Method and system for detecting faults in a flip-chip package

Details Method and system for detecting faults in a flip-chip package Method and system for detecting faults in a flip-chip package

1999-01-04

2001-01-30

Metjahic, Safet (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

C324S762010, C324S762010, C324S501000

Reexamination Certificate

active

06181153

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to detection of faults in semiconductor devices and more particularly to a method and system for allowing detection of faults in a flip-chip package without destroying the circuitry on a semiconductor die in the flip-chip package.
BACKGROUND OF THE INVENTION
Semiconductor dies typically include an active area having circuits formed therein. After fabrication of circuits on a semiconductor die, detection of faults is often desirable. Detecting these faults without destroying the circuitry on the semiconductor is also useful. Because the circuits were preserved during fault detection, the circuits can also undergo other non-destructive testing prior to deprocessing. Once the position of the fault is detected and other testing completed, the circuits may be deprocessed in order to determine the exact nature of the fault or to farther investigate the properties of the circuit.
Conventional semiconductor dies are mounted on a substrate to form semiconductor packages. In conventional packages, the die is mounted with the active area up, away from the substrate. In flip-chip packages, the die is mounted with the active area down, in proximity to the substrate. In either case, it is desirable to detect faults in the circuits in the active area.
Certain faults in the circuits, such as shorts, generate heat. In order to detect faults which cause hot spots, liquid crystals are conventionally used. For a conventional package, a thin layer of liquid crystal is poured over the circuits at the top of the die. For a flip-chip package, the back of the die is thinned, then a thin layer of liquid crystal is poured over the surface of the back of the die. Power is then provided to the circuits on the die. The liquid crystal changes phase over any hot spots in the circuits. Consequently, the liquid crystal appears to change color over these hot spots in the circuit. Alternatively, the liquid crystal moves away from the hot spots, leaving an exposed area of the die. These hot spots and, therefore, areas where the liquid crystal appears to have changed color mark the position of certain faults in the circuits. Consequently, the position of faults in the circuit can be detected.
Although conventional liquid crystal detection functions for circuits in conventional packages, the use of liquid crystal has several drawbacks. Liquid crystal is relatively expensive. Liquid crystal is also hazardous to the health of a user. In addition, the conventional method for using liquid crystal to detect faults may be relatively difficult to perform.
Accordingly, what is needed is a system and method for detecting faults in circuits on conventional packages and in particular flip-chip packages without destroying the circuits. The present invention addresses such a need.
SUMMARY OF THE INVENTION
The present invention provides a system and method for detecting a fault in a circuit of a semiconductor package. The semiconductor package includes a die having an active area and a substrate. The circuit is located on the active area of the die. The method and system comprise applying a liquid having a relatively low smoke point and which moves readily with respect to the semiconductor die to a surface of the semiconductor die. The liquid forms a thin layer on the exposed surface of the semiconductor die. The method and system further comprise applying power to the circuit and determining where a portion of the liquid has moved away from an exposed portion of the surface of the die.
According to the system and method disclosed herein, the present invention allows detection of certain faults in a circuit on a semiconductor die without destroying the circuit, thereby increasing overall system performance.


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Ferrier, S., “Thermal and Optical Enhancements to Liquid Crystal Hot Spot Detection Methods,” Hewlett-Packard Company, pp. 57-62.
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