Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
1999-03-05
2001-05-29
Arbes, Carl J. (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S430000, C029S743000, C228S041000, C228S245000
Reexamination Certificate
active
06237219
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a mounting apparatus for mounting conductive balls, for example solder balls, on a workpiece, and the method.
BACKGROUND OF THE INVENTION
Solder balls and the like conductive balls are often used in manufacturing the electronic components with bump; for example, a flip chip, a BGA (Ball Grid Array), etc. Suction head is a popular means for mounting the conductive balls on a chip, a substrate and other such workpieces.
Conductive balls kept in a vessel are picked up by a suction head having a number of suction holes provided in the bottom. Then the suction head moves to a place above a workpiece to have the conductive balls mounted on electrode of the workpiece. With this method, a number of balls can be carried to and mounted at once on a workpiece at a high operating efficiency.
In the above described mounting method using a suction head, however, the occurrence of a pickup error and a placing error with the conductive balls are not negligible. Namely, when a suction head is lowered to a dispensing vessel where a number of conductive balls are stored, the suction head does not always pick the conductive balls up rightly for sure, one conductive ball at each of the suction holes. For example, there may be a case where a plurality of conductive balls are sucked to by vacuum under one suction hole forming a chain of balls or a conductive ball is sticking on the bottom surface at a place other than the suction hole. The suction head goes up even if the sucking status remains as described above.
When a suction head is lowered on a workpiece to mount the conductive ball by releasing the sucking vacuum, it can not always be expected for sure that each and all of the conductive balls fall off the suction head to drop on the workpiece. Some of the conductive balls sometimes remain staying on the bottom surface of suction head even after it is lifted.
For detecting the existence of such redundant conductive ball sticking to the surface of suction head and such conductive ball still remaining on the suction head even after a mounting process is finished, there has been a detection system at work using a combination of a light sensor and a laser beam or the like light source. The above detection system recognizes the existence, or non-existence, of a conductive ball by making use of a variation in the amount of light received by the light sensor due to an interruption caused by a ball locating in the path of a light projected from the light source.
However, there are following problems in the above described detection system. The problems come from the machining errors during manufacture of a suction tool or the assembly errors thereof, and the level of precision during machining process for the suction hole. If there is a tilt with the bottom surface of a suction tool caused, for example, by a fabrication error, the bottom surface may not be precisely in parallel with the optical axis of a light sensor; in such a case, some difference may be caused in the interruption of projected light by a conductive ball depending on a place at which the conductive ball is being sucked to. If a wave form representing the amount of light received at the light sensor which exhibits a conductive ball under such a state is compared as it is with a threshold value for the purpose of judgement, the result of comparison may not always indicate correct status. It may misjudge the existence, or non existence, of the conductive ball. If there is a dispersion in the accuracy of machining for the tapered depth of the suction holes, then the height of the conductive balls being sucked to the suction holes may not be uniform. A judgement error may be induced likewise, also in this case.
SUMMARY OF THE INVENTION
The present invention aims to present an apparatus and the method for mounting conductive balls, in which the existence, or non-existence, of the conductive ball is detected at a high accuracy level.
A mounting apparatus for mounting conductive balls in accordance with a first mode of the present invention comprises a ball feeder for keeping conductive balls, a location setting device for setting a workpiece to a right place to be mounted with the conductive balls, a suction head comprising a suction hole provided in the bottom surface for sucking the conductive ball, a light sensor comprising a light source and a light detector, a transfer device for relatively transferring the suction head and the light sensor so as the bottom surface of said suction head passes through a space between said light source and light detector, a reference wave form memory for storing a first reference wave form that represents the variation in the amount of light detected at the light detector during the time when the suction head carrying the conductive balls rightly sucked to in a normal state passes through the space between the light source and the light detector, a read-out wave form memory for storing a first read-out wave form that represents the variation in the amount of light detected at the light detector before mounting of the conductive ball, and a control section for judging the existence, or non-existence, of the conductive ball on the bottom surface of suction head by comparing the first read-out wave form with said first reference wave form.
A mounting apparatus for mounting conductive balls in accordance with a second mode of the present invention comprises, in place of the reference wave form memory of the first mode storing the first reference wave form, a reference wave form memory for storing a second reference wave form that represents the variation in the amount of light detected at the light detector during the time when the suction head passes through the space between the light source and the light detector without carrying any conductive ball; in place of the read-out wave form memory storing the first read-out wave form, a read-out wave form memory for storing a second read-out wave form that represents the variation in the amount of light detected at the light detector after the conductive balls are actually mounted, and a control section for judging the existence, or non-existence, of the conductive ball on the bottom surface of suction head by comparing the second read-out wave form with the second reference wave form.
A mounting apparatus for mounting conductive balls in accordance with a third mode of the present invention comprises, in place of the reference wave form memory of the first mode, a reference peak value memory for storing data on peak value of reference wave form that represents the variation in the amount of light detected at the light detector during the time when the suction head passes through the space between the light source and the light detector carrying the conductive ball rightly sucked to in a normal state; in place of the read-out wave form memory, a comparative peak value memory for storing data on peak value of wave form that represents the variation in the amount of light detected at the light detector before the conductive ball is actually mounted, and a control section for judging the existence, or non-existence, of the conductive ball on the bottom surface of suction head by comparing the data on peak value with the data on peak value of the reference wave form.
As described in the above, an invented mounting apparatus detects the existence, or non-existence, of conductive ball at a high accuracy level by comparing, respectively, a reference wave form, or data on peak value of the reference wave form, with a wave form obtained when actually mounting the conductive ball, or data on peak value of the wave form. In this way, possible errors that could be caused by a tilt of the suction head, and a light interruption error which stems from machining errors during processing of suction holes, etc. are eliminated.
REFERENCES:
patent: 4772125 (1988-09-01), Yoshimura et al.
patent: 4851902 (1989-07-01), Tezuka et al.
patent: 4871110 (1989-10-01), Fukasawa et al.
patent: 4910757 (1990-03-01), Kiyasu et al.
pate
Arikado Kazuo
Eguchi Norifumi
Kasai Teruaki
Sasaguri Shinji
Arbes Carl J.
Matsushita Electric - Industrial Co., Ltd.
Ratner & Prestia
Trinh Minh
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