Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1999-07-30
2003-05-27
Patel, Jayanti K. (Department: 2625)
Image analysis
Applications
Manufacturing or product inspection
C348S095000, C250S559340
Reexamination Certificate
active
06571007
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a substrate, a head, an apparatus and a method each for arranging a plurality of minute electroconductive balls, which are bonded to form bumps on the electrodes of a semiconductor element, printed circuit board (PCB), etc., wherein a means for recognizing whether or not balls are held is provided.
2. Description of the Related Art
In the ball bump process which is applied in producing a semiconductor device, bumps are formed of minute electroconductive balls on the electrode portion (pad) of a semiconductor device or a PCB, and these devices and PCBs are bonded via the bumps with each other. In such a process, a ball-arranging substrate is used, in which minute electroconductive ball-arranging holes are formed, corresponding to the location of electrodes of the semiconductor device or a PCB.
In the process for forming bumps, the minute electroconductive balls are sucked and held in the ball-arranging through holes of the ball-arranging substrate by means of vacuum suction, etc. It is necessary that a single ball is exactly sucked in a single hole of the ball-arranging substrate. If a ball is not sucked, then a bump is not formed on the electrode, and if two or more balls are sucked in a single ball-arranging hole, the bump may contact the adjacent pad.
As a method for recognizing such a ball-sucking failure, it is known to irradiate a laser beam from the lateral and the rear sides of the ball-arranging substrate. If an error is recognized, the error is removed by removing excess minute balls or repeating such a ball-suction. When it is recognized that the balls are arranged on the substrate without an error, the ball-arranging substrate with the balls as be are transported to a bump-bonding stage, where the locations of the minute electroconductive balls of the substrate and the electrode pads of a semiconductor device are aligned with each other.
After the completion of the alignment, the ball-arranging substrate, on which the minute electroconductive balls are sucked, is lowered down on the semiconductor device, and then the minute electroconductive balls and the electrode pads are bonded with each other by means of heat pressing. In the case when bumps are formed of a low melting point metal at the electrode portions of a PCB, it is general that a flux is applied to the electrode portions, and minute balls are arranged at the electrode portions and then reflowed.
As set forth above, the prior art inspection for excess balls or lack of sucked balls includes a method for inspecting excess balls or lack of balls by irradiating light from the front or lateral side of the ball-arranging substrate. If there is lack of a ball, the light irradiated from the front side of the substrate reaches, through the open ball-arranging hole, the light-receiver located on the rear side of the ball-arranging substrate, so that lack of a ball can be detected. If there are excess balls, the light irradiated from the lateral side of the substrate is shut out, and thus the light does not reach the light-receiver located on the opposite side of the ball-arranging substrate, so that excess balls can be detected. However, this method of inspection does not have reproducibility in recognizing defects of the balls and is not used, in industrial production, when the diameter of the balls is less than 300 &mgr;m, particularly less than 200 &mgr;m, because the amount of light and the accuracy of the location recognition are not sufficient.
On the other hand, another method using the image-recognization method is known for inspecting the arranged balls. According to the method, the light is irradiated to the minute balls, which are held on the ball-arranging substrate, and the reflected light is inspected by a CCD camera. The reflected light is converted to binary images, i.e., the light reflected by the balls is converted to white image, and the light reflected by the substrate is converted to black image. Thus, the ball-arranging condition is recognized.
However, it has been considered that it was difficult to exactly recognize the minute balls sucked and held-on the ball-arranging substrate by the image recognizing method and this method was not applied in the industry. For example, in the case when the ball-arranging substrate is made up of a metal, e.g. stainless steel, the light reflected at the substrate itself causes erroneous recognization e.g. due to reflections from machinery defect and damage portions or due to insufficient intensity difference between the light reflected by the minute balls and that reflected by the ball-arranging substrate itself causing an insufficient contrast. Also burrs may be formed on the substrate, when metal working, e.g., mechanical working, electrodischarging and laser irradiation is applied. In such a case, the accuracy was remarkably influenced when the minute balls, whose diameter was less than 200 &mgr;m, were mounted on the chip, etc.
Furthermore, when the substrate used is made of glass, the irradiated light is transmitted through the glass and reaches the jig, which holds the glass substrate, and the light reflected by the jig causes errors in recognition of the balls as a metal arranging substrate does. That is, the transmitted light is irregularly reflected near the ball sucking hole to provide white bright images, causing the recognition of sucked balls to be uncertain. And the light is reflected by the defects scattered on the surface of the substrate, where the reflected light also gives white images. Such a reflected light may be erroneously recognized to be caused by the sucked minute balls.
The object of the present invention is to provide a ball arranging substrate, arranging head, arranging apparatus and arranging method, in which the conditions of sucked balls more precisely than before, by which ball bumps can be formed more exactly.
For example, as disclosed in Japanese Unexamined Patent Publication No. 4-250643, a conventional ball-arranging substrate is produced by forming ball-arranging holes on the substrate of a metal, e.g., stainless steel or a ceramic material, etc. by means of precise electrodischarging, laser-irradiation, electroforming, etching, etc.
When the ball-arranging substrate is a metal, e.g., stainless steel, misalignment is caused by thermal expansion of the arranging substrate during aligning between the ball-arranging holes and the electrodes due to a large difference in the thermal expansion coefficient between a metal substrate and silicon chip. When the ball-arranging holes are formed by means of laser irradiation or electrodischarging, a protuberance is formed around the holes and thus, dispersion of the height of sucked balls and a decrease in the sucking capability are observed. Furthermore, in the prior art it was difficult to precisely open the ball-arranging holes, of a diameter less than 100 &mgr;m, by means of a general purpose working apparatus. If the diameter of the ball-arranging holes must be less than 100 &mgr;m, the opened holes are narrowed by means of metal plating. However, the number of working processes is increased and the diameter of the opened holes is not formed uniformly, and the shapes of the holes are not formed as true circles. Thus, these defects result in misplacement of the arranged balls, and when bumps formed on a semiconductor device, or innerlead of TAB, or a printed circuit board, etc. are arranged at a narrow pitch, the precision of the ball arrangement is lowered.
Japanese Unexamined Patent Publication No. 7-95554, discloses a ball-arranging glass substrate. However, the disclosed substrate is not suitable for arranging minute electroconductive balls.
Another object of the present invention is to provide a ball-arranging substrate, a ball-arranging head, and an apparatus for arranging balls and also a method for arranging balls, in which the minute balls are arranged more precisely than before, and thus ball-bumps. are formed more exactly.
DISCLOSURE OF THE INVENTION
In order to achieve the object
Hashino Eiji
Shimokawa Kenji
Tatsumi Kohei
Chawan Sheela
Kenyon & Kenyon
Nippon Steel Corporation
Patel Jayanti K.
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