GB1592368A - Automated manipulative operation system - Google Patents

Description

(54) AUTOMATED MANIPULATIVE OPERATION SYSTEM (71) We, TEXAS INSTRUMENTS INCOR PORATED, a Corporation organized according to the laws of the State of Delaware, United States of America, of 13500 North Central Expressway, Dallas, Texas, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and - by the following statement: This invention relates to an automatic precision parts positioning or locating system and more particularly to a system for precisely positioning or locating parts in an automated manufacturing system.

- In the automated manufacture of almost any product a necessary step is to position precisely or to locate the item in process relative to an automated tool. For example, in the manufacture of semiconductor integrated circuits, one step involves making electrical connections from various contact points on the semiconductor element (called a "chip") to electrical leads providing electrical connections through the device housing to external circuit elements. The process of making these connections, once carried out on manually controlled bonding machines, is now generally carried out on computer controlled automated bonding machines of the types shown -in U.S. Patents No. 3,641,660 to A. L. Adams et al, No.

3,773,240 to R. Heim, and No. 3,776,447 to A. L. Adams et al. In these prior art systems as modified for use with large integrated circuit chips, the bonding is controlled by small computer, such as the Texas Instruments 960A minicomputer, manufactured by Texas Instruments Incorporated of Dallas, Texas. The computer has- stored therein a program for the particular type of integrated circuit chip to be bonded on the machine. After a lead frame with the integrated circuit chip affixed thereto as precisely positioned with respect to an index " position of the bonding tool tip in the bonder for the first bond, the computer operates the bonder so that all of the required connections, which may number as many as 14 to 20 or more between as many different locations, are made automatically.

Commonly in the prior art, especially with integrated circuit chips, the initial positioning of the assembly for the first bond has been carried out manually by operators using either a metallurgical microscope or a magnifying television monitor.

Both the manual positioning of the chiplead frame combination to the initial or index position with respect to the bonding tip for the first bond and the automated movement of the bonding tip to the various other bonding locations must be extremely accurate since the bonding locations or "pads" on the integrated circuit chip are typically only four mils square and the bonding ball formed at the end of the onemil connection wire is -about three mils in diameter. Nevertheless, a competent operator can make an alignment in about 1.1 seconds and the bonding operation can typically be carried out in another 3 to 4 seconds.

According to the present invention there is provided an automated system for performing a series of operations on a workpiece the system including: (a) tool apparatus operatively responsive to digital signals; (b) tool control means including means for storing digital signals and means for supplying from said means for storing to said tool apparatus a series of digital signals to cause said tool apparatus to perform a predetermined series of operations on a workpiece positioned at a known index position relative to said tool apparatus, said tool control means further being responsive to program modification signals; (c) means initially to position a workpiece proximate to said index position and within the operational range of said tool apparatus; (d) means obliquely lighting said workpiece to emphasize known features of said workpiece through production of an edge shadow of raised areas thereof; (e) image sensor means producing electrical signals indicative of a visual image including said workpiece when initially positioned; Q means receiving and digitizing said electrical signals to produce a series of diigtal electrical signals each indicative of the brightness level of a unique element 6f said visual image; and (g) program modification signal generating means comprising (1) means storing a series of binary signals indicative of the positions relative to each other of at least two known features of said workpiece when positioned in said known index position; (2) means re ceiving and analyzing said digital electrical signals and said stored binary siginals and producing therefrom program modification signals; and (3) means transmitting said program modification signals to said tool control means, whereby said tool apparatus is caused to perform correctly said predetermined series of operations on said workpiece in its position as sensed by the image sensor means.

An advantage of the present invention is that such an initial alignment procedure as well as the subsequent bonding operations may be fully automated By way of example, a lead frame with an integrated circuit chip affixed thereto, usually - by soldering, alloying, or a conductive epoxy adhesive may be delivered to the work station in the bonder and clamped thereon.

Although the lead frame can be positioned with fair accuracy on the bonder work station, the techniques of affixing the integrated circuit chip to the lead frame position on the chip on the frame to an "x-y" accuracy typically of only plus or minus five mils and an orientation accuracy typically of approximately plus or minus 5 degrees. Although the bonding pads on the "tingers" on the lead frame are about T/ mils square, the chip bonding pads are only four mils square, as mentioned above, thus it is ess'e'ntial 'that chip itself be accurately located and oriented with respect to the index position of the bonding tip.

When the chip is in position on the bonder work station the imaging device produces a digital "picture" of the lead frame-chip assembly. The lead frame "scene" is obliquely lighted so that the integrated circuit chip casts a distinctive "shadow" easily recognizable in the digital image.

The digital image of the chip area is then presented to the computer which searches the image for prominent features of the particular type of chip being processed, which feature have been previously stored in the computer memory. Upon the detection of the chip features and the determination of their position and orientation, the computer then supplies information to produce corrections in the stored program of the border control, computer. The system gives a bonding accuracy corresponding to location within x-y coordinate accuracy of one-quarter mil and orientation accuracy of 0.1 degree on a conventional bonder.

The system has speed advantages over the prior art system; for example, bonder chip alignment for automated bonding may be accomplished in approximately 60 milliseconds.' Further, by determining the position of the integrated circuit chip thrdugh recognition of prominent features of the functional pattern on chip surface, no special patterns must be added to each chip design to allow its automated processing.- Prior art manual alignment systems, for example, often matched a microscope reticle to a specially added metallization pattern placed on the periphery of integrated circuit chips solely for alignment purposes.

The system may be implemented in a number of ways such as by use of a separate computer and imager with already existing computer controlled tools of the prior art manual initial alignment type. Of course, a single computer may be programmed to control both the part alignment and the manufacturing process step or a single computer may be used to control part align- ment concurrently on a number of different automated tools.

An advantage of the present invention is that it can provide an integrated circuit lead bonding system easily adaptable for use with almost any integrated circuit chip without the necessity of providing special surface features on the chip solely for location purpose.

These and other objects and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings in which: FIGURE 1 is a pictorial illustration of a typical lead-frame integrated circuit chip assembly; FIGURE 2 is a block diagram of a system embodying the present invention; FIGURE 3 is an illustration of a digitized image of a typical integrated circuit chip displaying certain prominent features; FIGURE 4 is a diagramamtic flow chart illustrating the general procedural sequence carried out by the automated system in determining the poistion and orientation of the integrated circuit chip in apparatus embodying the present invention; ; FIGURE 5 shows a flow chart for finding the chip in the operations of a system embodying the present inventiobn; and FIGURE 6 shows a flow chart for computing the line indicative of the position and orientation of the chip in the operations of a system embodying the present invention.

The system of the present invenion will be disclosed by description of the specific example of a system for automatically positioning and bonding interconnections in an integrated circuit device.

Shown in Figure 1 is a typical integrated circuit assembly at a stage of manufacture prior to its enclosure in a protective housing or its encapsulation in protective plastic.

The assembly comprises a metallic lead frame 1 on the chip pad portion 2 of which is mounted a semiconductor integrated circuit element or "chip 3. Small metallic terminals or bonding pads 4 provide electrical connection to the internal elements of the integrated circuit chip. External electrical connections to the device are provided by small gold wires 22, usually about one mil in diameter which connect the bonding pads 4 to lead-frame fingers 5.

In the finished device all the elements within the dashed line 7 are within the protective housing or enclosure.

After the rails 8 and the supporting webs 9 of the lead-frame are cut off or otherwise removed subsequent to enclosure of the device, the external portions of the leadframe fingers form the external leads or contacts 6 of the finished device.

In the prior art the process of making all of the wire connections between the bonding pads 4 and the lead-frame fingers 5 has been automated by means of a computer controlled bonding machine. However, each chip lead-frame assembly had to be located or indexed manually by the operator before the bonding program could be put into operation. By the present invention the location indexing of the chip lead-frame assemblies is automated.

Turning now to Figure 2, there is shown a block diagram of a system embodying the present invention. The system comprises a digitally controlled bonder 10 of the type disclosed in the aforementioned U.S. Patents No. 3,641,660, No. 3,773,240 and No. 3,776,447. The bonder is controlled by bonder control computer 11 which may take the form of a small computer such as a TI 960A as previously mentioned programmed to cause the bonder to carry out the bonding operations schedule necessary to establish the multiple electrical connections between the various contacts on the integrated circuit chip and the lead-frame fingers. Thus, the bonder control computer will have stored in its memory the movements required of the bonding tip in connecting the wires to produce the connection pattern for the particular chip type.The bonder 10 and control computer 11 together with the manual chip indexing mechanism constitute a prior system of the type pre vioúsly described.

The system of this embodiment of the present invention.comprises in addition a video module (which includes an optics system13 and an image 14, a digitizer 15, memory interface electronics 16, and a TV monitor 18), a system control computer 17 and a manually controllable variable intensity light source 19. In the operation of the present system a chiD lead-frame assembly is supplied to the work station of the bonder 10 and clamped into position in a manner well known in the art. For example, the lead frame may be one of 10 or 20 connected together in a single assembly resembling a ladder which is fed into the bonder by sprocket drive in holes 21 and clamped in position by indexing pins through locator holes 32 (Figure 1) as is well known.

Clamped on the work station of the bonder, a chip-lead frame assembly is illuminated by light source 19 which is positioned to provide oblique lighting to produce a shadow as will be more fully explained later. The scene of the chip area of the assembly is focused by the optics system 13 onto the sensor array of the imager 14. The imager output signal is digitized in digitizer 15 and fed to the system control computer 17. A computer suitable for use as the system control computer 17 is the Texas Instruments 980A computer manufactured by Texas Instruments Incorporated of Villas, Texas. In the system control computer 17 the digitized chip scene image is analyzed using information about certain prominent features of that particular type of chip which information is stored in the memory of that computer.This analysis of each chip-lead assembly determines the correction factors to be supplied to the bonder control com putér 11 so that each bond point dictated by its program is adjusted to take into account the x-y position and angle orientation position differences for correct bonding of that particular assembly. The system control computer 17 also inputs to the memory interface electronics 16 to synchronize the image scan, digitization and other functions of the video module 12 with the timing of the system control computer 17. This direct control and synchronization of the video module 12 timing by the system control computer 17 allows the digital image to be fed to a direct memory access port of the control computer allowing a much faster transfer of image data than would be possible through the conventionally used I/O terminal of the computer.

The imager 14 may be any of several types presently commercially available such as a vidicon or a solid state charged couple device imager. In a system found satisfactory for use with a large number of different chip types, which may range in size from 12 to 400 mils in either length or width, it has proved satisfactory to use a relatively inexpensive (under $300) vidicon to produce an image of 400 picture elements by 250 picture elements. Such an image digitized'into a binary (2 gray level) signal has been found easily storable in a convenient sized memory while still proyiding more than adequate resolution for operation of the system.

The digitized image is sent to the system control computer 17 and may be simultaneously displayed on the TV monitor 18.

Such an image is depicted in Figure 3.

Shown in Figure 3 is the lead4ram'e chip pad 2 to which is soldered or alloyed the chip 3. Due to the unique lighting arrangement mentioned earlier i.e. the light source position slightly above and offset from the chip, a shadow 25 from two edges of the chip is prominent in the digital image.

While the presence of a feature such as the shadow is critical to the operation of the system, its exact size and shape are- not.

For example the width of the shadow may vary considerably from assembly to assembly depending on the thickness of the chip, the thickness of the solder and the position of the light source. It is this shadow which is used for what ordinarily is the most difficult step in the automated process, that of locating the chip itself.

The system control computer memory has previously been supplied with information typical of prominent? features in the image of each chip type to be processed. From the stored information and analysis of the digitized image of the chip on the bonder work station, the system control computer 17 determines and supplies to the bonder control computer 11 information to adjust its program to produce accurately located bonds on that chip.

The analysis of the digitized image by the system control computer, unalike known prior art systems is not a " pattern recognition" process but is more accurately described as a feature analysis process.

Thus, the computer 17 upon being presented with the digitized image is caused to search, for example, first horizontally then vertically, to locate the prominent shadow 25 feature.

Recognition of the shadow is not determined nearly so much by its shape as by its extent and definite contrast to the rest of the image. For example, in the image depicted in Figure 3 the lighting as well as the digitization threshold of the digitizer caused the chip pad 2 to be bright although it will typically have random dark areas which are small in comparison with the shadow 25.

Prominent features of the chip such as the corner or edge metallization pattern 26 will show as bright or dead white as will be bonding pads 28. The surface of the chipl it self will be dark although for purposes of clarity it is not so illustrated in Figure 3.

A search of the digitized image for the shadow can start anywhere but ordinarily will start from the left or top of an image such as that of Figure 3'.

The shadow 25 then, is detected by the location of an array of a predetermined size of dark picture elements (pixels). The computer having found the general location of the shadow then refers to the information stored in memory to determine what type of prominent features to look for and their characteristics such as size and approximate location relative to the shadow. For example, the edge metallization 26 will - be a long continuous bright area along the right and bottom edge of the shadow 25.

Or should such an edge metallization pattern, not be present on the chip type, the straight line pattern and spacing and location of the four bonding pads 28 along the left hand side of the chip and the four-pad array along the top of the chip can be closely predicted and found. Continuing with the analysis carried out by the computer then, having located the shadow area, for example the left shadow area, several samples are taken along the line of abrupt change at the 'right side of the shadow area 'and from these samples a first estimate is computed of the location and direction of the line defining the left edge metallization on the chin 'is made.

This estimate is used to determine the optimum region for the top shadow search.

After this top shadow is located, the lower edge of the top shadow is sampled to obtain an estimate of its location.' This estimate is used to obtain an improved estimate of the location of the left edge. At this stage, the location of the shadow area has led to a reasonably good estimate of the location of both the left and top edges of the metallization on the chip.

These approximations are now used to determine a pair of data windows. These data windows may be long and narrow portions of the digitized image which in dude the sharp transition areas at the edge of the chip metallization. Thus, a data window of approximately 100 pixels by 16 pixels is located over the left metallization edge and another similar window is located over the top metallization edge. Then, as data is processed across each window all of the transitions from light to dark pixels along the line of the metallization edge yield data points defining this line in the form of and y pairs. These x-y pairs can be used to determine the "least squares" line which best represents the actual location of the metallization edge. The simple equations which may be used for the computer analysis of the left edge, for example, is X=avy+bv For the top edge an analysis procedure is used to obtain x-y pairs for the equations Y=ahX+bh. It - can, easily be seen that the same technique can be used to establish a line along the left edge of the left bonding pad array and the top edge of the top bonding pad array. The orientation of these lines and their point of intersection are complete documentation of the position and orientation of the chip in the image which easily translates into correction factors to be applied to each bonding point in the bonder control program.

In setting up the system for a run of a particular chip type, a typical chip lead frame assembly is -clamped to the bonder work station. The operator informs the system control computer of the type of chip to be worked on, thus causing the system control computer 17 to supply from its memory the basic bonding program for that type of chip and to send it to the bonder control computer 11. The system control computer 17 selects from its own memory data identifying the prominent chip features to be used in aligning this particular type of chip. Observing the digital chip image on the TV monitor 18, the operator, then, if necessary, adjusts the angle of incidence and intensity of the light source 19 so that the features to be analyzed for alignment are made most prominent on the digitized image. The operator can then tell the system to make the first connection.A visual microscopic check by the operator then confirms the accuracy of the bond placement. If the bond placement is not accurate, the operator can quickly recalibrate the system.

On rare occasions, adjustment of the optics system'may be necessary or desirable or a different magnifying power may be required because of a considerable change in the size of chip processed. Thus, calibra tion or recalibration is necessary because the digital image is always defined by a set number of picture elements (in the present embodiment 250 by 400 elements) but the actual physical dimensions represented by the image are-functions of the magnifying power of the optics. The system control computer 17 is programmed to calculate the system calibration automatically from the input of four information pdints supplied by the operator. Manual operation of a cursor on the image display is available to the operator as well as manual movement of the binding tip.Thus, the operator after setting the optics magnification moves the cursor to indicate a particular bonding point on the image display and manually moves the bonder tiD to the same bonding point of the chip. These two data points and two additional data points or corresponding bonding positions on the display and the chip when supplied to the computer are all that are required for the computer to calculate the calibration of the system for the particular magnification setting of the optics system.

At times, the chip being bonded may have flaws or disturbing features such as a brightarea in what should be the darkest shadow area as illustrated at 30 in Figure 3. Such an area might be caused by slag left as a result of laser beam techniques used to separate the individual chips from the parent semiconductor slice. The program of the system control computer can easily be designed to overcome this fault by incorporating a search to determine if there is a second shadow and if so to use the right edge of this second shadow for feature analysis.

Also faults at sample points in the feature to be analyzed as shown at 31 in Figure 3 can distort the analysis unless recognized as bad data and discarded by the process program.

It is to be recognized that the number of elements in the digitized image array is not critical to operation of the present system but may vary from approximately 100 to 900 or more picture elements in each dimension depending upon design considerations.

Further, the particular type of computer used with the system is not in any way critical.

Thus, there has been disclosed a system for automatically precisely positioning an integrated circuit element for an automated digitally controlled bonding operation. The system has advantages over the prior art of faster operation due to a unique connection system between the system control computer and the video module of the system and the simpler computational processes usable with the technique of feature analysis as compared with those computational processes required for the technique of pattern recognition. The present system has further advantages over systems of the prior art in that its memory requirements are much smaller due to the use of a two gray level image system and the technique of feature analysis rather than pattern recognition.

Systems embodying the present invention are also applicable for use in performing many other industrial tasks such as automated part -handling or part transfer.

For example, the present system can easily carry out the transfer of a watch case from a conveyor belt to a test fixture by robot arm without the need of guide and orienttion fixtures dedicated solely to that specific operation for that specific part.

In such an application the conveyer belt may be automatically stopped when a watch case should be within the field of view of the imager. This field can be made relatively large with respect to the part and thus the stopping point of the conveyor belt need not be too critical. With lighting arranged to emphasize features of the watch case to be analyzed, computer analysis of the digitized image then locates the center of the watch case and by simple search at given distances from this center the bracelet anchors of the watch case are found and their orientation and thus the orientation of the case itself is determined.Thus the instructions to the robot arms for acquiring the watch case at a given index position are modified by the x-y and orientation differences of the watch case from index position and the robot arm is able to acquire a " standard " grip on the particular watch case for movement into a test fixture.

In the same way specified features of other parts can be analyzed from the digital image. A calculator for example may be lighted in such a way that the display window is very bright or very dark and can therefore easily be analyzed by the computer for determination of the exact location and orientation of the calculator with respect to a known reference position.

Many changes and modifications still within the scope of this invention will occur to those skilled in the- arts.

WHAT WE CLAIM IS:- 1. An automated system for performing a series of operations on a workpiece the system including: (a) tool apparatus operatively responsive to digital signals; (b) tool control means including means for storing digital signals and means for supplying from said means for storing to said tool apparatus a series of digital signals to cause said tool apparatus to perform a predetermined series of operations on a workpiece positioned at a known index position relative to said tool apparatus, said tool control means further being responsive to program modification signals.

(c) means initially to position a workpiece proximate to said index position and within the operational range of said tool apparatus; (d) means obliquely lighting said workpiece to emphasize known features of said workpiece through production of an edge shadow of raised areas thereof: (e) image sensor means producing electrical signals indicative of a visual image including said workpiece when initially posi tioned; (f) means receiving and digitizing said electrical signals to produce a series of digital electrical signals each indicative of the brightness level of a unique element of said visual image; and (g) program modification signal generating means comprising: (1) means storing a series of binary signals indicative of the positions relative to each other of at least two known features of said workpiece when positioned in said known index position; (2) means receiving and analyzing said digital electrical signals and said stored binary signals and producing therefrom program modification signals; and (3) means transmitting said program modification signals to said tool control means, whereby said tool apparatus is caused to perform correctly said predetermined series of operations on said workpiece in its position as sensed by the image sensor means.

2. An automated system as defined in claim 1 wherein said tool control means is programmable digital computer.

3. An automated system as defined in claim 1 or claim 2 wherein said program modification signal generating means is a programmable digital computer.

4. An automated system as defined in claim 1 wherein said tool control means and said program modification signal generating means together comprise a single programmable digital computer.

5. An automated system as defined in claim 3 or 4 wherein said digital electrical signals are applied to a direct memory access (DMA) port of said program modification signal generating means.

6. An automated system as defined in claim 3, 4 or 5 wherein said image sensor means is synchronized and controlled by signals from said program modification signal generating means.

7. An automated system as defined in any preceding claim wherein said digital electrical signals are binary signals.

8. An automated system for performing a series of operations on a workpiece, the system being substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. be analyzed, computer analysis of the digitized image then locates the center of the watch case and by simple search at given distances from this center the bracelet anchors of the watch case are found and their orientation and thus the orientation of the case itself is determined. Thus the instructions to the robot arms for acquiring the watch case at a given index position are modified by the x-y and orientation differences of the watch case from index position and the robot arm is able to acquire a " standard " grip on the particular watch case for movement into a test fixture. In the same way specified features of other parts can be analyzed from the digital image. A calculator for example may be lighted in such a way that the display window is very bright or very dark and can therefore easily be analyzed by the computer for determination of the exact location and orientation of the calculator with respect to a known reference position. Many changes and modifications still within the scope of this invention will occur to those skilled in the- arts. WHAT WE CLAIM IS:-

1. An automated system for performing a series of operations on a workpiece the system including: (a) tool apparatus operatively responsive to digital signals; (b) tool control means including means for storing digital signals and means for supplying from said means for storing to said tool apparatus a series of digital signals to cause said tool apparatus to perform a predetermined series of operations on a workpiece positioned at a known index position relative to said tool apparatus, said tool control means further being responsive to program modification signals.

(c) means initially to position a workpiece proximate to said index position and within the operational range of said tool apparatus; (d) means obliquely lighting said workpiece to emphasize known features of said workpiece through production of an edge shadow of raised areas thereof: (e) image sensor means producing electrical signals indicative of a visual image including said workpiece when initially posi tioned; (f) means receiving and digitizing said electrical signals to produce a series of digital electrical signals each indicative of the brightness level of a unique element of said visual image; and (g) program modification signal generating means comprising: (1) means storing a series of binary signals indicative of the positions relative to each other of at least two known features of said workpiece when positioned in said known index position; (2) means receiving and analyzing said digital electrical signals and said stored binary signals and producing therefrom program modification signals; and (3) means transmitting said program modification signals to said tool control means, whereby said tool apparatus is caused to perform correctly said predetermined series of operations on said workpiece in its position as sensed by the image sensor means.

2. An automated system as defined in claim 1 wherein said tool control means is programmable digital computer.

3. An automated system as defined in claim 1 or claim 2 wherein said program modification signal generating means is a programmable digital computer.

4. An automated system as defined in claim 1 wherein said tool control means and said program modification signal generating means together comprise a single programmable digital computer.

5. An automated system as defined in claim 3 or 4 wherein said digital electrical signals are applied to a direct memory access (DMA) port of said program modification signal generating means.

6. An automated system as defined in claim 3, 4 or 5 wherein said image sensor means is synchronized and controlled by signals from said program modification signal generating means.

7. An automated system as defined in any preceding claim wherein said digital electrical signals are binary signals.

8. An automated system for performing a series of operations on a workpiece, the system being substantially as hereinbefore described with reference to the accompanying drawings.