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Pad Deletion Test Technique

IP.com Disclosure Number: IPCOM000041696D
Original Publication Date: 1984-Mar-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Goodman, DS: AUTHOR [+2]

Abstract

Testing of isolated pads, which have been either completely or incompletely isolated by laser severing of the pad neck, may be accomplished by momentarily heating the pad with a laser and measuring the thermal result on the other side of the neck. Incompletely severed necks retain thermally conductive electrical connection material, which material provides faster heat transfer than the characteristic heat transfer of a completely severed neck. A ceramic substrate may contain on its top (chip-side) surface a number of engineering change (EC) pads that can be used to repair or modify the circuits interconnecting individual chips and off-module connectors; Fig. 1 illustrates one of these EC pads which has been modified for one kind of rework operation (a so-called "delete").

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Pad Deletion Test Technique

Testing of isolated pads, which have been either completely or incompletely isolated by laser severing of the pad neck, may be accomplished by momentarily heating the pad with a laser and measuring the thermal result on the other side of the neck. Incompletely severed necks retain thermally conductive electrical connection material, which material provides faster heat transfer than the characteristic heat transfer of a completely severed neck. A ceramic substrate may contain on its top (chip-side) surface a number of engineering change (EC) pads that can be used to repair or modify the circuits interconnecting individual chips and off-module connectors; Fig. 1 illustrates one of these EC pads which has been modified for one kind of rework operation (a so-called "delete"). The connection 1 between the EC pad 2 and the via point 3 has been broken by using a laser to burn away a portion of the conducting path between them. In some cases, the delete operation may fail because the laser is improperly aligned or because conducting debris is left in the vicinity of the cut. For this reason, current manufacturing procedures specify inspection of a sampled subset of the deletes; the inspection is carried out by human operators using low- power stereo microscopes. An automated technique for inspection of EC pad laser deletes, using thermal imaging, is illustrated schematically in Fig. 2. A laser "L" (possibly the same laser used to perform the d...