Metal working – Means to assemble or disassemble – Means to assemble electrical device
Reexamination Certificate
1998-12-02
2001-02-13
Rosenbaum, Icuda (Department: 3729)
Metal working
Means to assemble or disassemble
Means to assemble electrical device
C029S739000, C029S741000, C198S468400
Reexamination Certificate
active
06185815
ABSTRACT:
PRIORITY CLAIM
The present application claims priority under 35 U.S C. §119 based upon Swiss application no. 1997 2807/97, filed Dec. 7, 1997.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a semiconductor mounting apparatus with a chip gripper which is moveable back and forth between a first location and a second location by means of a lever mechanism, in order to lift a chip from a chip carrier at the first location and to lay the chip on a substrate at the second location. Such an apparatus, described as a “pick and place” apparatus is used as a component of a mounting machine known as a “die bonder” in semiconductor mounting. It serves to mount the numerous similar chips of a wafer, which are located next to one another on a carrier, one after another on a substrate, for example, a metal lead frame. Coordinated with each pick and place movement, the wafer table on which the chip carrier is located makes available a next chip at said first location, and the substrate is also advanced in order to make available a new substrate location at the second location. For lifting up and subsequent laying down of the chips, the chip gripper can be raised and lowered in a known manner, either together with the whole apparatus or on its own relative to the apparatus. Extremely high demands are made on mounting apparatus of this type. For the further processing of the mounted chips (contacting of the integrated circuit in the wire bonder), the chips must be accurately positioned on the substrate, which requires a correspondingly accurate arrival at the second location by means of the chip gripper, and also necessitates the previous precise transporting to the first location for lifting up the chip. On the other hand, high speeds and short cycle times of the movement sequences are required, which cause correspondingly high accelerations and inertial forces to occur on the parts moved.
2. The Background Art
Up until now different lever mechanisms have been used to produce the alternating movements of the chip gripper, which sometimes include guide slots (for example, in the manner of the known maltese transmission arrangement). Such slots are disadvantageous for achieving precise movement because of the considerable shearing forces occurring with them, and have to be serviced accordingly. With another known mechanism, the chip gripper is seated at the end of a lever pivoting back and forth, that is to say it performs a curve-shaped movement corresponding to the swinging displacements of the lever, which must always be stopped in the end positions, wherein there is a strong tendency for vibration. With the known arrangements it is therefore difficult to satisfy the demands existing in practice with respect to accuracy as well as to speed.
The object of the invention is to overcome the existing disadvantages of the prior art with a semi-conductor mounting apparatus of the type described in the introduction. The pick and place mechanism must, above all, ensure accurate positioning of the chip gripper in both end positions, but along with this also make possible rapid back and forth movements, that is to say short cycle times.
BRIEF DESCRIPTION OF THE INVENTION
This object is solved in accordance with the invention with the characterising features of claim
1
. According to this, the lever mechanism of the apparatus is provided with a first pivoted lever which is seated on a shaft mounted equidistantly between the first and second locations and is driven in alternating pivoting directions between two end positions, in which it is directed towards one or the other end position. A second pivoted lever is mounted on the end of the first pivoted lever. It is driven the opposite way around with respect to the direction of pivoting of the first pivoted lever, and with a certain gear ratio with respect to the pivoting movement thereof; at its end it is connected to the chip gripper. Said gear ratio, as well as the lengths of the two pivoted levers are matched to each other in a particular manner, that is to say that in the two end positions of the first pivoted lever, the two pivoted levers are in an extended position with respect to one another and the chip gripper has arrived over one or the other location.
Such matching is produced when, respectively:
n=
360°/&PHgr;;
h
1
/
h
2
=
n−
1;
h
1
+
h
2
=
S,
wherein:
n=gear ratio
&PHgr;=pivoting range of the first pivoted lever between the end positions
h
1
=length of the first pivoted lever
h
2
=length of the second pivoted lever
S=distance between the pivoting axis of the first pivoted lever and the first or the second location
As can be seen (also with reference to specific examples described later on), different embodiments with different, matched pivoting ranges, gear ratios and lever proportions are possible. With respect to the object of the invention, with this type of lever mechanism, of primary importance is the condition that at the end of each movement cycle the chip gripper always reaches its end position (that is to say the first or the second location) in the direction of the extended pivoted lever, that is to say the movement components at right-angles to the longitudinal direction of the levers disappear in the end positions. The inertial force of the accelerated chip gripper then acts in the direction of the extended levers and contributes in a certain way to the stabilising of the extended position. Lastly, an occasional over-swing of the first pivoted lever in the extended positions (which must be stopped at the end of its pivoting range) is of diminishing influence on the end positions of the chip gripper. Such advantageous kinematic and dynamic properties of the lever mechanism endow the mounting apparatus according to the invention with high and long-term stable positioning accuracy and at the same time allow short cycle times.
A particularly simple and advantageous embodiment of the invention is produced where the pivoting range &PHgr;=180°, the gear ratio n=2, and the lever proportions h
1
/h
2
=1. A lever mechanism with these parameters is known per se as a so-called straight-line mechanism, which means that a body moved by it—in this case the chip gripper—moves in a straight line.
As described hereinabove, the apparatus according to the invention can, in principle, also be produced using other parameters (even with values of n which are not integer numbers). Particular further configurations of the apparatus according to the invention defined in claim
1
are described in the dependent claims.
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Chang Rick Kiltae
ESEC SA
Ritchie David B.
Rosenbaum Icuda
Thelen Reid & Priest LLP
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