Browse Prior Art Database

Test Pad Multiplexing

IP.com Disclosure Number: IPCOM000084627D
Original Publication Date: 1975-Dec-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Jadus, DK: AUTHOR [+2]

Abstract

Test site chips and kerfs are presently used to evaluate semiconductor products, monitor product performance, and diagnose device and circuit failures. However, their usefulness is limited because of the small number of test pads that are available for external electrical connections to the various devices and circuits contained on the chips.

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Test Pad Multiplexing

Test site chips and kerfs are presently used to evaluate semiconductor products, monitor product performance, and diagnose device and circuit failures. However, their usefulness is limited because of the small number of test pads that are available for external electrical connections to the various devices and circuits contained on the chips.

One solution is to multiplex a limited number of kerf or test site pads to a greater number of circuit or device test points than could normally be accommodated through fixed access. The primary beneficial effect is to reduce the number of special test sites or personalized masks that are currently being used.

Multiplexing is accomplished by employing decoders or shift registers to act as switches for access to many test points from a limited number of external test pads. Although this scheme depends upon the manufacturing yield for an extra circuit, this disadvantage can be partially circumvented by using one address as a connection to a metal bus for continuity checks, and another address as an open check.

For example, in the decoder technique, using the same number of pads for each decoder, the number of pads, n, available for address line inputs to each decoder are given by the formula: n = P-K over T - S, where: p = Available test pads on the chip; k = Nonswitched common power supply, ground, and signal input/ output (I/O) pads; s = Signal I/O pads to be switched by each decoder; t = Number of deco...