Wire bonding external appearance inspecting apparatus

A wire bonding external appearance inspecting apparatus for inspecting wires bonded to a semiconductor chip and the vicinity thereof, comprises a plurality of illuminating units of different illumination directions, for illuminating the semiconductor chip and the vicinity thereof, and a controller for selecting and operating any one of the plural illuminating units according to the inspection places thereof. Since an optimum illumination can be obtained according to inspection items, a camera can take plural different images according to objects to be inspected, so that the inspection reliability can be improved.

BACKGROUND OF THE INVENTION 
The present invention relates to an apparatus for inspecting the external 
appearance of wire bonding between a semiconductor chip and leads. 
After wire bonding between a semiconductor chip and leads has been 
completed, it is necessary to inspect whether wires are bonded at their 
correct positions, in straight lines without being curved, not 
disconnected, etc. These external appearance inspections can be carried 
out by automatically processing an image obtained by a camera. 
During inspection, it is necessary to illuminate the semiconductor chip, 
wires, and leads to be inspected. In the prior-art inspection, these 
objects to be inspected have been illuminated as shown in FIG. 4. In the 
drawing, a bed 13 of a lead frame 18 is supported by tie bars 15, and 
semiconductor chips 11 are mounted on this bed 13. Wires 17 are connected 
between electrodes 11a of the semiconductor chip 11 and leads 14 arranged 
near the bed 13 as shown. 
These objects to be inspected are imaged by a camera 21 disposed thereover 
under illumination of a downward illuminating means 2 disposed in the 
vicinity of the camera 21 for illuminating the objects from above. 
In the prior-art apparatus, however, since only a single illuminating means 
is provided, the illumination direction is limited to one direction, thus 
causing a problem in that the illumination intensity is not sufficient, 
for each of the items to be inspected and therefore the inspection 
reliability is inevitably degraded. In more detail, there are some 
inspection items such as the detection of the position of a reference mark 
12 representative of a reference position used to determine the 
coordinates of the semiconductor chip 11, the detection of the position of 
another reference mark 16 representative of a reference position of a lead 
frame 18, the inspection of shapes of the leads 14, the inspection of 
shapes of the bonded wires 17, etc. 
In each of these inspections, the optimum illumination direction differs. 
For instance, when the position of the reference mark 12 is required to be 
detected, it is preferable to illuminate the semiconductor chip 11 from 
above. When inspecting other items, however, this illumination direction 
is not preferable and therefore a satisfactory image cannot be obtained. 
Where a high quality image cannot be obtained by the camera 21 for 
inspection purposes, there exists a problem in that the inspection 
reliability is degraded and therefore a sufficient guarantee for the 
product quality cannot be achieved. In addition, where the inspection is 
made on the basis of a dissatisfactory image, there exists a problem in 
that a long image processing time is required, thus increasing the 
inspection cost. 
SUMMARY OF THE INVENTION 
Accordingly, an object of the present invention is to provide a wire 
bonding external appearance inspecting apparatus by which optimum 
illumination directions can be selected according to which items are to be 
inspected. 
To achieve the above-mentioned object, the wire bonding external appearance 
inspecting apparatus for inspecting external appearances of wires bonded 
to a semiconductor chip and the vicinity thereof according to the present 
invention is includes a plurality of illuminating means of different 
illumination directions, for illuminating the semiconductor chip and the 
vicinity thereof; and control means for selecting any of said plural 
illuminating means according to inspection places and controlling 
operation thereof. 
During the inspection, the illumination direction differs according to the 
item to be inspected, such as the position of the semiconductor chip, the 
positions and shapes of the leads, the shapes of the wires, etc. 
Therefore, a plurality of illuminating means of different illumination 
directions are provided, and the operation of the illuminating means is 
controlled according to the items being inspected in order to obtain the 
optimum illumination, and improve the inspection reliability. 
In the inventive apparatus first illuminating means for illuminating the 
semiconductor chip from above, second illuminating means for illuminating 
the same from below, and third illuminating means for illuminating the 
same from the side are provided as the plural illuminating means thus, one 
illumination direction to the semiconductor chip can be selected from the 
above three directions, so that it is possible to illuminate the 
semiconductor chip from the optimum direction according to the inspection 
places. 
The first, second and third illuminating means are connected to first, 
second and third power sources, respectively, and further the control 
means selects and operates any one of the three illuminating means by 
controlling the on-off operation of the three power sources thus, any one 
of the power sources can be turned on by the control means to supply power 
to the corresponding illuminating means.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the present invention will be described hereinbelow with 
reference to the drawings. FIG. 1 is a block diagram of the embodiment of 
the wire bonding external appearance inspecting apparatus. The inspecting 
apparatus is provided with downward illuminating means 2, transmissible 
illuminating means 3 and ring illuminating means 4. The illuminating means 
2, 3 and 4 are connected to three power sources 2a, 3a and 4a, 
respectively. Further, these power sources 2a, 3a and 4a are connected to 
an automatic controller 1. The on-off operation of the respective power 
sources 2a, 3a and 4a is controlled automatically according to the items 
to be inspected by the automatic controller 1. 
The illuminating means 2, 3, 4 are arranged as shown in FIG. 2. In the same 
way as discussed for FIG. 4, wires 17 are bonded between a semiconductor 
chip 11 mounted on a bed 13 and leads. A camera 21 for picking up or 
taking an image of the wires 17 to be inspected is positioned over the 
semiconductor chip 11. The illuminating means 2, 3, 4 are arranged in the 
vicinity of the object to be inspected. The downward illuminating means 2 
is located over the semiconductor chip 11; the transmissible illumination 
means 3 is located under the semiconductor chip 11; and the ring 
illuminating means 4 of annular shape is located so as to enclose the 
periphery of the semiconductor chip 11. 
The downward illuminating means 2 is used to detect a reference mark 12 on 
the semiconductor chip 11. The upper surface of the reference mark 12 is 
finished into a mirror surface state. Therefore, when the downward 
illuminating means 2 illuminates the reference mark 12 from above, the 
light is reflected upward from the reference mark 12 to the camera 21. On 
the other hand, since the other surface of the semiconductor chip 11 is 
finished rather roughly, the illumination light irradiated thereupon is 
reflected in a diffused manner. The camera 21 is disposed over the 
semiconductor chip 11 and the downward illuminating means 2 is disposed 
over the reference mark 12. The optical axis of the camera 21 is in the 
same direction as the illumination direction of the downward illuminating 
means 2. Therefore, the camera 21 can accurately detect the position of 
the reference mark 12 because the reference mark 12 is recognized as being 
bright while the remaining surface area of the semiconductor chip 11 is 
recognized as being dark such that a clear difference in brightness 
between the two exists. 
The transmissive illuminating means 3 is suitable for inspection of the 
reference mark 16 of the lead frame 18 or the shape of the leads 14. When 
the transmissible illuminating means 3 illuminates the semiconductor chip 
11 from below, light is transmitted through the semiconductor chip 11 
toward the camera 11, except the leads 14 formed of an Fe-Ni alloy. 
Therefore, since a hole is formed in the tie bar 15 as a reference mark 
16, light is also transmitted through this reference hole 16. Accordingly, 
the locations of the leads 14 and the tie bar 15 (except the reference 
mark 16) can be recognized by the camera as clear shadow portions, so that 
it is possible to detect the position of the reference mark 16 and the 
presence or absence of curves in the leads 14. 
The ring illuminating means 4 is used to inspect the shapes of the wires 
17. FIG. 3 shows the way of illuminating the wires 17 by the ring 
illuminating means 4. The semiconductor chip 11 located at the center of 
the ring illuminating means 4 is illuminated by light transmitted radially 
inward from the inner circumferential side surface of the ring 
illuminating means 4. Since there exist height difference between the 
wires 17, and the semiconductor chip 11 and the leads 14 as shown in FIG. 
3, the illumination light transmitted from the ring illuminating means 4 
is reflected from the wires 17 upward to the camera 21, and therefore the 
bright wires 17 are imaged by the camera 21. That is, it is possible to 
sufficiently recognize the curved conditions of the wires 17 on the basis 
of clear differences in brightness between the wires and the other 
portions. 
As described above, the different illuminating means 2, 3, 4 are 
respectively used by sending on the items to be inspected. The respective 
power sources 2a, 3a and 4a are controllably turned on or off by the 
automatic controller 1, so that the object to be inspected can be 
illuminated by an optimum illuminating means of the downward illuminating 
means 2, the transmissible illuminating means 3 and the ring illuminating 
means 4 depending on the items being inspected. Here, the procedures for 
the respective inspections are previously input into the automatic 
controller 1. Therefore, power supply from the respective power sources 
2a, 3a and 4a to the respective illuminating means 2, 3 and 4 is 
automatically controlled according to the inspection items in accordance 
with the procedures input into the automatic controller 1. 
As described above, according to the present embodiment, since three kinds 
of illuminating means are automatically and controllably selected and 
operated so that an optimum illumination can be obtained according to the 
items being inspected, it is possible for the camera 21 to sufficiently 
recognize the objects to be inspected. Therefore, it is possible to more 
clearly discriminate whether products are defective or non-defective, thus 
improving the inspection reliability. In addition, since the camera 21 can 
take a clear image, the image processing can be executed smoothly and the 
image processing speed can be increased, thus reducing the inspection 
cost.