Patent Application
20110014852
This invention relates generally to the field of chip assembly and more particularly to a method and system for pick and place tool tip exchange.
Various packaging techniques for Integrated Circuits (ICs) have been developed to satisfy demands for miniaturization. Improved techniques for miniaturization of ICs enabling the integration of millions of circuit elements into a single IC semiconductor die have resulted in an increased demand for methods to package the semiconductor die reliably in a mass-production.
Flip chip assembly is a mounting method used for mounting a semiconductor die to an external circuitry such as a circuit board that obviates employment of connecting wires. Instead, a solder ball is deposited onto each semiconductor die contact pad, which is then directly connected to a respective contact of the external circuitry.
For mounting the semiconductor die to the external circuitry a pick and place tool is used. The pick and place tool picks the semiconductor die with its tip at a predetermined location—using, for example, gripping jaws or suction—and places it onto a respective location on an external circuitry which is hold at a predetermined location on a work piece holder such that the solder balls are facing the external circuitry. The solder balls are then molten to produce an electrical connection with respective contacts of the external circuitry using, for example, ultrasonic heating.
With increasing miniaturization the flip chip assembly needs to provide improved quality of contact between the semiconductor die contact pads and the respective contacts of the external circuitry. In order to ensure a same quality of contact for all contact pads of the semiconductor die it is necessary to provide a highly accurate parallel orientation of the semiconductor die with respect to the external circuitry—i.e. between a plane tool tip surface accommodating a surface of the semiconductor die opposite the solder balls and a plane work piece holder surface accommodating the external circuitry.
In order to provide flexibility in a mass production assembly line, state of the art pick and place assembly equipment is typically provided with interchangeable tool tips in order to accommodate different sized semiconductor dies.
Unfortunately, the provision of interchangeable tool tips substantially reduces the accuracy of the parallel orientation between the tool tip surface and the work piece holder surface, i.e. it is not possible to reliably mount the interchangeable tool tips at a high level of accuracy of the parallelism, thus, impeding use of pick and place tools having interchangeable tool tips in the mass production of highly miniaturized ICs.
It would be highly desirable to overcome these drawbacks and to provide a method and system for pick and place tool tip exchange with a grinding process for ensuring a predetermined level of accuracy of the parallel orientation.
In accordance with the present invention there is provided a method for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The method is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. A grinding plate is provided onto the work piece holder surface and a grinding material is deposited thereupon. The tool tip is then moved to a predetermined distance above the grinding plate top surface. The tool tip surface is then moved relative to the grinding plate top surface in a plane oriented substantially parallel to the grinding plate top surface. Through abrasive action of the grinding particles, material is removed from the tool tip surface such that the tool tip surface is oriented parallel to the work piece holder surface 108 at an increased level of accuracy. At a plurality of predetermined locations on the tool tip surface a distance between the tool tip surface and the work piece holder surface is measured and a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface is determined in dependence upon the measured distances. Grinding the tool tip surface, measuring the distances, and determining the level of accuracy is then repeated until the level of accuracy is above a predetermined threshold.
In accordance with the present invention there is provided a system for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The system is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. The system comprises an output port for being connected to a control mechanism of the assembly device. The system further comprises an input port for being connected to a height measurement device for receiving a signal in dependence upon measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface. Electronic circuitry is connected to the input port and the output port. The electronic circuitry is used to: determine a level of accuracy of a parallel orientation of the tool tip surface with respect work piece holder surface in dependence upon the measured distances; determine a particle size of the grinding material in dependence upon the measured distances; determine a grinding distance between the tool tip surface and the work piece holder surface in dependence upon the measured distances and generating a grinding distance control signal in dependence thereupon; generate a grinding movement control signal indicative of a relative movement between the tool tip and the work piece holder; and, provide the grinding distance control signal and the grinding movement control signal to the output port.
In accordance with the present invention there is further provided a storage medium having stored therein executable commands for execution on a processor. The processor when executing the commands performs a method for ensuring a predetermined level of accuracy of a parallel orientation of a tool tip surface with respect to a work piece holder surface of an assembly device. The method is implemented in an assembly device comprising a work piece holder having a substantially plane work piece holder surface. The work piece holder surface is used for accommodating a first component thereupon. The assembly device further comprises a tool tip having a substantially plane tool tip surface for accommodating a second component thereupon. The tool tip is used for placing the second component at a predetermined location onto the first component. The processor receives a measurement signal from a height measurement device mounted to the assembly device. The measurement signal is indicative of measurements at a plurality of predetermined locations on the tool tip surface of a distance between the tool tip surface and the work piece holder surface. The processor then determines a level of accuracy of a parallel orientation of the tool tip surface with respect to the work piece holder surface in dependence upon the measured distances and a particle size of the grinding material in dependence upon the measured distances.
Exemplary embodiments of the invention will now be described in conjunction with the following drawings, in which:
a and 3b are a simplified block diagrams illustrating in cross-sectional views a tool tip placed above a grinding plate with grinding material placed therebetween in the method according to the invention described in
The following description is presented to enable a person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the invention. Thus, the present invention is not intended to be limited to the embodiments disclosed, but is to be accorded the widest scope consistent with the principles and features disclosed herein.
While the invention will be described in combination with a pick and place equipment for flip chip assembly, it will become apparent to those skilled in the art that the invention is not limited thereto but is also applicable for various other pick and place assembly equipment as well as other assembly equipment where accurate parallel orientation of two facing work surfaces with respect to each other is of importance.
Referring to
Referring to
At 10, a plurality of locations on the tool tip surface 112 are determined for determining the parallel orientation using, for example, a processor 114 of grinding control system 116. For example, the locations are determined in dependence upon a size of a contact surface of the second component and in dependence upon a predetermined threshold for the accuracy. As is well known, a plane is, for example, defined in space by the coordinates of three points, therefore, it is possible to determine the orientation of the tool tip surface based on three measurements. However, in order to increase accuracy the number of locations is increased. For example, the locations are determined in x and y coordinates for various sizes and levels of accuracy during an empirical test phase and stored in the form of a look up table in memory 118 of the grinding control system 116. Using height measurement device 120 connected to measurement control port 122 a vertical distance between the tool tip surface 112 and the work piece holder surface 108 is measured at the predetermined locations—at 12.
For example, the processor 114 provides control signals indicative of the x and y coordinate of each location and in response thereupon the height measurement device 120 performs the measurement at the respective location and provides a signal indicative of a distance to the processor 114. The height measurement device 120 comprises, for example, a mechanical touch sensor having a needle 124 that is movable between contact with the tool tip surface 112 and the work piece holder surface 108. At times other than measurement times the height measurement device 120 is retracted and, optionally, covered for protection. Alternatively, an optical measurement device is employed. Using the processor 114, a level of accuracy of a parallel orientation of the tool tip surface 112 with respect to the work piece holder surface 108 is then determined in dependence upon the measured distances—at 14.
If the level of accuracy is above the predetermined threshold, a signal indicative thereof is, for example, displayed on display 126 of the grinding control system 116. If the level of accuracy is below the predetermined threshold, a particle size of grinding material is determined in dependence upon the measured distances, for example, based on a difference between the distances—at 16. For example, in case of a larger difference between the distances a larger amount of material is to be removed from the tool tip surface 112 using larger sized grinding material particles. At 18, a grinding distance between the tool tip surface 112 and a grinding plate top surface 128 of grinding plate 130 is determined in dependence upon the measured distances or the grinding material particle size. For example, for larger grinding particles a larger grinding distance is used. At 20, a grinding time interval is determined in dependence upon the measured distances and, optionally, the grinding material particle size. For example, grinding material particle sizes, grinding distances, and grinding time intervals have been determined for various parameter combinations during an empirical test phase and stored in the form of a look up table in the memory 118 of the grinding control system 116.
At 22, the grinding plate 130 is provided onto the work piece holder surface 108 and hold in place using, for example, the clamping mechanism used for holding the first component, followed by depositing the grinding material having the predetermined particle size onto the top surface 128 of the grinding plate 130—at 24. For example, the tool tip 112 is made of tungsten carbide (WCr) with a hardness of approximately 9 Mohs. The grinding plate 130 is made of a material having a hardness greater equal to the hardness of the tool tip 112 such as, for example, aluminum oxide (Al2O3). As grinding material an abrasive paste comprising particles having a hardness greater than the tool tip 112 and the grinding plate 130 is used such as, for example, a diamond paste—having a particle hardness of 10 Mohs. Depending an the measured distances the particle size chosen is, for example, 45 μm, 25 μm, 10 μm, 3 μm, or smaller. As is evident, while described for grinding of a very hard material, this process is also possible to implement for grinding various other materials such as various types of steel or plastic materials with proper adaptation of the grinding material.
At 26, the tool tip surface 112 is then moved to the predetermined grinding distance D above the grinding plate top surface 128, using the head assembly 104 controlled by the processor 114 via control port 132, as illustrated in
As is evident, it is possible to implement the method for ensuring a predetermined level of accuracy according to the invention in an automated fashion using the system 116 described in
The system 116 is implemented using, for example, a workstation comprising the processor 114 for executing executable commands stored in the memory 118 for performing the processing steps described above. Alternatively, at least a portion of the processing steps are performed in a hardware implemented fashion. As is evident, it is possible to provide the system 116 and the height measurement device 120 as a retrofit for installation in existing assembly equipment. Furthermore, some existing assembly equipment comprises a height measurement device such as an integrated tough down sensor, which is possible to employ for the distance measurements controlled by the system 116.
Numerous other embodiments of the invention will be apparent to persons skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07291574.7 | Dec 2007 | EP | regional |
| PCT/IB2008/055441 | Dec 2008 | IB | international |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2008/055441 | 12/19/2008 | WO | 00 | 9/20/2010 |
