HK1144235B - Method for picking up semiconductor chips from a wafer table and mounting the removed semiconductor chips on a substrate - Google Patents

Description

Method of picking up semiconductor chip from wafer stage and method of mounting removed semiconductor chip on substrate

Technical Field

The invention relates to a method of the kind mentioned in the preamble of claim 1 for picking up semiconductor chips provided on a wafer table. The invention further relates to a method for mounting a removed semiconductor chip on a substrate.

Background

In the art, a mounting apparatus for mounting a semiconductor chip is called a die bonder. The mounting device is used for mounting a large number of uniform chips of a wafer, which are located next to one another on a chip carrier, one by one on a substrate, for example on a metal lead frame. The die bonder comprises a wafer stage on which the chip carrier is located; a transport system for providing a substrate; and a pick and place system to remove a semiconductor chip from a chip carrier and place it on the substrate. The pick and place system includes a bond head having a chip gripper that is moved back and forth by a drive system. The chip holder is rotatable about a vertical axis so that the rotational position of the semiconductor chip can be changed as desired. The chip gripper, which is referred to in the art as a "pick-up tool" or "die chuck", includes an exchangeable gripping member, which is a suction member to which a vacuum may be applied.

There is a very high demand for such mounting devices. They need to be placed on the substrate in a precise position for further processing of the mounted chips. Two cameras are provided on the die bonder to ensure that the semiconductor chip can be placed on the substrate with an accuracy in the micrometer range. The first camera measures the position of the semiconductor chip to be picked up by the chip gripper and provides position data related to the first coordinate system. The second camera measures the position of the substrate area on which the semiconductor chip is to be placed and provides position data related to a second coordinate system. The pick-and-place system controls the bond head based on information provided by the camera in such a way that the chip gripper is able to remove the semiconductor chip from the wafer table and to place it at the correct position on the substrate area in a precisely positioned manner. The position of the pick-and-place system is related to a third coordinate system, which is independent of the coordinate system of the camera.

During operation of the die bonder the problem arises that the relative positions of the three coordinate systems may change due to different conditions. The temperature at different locations of the die bonder can often vary, either intentionally or unintentionally. This often has the consequence that the conversion of the target coordinates determined in the coordinate system of the first camera or the coordinate system of the second camera into motion coordinates for the pick-and-place system is no longer as accurate as required.

Disclosure of Invention

The present invention is based on the object of providing a method for picking up and mounting semiconductor chips which ensures a high accuracy in placement regardless of external environments and variations. This object is achieved according to the invention by the features of claim 1.

The invention relates to a method for picking up or optionally mounting a semiconductor chip on a substrate, wherein

-providing a semiconductor chip on a wafer table;

-providing the substrates on a substrate table one by one;

-the first camera detects the position and orientation of the semiconductor chip provided on the wafer stage and to be mounted as the next one;

-the second camera detecting the position and orientation of the substrate area on which the semiconductor chip is to be mounted;

the chip gripper picks up the semiconductor chip provided on the wafer stage and mounts it on the substrate, and holds the chip gripper on the bonding head, and the pick-and-place system, preferably with two linear drives, transports the bonding head with the chip gripper back and forth between the wafer stage and the substrate.

According to the invention, with a first coordinate system KS₁The position of the semiconductor chip to be mounted next detected by the first camera is provided in the form of the associated position data to be associated with the second coordinate system KS₂The relative position data is provided in the form of the position of the substrate area on which the semiconductor chip is to be mounted, and the position of the bond head is related to the third coordinate system KS₃And (4) correlating.

The present invention proposes to provide a mark on the bonding head whose position can be measured by a camera. Since, for constructional reasons, it is not possible to arrange the marking in the focal plane of the camera, the invention further proposes a preferred embodiment in which a lens is attached above the marking, which lens ensures that the marking is also imaged in a clearly defined manner.

The invention further proposes to use a first fixed mapping function F and a first variable correction vector K₁A first coordinate system KS₁Converting into a third coordinate system KS of a pick-and-place system₃And using a second fixed mapping function G and a second variable correction vector K₂The second coordinate system KS₂Converting into a third coordinate system KS of a pick-and-place system₃. When the die bonder is first set up or also in the case of a normal new setting of the die bonder, the mapping functions F and G and their inverse are determined on the one hand and the two correction vectors K are used₁And K₂Is set to 0. Although the mapping functions F and G do not change until the next usual new setting of the die bonder, the correction vector K is readjusted upon the occurrence of a predetermined event₁And K₂. The predetermined event should be understood as the following event: can be at a high levelSexual expectation of three coordinate systems KS₁、KS₂And KS₃To the extent that placement accuracy is reduced, relative to each other.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate one or more embodiments of the invention and, together with the detailed description, serve to explain the principles and implementations of the invention. The figures are not shown true to scale.

Fig. 1 shows a top view of a mounting apparatus for mounting a semiconductor chip;

FIG. 2 shows a side view of a camera, a bond head and a wafer stage; and

fig. 3 shows a top view of a bond head and three different coordinate systems.

Detailed Description

Fig. 1 schematically shows a top view of a mounting apparatus for mounting semiconductor chips, which is a so-called die bonder, within the scope required for understanding the present invention. Fig. 2 shows a side view of a partially mounted device. The die bonder includes a wafer stage 1 on which a semiconductor chip 2 to be mounted is provided, a substrate stage 3 on which a substrate 4 to be mounted is provided by a transfer device (not shown), and pick-and-place systems 5 and 7, which pick-and-place systems 5 remove the semiconductor chip 2 from the wafer stage 1 and place it on the substrate 4. The pick and place system 5 includes a bond head 8 with an exchangeable chip gripper 9 (fig. 2) and two linear position control drives for moving the bond head 8 in two orthogonal directions designated as the x-direction and the y-direction. A third drive (not shown) is used to raise or lower the bond head 8 or the chip gripper 9 in the z-direction, which extends perpendicular to the plane of the drawing. The first camera 6 is used to determine the position of the next semiconductor chip 2 to be removed. The second camera 7 is used to determine the position of the substrate area of the substrate 4 on which the semiconductor chip 2 is placed. The first camera 6 is typically arranged in a fixed manner. The second camera 7 is also arranged in a fixed manner or can be moved with a separate drive in at least one or two directions extending parallel to the surface of the substrate 4. Such pick-and-place systems 5 are known, for example, from EP 923111, EP 1480507, DE102004026534 and EP 1612843.

A marker 10 (fig. 2) is attached transversely to the bond head 8 in a manner visible in an image provided by the first camera 6 when the bond head 8 is in the field of view of the first camera 6 and visible in an image provided by the second camera 7 when the bond head 8 is in the field of view of the second camera 7.

Fig. 2 shows a side view of the first camera 6, the bond head 8 and the wafer stage 1. The visible field, which is delimited in the figure by the line 6a, faces the wafer stage 1, so that in the image provided by the first camera 6 the next semiconductor chip to be removed is imaged in a clearly defined manner. The focal plane of the first camera 6 lies on the plane defined by the semiconductor chip 2 to be removed. The focal plane of the second camera 7 (fig. 1) is located on the plane defined by the surface of the substrate 4 to be mounted. It is not possible to attach the tag 10 to the bond head 8 in such a way that it is imaged in a clearly defined manner by the cameras 6 and 7 without adjusting the focal plane. In order to still ensure that the mark 10 is imaged in a clearly defined manner, a lens 11 is advantageously attached to the bond head 8 above the mark 10. The lens 11 is located between the marker 10 and the respective camera 6 and 7 and ensures that the marker 10 is imaged in a sufficiently sharp defined manner in the image of the respective camera 6 and 7. In order to ensure that the marking 10 is imaged in a clearly defined manner, it is also possible to foreseeably adjust the focal plane of the camera instead of providing the lens 11. The solution with the lens 11 is simple, fast and economical, because the lens 11 makes it possible for the lens system of the cameras 6 and 7 to be adjusted to a small extent only.

The first camera 6 supplies its image data to a first image processing unit which determines the next from the image dataFrom the position and orientation of the semiconductor chip 2 to be mounted and in a first coordinate system KS₁The form of the associated location data provides them. These position data are composed of three numbers (p, q,) Are composed, and the two numbers p and q represent the positions of the reference points of the semiconductor chip 2, and the numbersThe angle of rotation of the semiconductor chip 2 relative to its setpoint position is determined.

The second camera 7 supplies its image data to a second image processing unit which determines the position and orientation of the substrate area on which the semiconductor chip 2 is to be mounted from the image data and in a second coordinate system KS₂The form of the associated location data provides them. These position data are composed of three numbers (u, v, ψ), and these two numbers u and v represent the position of the reference point of the substrate area, and the number ψ determines the angle by which the substrate area is rotated with respect to its set point position.

A first linear drive of the pick-and-place system provides a number x_MAnd a second linear drive of the pick-and-place system provides a number y_MWhich together form the representative mark 10 relative to a third coordinate system KS₃Position (x) of_M，y_M)。

The chip gripper 9 is rotatable about a rotation axis 12 (fig. 2). The suction opening of the chip gripper 9 defines the position of the gripper shaft 13 (fig. 2) of the chip gripper 9. The clamp shaft 13 is in a third coordinate system KS₃Position (x) of_G，y_G) Given by:

(x_G，y_G)＝(x_M，y_M)+D+E

wherein the vector D describes the position (x) of the rotation axis 12 relative to the marker 10_M，y_M) And vector E describes the position of the clamp shaft 13 relative to the axis of rotation 12The position of (a). The vector D is a fixed vector to be determined once. The vector E is a vector that rotates in synchronization with the chip gripper 9: the length thereof has a fixed amount, but the direction thereof changes when the chip holder 9 rotates about the rotation axis 12. In this ideal case, the rotation shaft 12 and the chucking shaft 13 always coincide, i.e., E is 0, regardless of the rotational position of the chip chucking 9.

FIG. 3 shows three coordinate systems KS₁、KS₂And KS₃The correlation between them. In order to ensure that the semiconductor chip 2 can be placed on the substrate 4 in a correctly positioned manner, it must be possible to calculate the chuck axis 13 of the chip chuck 9 in the first coordinate system KS₁And in a second coordinate system KS₂The current position in both. The first mapping function F is therefore determined in a first or in general a new setting of the installation device, wherein the function F defines the first coordinate system KS₁Mapping to a third coordinate System KS₃. This takes place with the aid of the marker 10: two linear drives of the pick-and-place system 5 move the bond head 8 with the mark 10 to k different positions (x) within the field of view of the first camera 6_n，y_n) Where n is 1 to k, and the first image processing unit determines the relative position (p) of the marker 10 from the image provided by the first camera 6_n，q_n). A first mapping function F is calculated from the obtained data records. Thus, the following applies:

(x，y)＝F(p，q)

then, an inverse function F of the mapping function F is calculated^-1Thereby to make

(p，q)＝F^-1(x，y)

Furthermore, the first correction vector K₁Is set to a value K₁＝0。

Similarly, a second coordinate system KS is determined₂Mapping to a third coordinate System KS₃Second mapping function G and its inverse function G^-1. Thus, the following applies:

(x，y)＝G(u，v)

and vice versa

(u，v)＝G^-1(x，y)

In addition, the second correction vector K₂Is set to a value K₂＝0。

To determine a first coordinate system KS₁Associated target coordinates using the first camera 6 and the first coordinate system KS₁The pick-and-place system 5 has to move the bond head 8 to said target coordinates so that the chip gripper 9 can pick up the semiconductor chip 2 provided on the wafer table 1. To determine a second coordinate system KS₂Associated target coordinates using the second camera 7 and the second coordinate system KS₂The pick-and-place system 5 has to move the bond head 8 to said target coordinates so that the chip gripper 9 can place the semiconductor chip 2 in a correctly positioned manner. In these two coordinate systems KS₁And KS₂All calculations were performed. Only after all calculations to be determined have been completed, the target coordinates are converted into a third coordinate system KS by means of the respective mapping functions F and G₃The motion coordinates of (2). Thus, both vectors D and E are determined to be associated with the first coordinate system KS₁Correlated vector D₁And E₁And a second coordinate system KS₂Correlated vector D₂And E₂. Therefore, the third coordinate system KS₃For moving the bond head 8 only and not in the third coordinate system KS₃Do any calculations. Third coordinate system KS₃Given by the mechanics of the pick-and-place system 5, i.e. the coordinates x and y are position values provided by two linearly driven encoders and are thus not an accurate orthogonal coordinate system.

When mapping functions F and G are determined, the inverse F is determined^-1And G^-1And vector D₁、E₁、D₂And E₂The semiconductor chips 2 can then be mounted one by one in the production phase, because:

taking an image of the next semiconductor chip 2 with the first camera 6 and calculating the first coordinates of the semiconductor chip 2 from the imageLine KS₁Correlated position data (p)_W，q_W，) Thus, when the semiconductor chip 2 is not rotated relative to its setpoint position,

-calculating the third coordinate system KS by the following equation₃Relative position (x)_W，y_W) Said position (x)_W，y_W) Is the reference point that needs to be obtained by the mark 10 so that the gripper shaft 13 of the chip gripper 9 passes through the semiconductor chip 2:

(x_W，y_W)＝F[(p_W，q_W)-D₁-E₁+K₁]

-approaching the calculated position (x)_W，y_W) And picking up the semiconductor chip 2 with the chip gripper 9;

capturing an image of the substrate area on which the semiconductor chip is to be mounted with the second camera 7, and calculating the second coordinate system KS of the substrate area from the image₂Correlated position data (u)_S，v_S，ψ_S) Thus, when the substrate region is not rotated relative to its setpoint position, ψ_S＝0；

-calculating the third coordinate system KS by the following equation₃Relative position (x)_S，y_S) Said position (x)_S，y_S) Is the reference point that needs to be obtained by the mark 10 so that the gripper axis 13 of the chip gripper 9 passes through the substrate area:

(x_S，y_S)＝G[(u_S，v_S)-D₂-E₂+K₂]

-approaching the calculated position (x)_S，y_S) Make the chip gripper 9 about an angleOptionally rotated, and the semiconductor chip 2 is placed on the substrate area.

In order to maintain the placement accuracy of the die bonder at the same height level throughout production, readjustment of the first correction vector K is performed during the occurrence of a predetermined event₁And a second correction vector K₂. Using a mark 10 provided on the bond head 8, the mark is brought into the field of view of the first camera 6 for readjusting the first correction vector K₁And into the visual domain of the second camera 7 for readjusting the second correction vector K₂. Readjusting the first correction vector K as follows₁：

Using a third coordinate system KS₃Relative coordinate (x)_R，y_R) Moving the bond head 8 to a set point position R ═ x_R，y_R) Wherein the marker 10 is located within the field of view of the first camera 6;

calculating the relative first coordinate system KS of the marker 10 by the following equation₁Position of set point (p)_R，q_R)：(p_R，q_R)＝F^-1(x_R，y_R)；

Taking an image of the marker 10 with the first camera 6, determining the marker 10 relative to the first coordinate system KS using the image of the first camera 6₁Actual position (p) of_M，q_M) And an

-calculating a first correction vector K as the difference between the approximated set point position and the measured actual position by the following equation₁：

K₁＝(p_R，q_R)-(p_M，q_M)，

Obviously, the first correction vector K₁And a first coordinate system KS₁And (4) correlating.

Similarly, readjust as followsSecond correction vector K₂：

Using a third coordinate system KS₃Relative coordinate (x)_T，y_T) Moving the bond head 8 to a set point position T ═ x_T，y_T) Wherein the marker 10 is located within the field of view of the second camera 7; -calculating a set-point position (u) of the marker 10_T，v_T) Relative to a second coordinate system KS₂Is calculated as (u)_T，v_T)＝G^-1(x_T，y_T)；

Taking an image of the marker 10 with the second camera 7, determining the second coordinate system KS of the marker 10 using the image of the camera 7₂Actual position (u) of_M，v_M) And an

-calculating a second correction vector K as the difference between the approached setpoint position and the measured actual position₂：

K₂＝(u_T，v_T)-(u_M，v_M)，

Obviously, the second correction vector K₂And a second coordinate system KS₂And (4) correlating.

There is a capability to trigger readjustment of the correction vector K₁And K₂In particular the following four events:

since the last calibration, a predetermined number of semiconductor chips 2 are mounted;

the temperature measured at the predetermined position of the pick-and-place system 5 has changed by more than a predetermined value since the last calibration.

-stopping production;

the actual position of the mounted semiconductor chip detected and calculated by the second camera 7 after mounting deviates from the set point position by more than a predetermined amount.

After completing the correction vector K₁And K₂After readjustment, canThe mounting of the semiconductor chip 2 is continued as described above, but now the updated correction vector K₁And K₂May not be 0.

The present invention is applicable to a known pick-and-place system in which the wafer stage 1 and the stage 3 for the substrate 4 are arranged in parallel planes, and also to a pick-and-place system as described in EP 1480507 in which the wafer stage 1 and the stage 3 for the substrate are arranged in a manner inclined to each other, and in which the bond head 8 is pivotally moved about a horizontal axis in addition to being moved in the x-direction and the y-direction.

The above-described embodiment is a preferred embodiment wherein the bond head is moved to the first set-point position R and the second set-point position T, respectively, for adjustment and readjustment, and the third coordinate system KS of the first set-point position R and the second set-point position T is stored₃The associated coordinates are used to readjust the two correction vectors K₁And K₂. In this example, respectively by means of an inverse function F^-1And G^-1The corresponding set point position of the marker 10 is calculated. Another embodiment is explained below in which the first coordinate system KS of the marks 10 (or any other random reference point on the bond head 8) is additionally stored when the bond head 8 is located at the first or second set point position₁The associated coordinates or marks 10 (or any other random reference points on the bond head 8) and a second coordinate system KS₂The associated coordinates are then used to readjust the two correction vectors K₁And K₂。

The pick-and-place system includes as part a pick-up system for picking up semiconductor chips from a wafer stage. Third coordinate system KS₃Is a coordinate system inherent to the pick-and-place system and will therefore be referred to as coordinate system KS in the following. To ensure that a readjustment is possible, in a setup phase, a readjustment is first performed, in which the bond head 8 is moved to a first setup point position located in the field of view of the first camera 6, and the coordinates (x) of the first setup point position in relation to the coordinate system KS are determined and stored_SP1，y_SP1) And position of the first set pointAnd a first coordinate system KS of the first camera 6₁Relative coordinate (p)_SP1，q_SP1). Readjusting is performed at the production stage in such a way that the bond head 8 is moved to the coordinates (x) of the first set-point position_SP1，y_SP1) And the first coordinate system KS of the set point position is determined again₁Relative coordinate (p)_SP1’，q_SP1'). Difference vector (p)_SP1’，q_SP1’)-(p_SP1，q_SP1) Containing information about a first coordinate system KS₁The displacement of the coordinate system KS that has occurred since the setting in the setting stage. Any random reference point on the bond head 8 can be used to define the bond head 8 with respect to the first coordinate system KS₁To the first set point position. The above-mentioned marks 10 are preferably used to define the reference points.

In a similar manner, the second coordinate system KS of the second camera 7 is detected and corrected₂A displacement of the coordinate system KS relative to the bond head 8, so that a further adjustment is made in a setting phase, in which the bond head 8 is moved to a second set-point position located in the field of view of the second camera 7, and the coordinates (x) of the second set-point position in relation to the coordinate system KS are determined and stored_SP2，y_SP2) And a second coordinate system KS associated with the second camera 7 for a second set point position₂Relative coordinates (u)_SP2，v_SP2). Readjusting is performed at the production stage in such a way that the bond head 8 is moved to the coordinates (x) of the second set-point position_SP2，y_SP2) And again determines the coordinate system KS of the second camera 7 for the position of the second set-point₂Relative coordinates (u)_SP2’，v_SP2'). Difference vector (u)_SP2’，v_SP2’)-(u_SP2，v_SP2) Containing information about a second coordinate system KS₂The displacement that has occurred since the setting in the setting phase with respect to the coordinate system KS. Also in this case, any random reference point on the bond head 8 can be used to define the bond head 8 with respect to the second coordinate system KS₂To the second set point position. Is preferably defined using the above-mentioned mark 10A reference point.

Determining a reference point and a first coordinate system KS₁And a second coordinate system KS₂The associated coordinates include: images are taken with the first camera 6 and the second camera 7 and the coordinates of the reference points are determined by means of conventional image estimation.

Then, the semiconductor chip is preferably mounted in the following manner:

-with a first coordinate system KS₁A form of the relevant position data providing the position of the semiconductor chip 2 to be mounted next detected by the first camera 6;

-in a second coordinate system KS₂A form of the relevant position data, which provides the position of the substrate area on which the semiconductor chip 2 is to be mounted, detected by the second camera 7;

-in a setup phase, determining a first coordinate system KS₁A first mapping function and its inverse function mapped to the coordinate system KS, a first correction vector being set to a value of 0, determining a second coordinate system KS₂A second mapping function mapped to the coordinate system KS and its inverse, and the second correction vector is set to a value of 0;

in the production phase, the semiconductor chips 2 are mounted one by one, so that

Capturing an image of the semiconductor chip 2 to be mounted next with the first camera 6 and determining the semiconductor chip 2 relative to the first coordinate system KS₁And by means of the first mapping function and taking into account the first correction vector, thereby calculating a position relative to the coordinate system KS to which the pick-and-place system 5 needs to move the bond head 8 in order to pick up the semiconductor chip 2;

capturing an image of the substrate area on which the semiconductor chip 2 is to be mounted next with the second camera 7 and determining the substrate area relative to the second coordinate system KS₂And calculating a position associated with the coordinate system KS, the pick-and-place system, by means of a second mapping function and taking into account a second correction vectorThe system 5 needs to move the bond head 8 to this position in order to place the semiconductor chip 2 on the substrate area;

and such that the readjusting in the production phase comprises readjusting the first correction vector and the second correction vector by the steps of:

-moving the bond head 8 to a first set point position;

capturing an image of the marker 10 with the first camera 6 and determining the marker 10 relative to the first coordinate system KS from the image of the first camera 6₁Actual position of, and

-calculating a first correction vector K as the difference between the stored set-point position and the determined actual position₁；

-moving the bond head 8 to the second set-point position;

capturing an image of the marker 10 with the second camera 7 and determining from the image of the second camera 7 the relative second coordinate system KS of the marker 10₂Actual position of, and

-calculating a second correction vector K as the difference between the stored set-point position and the determined actual position₂。

While embodiments and applications of this invention have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts herein. Accordingly, it is not intended that the invention be limited, but rather that it be defined by the following claims and their equivalents.

Claims (5)

1. A method for mounting a semiconductor chip (2) provided on a wafer table (1) on a substrate (4) by means of a pick-and-place system (5) having a bond head (8), wherein a marking (10) is attached to the bond head (8), wherein in the method,

capturing an image of a semiconductor chip (2) provided on the wafer stage (1) with a first camera (6) and in a first coordinate system KS₁The position of the semiconductor chip (2) determined from the image is provided in the form of associated position data,

capturing the base with a second camera (7)An image of the plate area and a second coordinate system KS₂Providing the location of the substrate area determined from the image in the form of associated location data, an

-the position of the bond head (8) is related to a coordinate system KS intrinsic to the pick-and-place system (5); the method comprises a setting phase and a production phase,

the setting phase comprises:

determining a first mapping function and its inverse mapping said first coordinate system KS1 to said coordinate system KS,

the first correction vector is set to a value of 0,

determining said second coordinate system KS₂A second mapping function and its inverse mapped to said coordinate system KS, an

Setting the second correction vector to a value of 0; and

the production phase comprises:

mounting the semiconductor chips (2) one by one, comprising

Capturing an image of the semiconductor chip (2) to be mounted next with the first camera (6),

determining the semiconductor chip (2) relative to the first coordinate system KS from the image of the first camera (6)₁In the position of (a) in the first,

calculating a position relative to the coordinate system KS to which the pick-and-place system (5) needs to move the bond head (8) in order to pick up the semiconductor chip (2) by means of the first mapping function and taking into account the first correction vector;

-taking an image of a substrate area on which a semiconductor chip (2) is to be mounted by means of the second camera (7),

determining the substrate area relative to the second coordinate system KS from the image of the second camera (7)₂A position of, and

calculating, by means of the second mapping function and taking into account the second correction vector, a position relative to the coordinate system KS to which the pick-and-place system (5) needs to move the bond head (8) in order to mount the semiconductor chip (2) on the substrate area; and

readjusting the first and second correction vectors when a predetermined event occurs, the readjusting the first and second correction vectors comprising:

-moving the bond head (8) to a first set-point position in which the mark (10) is located in the field of view of the first camera (6);

calculating said markers (10) relative to said first coordinate system KS₁Is set to the first set-point position of (c),

-taking an image of the marker (10) with the first camera (6),

determining the markers (10) relative to the first coordinate system KS from the image of the first camera (6)₁Is detected in the direction of the actual position of the sensor,

calculating a difference between the calculated set-point position and the determined actual position of the marker (10) as the first correction vector K₁；

Moving the bond head (8) to a second set-point position in which the marker (10) is located in the field of view of the second camera (7),

calculating said markers (10) relative to said second coordinate system KS₂The second set point position of (a);

capturing an image of the marker (10) with the second camera (7),

determining the markers (10) relative to the second coordinate system KS from the image of the second camera (7)₂Actual position of, and

calculating a difference between the calculated set point position and the determined actual position of the marker (10) as the second correction vector.

2. The method of claim 1, wherein the predetermined event is at least one of:

since the last calibration, a predetermined number of semiconductor chips (2) are mounted;

the temperature measured at a predetermined position of the pick-and-place system (5) has changed by more than a predetermined value since the last calibration;

stopping production;

the actual position of the mounted semiconductor chip detected and calculated by the second camera (7) after mounting deviates from the set point position by more than a predetermined amount.

3. A method according to claim 1 or 2, wherein the marking (10) applied to the bond head (8) is imaged sufficiently sharply on the respective camera (6, 7) by means of a lens (11) attached to the bond head (8).

4. A method according to claim 1 or 2, wherein the determining the first mapping function comprises moving the bond head (8) to a plurality of different positions such that the mark (10) is located in a field of view of the first camera (6), taking an image with the first camera (6) and determining a relative position of the mark (10) from the image provided by the first camera (6), and wherein the determining the second mapping function comprises moving the bond head (8) to a plurality of different positions such that the mark (10) is located in a field of view of the second camera (7), taking an image with the second camera (7) and determining a relative position of the mark (10) from the image provided by the second camera (7).

5. A method according to claim 3, wherein the determining the first mapping function comprises moving the bond head (8) to a plurality of different positions such that the mark (10) is located in a field of view of the first camera (6), taking an image with the first camera (6) and determining a relative position of the mark (10) from the image provided by the first camera (6), and wherein the determining the second mapping function comprises moving the bond head (8) to a plurality of different positions such that the mark (10) is located in a field of view of the second camera (7), taking an image with the second camera (7) and determining a relative position of the mark (10) from the image provided by the second camera (7).