reduce dispersion, which might otherwise be caused in optical prisms due to long propagation distances. For example, such narrow bandwidth illumination 3 can be achieved by filters (not shown).

For example, the object can be positioned in the vicinity of and overlapping the opening 2 by the object holder 30, which preferably has a vacuum tip to suck the object 10 from above. The object 10 is aligned with the optical axis A of the system, and its position relative to the base can be changed and adjusted by the object bracket to arrange the object to achieve an effect that the symmetrical object point is located on a plane parallel to the reference plane of the aperture or datum middle. Light 3 provides diffuse backlighting. The leads or pins 81 of the object 10 and the package 82 of the object 10 are then backlit by the light 3 by placing the object under inspection with leads in said diffuse light.

As mentioned above, datum 1 provides the reference surface for the system. Preferably, the datum and the reference plane are at least substantially perpendicular to the optical axis of the system. The opening 2 is formed on the datum 1 and defined by four reference sides 12 or two pairs of parallel reference sides 12, wherein the distance between two opposite reference sides is known. The distance between two opposing reference edges 12 of the fiducial 1 is slightly larger than the outer dimension of the largest IC component to be tested. To provide a stable reference surface, Datum 1 is made of a mechanically strong and stable material such as carbide or invar. The upper surface of the benchmark 1 is ground and polished to a fairly high level of flatness. The reference edge 12 of the datum 1 is made sharp and straight, and precisely finished. The walls of the holes constituting the datum 1 of the reference edge 12 may be painted black to avoid or reduce reflections from opposing lighting.

After leaving the plane of the reference, projection light from the respective light source and having an angle of incidence within a certain angular range impinges on the respective side prism 5 . This is shown in Figure 1, the preferred embodiment being illustrated includes two optical side prisms for inspection of the two sides of the IC component, which sides contain the leads of the IC. Both optical side prisms 5 are placed symmetrically with respect to the optical axis A of the system. Each optical side prism has six sides and a four-sided cross-section that includes an incident face 61, an exit face 62, and an internal reflection face 52 that cooperates with the entry face and the exit face for objects and The internal reflection of the projection of the outline of the aperture through the exit surfaces of the respective sides in an exit direction to the imaging surface 110 allows a first projection path between said outline and the imaging surface to be determined.

Refraction is possible at the entrance and exit faces of the side prisms, depending on the angle at which the projected light hits the respective faces. When the reflective surface of the side prism is inclined relative to the imaging surface, the reflected light entering through the incident surface at a certain predetermined angle range is adjusted to be parallel to the central axis of the system, and the outgoing surface is perpendicular to the central axis. As a result, the projections off the respective side prisms are adjusted parallel to said central axis A, ie the optical axis of the system.

The system also includes an optical central prism 6, which has an incident refraction surface 63 and an exit refraction surface 64, wherein the incident projection light of the object contour and the aperture is refracted at both the incident refraction surface 63 and the exit refraction surface 64, so as to A second projection path is formed between the outline and the imaging surface 110 . The central prism 6 has a six-sided cross-section, 8 sides in the case of two side prisms and 10 sides in the case of four side prisms. The central prism 6 has an axis around which the central prism is placed symmetrically, wherein the axis of the central prism coincides with the central axis A of the system when the central prism is placed in the system.

When the exit refraction surface 64 of the central prism is inclined at a certain angle relative to the central axis so that the light rays coming out from the exit refraction surface are refracted to be parallel to the optical axis A, the incident refraction surface is parallel to the imaging plane, that is, perpendicular to the central axis of the system , and is therefore perpendicular to the normal to the central prism.

According to a preferred embodiment, when two opposite side prisms are used, two partial rectangular prisms 8 are placed under the optical side prisms and the central prism, i.e. at (i) the respective exit faces 62 of the side prisms and the exit faces of the central prism. Between the refractive surface 64, and (ii) the imaging surface 110, the partial rectangular prism is adjusted to point to the optical axis A of the detection system. Furthermore, each partial rectangular prism 8 is placed symmetrically with respect to the optical axis of the system. This placement of the partial rectangular prisms may allow the projection light entering each partial rectangular prism to be shifted toward the central optical axis A of the system to reduce the image area required to acquire the projected image.

Each partial rectangular prism 8 comprises an entrance face and an exit face perpendicular to the optical axis, and two internal reflection faces for reflecting projection light which passes said prism in its path. The entrance surface is dimensioned to receive the light of projection path 91 and projection path 92 , ie light leaving side prism 5 and central prism 6 respectively. The respective projection lights are first projected vertically to the incident surface, then projected to the first reflective surface at an angle of 45 degrees, and reflected at an angle of 90 degrees. The projected light is then projected onto the second reflective surface at an angle of 45 degrees, so that the light is parallel to the central axis A after the final reflection. Since the projected light enters the respective partial rectangular prisms parallel to the system optical axis, each reflective surface is inclined at an angle of 45 degrees with respect to said axis A, so that the directions of the respective projected lights have no difference compared to the projected light incident and exiting the partial rectangular prisms. is altered by the partial rectangular prism, but only by moving closer to the optical center axis of the system. Thus, the image area for double-sided inspection is reduced, resulting in an increase in effective image resolution and thus improved measurement accuracy.

Preferably, a lens (not shown) coupled to the video camera 7 and placed in alignment with the optical axis of the system is provided. On the imaging plane a sensor board is placed, which belongs to the video camera 7, and a single image is acquired which contains the outline of the reference edge 12 of the fiducial 1, the projections of the lead terminals 81 of the object 10 and the outline of the package 82. This image is generated for one side of the object by projecting the outline of the reference edge 12 of the fiducial 1, the lead terminal 81 of the object 10, and the outline of the package body 82 along two projection paths 91 and 92, the two projection paths 91 and 92 have two different directions, corresponding to two different viewing angles θ1 and θ2 respectively, thus containing three-dimensional information. The images captured by the video camera 7 are digitized and analyzed using digital image processing methods, such as edge detection methods. That is, the system extracts the relative positions of features such as the package outline and lead terminals of the object 10, and calculates mechanical parameters such as lead spacing and connector dimensions by correlating and analyzing the acquired images.

Referring to Fig. 2, two projection light paths of the left side prism and the central prism are shown respectively, wherein only the configuration of the prism on one side is disclosed, because the preferred configuration is symmetrical with respect to the optical axis, so the corresponding projection light paths pass through An opposing second side prism (not shown) as shown in FIG. 1 is generated.

Both projection paths as shown in Fig. 2 start from a point P of the object, which defines the contour point of the object to be inspected, wherein this point can follow the two paths provided by the optical side prism 5 and the central prism 6. Projection paths 91 and 92 are observed. The object point P should then lie in a plane that can be focused by the system. The two different projection paths 91 and 92 provide two different views of an object point at two different viewing angles θ1 and θ2.

The first projection path 91 is defined by the total internal reflection of the inner surface 52 of the optical side prism 5 . The first projection path 91 is related to the first viewing angle θ1. This is shown in FIG. 2 , the first projection path includes paths a, b and c, which start at the object point P and end at the imaging plane 110 .

The second projection path 92 is defined by the refraction of the central prism 6 at the entrance refraction surface 63 and the exit refraction surface 64 . The second projection path 92 is related to the second viewing angle θ2. This is shown in FIG. 2 , the second projection path includes paths d, e and f, which start at the object point P and end at the imaging plane 110 .

Two different viewing angles θ1 and θ2 are provided by a predetermined angle between the plane of the reflective surface 52 of the side prism 5 and the plane of the incident refractive surface 63 of the central prism 6 .

Although only the reflections at the reflective surfaces 52 of the side prisms 5 are used to move the projected light parallel to the optical central axis A, the projected light of the second projection path through the central prism is moved twice at the incident refraction plane and the exit refraction plane to The light is adjusted so that it is parallel to the optical axis A.

To move the projected light towards the optical axis, i.e. the normal to the central prism, the central prism must have a higher refractive index than the other media outside. According to a preferred embodiment of the invention, the other medium is air, which has a refractive index of about 1.

As shown in FIG. 2 , between the surface 100 and the imaging surface 110 , the projection light of the first projection path 91 and the projection light of the second projection path 92 are adjusted to be parallel to the optical axis A of the system.

According to the present invention, the optical path difference between the two projected light rays is compensated at the exit surface 100, which is set parallel to the reference 1 and aligned with the bottom surface of the optical side prism 5, but the viewing angle between θ1 and θ2 The maximum permissible angular difference is maintained, maintaining sufficient clearance in the image between the lead tip 81 and the reference edge 12 .

The optical path difference 6 on the surface 100 between the first projection path 91 and the second projection path 92 can be calculated by formula 1:

δ=[a/n1]+[(b+c)/n2]-[(d+f)/n1]-e/n3 where a, b, c, d, e and f are projection paths 91 and 92 The partial length of n1 is the refractive index of the medium other than the optical prism, n2 is the refractive index of the material of the optical prism 5, and n3 is the refractive index of the material of the central prism 6. Here, the optical path can be expressed as: Lo=Lg*n, where Lo is the optical path, Lg is the geometric length, and n is the refractive index of the material through which the geometric length passes.

Since the medium other than prism 5 is preferably air, n1 is equal to 1, so formula 1 can be written as:

δ=a+[(b+c)/n2]-(d+f)-[e/n3] By selecting materials with suitable refractive indices n2 and n3 respectively, the first projection path 91(a+b+c) The optical path difference δ between the second projection path (d+e+f) can be compensated.

It is also possible to use another medium than air as another medium, such as another gas, liquid, or glass.

As mentioned above, one aspect affecting the optical path of the two projection paths 91 and 92, which come from such as reference edge 12 or the same object point of the lead end 81 of the object.

Another aspect of reducing the optical path difference between the two projection paths is to adopt appropriate viewing angles θ1 and θ2, and appropriate dimensions of the optical side prisms 5 and/or central prisms 6 .

According to a preferred embodiment of the present invention, another aspect affecting the equality of the optical paths of the two projection paths 91 and 92 is the size of the aperture 2 of the reference 1, and the relative relation of the optical side prism 5 and/or central prism 6 to the reference 1 and Setting of opening 2 of datum 1.

Although the present invention has been described in detail with reference to the preferred embodiments, it should be understood that various changes, substitutions and alterations could be made therein without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (5)

1. An optical inspection system for inspecting an object in the form of a leaded integrated circuit component, said system having an optical axis and comprising: A reference (1) having an opening (2) defined by a reference edge (12) in the reference, said reference providing a reference plane at least substantially perpendicular to the optical axis (A) of the system, wherein the The object (10) is positioned at a predetermined position in an overlapping relationship with the opening (2) of the reference (1); A lateral diffuse light source (3) for illuminating diffused light laterally onto the object and through the aperture (2), thereby passing through the aperture (2) in several projection directions, including the lead wire for the object (10) being positioned The contour image of the contour and the reference edge (12) is projected; The optical side prism (5) is used to receive the first projection light of the contour image from the first projection direction, and the side prism has: an incident surface (51), an outgoing surface (62) and an internal reflection surface (52), the The internal reflection surface cooperates with the incident surface and the exit surface to internally reflect the first projection light so that it passes through the exit surface of the side prism and points to the imaging surface in the exit direction; an optical central prism (6) positioned to receive the second projection light of the profile image from the second projection direction, said central prism (6) having at a predetermined position: an incident refraction surface (63) and cooperating with the incident refraction surface The outgoing refraction surface (64), so that the second projected light is refracted to the imaging surface (110) by the incident refraction surface and by the exit refraction surface; wherein the side prisms (5) and the central prism (6) are designed and placed so that the projection paths of the first and second projections have the same Optical path. 2. The system of claim 1, further comprising an image detection system disposed on the imaging plane for detecting the two projected images of the contour. 3. The system of claim 2, wherein the image detection system comprises a lens and a camera (7) with an image sensor. 4. The system according to one of claims 1 to 3, wherein said first projection direction and said second projection direction correspond respectively to a first viewing angle (Θ1) and a second viewing angle (Θ2), these two viewing angles different from each other. 5. The system according to one of claims 1 to 4, further comprising a partial rectangular prism (8), which is placed between the exit face and the imaging face of the side prism and the central prism, for converting the partial rectangular prism into the partial rectangular prism. The projection of the prism is moved parallel and close to the optical axis of the system.

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