Abrading – Work holder
Reexamination Certificate
1999-07-20
2001-01-30
Banks, Derris H. (Department: 3723)
Abrading
Work holder
C125S035000, C451S340000
Reexamination Certificate
active
06179698
ABSTRACT:
BACKGROUND
This invention relates to the field of failure analysis of integrated circuits and semi-conductors. More particularly, a self-aligning tool is provided for cross-sectioning an integrated circuit in a hands-free mode of operation.
When an integrated circuit (IC) fails to operate, or fails to operate as expected, it may be subjected to failure analysis in order to determine the cause of the failure. For example, when a newly designed circuit is first manufactured, it is usually tested to ensure that it operates correctly. If it does not, operational testing of the part may be able to identify a symptom of the fault or the general area in which the fault may lie, but may not be able to determine the exact cause of the failure (e.g., bad soldering, an open or shorted line). Therefore, one goal of failure analysis is to determine the cause of the part's failure by examining one or more areas or suspected points of failure.
Thus, failure analysis often requires locating a specific element (e.g., junction, line) or area of an IC for close examination (e.g., under a powerful microscope). Typically, a cross-section of the IC is taken at the suspected area in order to gain an unobstructed view. Because of the microscopic level of detail involved (e.g., sub-micron units of measure in some cases), however, it is essential that just enough of the IC is removed to expose the desired element, but no more.
If a relatively large portion of the circuit must be removed little precision is required at first—i.e., the part may be sawn or cut roughly in order to remove most of the extraneous material. However, in the latter stages of the cross-sectioning effort great care and precision are required in order to uncover the desired area without introducing any new fractures or other errors. Many failure analysis operations employ an abrasive surface, such as a milling disk (e.g., a circular piece of sandpaper), to grind away the edge of the IC to uncover the suspected fault.
One tool for cross-sectioning an IC with a milling disk is a hand-held tool. A die may be secured to this tool, which is then guided by the operator to grind away the unneeded portion of the IC. The die can be removed from the tool for examination (e.g., to determine if the area of interest has been uncovered yet).
This tool is deficient in several respects. First, it requires continuous human operation and attention regardless of how much of the IC needs to be ground away in order to reach the target area. Also, the angle at which the die is cross-sectioned depends upon the angle at which the operator holds the tool. Because there is no mechanism for ensuring that the same angle is maintained throughout the cross-sectioning, the operator may inadvertently remove too much of the IC. In addition, this tool can only be used with IC dies, not packages. Finally, this tool is relatively expensive to use due to the need for constant human attendance.
Another tool for cross-sectioning an IC by grinding an edge with a milling disk is more automated than the tool described above, but still suffers from significant shortcomings. This tool, which can accommodate dies but not packages, includes a mechanical arm to hold an IC for grinding. The IC must be encased in wax, however, in order to be held by the arm. In addition, the arm must be continually adjusted to ensure that the IC is placed in contact with the abrasive surface. The IC must be removed from the arm to be examined, thus requiring the wax to be removed (e.g., melted) prior to examination, and then re-applied if further grinding is necessary. Repeatedly mounting the IC in wax makes it very easy to misalign the IC in between grinding evolutions, and the effort required to repeatedly prepare the IC for examination and then grinding adds a significant amount of time to a failure analysis operation.
Thus, what is needed is a cross-sectioning tool that can operate without a human operator's continuous participation and which facilitates easy re-alignment of an IC that is being cross-sectioned so as to maintain the same angle of cross-sectioning. Also, the tool should be able to handle ICs of various sizes, including both dies and packages.
SUMMARY
In one embodiment of the invention a tool is provided for facilitating the cross-sectioning of an integrated circuit (IC). In this embodiment the tool is capable of operation without continuous human activity and accepts ICs of various sizes. Further, the tool is self-aligning so that after an IC is removed from the tool, examined, and replaced, the IC returns to substantially the same alignment that it had prior to its removal.
In this embodiment the tool includes an enclosure, such as a carriage or cage, which partially or fully defines a passage. At one end of the passage an IC may be inserted or removed. The other end of the passage opens upon an abrasive surface that is used to grind or polish the IC. The enclosure includes two or more fixed walls to help stabilize the circuit, and an adjustable wall allows the tool to accommodate ICs of various sizes (e.g., dies and packages). The adjustable wall is, in one embodiment of the invention, continuously movable along tracks or guides that form part of the enclosure. Further, the adjustable wall is configured to be releasably secured in a selected positions along the tracks so as to stabilize an IC and help the IC maintain a particular orientation (e.g., angle) to the abrasive surface.
The tool also includes a frame comprising a plurality of rails or guides along which the enclosure may be relocated. In one embodiment of the invention the enclosure can be positioned at virtually any location along the frame. Further, the enclosure is releasably securable in a selected location, similar to the semi-permanent manner in which the adjustable wall may be located within the enclosure.
During a cross-sectioning operation the frame provides a base or support for the enclosure, which stabilizes the IC for grinding and polishing as it is in contact with the abrasive surface. In one embodiment of the invention the force of gravity is sufficient to maintain contact between the IC and the abrasive surface. However, in an alternative embodiment a small weight or force may be applied to the IC.
Because the enclosure may be selectably positioned at various locations along the frame, as one portion of the abrasive surface becomes worn, the IC can be relocated to a portion that is less worn. In various embodiments of the invention different types of releasable connectors, such as screws and wing nuts, are used to movably secure the adjustable wall within the enclosure and the enclosure within the frame.
REFERENCES:
patent: 2431469 (1947-11-01), Eyles
patent: 3809050 (1974-05-01), Chough et al.
patent: 6030282 (2000-02-01), Mahnapour
Banks Derris H.
Park & Vaughan LLP
Sun Microsystems Inc.
Vaughan Daniel
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