Method and apparatus for identifying failure sites on IC chips

DETAILED DESCRIPTION In accordance with the present invention, a method and apparatus for identifying failure sites on a defective IC package or chip by utilizing a reusable liquid crystal device which can be mounted to various IC chips for detecting failure sites are provided.
In a preferred embodiment, a method for identifying failure sites on an IC chip can be carried out by the operating steps of first providing a substrate that is substantially transparent, then coating an electrically conductive material layer on a first side of the substrate while substantially retaining the transparency of the substrate, then coating a layer of liquid crystal on a second side of the substrate, then positioning the substrate with the second side contacting a top surface of an IC device to be tested, then flowing an electrical current through the electrically conductive material layer and heating the liquid crystal material to a temperature not higher than its transition temperature, and then inputting a signal to the IC device and detecting hot spots formed under an optical microscope.
The method may further include the step of providing a thermally conductive fluid between the substrate and the top surface of the IC device.
The thermally conductive fluid may be conveniently a liquid glycerin for facilitating heat transfer between the substrate and the IC device.
The substantially transparent substrate may be advantageously a glass substrate.
The electrically conductive material layer may be coated on the substrate in a serpentine pattern or along an outer periphery of the first side of the substrate while substantially retaining the transparency of the substrate.
The liquid crystal material coated has a clear/opaque transition temperature which may also be coated on the first side of the substrate on top of the electrically conductive material layer.
The method may further include a step of flowing an electrical current between about 1 volt DC and about 50 volt DC through the electrically conductive material layer for heating the liquid crystal material to a temperature not higher than its transition temperature, and preferably to a temperature not more than 10