Stone working – Sawing – Rotary
Reexamination Certificate
2000-02-09
2001-04-03
Banks, Derris H. (Department: 3723)
Stone working
Sawing
Rotary
C125S035000, C451S339000
Reexamination Certificate
active
06209532
ABSTRACT:
CROSS REFERENCE TO PRIOR APPLICATIONS
This application is related to Ser. No. (09/164,581), Ser. No. (09/500,507) and Ser. No. (09/431,703), the contents of all of which are incorporated herein by reference.
FIELD OF THE INVENTION
The present invention relates to the handling of the semiconductor devices that have been deemed as “Known Good Die” (KGD) in low and medium volume process flows.
BRIEF DESCRIPTION OF THE PRIOR ART
In the present state of the art, KGD products that are processed in a low and medium volume process flow do not have the proper tooling to insure that the KGD will not be damaged by the handling methods presently in place. Once the die has been tested as good, special handling procedures must be employed to insure that the die remains good and is not damaged during further processing. The handling tools are for low and medium volume KGD product lines where manual and semi-automatic operations are normal procedure.
The most common method of die movement in low and medium volume process flows is to pick the die up on its surface with a vacuum pencil or vacuum pickup tool that exerts contact force upon the top surface of the die (i.e., the surface containing the active and/or passive circuit elements). Occasionally, when the vacuum pickup tool comes into contact with the die, a loose piece of silicon or other hard foreign material may come between the pickup tool and the die surface. This results in a scratch on the surface of the die. Some of the scratches do not damage the underlying layers. However, sometimes the force exerted by the vacuum pickup tool is sufficiently great to cause the scratch to penetrate the protective overcoat on the die and then scratch the underlying metal layers where the metal can be short circuited to adjacent leads or open circuited so that current is not conducted. With the fine line geometries that exist in modern devices, it is impossible to economically visually inspect out the damage that occurs when a die receives a microscratch that bridges or opens the metal. At, for example, 40× and 100× inspection, these product-killing defects are not observable. Many of the microscratches appear to be small, less than a 0.5 mil spot of foreign material upon the die surface. A small spot of foreign material on the die surface is not in itself rejectable since such material can generally be removed. However, if the die is improperly handled after electrical test and microscratches are generated by die topside handling, then the customer would have no recourse but to screen out all anomalies on the die surface because the supplier could not guarantee that the small dots appearing on the die surface were not microscratches instead of foreign material. The visual yield loss due to this lack of confidence in the die handling can be very large, because it is almost impossible to keep small pieces of foreign material off of the KGD surface during the burn-in and testing operations.
When the KGD is shipped to the customer, it is assumed that the product quality is equal to that of a packaged part. If the supplier has handling processes that allow the top of the KGD to be contacted after testing of the KGD, then the possibility of a defect that cannot be screened out has been introduced. The customer of the KGD will also require deployment of soft handling technology in the multichip module (MCM) line to insure product integrity of the KGD. The customer must do this because it is not prepared to electrically screen a KGD.
At the customer's end of the process flow; if the die is not handled with proper precautions, then the customer also can create damage to the KGD that will cause the applications to be unsuccessful. Prior work with KGD and MCM has shown that the largest source of die failure on an MCM is related to the handling of the KGD. The microscratches that have been mentioned are the cause of failures in KGD at the MCM level. The microscratch problem causes yield loss in the MCM assembly and undermines the product integrity of the MCM. The KGD and MCM lines are low volume, generally less than 1,000 units per month or medium volume, generally less than 10,000 units per month, product assembly lines. Most of the suppliers and customers of KGD and MCM product operate in the low and medium volume line configurations. These lines are generally manual or semi-automatic as opposed to substantially fully automated as is the case of high volume devices.
SUMMARY OF THE INVENTION
Special tooling and a new process flow have been developed that insures that the KGD is handled only on the backside or the edge of the die rather than on the front side which contains the active and passive elements. This tooling insures that the die in the wafer form or the die form is not contacted on the surface during processing. This lack of contact prevents the microscratches from occurring in low and medium volume KGD lines. Each step in the handling of the die has been streamlined so that the number of times that the die is to be handled is minimized. The KGD assembly flow and disassembly flow can be used for temporary contact die carriers such as, for example, the Texas Instruments DieMate™ carrier or the KGD using existing process infrastructure approaches.
Each step has unique tools that insure that the principle behind the “soft handling” of not contacting the top surface of the KGD with significant force is maintained initially, the wafer is cleaned, inspected, mounted on a flexible backing and sawed to separate the dice with inspection then taking place in standard manner. The flexible tape is then stretched to provide a space between the dice and a vacuum pencil in accordance with the present invention is then disposed between adjacent dice and under the back side of one of the dice to lift that die and load the die in a test carrier of the type, for example, discussed in the above mentioned application. Testing of the die then takes place in the manner discussed in the above mentioned application while in the test carrier. Dice that test positively are then cleaned, again tested and then placed on an adhesive material, such as, for example, Gel Pac™, all of which is standard in the art, prior to shipment to the customer.
The assembly of the test carrier breaks the wafer down into the semiconductor dice and then loads the dice into the appropriate test carrier. This is accomplished by placing the wafer upon a ring carrier with standard adhesive tape where the wafer can be cleaned, inspected, and sawed in accordance with prior art techniques. Once the wafer has been singulated, special tools that are employed in accordance with the present invention to provide the soft handling flow come into play. The first tool is the vacuum pencil that picks up a die from the backside. The second tool is a tape relief machine which is employed to push the die upward and away from the tape so that the vacuum pencil can slide under the die for removal from the tape. Once the die is pushed up, the vacuum pencil slides under the die and picks it up from the backside. The operator then places the die onto a soft handling carrier. The soft handling carrier is the third unique tool in accordance with the present invention. It is used to transport the bare die around the work area when it is not on the soft handling carrier. This carrier has die positions for locating the die designed to be preferably about 30% larger than the die surface with a corner locating grid for placement accuracy. Between the corner locating grid and the base of the soft handling carrier is a fresh sheet of lint-free paper which is changed with each load and unload operation. The lint-free paper insures that the die has a soft surface against which to be projected. Each grid location on the soft handling carrier has vacuum holes for supporting the top side of the die against the lint-free paper when the die is to be flipped onto the tape. The fourth unique tool in accordance with the present invention is the integrated carrier loading and continuity tester. At the base of the visual lo
Arnold Richard W.
Wilson Lester L.
Banks Derris H.
Brady III Wade James
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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