Electrical test method with vision-guided alignment

A method for electrically testing devices fabricated on successive frames of a web of substrate, each frame including an associated plurality of fiducial marks and an associated device having a series of test pads, comprising:

• a) advancing the web of substrate along a web transport path until a particular frame is proximate to a digital imaging system;
• b) using the digital imaging system to capture a digital image of at least a portion of the particular frame including the associated plurality of fiducial marks and the test pads of the associated device;
• c) automatically analyzing the captured digital image to determine positions of the plurality of fiducial marks and the test pads within the captured digital image;
• d) determining spatial relationships between the determined positions of test pads and the determined positions of the plurality of fiducial marks in the captured digital image;
• e) advancing the web of substrate along the web transport path until the particular frame is proximate to an electrical test fixture including a set of test probes adapted to make electrical contact with corresponding test pads of the associated device;
• f) stopping the web of substrate;
• g) using a fiducial sensing system to sense positions of the associated plurality of fiducial marks;
• h) adjusting a position of the electrical test fixture responsive to the spatial relationships between the determined positions of test pads and the determined positions of the plurality of fiducial marks in the captured digital image and the sensed positions of the associated plurality of fiducial marks so that the test probes are aligned with the corresponding test pads;
• i) moving the test probes into electrical contact with the corresponding test pads;
• and
• j) performing an electrical test of the particular device using a test instrument associated with the set of test probes.